The dynamics of S0 galaxies
Anne Mathieu & Michael Merrifield
University of Nottingham
anne.mathieu@nottingham.ac.uk
()
A correlation between supermassive black hole mass
and galaxy light concentration in bulges
Alister W. Graham
IAC
agraham@ll.iac.es
()
The global distribution of stars within elliptical
galaxies and spiral galaxy bulges is shown to be intimately related to
the mass of their central supermassive black holes.
More massive galaxies are not simply bigger versions of less
massive galaxies, as had been frequently assumed in the past.
Their entire structure is different, such that more massive
galaxies are more centrally concentrated. The precise degree
of concentration has now been shown to correlate tightly
with the mass of the central supermassive black hole.
This relation is at least as good, if not better than, the
relation between the mass of a supermassive black hole and
that of it's host galaxy announced last year (2000).
Moreover, it provides what should be useful insight into the
formation of both galaxies and their central black holes
The distribution of disks in the $\mu_0$--$\log h$ plane
and the inclination correction
Alister W. Graham
IAC
agraham@ll.iac.es
()
This presentation reveals that a further fundamental
modification needs to be made to the Freeman law, such that
not only do LSB galaxies possess fainter central surface
brightnesses than the canonical Freeman value, but the upper
limit is in fact an upper (bright) `envelope' of points in
the central disk surface-brightness - log(scale-length)
diagram. A morphological-type dependence in this
$\mu_0$--$\log h$ plane of spiral galaxy disks is shown, such
that the upper bright envelope is defined by early-type (~$<$Sc)
spirals while the late-type spirals have smaller and fainter
disks. This realisation has enabled a novel new approach to
determining disk opacity.
Structure, Kinematics, and Dynamics of Bulges
M. Bureau
Columbia University, USA
bureau@strw.leidenuniv.nl
()
A historical overview of our understanding of bulges is first presented and
key results highlighted. Then, three topics of current interest are reviewed,
focusing on structural and dynamical issues. The topics are: i) The evidence
for two classes of bulges, $R^{1/4}$ and exponential, and its significance for
bulge formation; ii) The three-dimensional structure of bulges, in particular
the relationship between boxy/peanut-shaped bulges and bars; iii) The nuclear
properties of bulges, and their possible effects on bulge dynamics and secular
evolution. As a conclusion, new prospects offered by wide-field integral-field
spectroscopy (and other instrument developments) are illustrated and the need
for multi-scale dynamical modeling is emphasized.
The local star formation history of the Galaxy
Andreas Just
ARI, Heidelberg
Germany
just@ari.uni-heidelberg.de
()
\documentstyle{article}
\begin{document}
\begin{center}
\section*{The local star formation history of the Galaxy}
\subsection*{A.\ Just\\ Astron.\ Rechen-Inst.\ Heidelberg, Germany}
\end{center}
The local age distribution of main sequence stars changes dramatically with the
mass for stars with a lifetime shorter than the age of the galactic disk (i.\
e.\ above $\approx 0.9 M_{\odot}$). The difference between the present day
mass function (PDMF) and the initial mass function (IMF) depends strongly on the
long term star
formation history (SFR(t)). Additionally dynamical heating of the disk leads to
an increasing vertical scale height of stellar populations with increasing age.
These results in an enhanced relative contribution of young stars in the solar
neighbourhood and a variation of the velocity distribution as a function of mass
along the main sequence. Both effects can be effiently used to determine the SFR
from the PDMF and kinematical data.
We use a self-consistent disk model to compute
the PDMF and the local velocity distribution of the stars from the
SFR and the observed heating function.
We find, that the shape of the SFR is
similar to that used by Lynden-Bell 1975 to solve the 'G-dwarf problem' showing
a strong maximum in the first Gyr and a moderate decline in the second half of
the disks life.
\end{document}
The interaction of galactic disks with satellite galaxies
A. Just, J. Pe\~narrubia
ARI, Heidelberg
Germany
just@ari.uni-heidelberg.de
()
Merging processes of satellite galaxies with the mother galaxy lead to a
dynamical heating of the disk. Since the energy of the satellite goes into
different channels (dynamical friction with the dark halo, radial
expansion or contraction of the disk, inclining the disk, and heating of
the disk) it is necessary to use detailed numerical computations for a
quantitative analysis of the disk heating process. Up to now numerical
simulations cannot follow the evolution of the internal structure of thin disks
due to artificial heating and resolution problems. With our particle mesh
code SUPERBOX we are now able to compute the galaxy-satellite interaction
with $10^7$ particles in a mesh of $1024^3$. First simulations show the
efficiency of the code for the analysis of the evolution of thin disks.
Spatial distribution of ionized gas and stars in ring galaxies
Y.D. Mayya(1), R. Romano(1) and V. Korchagin(2)
(1) INAOE, Mexico
(2) Inst. of Physics, Rostov, Russia
ydm@inaoep.mx
()
We use H$\alpha$ and continuum band observations in the optical and near
infrared bands of a sample of ring galaxies to study the distribution of
ionized gas with respect to the position of the stellar ring and the
underlying disk. Three of our ring systems are found to contain their
star-forming rings well inside the stellar disk. These findings
will be discussed in the context of ring formation scenarios.
Intermediate-band Surface Photometry of the Edge-on Galaxy: NGC 4565
Hong Wu
NAOC, China
wu@bac.pku.edu.cn
()
We present a deep, 42.79 hr, image of the nearby, edge-on galaxy
NGC 4565 in the Beijing-Arizona-Taipei-Connecticut (BATC) 6660A
band using the large-format CCD system on the 0.6m Schmidt telescope
at the Xinglong Station of the National Astronomical Observatories
of China (NAOC). We obtain a final image that is calibrated to an
accuracy of 0.02 mag in zero point, and for which we can measure
galaxy surface brightness to an accuracy of 0.75 mag at a surface
brightness near 29th mag arcsec^-2 at 6660A. We analyze the faint
outer parts of this galaxy using a two-dimensional model comprised
of three components: an exponential thin disk, an exponential thick
disk, and a power-law halo. Combined with a need to provide a cut-off
radius for the disk, a total of 12 parameters are included in our model.
We determine the best values of our model parameters via 10,000 random
initial values, 3,700 of which converged to final values. The thin
disk and thick disk parameters we determine here are consistent with
those of previous studies of this galaxy. However, our very deep
image permits a better determination of the power law fit to the halo,
with best value of r^-3.88. The axis ratio of the halo is 0.44 and
the core radius is 14.4 kpc (for an adopted distance of 14.5 Mpc.
SED, Metallicity and Age of Halo Globular Clusters in M33
J. Ma
NAOC, China
majun@bac.pku.edu.cn
()
In this paper we study the properties of the halo globular
clusters in the nearby spiral galaxy M33. CCD images of
M33 were obtained as a part of the BATC Color Survey of the
sky in 13 intermediate-band filters from 3800 to 10000 A.
By aperture photometry, we obtain the spectral energy
distributions (SEDs) of these globular clusters. Using
theoretical stellar population synthesis models, we estimate
the ages of these star clusters in different models of
metallicity. The results show that the most sample halo
globular clusters (six of the 9 in our sample) fit the models
of metallicity of 0.004, the other three fit the models of
metallicity of 0.008 and 0.0004, respectively. It means that
they are all metal poor. The ages of these clusters are all
1.6 10^9 years. As Chandar, Bianchi, \& Ford did, we
estimate the ages of our sample clusters by comparing the
photometry of each object with models for different values
of metallicity.
Optical Structure of Disks
K.C. Freeman
Mount Stromlo Observatory, Australia
kcf@mso.anu.edu.au
()
I will review some of the important optical
properties of disks.
These include aspects of the structure of disks, and some comments
on the Tully-Fisher law, the significance of bulges and thick disks,
and the pure disk galaxies.
Simulations of stellar and gaseous morphologies in spiral galaxies
Simon Berman
University of Oxford
simon@thphys.ox.ac.uk
()
The stellar and gaseous components of spiral galaxies have
been modelled using a code incorporating finite difference
hydrodynamics and an N-body solver. The simulations reveal
morphological differences in the two components which mirror
the dual morphologies that have been seen in $B$ band and
$K'$ band observations of many spiral galaxies.
NGC 1023 (Arp 135): A Prototype for the Study of S0 Galaxies?
Mansie Iyer and Caroline Simpson
FIU, USA
miyer01@fiu.edu
()
\begin{documnet}
\begin{abstract}
Lenticular, or S0 galaxies, fall under the category of early-type galaxies, which are
thought to be gas-deficient. Recent studies, however, on a number of S0 galaxies show that this is not
necessarily true, as large amounts of gas have been detected in some of these galaxies. The gas
in these systems can have very different morphologies and its origin and subsequent evolution are still very much under
debate. There is, however, very strong evidence that the gas present in these systems
is of an external origin and is not due processes within the galaxy
itself. Furthermore, it is believed that galaxy interactions, mergers, and
collisions play an important role in shaping the kinematics and structure of S0 galaxies as
they do with other galaxy types.
NGC 1023 is one such gas-rich lenticular galaxy. An initial look at this galaxy indicates that we are observing this
system in the process of accreting gas (external origin) from its gas-rich dwarf companion, which is the proposed
mechanism for the origin of gas in many gas-rich lenticular galaxies. The intention of this study is to perform an in-depth analysis of the structure and kin
ematics of NGC 1023. The results of this study will then be compared to other gas-rich lenticular
galaxies in an attempt to better understand S0 galaxies and their overall role in our understanding of galaxy evolution.
\end{abstract}
\end{document}
Proto galaxies and Galaxy Morphology
Peter Williams
Astronomical Institute, Tohoku University, Japan
williams@astr.tohoku.ac.jp
()
In light of the various problems encountered in recent
numerical simulations looking at the formation of galaxies
in a cosmological setting, and in order to provide a
counterpoint to these currently popular approaches to studying
the problem of galaxy formation, an alternative approach was
adopted: to focus on the physics of galaxy formation, decoupled
from issues of a cosmological nature, using idealized isolated
initial conditions, and a minimal set of physical processes
evolved into the fully non--linear regime, with the aim of
gauging to what extent such a minimal prescription can reproduce
the characteristics of bright galaxies in the local Universe.
In each of the 57 star forming Tree--SPH simulations carried out,
roughly 40000 particles were used, enabling gas, stellar, and
dark matter mass profiles, and related gross structural parameters
to be reliably measured in the resultant quiescent numerical
galaxies, enabling tentative morphological types to be estimated.
Constraining the SPH Kernel Radius in Galaxy Simulations
Peter Williams
Astronomical Institute, Tohoku University, Japan
williams@astr.tohoku.ac.jp
()
In many SPH simulations of galaxy formation a lower limit is imposed on
the kernel radius $h$, equal to the gravitational softening length
$\epsilon$, while $\epsilon$ is held constant. It has been found that
such a constraint compromises the spatial resolution and accuracy to which
hydrodynamical quantities are evaluated to the extent that the evolution
of the gross features of the resultant numerical galaxies are affected,
and the ability to capture shocks vastly reduced. When $h$ is allowed to
evolve freely to maintain a roughly constant number of neighbours in
SPH summations, such effects are avoided, and the gross structure and
evolution are converged for gas particle numbers of a few thousand per
galaxy, and furthermore, at a decreased computational cost.
astrojupiter17@yahoo.com
()
Secular Evolution in Barred Galaxies: Observations
Michael R. Merrifield
University of Nottingham
michael.merrifield@nottingham.ac.uk
()
The distinction between barred and unbarred galaxies is a
rather artificial one. Quantitative measurements indicate
that galaxies possess a broad continuum of bar strengths,
and that the bar strength also depends to some extent on
the bandpass in which the observation is made. In addition,
there is evidence that bar strength can evolve dramatically
with time, so a galaxy that is barred at one epoch may
appear unbarred at a later date. Other properties of a bar,
such as its pattern speed, might also be expected to display
secular evolution. Thus, a snapshot measurement of a barred
galaxy's current properties by no means fully characterizes
the system. This talk will review the quantitative analysis
of a bars' properties, and the accompanying evidence that
these properties evolve with time.
Tracing the disk and the halo of the Milky Way with kinematics of sdB stars
Martin Altmann,
Klaas S. de Boer
Heinz Edelmann
Sternwarte d. Univ. Bonn,
Sternwarte d. Univ. Bonn,
Dr. Remeis Sternwarte, Bamberg
maltmann@astro.uni-bonn.de
()
We have analysed the kinematics of a sample of 110 hot
subdwarf stars, located mainly at high galactic latitudes
on the South Polar Cap (SPC) of the Galaxy.
For 2/3 of the stars, new proper motions, spectroscopical
and photometrical data are presented. The vast majority of
the stars show a kinematical behaviour that is similar to
that of thick disk stars. Some, especially the nearer
objects, have velocities rather fitting to solar, i.e. thin
disk, kinematics. 15 objects have orbital velocities
which differ from the disk orbital velocity by a great
extent. These are members of the galactic halo. The
dispersion of the orbital velocities is somewhat larger and
the mean value for the orbital velocity is a bit higher
than expected for a thick disk alone. Therefore the sdB
stars of this sample belong to both thin and thick disk,
as well as the halo component.
Apart from studying the current kinematics, we also
calculated the orbits using the galactic potential model
of Allen \& Santillan (1991). While most stars feature
orbits with thin or thick disk character, a few reach far
above the galactic plane and have large eccentricities
($ecc$). Most orbits have an eccentricity of less than 0.5,
a few have an $ecc$ of more than 0.7. The region of
$0.5\le ecc \le 0.7$ is nearly unpopulated. This indicates
that the (thick) disk and the halo are kinematically disjunct.
The statistics of the $z$-distance at given time intervals
in the orbits of the stars leads to the $z$-probability
distribution of the sample. From the logarithmic histogram,
a scale height can be derived. The histogram clearly shows
two different slopes, one for the disk stars and one for
the halo component. The disk component's slope leads to a
scale height of 1.0 ($\pm$0.1)~kpc, which is consistent
with the result of an earlier study using about 1/3
of our current sample, published in de Boer et al. (1997).
This scale height of 1 kpc fits well with other results
for the scale height of the thick disk. The other component
has a scale height of $\sim$6~($\pm2$)~kpc, meaning that
it has a much flatter gradient than the disk component.
The sdB stars clearly show a rather diverse kinematical
behaviour, with the vast majority being disk stars, but we
show that a halo minority exists. Therefore the kinematic
history and population membership of the sdB stars
on the whole is different than that of the cooler HBA stars,
which are predominantly or even exclusively halo objects
(Altmann \& de Boer 2000). This leads to the question,
whether the halo sdB stars are of similar origin as the
HBA stars, or whether their kinematical behaviour is
caused by another process, such as infalling stellar
aggregates or inner disk events.\\[0.5cm]
{\bf References:}\\[0.2cm]
Allen, C. \& Santillan, A. 1991, RMxA 22, 255\\
Altmann, M. \& de Boer, K.S. 2000, A\&A 353, 135\\
de Boer, K.S., Aguilar-S\'anchez, Y., Altmann, M. et al. 1997, A\&A 327, 577\\
Formation and evolution of galactic disks
Vladimir Avila-Reese
Claudio Firmani
(A) IA-UNAM, Mexico
(B) Osservatorio Astronomico di Brera, Italy
avila@astroscu.unam.mx
()
I will discuss the formation and evolution of galactic
disks within growing CDM halos. The main questions to
be explored are (i) the influence of the halo mass, mass
aggregation history, spin parameter, and the disk mass
fraction upon the radial stellar surface density profile
and the rotation curve decomposition of disk galaxies,
(ii) the Tully-Fisher (TF) and magnitude-radius relations,
(iii) the correlations of the residuals of the TFr relation
with other structural and luminous galaxy properties. In
particular, I will show that the introduction of star
formation alleviates the potential difficulty to explain that
the TFr of high and low surface brightness galaxies is similar,
in spite of that the shape of their rotation curves at a given
luminosity seems to depend on the surface brightness.
Theoretical and observational results will be presented in
this talk.
Dynamical influences on star formation in spiral galaxies
Tony Wong
Leo Blitz
ATNF, Australia
UC Berkeley, USA
Tony.Wong@atnf.csiro.au
()
Most star formation in disk galaxies appears to occur spontaneously
once molecular gas has formed. However, the star formation efficiency
(SFE = SFR per unit H$_2$ mass) is not always constant within galaxies,
but appears to be affected by the presence of even weak bars. We show
two examples of this phenomenon from the BIMA Survey of Nearby Galaxies
(BIMA SONG). Along bars in NGC 4321 and 4736, the SFE appears to be
suppressed. However, in the resonance ring surrounding the nuclear bar
in NGC 4736, the SFE is enhanced. Moreover, along 4736's ring one
finds a twofold symmetry in the distribution of HI and H$\alpha$
emission but a threefold symmetry in the CO emission. We discuss how
these features may be related bar kinematics. In particular, the
effects of galaxy dynamics on the SFR are more complex than simple
models (e.g., gas consumption timescale $\propto$ orbital timescale)
would predict.
Conference Summary
rix@mpia.de
()
Gas morphology and dynamics in the central kpc: embedded bars and nuclear spirals
Witold Maciejewski
Osservatorio Astrofisico di Arcetri, Italy, and
Jagiellonian University Observatory, Poland
witold@thphys.ox.ac.uk
()
High-resolution observations of galactic centers unveiled
complex structures residing there: inner bars and spirals
are very common. Hydrodynamical simulations and arguments
based on the density-wave theory imply that the nuclear
spiral is a common response of the gas to a large-scale
non-axisymmetric potential. Nevertheless, various distinct
fundamental modes of gas flow can exist in galactic nuclei.
Gas inflow to the center, enabled by the nuclear spiral, can
in other modes be prohibited, with gas accumulating on the
nuclear ring. Stellar nuclear bars modify the flow in a way
that shows a fine balance between the strength of the bar
and the morphology of the inflowing gas. Recent detection
of $m=1$ modes in gas flow may indicate that self-gravity
plays an important role in the dynamics of the nuclear gas.
hliszt@nrao.edu
()
Morphology of 3D bars
P.A. Patsis
Research Center for Astronomy, Academy of Athens
ppatsis@cc.uoa.gr
()
We analyze the orbital structure in a class of 3D models for galactic
bars. We examine the changes introduced in the system as the pattern
speed, the strength of the bar, and the properties of the central
bulge vary. We investigate the building blocks of the 3D bars and in
particular those that could give boxy and peanut-shaped edge-on
profiles. We find the parameters that favor the formation of secondary
3D bars along the minor axis, as well as disks embedded in the bulge
and inclined in respect with the equatorial plane. The boxy isophotes
in the face-on views of barred galaxies are also discussed.
Star Formation along the Hubble Sequence: Results from a new Halpha Galaxy
Survey
Shane, Neville; James, Phil
ASTROPHYSICS RESEARCH INSTITUTE, LIVERPOOL JOHN MOORES UNIVERSITY, UK
nss@astro.livjm.ac.uk
()
We are conducting a large survey of star formation within ~400 nearby
(v<3000km/s) spiral and irregular galaxies through imaging of the H-alpha
emission. H-alpha emission is produced by high mass, short lived stars and
is thus a near instantaneous measure of the current star formation rate.
We will present here some of our first results, investigating the
variation of star formation rate and luminosity normalised star formation
rate along the Hubble Sequence for disk galaxies.
Our survey sample has been selected from the Uppsala Galaxy Catalogue to
include all observable galaxies out to 3000km/s. Previous studies have
concentrated on large, bright galaxies, whereas ours also includes many
smaller and less luminous specimens. We are utilizing 14 weeks of time on
the 1m Jacobus Kapteyn Telescope on La Palma.
Kinematics of Galaxy Disks
M. Kregel
P.C. van der Kruit
W.J.G. de Blok
K.C. Freeman
Kapteyn Astronomical Institute, Groningen, The Netherlands
Kapteyn Astronomical Institute, Groningen, The Netherlands
ATNF, Sydney, Australia
MSSSO, Canberra, Australia
kregel@astro.rug.nl
()
We present observations of the disk kinematics in a sample
of edge-on spiral galaxies. For these galaxies we obtained
HI synthesis maps using the ATCA and optical absorption
line spectra using the SSO 2.3m, the WHT and the VLT.
We use the HI data to derive the rotation curves by
applying a new least-squares fitting algorithm to the major
axis position-velocity maps. The stellar rotation and
velocity dispersion are determined from the optical spectra
using a cross correlation technique.
Dynamics of Stellar Orbits in Disk Galaxies
Taihei Yano, Kan-ya Yukitoshi, and Naoteru Gouda
NAO, Japan
yano@pluto.mtk.nao.ac.jp
()
We have investigated the dynamics of stellar motions
in galactic potentials with bar like perturbed potential
in order to clarify whether the structures
such as 2-armed spiral structures or bared structures are
constructed in galaxies.
In this investigation, we verify whether the axis of oval orbit
align with that of the perturbed potential. When the axis is aligned with
the bar the structures will be constructed, and when axis is aligned
perpendicular to the bar no structures are constructed.
Earn \& Lynden-Bell(1996) introduce the condition that orbits align with the bar
around the Lindblad resonance.
We consider the more general case, i.e., we discuss
how the orbit behaves in all regions of a galaxy.
Our results are as follows;
When $r/r_{ILR} > 1$, the axis of the oval orbit is aligned with that of the
perturbed potential. On the other hand,
when $r/r_{ILR} < 1$, the axis of the oval orbit is aligned perpendicular to
that of the perturbed potential.
Therefore the structures in galaxies appear in the outer region of
inner Llindblad resonance.
These results are consistent with the linear analysis of eauations of motion.
deborah@astroscu.unam.mx
()
High spectral resolution kinematics of galaxies: the figure of eight effect
close to the galaxy's center.
Emanuela Pompei
Ezio Pignatelli
ESO, Chile
Dip. di Astronomia, Univ. di Padova, Italy
epompei@eso.org
()
We present here high spectral resolution observations of
stellar and gaseous kinematics of three nearby galaxies.
Each of these objects is a clear example of the different
kinematical conditions that can be found in galaxies: stars
moving faster than gas, gas and stars moving in the same
way, gas rotating faster than the stars.
The data were then used to investigate the figure of eight
effect, which is a clear signature of a bar in an edge-on
galaxy, very close to the galaxy's center, successfully
identifying a (nuclear?) bar in one the objects observed.
Mass models were applied to the data to derive the global
gaseous and stellar potential.
The Gasesous Properties of Seyfert Host Galaxies
C.G. Mundell
A.R.I.
cgm@astro.livjm.ac.uk
()
Neutral hydrogen (HI) is a key tracer of galactic structure
and dynamics and responds most readily to perturbations
caused by tidal disturbance and non-axisymetric
gravitational potentials. Such perturbations have also
been mooted as possible triggers of nuclear activity in
galaxies although no conclusive links have yet been
established. I present here an HI imaging study of a
heterogeneous sample of nine nearby Seyfert galaxies
and describe plans for a new HI survey which aims to
investigate the role of the host gas in triggering and
fuelling of nuclear activity on a statistical basis.
rromano@inaoep.mx
()
Galactic Warps and Bars in Axisymmetric Halos
Makoto Ideta
Department of Astronomy, Kyoto University
ideta@kusastro.kyoto-u.ac.jp
()
Dynamical evolution of galactic warps and bars embedded in oblate and
prolate halos is examined by using $N$-body simulations. In
particular, a configuration such that the symmetry axis of disks is
aligned to the short axis of halos is considered. Then, it is found
that the warpings in oblate halos disappeared at the end of
simulations, while in prolate halos, they can survive for a long time.
On the other hands, the bars in oblate halos can last for a long time,
while in prolate halos, they dissolved eventually within a Hubble
time. This finding suggests that galactic bars would not coexist with
galactic warps, and so, there may exist a difference of the frequency
of warpings in barred and non-barred galaxies.
Dynamical Modeling of Stellar Nucleus of M31
Niranjan Sambhus
S. Sridhar
IUCAA, India
nbs@iucaa.ernet.in
()
The peculiar twin peaked nucleus of M31 hosts a supermassive
black hole. We present stellar dynamical models of this
double-peaked nucleus, based on HST photometry, and Tremaine's
model of an eccentric stellar disk in orbit round the
supermassive black hole. Using a Schwarzschild-type method,
we derive the disk potential from the photometry. We
construct stellar orbits in the combined potential of the
disk and the supermassive black hole, allowing for the
possibility of a non-zero pattern speed for the stellar
disk. Model disks are generated by populating these orbits
with stars. Comparisions with the available two dimensional
photmetric and kinematic maps are presented. Our results
support Tremaine's model, extended to include a more
massive disk and a non-zero pattern speed.
Density waves in the central kpc of galaxies: the role of nuclear spirals, bars and m=1 modes.
Eric Emsellem
CRA-Lyon, France
emsellem@obs.univ-lyon1.fr
()
Density waves in the central kpc of galaxies, taking the form of spirals,
bars and/or lopsided density distributions are potential actors of the
redistribution of angular momentum. They may thus play an important role
in the overall evolution of the central structures, not mentioning the
possible link with the active/non-active central mass concentration.
I will present kinematical evidences for the presence of such structures
using new sets of observations, including two-dimensional (OASIS/CFHT) and
long-slit (ISAAC/VLT) spectrography of nuclear bars and spirals.
I will also discuss the importance of m=1 modes in the nuclear
regions of galaxies, illustrating this with newly revealed cases and
original N body simulations. The implications of these observations/models
will be discussed in the context of AGN, starburst and dynamical evolution.
The properties of the dense interstellar medium in the central regions of starburst and normal galaxies
S. Huettemeister
AIRUB Bochum, Germany
huette@astro.ruhr-uni-bochum.de
()
The physical properties of the dense component of the
Interstellar Medium (ISM), i. e. molecular gas, in
the centers of galaxies are significantly different
from what is found in more quiescent disk regions
like spiral arms. The dense ISM in the central part of a
galaxy is, on average, both warmer and denser than in the
disk, but in detail shows a complex multi-component
structure. This may include diffuse, unbound gas, and dense,
warm star-forming cores, as well as cool dense cores,
depending on whether the central region in question is
engaged in a starburst or (relatively) less active. Even
among starburst regions, there are very significant
differences in the structure and dominating component of
the gas, depending on the degree of central concentration,
the evolutionary state of the burst and - possibly - the
presence of an AGN.
Multilevel, multispecies studies of molecular lines,
preferably at high resolution, are a powerful diagnostic
to derive the structure and physical properties of the
gas. A special role falls to the ratio of the CO
isotopomers $^{12}$CO and $^{13}$CO, but high-density
tracers like HCN, HNC and CN are crucial in showing that
not all starburst regions are identical.
Using these diagnostics, the changes in gas properties, and
therefore the conditions governing star formation, can be
traced from the disk through the bar (a frequent ingredient
when gas is being concentrated to the center) to the
nuclear region. The conditions dominating the gas reflect
- and feed back on - kinamatical and secular evolutionary
processes in both the disk and the center of a galaxy,
making a closer connection of studies of physical and
dynamic properties of disk galaxies a worthwhile goal.
Molecular gas in the barred spiral galaxy M83
A. Andersson (1), T. Wiklind (2), H. Olofsson (1), G. Rydbeck (2)
(1) Stockholm Observatory, (2) Onsala Space Observatory
andreas@astro.su.se
()
We have mapped the barred spiral galaxy M83 in the CO(1-0)
and CO(2-1) lines using the Swedish-ESO Submillimetre
Telescope (SEST). The coverage is in both transitions
complete out to a radius of 4\farcmin 5 (rougly the extent
of the optical disk) and the spacing is 1/3 of the beam
width, a basic condition for improving the resolution by
use of deconvolution techniques. The CO emission is
concentrated to the nucleus, the bar and the arms. The
velocity field is regular, with deviations in conneciton
with the bar and the arms. After subtracting the axi-
symmetric part we find that the residual velocites is
spiral shaped and we see indications that the spiral arms
are a result of a spiral density wave. We have also
observed M83 in infrared (J and K) and we are preparing to
model the velocity field and compare the results to the
findings above.
Characteristics of the Galaxy's Thick Disk
W.J. Schuster, A. Moitinho, L. Parrao, E. Covarrubias
1-2. - Observatorio Astronomico Nac., UNAM, Mexico
3. - Instituto de Astronomia, UNAM, Mexico
4. - UDLA, Puebla, Mexico
schuster@astrosen.unam.mx
()
$uvby-\beta$ photometry has been obtained for more than 2100
high-velocity and metal-poor stars. Although our original
intent was the study of the Milky Way's halo, many of these
program stars are from the Galaxy's old-thin and thick disks,
permitting us to study and compare these different stellar
populations. Many of these stars are also found in the
Hipparcos catalogue, and a new photometric calibration for
the absolute visual magnitudes of metal-poor stars is being
developed. This new calibration plus kinematic data gleaned
from many data bases is allowing us to study the kinematic
characteristics of the thick disk in comparison with the
halo and old thin-disk stellar populations. Here are shown
the characteristics of our new photometric absolute-magnitude
calibration plus various kinematic diagrams comparing the
thick disk of the Galaxy. In the future the $uvby-\beta$
photometry will be compared to stellar isochrones to derive,
study, and compare the ages of thick-disk stars.
Three dimensional HI gas distribuiton in Milkyway Galaxy
Hiroyuki Nakanishi, Yoshiaki Sofue
Institute of Astronomy, University of Tokyo
hnakanis@ioa.s.u-tokyo.ac.jp
()
We derived a new three dimensional map of
neutral hydrogen gas (H {\sc i})
in our Galaxy using the latest H {\sc i} survey data cubes and rotation
curve. The H {\sc i} disk extends as far as 23 kpc, and its size is 1.6
times larger than that of the stellar disk.
H {\sc i} mass is $5.5 \times 10^9 M_\odot$, which is 3\% of the
dynamical mass.
Though it is believed that the Galaxy has some spiral H {\sc i} arms,
we found the Galaxy has three H {\sc i} rings rather than
spiral arms.
The most noticeable feature is a very large H {\sc i} ring at 17 kpc.
It has very high column density and has 64 \% of the total H {\sc i}
mass. It strongly warps from $z \simeq -1$ kpc to $\simeq +1.5$ kpc.
The middle ring locates at around $R = 13$ kpc and has 27 \% of total
H {\sc i} mass. This ring corresponds to so-called Outer arm.
The smallest ring locates at around $R=8$ kpc and has 11 \% of
the total H {\sc i} mass. This ring corresponds to a complex of
Sagittarius arm and Perseus arm.
One possible interpretation of 17 kpc ring is that the
spatial mass density is
not high enough for star formation in it, and the primordial H {\sc i} gas
remains. In addition we found that the H {\sc i} gas is lacking at
$R=10$ kpc.
This radius coincident with the corotation radius
if the pattern speed of about 20 km s$^{-1}$ pc$^{-1}$is assumed.
Instabilities and Modes of Collisionless Disks
Christopher Hunter
Florida State U.
hunter@math.fsu.edu
()
\documentstyle{article}
\begin{document}
\title{Instabilities and modes of collisionless stellar disks}
\author{C. Hunter \\
Florida State University, Tallahassee, Florida 32306-4510, USA}
\maketitle
\begin{abstract}
Oscillations of flat collisionless stellar disks are described by a
linearized perturbational analysis of the collisionless Boltzmann
equation. The orbits in a circularly symmetric disk are regular, and
have well-defined action and angle variables. Kalnajs (1971,1976)
showed how their responses to perturbations can be determined, and
gave a compact matrix method for solving self-consistently for the
oscillations of a disk which is composed of a population of orbits.
There have been few implementations of this method for stellar disks
since then. The most successful have been to singular scalefree disks
(Zang 1976, Evans \& Read 1998). This talk will discuss some new
approaches to the implementation, and describe some numerical results
for disks with a simple non-singular rotation curve.
This work has been supported by NSF through grants DMS-9704615 and
DMS-0104751.
\end{abstract}
\end{document}
Magnetic fields in spiral arms and bars
Rainer Beck
MPIfR Bonn, Germany
rbeck@mpifr-bonn.mpg.de
()
Linearly polarized radio continuum emission is a powerful tool to study
the strength and structure of interstellar magnetic fields in galaxies.
Interstellar magnetic fields with a well ordered spiral structure exist
in grand-design, flocculent and even irregular galaxies. In grand-design
galaxies the fields are aligned parallel to the optical spiral arms, but
the strongest regular fields are found in interarm regions, sometimes
forming ``magnetic spiral arms'' between the optical ones. Within the
optical spiral arms, processes related to star formation tangle the
fields so that very little polarization is observed.
Faraday rotation of the polarization vectors reveals patterns which
support the existence of coherent large-scale fields in galactic disks
generated by dynamos. The majority of field structures in galaxies cannot
be described by one single dominating dynamo mode, but requires a
superposition of modes. In a few galaxies an axisymmetric spiral field
(the ground mode of dynamo action) dominates. As the inward direction is
favoured, some special symmetry of the seed field is needed.
The first radio polarization survey of barred galaxies is presented,
observed with the VLA and the ATCA. The magnetic field is mostly aligned
with the gas flow around the bar, except for the upstream region where
the magnetic field structure deviates from that expected from
hydrodynamical models. Within (and interior to) the circumnuclear
ring the field is again of spiral shape, indicating dynamo action,
which leads to magnetic stresses, possibly driving an inflow of gas
towards the active nucleus.
Present-day radio polarization observations are limited by sensitivity.
Next-generation radio telescopes (e.g. the Square Kilometer Array) will
be able to reveal the full wealth of magnetic structures in galaxies.
Bar dynamical friction and disk galaxy dark matter content
Victor P. Debattista
Astronomiches Institut, Universitat Basel, Switzerland
debattis@astro.unibas.ch
()
I discuss recent results, both theoretical and
observational, on the pattern speeds of bars and what they
tell us on the dark matter content of their galaxies.
High Resolution Radio Continumm Observatins of the Barred Spiral Galaxy NGC 3367
J.Antonio Garcia-Barreto
J. Franco
L. Rudnick
IA-UNAM, INAOE, Mexico
IA-UNAM, Mexico
U. Minnesota
tony@inaoep.mx, tony@astroscu.unam.mx
()
New observations of the radio continuum emission from the barred spiral galaxy NGC 3367 at 1.4 GHz, with an
angular resolution of 2$''.1$ and at 8.4 GHz with an angular resolution of $0''.28$ are presented. In the map
at 1.4 GHz, the triple source: a central radio source in addition to two lobes straddling the center, was
primarily detected as in previous $4''$ observations. The central radio source connects with the south-west
lobe with a projected structure of approximately 2.5 kpc long by approximately 850 pc wide, forming a jet.
The map at 8.4 GHz shows a circumnuclear structure located within a radius of about 300 pc, most likely
associated with regions of recent star formation, a compact unresolved source (smaller than 65 pc in diameter)
from the center of the galaxy. The compact core, jet and lobes form a small, low power counter part to radio
galaxies with a flow axis which is out of the plane of the galaxy. The circumnuclear structure
is believed to be in the plane of the galaxy and it is most likely the result of galactic dynamics under a non-
axisymmetric gravitational potential.
Dynamical evolution of M92 Globular Cluster - Proving
the Milk-Way disk-shocking
M.R. de Oliveira, A. Fausti, H. Dottori, R.R. de Carvalho
OBSPM, France
UFRGS, Brasil
ON, Brasil
marcio.oliveira@obspm.fr
()
Treecode N-body numerical simulations are used to study the dynamical evolution
of the globular cluster M92 in the Galaxy gravitational field during the last
two Gyr, which corresponds to aproximately 16 perigalactic transits. We obtained
the dynamical initial conditions two Gyr ago, by letting a particle evolve in
the galactic potential from its present position and inverting the observed
spatial velocity vector of the cluster. The cluster was modelled with 16384
particles covering a mass spectrum from 0.1-1.2 M$_{\odot}$, initially
distributed in a Plummer model with a half mass radius of 1.5\,pc and a
equivalent King tidal radius of 10\,pc. During the simulation we observe the
appearance of several hundreds of parsecs of long tidal tails, which tend to
align with the cluster orbit. The model reproduces quite well the observed
density profile and surface density map recently obtained, including the
isodensities orientation. The model points to a cluster upper limit mass loss r
ate of
$\simeq 6\%$ per Gyr. Over the 2 Gyr covered by this simulation the cluster halo
tends to swell and the core to shrink.
sellwood@physics.rutgers.edu
()
Spiral Structure observed in Near-Infrared
P.Grosbol
ESO, Germany
pgrosbol@eso.org
()
Near-infrared observations of the spiral pattern in galaxies reveal
the underlying density perturbations in the disks much better than
maps in visual bands although some population effects are still
present. A preliminary analysis of the spiral structure in 50 nearby
spiral galaxies observed in the K band with SOFI/NTT is presented
including the distribution of arm amplitudes and pitch angles.
Synthetic rotation curves were derived using the K surface photometry
and HI velocity width data. The extent of the main, symmetric spiral
pattern was compared to radial separations between resonances derived
from the rotation curves in order to find possible pattern speeds for
an underlying density wave. The dynamic implications of this
comparison are discussed.
Nested Bars, Inner Disks, and Nuclear Rings in Barred Galaxies
Peter Erwin
IAC, Spain
erwin@ll.iac.es
()
I present results of a high-resolution imaging survey of barred S0--Sa galaxies which show the central regions of these galaxies are surprisingly complex, and often dominated by dynamically cool
components. In particular, inner bars -- secondary, small-scale bars (typically less than a kiloparsec in radius) located inside of, and probably rotating faster than, the large-scale primary bars -- are present in about one quarter to one third of all such galaxies. A third of SB0's appear to host kiloparsec-scale \textit{disks} within
their large-scale bars; but the frequency of such inner disks appears to be much lower for later Hubble types. In addition, there are three examples of purely \textit{stellar} nuclear rings --- possibly the fossil remnants of past circumnuclear starbursts.
I also comment on results from an ongoing analysis of about 45 known double-barred systems (extending to Hubble types as late as Sbc), and discuss their characteristic sizes, orientations, and implications for the formation and evolution of these structures.
Fitting a Galactic Model to an All-Sky Survey
Jeffrey A. Larsen and Roberta M. Humphreys
Larsen - Lunar and Planetary Laboratory, Univ. of Arizona
Humphreys - University of Minnesota
roberta@aps.umn.edu
()
We use star counts from the APS Catalog of the POSS I to develop a galactic
model optimized for large, statistically significant datasets uniformly
distributed over the sky. We have selected an 88 field subset, 16 square degrees
each, from the catalog for a program of magnitude limited star counts.
We have developed a simple three component (disk, halo, thick disk) model
optimized for efficiently and objectively analyzing the star count data.
Our model not only produces model counts for our multi-directional data but
also returns a ``goodness of fit" statistic. We use a genetic algorithm, a
robust optimization technique well-suited for this large multi-directional
and multiple parameter study, to optimize the fit and derive a self consistent
set of global parameters to model the galaxy. The results from 12 independent
executions or trials yielded consistent results. All of the model fits produced
a flattened inner halo with c/a of 0.5 to 0.6. The radial scale length
of the disk and the density normalization to the plane for the thick disk and
halo are consistent with previous work. Our model results all yielded a scale
height for the thick disk of 900 pc. The most surprising results from
these global fits, are relatively high values ( greater than 4 kpc) for the
de Vaucouleurs radius for the halo and the radial scale length of the thick disk.
The radial scale length for the thick disk is significantly larger than that
for the old/thin disk and if confirmed with additional work, may imply an
independent origin for the thick disk. We also present evidence that the
scale height and normalization of the thick disk may be variable with
direction.
A Large Asymmetry in the Distribution of Faint Stars in the Inner Galaxy
Jennifer E. Parker, Dr. Roberta M. Humphreys, Dr. Jeffrey A. Larsen
Parker & Humphreys - University of Minnesota, USA
Larsen - Lunar Planetary Lab, University of Arizona, USA
parker@astro.umn.edu
()
Larsen and Humphreys [1996] reported evidence for a significant asymmetry in the number of faint blue stars on either side of the line to the Galactic center from l = ±20° to ±45° at b = +30°, with significantly more stars observed in the first quadrant. We present a more complete survey of the faint stars on either side of the Sun-Center line, analyzing star counts from 40 paired POSS I fields from l = ± 20° to ± 75° and b = +20° to +50°. Using a galactic model, GALMOD [Larsen and Humphreys, 2001], we sampled color ranges to distinguish between halo/thick disk and disk stellar populations. Our analysis shows that the observed stellar excess increases with fainter magnitudes and is comprised of mainly halo/thick disk stars. It is possible the excess in star counts could be due to a bar-induced "wake", a disk interaction from a merger or that the asymmetry is an indication that the thick disk/inner halo is triaxial. A "wake" would suggest that the asymmetry is also present below the plane, so we are investigating 40 additional fields below the galactic plane. Spectroscopic observations have also been made using both the CTIO 4meter and the KPNO WYIN 3.5 meter telescopes with HYDRA a multiobject spectrograph. Over 1000 spectra are currently being analyzed to determine the nature and kinematics of the stars responsible.
The Connection Between Star Formation and Resonant Dynamics in Early-Type Disk Galaxies
R. Buta
University of Alabama
buta@sarah.astr.ua.edu
()
Resonance rings are remarkable for the idiosyncrasies
of their shapes, relative bar orientations, and star formation
characteristics. However, there has been little
investigation of the full meaning of these idiosyncrasies.
In this presentation, I would like to resurrect some
earlier observations of the distribution of HII
regions in early-type barred galaxies and highlight
how the distribution of star formation in resonance
rings likely connects to periodic orbit shapes but,
surprisingly, not to bar strength. If an inner ring has
an intrinsic axis ratio of 0.7 or less, it will
show HII regions "bunched up" near the ring major
axis, while a round ring will show a more uniform
azimuthal distribution of H-alpha flux. However,
two galaxies with widely different intrinsic
ring shape can have the same bar strength. I will
discuss possible interpretations of these effects.
I will also discuss recent HST observations of two
dissimilar resonance ring galaxies, NGC 3081 and
NGC 4622. NGC 3081 is a classic, well-studied
resonance ring barred galaxy with an intense inner
ring of star formation. The new HST observations
resolve the ring into many point or near-point
sources. The distribution of these sources is tied
directly to the bar in that most are located
around the ends of the bar. The luminosity function
of the sources depends on azimuth in the sense
that the brightest sources are 1 mag brighter
near the ends of the bar than near the bar minor
axis. Star formation is intimately connected
with resonant dynamics in this galaxy.
NGC 4622 is a nonbarred resonance ring galaxy
with leading spiral structure and
whose inner ring is probably tidally-driven.
The galaxy is well-known for showing two sets
of spiral arms, a pair of outer arms opening
outward in the clockwise direction, and a single
inner arm opening in the opposite sense.
In my presentation, I will reveal the surprising
conclusion that the HST data lead us to when we ask
which set of arm(s) is leading in NGC 4622.
The issue has been an open question for years
due to the low inclination of the galaxy,
and the interpretation depends also on a
on a groundbased velocity field which I will
show. I will also discuss the star formation
in the peculiar tidal resonance ring. Evidence for
an interaction will also be presented.
The de Vaucouleurs Atlas of Galaxies
R. Buta (1), H. G. Corwin, Jr. (2), S. C. Odewahn (3)
(1) University of Alabama, (2) IPAC, (3) Arizona State University
buta@sarah.astr.ua.edu
()
In 1959, Gerard de Vaucouleurs published a galaxy classification
system (Handbuch der Physik, 53, 275) that is still widely used by
modern astronomers. His system
was a revision of an earlier one by Hubble (1926, ApJ, 64, 321),
but his point of view had a number of advantages over Hubble.
De Vaucouleurs' classification system provided a better description of
what a galaxy looks like without being too unwieldy. His approach gave
greater emphasis and more accurate recognition to specific details that
have a bearing on the way galaxies evolve. He published large catalogues
summarizing classifications and other basic information for tens of
thousands of bright galaxies. These advantages have
made de Vaucouleurs' system the most-used galaxy classification system
today. However, a major disadvantage of his system is that no galaxy
atlas has ever been prepared that illustrates his notation and point
of view. This means that most astronomers use the
de Vaucouleurs system without really understanding it.
We are preparing a new galaxy atlas that will document
the de Vaucouleurs revised Hubble galaxy classification system
with modern digital images. The principal goals are to make the de Vaucouleurs
revised Hubble system more accessible and more understandable
to modern astronomy researchers, students, and amateurs, and to summarize
what has been learned about the features defining galaxy
morphology since the 1950s. The atlas will also address other
aspects of morphology that have come to the forefront since de
Vaucouleurs published his system and will be up-to-date on our understanding
of the physical processes that underly galaxy morphology. Finally, by
exclusively using images from electronic detectors, it will be the
first major galaxy atlas geared to illustrating classical
galaxy types using today's standard imaging methods, as opposed to
photographic plates.
The need for the atlas is becoming increasingly felt as modern technology
provides more and more high quality images of galaxies seen from a vast
range of distances and times. It is expected that the morphology of galaxies
would undergo significant changes during their formative period, and it
is likely that very distant galaxies are showing the structures they had
before a steady state had been achieved. The great value of the proposed
atlas will be in the description it will provide of normal galaxies in
equilibrium, where gravity has run its course and things have for the most
part settled down.
This poster will summarize the scope and needs of the atlas, and will be
used to seek input from the astronomical community as to what will be most
useful and, most importantly, to locate as many high quality images
as we can find. More details on the project can be found at
http://bama.ua.edu/~rbuta/gvatlas/.
The Molecular Gas Distribution in Polar Ring Galaxies
E.Schinnerer, N.Z. Scoville
CalTech, USA
CalTech, USA
es@astro.caltech.edu
()
Polar ring galaxies are peculiar objects with rings of $\sim$ 10 to
25~kpc diameter which are oriented almost perpendicular to the main
stellar disk. In the generally accepted picture, a pre-existing S0
galaxy captures a satellite galaxy, or accretes material located
between interacting galaxies. Recently a much more violent formation
process was suggested: a galaxy merger between two disk galaxies. In
order to distinguish between these scenarios, we mapped the molecular
gas distribution in two representative polar ring galaxies (NGC~660
and NGC~2685) using the Owens Valley Radio Observatory (OVRO)
millimeter array. NGC~660 is the only late-type galaxy among the known
polar ring galaxies. Our recent observations of the molecular gas
content suggest the presence of a molecular gas spiral out to 5.5~kpc
in the disk. Within the central gas concentration at radius $\leq$
$330~pc$ strong streaming motions are seen, suggesting the presence of
a stellar bar. NGC~2685 which is one of the few kinematically
confirmed polar ring galaxies shows CO line emission associated with
the HII regions in the polar ring but no line emission is detected in
the host S0 disk.
N-body simulations of resonance rings
Rautiainen, Pertti and Salo, Heikki and Laurikainen, Eija
Department of Physical Sciences, Astronomy Division,
University of Oulu, Finland
pertti.rautiainen@oulu.fi
()
We have studied formation of resonance rings in N-body
simulations of barred galaxies. The gas component is
modeled as inelastically colliding particles. These
models often have several modes: primary and secondary
bars and/or outer spiral structure, each with separate
pattern speed. Even when several modes are present,
the rings are usually related to resonances. However,
the shapes of the rings can exhibit cyclic changes
depending on the relative orientation of the modes. For
example, a nuclear ring can follow the orbit loops
introduced recently by Maciejewski and Sparke. Multiple
modes can also explain misaligned rings found in some
galaxies. We also found that some rings can be related
to resonances induced by almost steadily rotating spiral
arms.
Old stellar Galactic disc in near-plane regions according to 2MASS: scalelengths, cut-off, flare and warp
M Lopez-Corredoira
A Cabrera-Lavers
F. Garzon
IAC, Spain
acabrera@ll.iac.es
()
By using two different methods, we analyze the stellar
old population in the near infrared data on the Galactic plane
of the 2MASS survey.
The first method is based on the isolation of the red clump giant
population and the inversion of its star counts to obtain directly
the density distribution along the line of sight. The second method
is a fitting of the parameters of a disc model on the star counts
in 820 regions.
Results from both independent methods are consistent with each other.
The qualitative conclusions are that the disc is well fitted by
an exponential distribution along both the galactocentric distance and height.
There is not an abrupt cutoff in the stellar disc (at least within
$R<15$ kpc). There is a strong flare, i.e.
an increase of scaleheight towards the outer Galaxy; this flare does
not begin in the solar circle but it continues toward the inner Galaxy,
i.e. there is a decrease of the scaleheight towards the inner Galaxy.
Another remarkable fact is the existence of a warp in the old stellar
population whose amplitude is coincident with the amplitude of the gas warp.
All this information is quantified too.
none
edo@astro.rug.nl
()
Mass Concentration and Bar Dissolution in Spiral Galaxies
M.Das, P.J.Teuben, S.N.Vogel, M.W.Regan, K.Sheth, A.Harris
Authors 1,2,3,6 : University of Maryland, USA
Author 4 : STSci ,USA
Author 5 : Caltech, USA
mousumi@astro.umd.edu
()
Gas inflow in barred galaxies results in
mass accumulation in the centers of these galaxies, which affects
the shape of the orbits supporting the bar structure. Simulations of
bars predict that the bar ellipticity decreases with the mass buildup
in the center and can eventually lead to bar dissolution. We have used
the near IR and CO data of the BIMA Survey of Nearby Galaxies (SONG)
to investigate whether there is observational evidence that bar ellipticity
decreases with the central mass concentration. We have used the CO
rotation curves to determine the ratio of the dynamical mass within the
bulge to that in the bar; this is a measure of the mass concentration.
The bar isophotes in the near IR images were used to determine the bar
axes and the ellipticity; the intensity profile was used to determine
the bulge diameter. Our results
show that there is a significant negative correlation between bar
ellipticity and central mass concentration. This is the first observational
evidence that bar ellipticity decreases with nuclear mass; it may indicate
that the central mass buildup in bars results ultimately in the dissolution
of the bar itself.
Midplane Stellar Orbits and Mass distribution in the Presence of 3D Spiral Arms
Barbara Pichardo, Marco Martos, Edmundo Moreno y Julia Espresate
Instituto de Astronomia, UNAM
barbara@astroscu.unam.mx
()
We have modeled galactic spiral arms as a superposition of
inhomogeneous oblate spheroids, and added its contribution to an
axisymmetric model of the Galactic mass distribution. The strength,
angular speed, pitch angle, central density of the spiral arms, and
the spatial extent of the adopted spiral density pattern, were
selected within a range of possibilities suggested by observations
and, mostly, theory, giving us a plausible model for the Galactic
potential outside the inner Lindblad resonance. A given locus for the
spiral pattern as delineated by HII regions, was assumed; this results
in a pitch angle that is consistent with local measurements. With
this pitch angle, self-consistent spiral arms models terminate at the
4/1 resonance, as predicted for Contopoulos and Grosb{\o}l for strong
spirals. Then our Galaxy is seemingly much closer to a strong spiral
than to a weak spiral and nonlinear theory applies. Orbits in the
Galactic plane are analyzed in the non-inertial reference frame of the
spiral arms, and also followed in the inertial frame with origin at
the Galactic center. Defining in an inertial frame the sense of
orbital motion around the Galactic center gives a clean separation of
prograde and retrograde orbits in a Poincar\'e diagram. Orbital chaos
begins to manifest in the prograde region if we increase the mass in
the arms and/or its pitch angle. According to our exploration, the
Sun's orbit might conceivably lie in a region of chaotic
behavior. Even in the weak regime, the orbital structure is clearly
modified from that obtained in models in which the spiral structure is
not considered, or in which its contribution to the total potential is
represented as a perturbing, simple periodic term. In general, the
full integration of the force indicates that the usual local
approximation for the arms perturbation is not valid.
Simulations of the Magellanic System: Internal Structure of the Clouds
irapuan@discovery.saclay.cea.fr
()
Much of our understanding of the nature of the interaction between the Magellanic Clouds and our own Galaxy has emerged from numerical simulations. Features like the Magellanic Stream, the inter-cloud region and the Wing are thought to be produced by the tidal interaction among the members of this triple system. Here I use a TREESPH code to simulate self-consistently the Large and Small Magellanic clouds orbiting a fixed potential representing our Galaxy.
The orbital reconstruction, galaxy models models and initial conditions are based on the observational constrains (morphology and kinematics in various wavelengths, proper-motions, distribution of different stellar types and gas), however a considerable amount of free parameters remains unconstrained, and a great number of simulations is required. A large number of simulations have already been run. This is an ongoing work, whose main objective is to study the development of the internal structure of the clouds and inter-cloud region, to find the dynamical parameters responsible, for example, by the formation of the off-centered bar in the LMC or its external ring-like structure.
Comparing Molecular Gas and Star Formation Properties in the Central Regions of Barred and Unbarred Spirals
K. Sheth, S.N. Vogel,P.J. Teuben, A.I. Harris, M.W. Regan, M.D. Thornley
(1)Caltech
(2,3,4) U. Maryland
(5) StScI
(6) Bucknell University
kartik@astro.caltech.edu
()
A comparative study of the molecular gas properties and associated
star formation activity in the 44 galaxy sample from the BIMA Survey
of Nearby Galaxies shows striking differences between barred and
unbarred spirals. The mean nuclear molecular gas surface density of
barred spirals ($\langle$$\Sigma_{nuc}$$\rangle$=309$\pm$71 \Msun\
pc$^{-2}$) is three times higher than that of unbarred spirals
($\langle$$\Sigma_{nuc}$$\rangle$=107$\pm$29 \Msun\ pc$^{-2}$). Nine
out of the eleven bars with $\Sigma_{nuc} >$ 300 \Msun\ pc$^{-2}$ are
early types. Thse differences mirror the differences in star formation
activity noted by earlier studies. Our sample shows that above a
$\Sigma_{nuc} >$ 100 \Msun\ pc$^{-2}$, the star formation rate
typically scales with the gas surface density (Schmidt law), but there
are notable exceptions where star formation appears to be inhibited
despite overwhelmingly large $\Sigma_{nuc}$. Below 100 \Msun\
pc$^{-2}$, the estimated star formation rates are higher than
expected. We will discuss plausible reasons for these results. We
have also confirmed the main finding of the NRO-OVRO survey that
barred spirals are more centrally concentrated than unbarred spirals.
The median value of the concentration parameter for barred spirals
(f$_{con}$=$\Sigma_{nuc}$/$\Sigma_{disk}$=27.7) is a factor of four
higher than that for the unbarred spirals (f$_{con}$=6.2). These data
further implicate the large scale bars in transporting large amounts
of molecular gas to the center.
Simulations of the Magellanic System: Internal Structure of the Clouds
Irapuan Rodrigues
CEA-Saclay / Fellow of the brazilian CNPq
irapuan@discovery.saclay.cea.fr
()
Much of our understanding of the nature of the interaction between the Magellanic Clouds and our own Galaxy has emerged from numerical simulations. Features like the Magellanic Stream, the inter-cloud region and the Wing are thought to be produced by the tidal interaction among the members of this triple system. Here I use a TREESPH code to simulate self-consistently the Large and Small Magellanic clouds orbiting a fixed potential representing our Galaxy.
The orbital reconstruction, galaxy models models and initial conditions are based on the observational constrains (morphology and kinematics in various wavelengths, proper-motions, distribution of different stellar types and gas), however a considerable amount of free parameters remains unconstrained, and a great number of simulations is required. A large number of simulations have already been run. This is an ongoing work, whose main objective is to study the development of the internal structure of the clouds and inter-cloud region, to find the dynamical parameters responsible, for example, by the formation of the off-centered bar in the LMC or its external ring-like structure.
Numerical Simulations of Disk Galaxy Formation
Julio F. Navarro
University of Victoria
Canada
jfn@uvic.ca
()
I will present our latest results concerning simulations of galaxy formation in a hierarchically clustering universe. I will emphasize
recent progress on the viability of Cold Dark Matter on the scale of individual galaxies. In particular I plan to concentrate on issues
concerning dark matter halo substructure, the evolution of galaxy disks in realistic CDM halos, and the origin of disk galaxy scaling
laws.
Pattern Speed of Bars
Joris Gerssen
Space Telescope Science Institute
gerssen@stsci.edu
()
The key parameter of any barred galaxy model is its pattern speed.
Most determinations of this crucial parameter have relied on indirect
measurements by either identifying morphological features with
resonances or by modelling kinematical data sets such as velocity fields.
A direct, non-model dependent, method to trace the pattern speed of a
bar has been developed by Tremaine and Weinberg (1984). We present
the results of an application of this method to five barred galaxies
and conclude that all bars in this sample are consistent with being
fast rotators. The apparent lack of bar deceleration in these five
galaxies suggests that they cannot have centrally-concentrated dark
matter halos.
The Intrinsic Ellipticity of Spiral Disks
Andersen, D.R.$^{1,2}$, Bershady, M.A.$^{3}$
1. Penn State University
2. MPIA Heidelberg
3. UW-Madison
andersen@astro.wisc.edu
()
We present estimates of the intrinsic ellipticity for a sample of 25
relatively face--on spiral disks based on H$\alpha$ velocity fields
and $R$ and $I$-band imaging. We show how differences between
kinematic and photometric inclination and position angles can be used
to determine the intrinsic ellipticity of galaxy disks. Our findings
suggest disks span a range of ellipticities from $\epsilon= 0$ (circular)
to $\epsilon=0.2$. If galaxies in Tully-Fisher studies have a similar
distribution of disk ellipticities, this would account for roughly
50\% of the scatter in the Tully--Fisher relation.
oyam@inaoep.mx
()
palacios@inaoep.mx
()
Velocity Fields of Disk Galaxies
Peter Teuben
University of Maryland, College Park, MD, USA
teuben@astro.umd.edu
()
In this talk an overview will be given on how velocity
fields for disk galaxies are derived and interpreted.
Some recently developed techniques will also be discussed,
and applied to the BIMA Survey of Nearby Galaxies (SONG).
Influences of bars, spiral arms, and oddly shaped halos
will be contrasted and identified.
Global properties of disks from the Flat Galaxy
Catalog
I.D.Karachentsev {1}, V.E.Karachentseva {2}, Yu.N.Kudrya {2},
S.N.Mitronova {1}, and S.L.Parnovsky {2}
{1} Special Astrophysical Observatory, Russian Academy of
Sciences, {2} Astronomical Observatory, Kiev State University
ikar@luna.sao.ru
()
We discuss optical, NIR and HI properties of
thin edge-on galaxies from
the Revised Flat Galaxy Catalog. The RFGC covers the entire sky and
contains 4236 galaxies with blue angular diameters a_25 > 0.6 arcmin
and apparent axial ratios a/b > 7. About 1000 of them have been observed
with the Arecibo radio telescope and the 6-m optical Russian telescope.
The blue LF of the galaxies is described by Shechter's function with
alpha = -1.14 and M^* = -20.1. The basic parameters of the galaxies: linear
diameter, surface brightness, axial ratio, hydrogen mass-to-luminosity
ratio, and total mass-to-luminosity ratio are considered as a function
of their morphological type and rotation amplitude. There is a linear
correlation between the HI mass of the galaxies and their angular momentum
expected when the gaseous disks of dwarf and giant spirals are situated
near the boundary of gravitational instability favoring star formation.
The local relative number of flat galaxies with apparent axial ratios
a/b > 7 is 1/17. Being compared with a fraction of flat galaxies in the
Deep HST fields, it can give us information about a rate of secular
evolution of disks.
Unveiling the behavior of the ionized gas in nearby irregular galaxies
Margarita Valdez-Gutierrez (1,2), Margarita Rosado (2), Leonid Georgiev (2), Ivanio Puerari (1), Jordanka Borissova (3), Radostin Kurtev (3), Lorena Arias (1)
(1) INAOE, Mexico (2) IA-UNAM, Mexico (3) Sofia, Bulgaria
mago@inaoep.mx
()
We present the first results of a long term project devoted to study
the interrelationship between gas and stars in nearby irregular galaxies.
In particular, our results focused on the kinematics and dynamics of the
ionized gas of NGC 4449 and IC 1613 are highlighted.
The gravitational torque of bars
D.L. Block (1), I. Puerari (2), J.H. Knapen (3,4), B.G. Elmegreen (5),
R. Buta (6), S. Stedman (4), D.M. Elmegreen (7)
(1) Wits University, South Africa (2) INAOE, Mexico (3) INGT, Spain
(4) University of Hertforshire, UK (5) IBM Research Division, USA
(6) University of Alabama, USA (7) Vassar College, USA
puerari@inaoep.mx
()
We determined the relative bar torques of 45
galaxies observed at
K-band with the 4.2m William Hershel Telescope. The relative bar torque
is calculated by transforming the light distributions into potentials
and deriving the maximum ratios of the tangential forces relative to the
radial forces. We found that the relative bar torque correlates only
weakly with the optical bar type listed in the Revised Shapley-Ames and
the de Vaucouleurs systems. In fact, some classically barred galaxies
have weaker relative bar torques than classically unbarred galaxies.
Applications to the bar torque measurement to the high-redshift universe
are briefly discussed.
The Spatial Distribution of the Star Formation in (S+S) Binary Galaxies
H.M. Hernandez-Toledo (1), I. Puerari (2) and C. Conselice (3)
(1) Instituto de Astronomia, UNAM, Mexico (2) INAOE, Mexico (3) Space Telescope Science Institute, USA
puerari@inaoep.mx
()
We report some preliminary results of a photometric study of the spatial distribution of the Star Formation in (S+S) Binary Galaxies from the Catalogue of Isolated Pairs of Galaxies, Karacehntsev (1972)
The Milky Way
Walter Dehnen
MPIA, Heidelberg
dehnen@mpia.de
()
In this review talk, I am going to give an overview about
our observational picture of the Milky Way as a galaxy and
compare it with disk galaxies in general. The Milky Way can
be observed in much greater detail than any other galaxy
and hence plays a crucial role in our understanding of
galaxy formation in general and the formation of luminous
spiral galaxies in particular.
Bloated Dwarfs: The Thickness of the HI Disks in Irregular Galaxies
Elias Brinks
Departamento de Astronomia
Universidad de Guanajuato
Mexico
ebrinks@astro.ugto.mx
()
Somewhat counterintuitively, the gas disks of irregular galaxies, such
as Holmberg~II, Holmberg~I, or DDO~47, are thicker than those of much
larger, normal disk galaxies, both in relative as well as in absolute
terms. In retrospect, this is easily understood. The velocity
dispersion of the gas throughout galaxy disks is regulated by the star
forming activity and is of the same order, 6--9 km\,s$^{-1}$, in dwarf
galaxies as in spirals. The gravitational potential of irregulars is
considerably smaller, though, with as a result a thicker or puffed--up
disk, at least as far as the neutral gas as traced in HI is
concerned. I will explain several methods which can be used to derive
the scaleheight of the gas in irregular galaxies and discuss the
consequences a puffed--up disk has on the possible escape of metals
into the halo as a result of supernova explosions within OB
associations. I will also comment upon how a puffed--up disk
increases the cross section of irregular galaxies, increasing the
probability for intercepting lines of sight towards QSOs, and how the
shape of the gas disks can be used to constrain, in principle, their
dark matter content.
The 3D structure of the Galactic bulge from the MACHO red clump stars
Roger Fux(1), Tim Axelrod(1), Piotr Popowski(2)
(1) RSAA/ANU, Australia
(2) LLNL, USA
fux@mso.anu.edu.au
()
The MACHO experiment has collected $V$ and $R$ band stellar
photometry within a roughly $8^{\circ}\times 8^{\circ}$
area of the Galactic bulge centred on
$(l,b)\approx(4^{\circ},-6^{\circ})$. These data and
additional new $I$ band observations are used to recover
the 3D structure of the bulge/bar as mainly traced by the
$\sim 3\cdot 10^6$ red clump stars enclosed in this region.
Arm vs. interarm star formation processes in disk galaxies
J.H. Knapen(1, 2) & S. Stedman(2)
(1) ING, Spain
(2) Univ. Hertfordshire, UK
knapen@ing.iac.es
()
We present first results of an ambitious study aimed at determining the
relative prominence of star formation in arm versus interarm regions in
spiral disks and as a function of radius. We have collected $B, I$,
near-IR $K'$, and H$\alpha$ imaging of a complete sample of 57 spiral
galaxies of all types. We will show the characteristics of this data
set and outline how parameters describing the young and old stellar
populations are obtained across the different disk components,
concentrating on bars and spiral arms.
Radial structures of galactic disks
M. Pohlen, R.-J. Dettmar, R. L"utticke
AIRUB Bochum, Germany
pohlen@astro.ruhr-uni-bochum.de
()
We will present the results from our new deep imaging survey
on a morphologically selected sample of about 70
edge-on disk galaxies. We will address the question of the
global structure of galactic stellar disks especially the
radial surface brightness profiles at large galactocentric distances.
We find that the radial profiles are better described
by a two-slope exponential profile, characterized by an inner-
($h_{in}$) and outer- ($h_{out}$) scalelength separated at a
break radius $R_{b}$, rather than a sharp truncated exponential.
The position of the mean value for the break radius is at
$R_{b} = 2.4\pm0.8 h_{in}$. The inner scalelength is consistently
larger than the outer: $h_{in}/h_{out} = 4.5\pm1.8$.
First results will be given for face-on equivalents serving as the
crucial test to assure the findings for the edge-on sample without
suspected geometrical line-of-sight effects. We undoubtedly confirm
the deduced two-slope or smooth truncation structure in a few cases.
In addition, some caveats will be given concerning the available
characteristic disk parameters and their model dependence such
as scalelength or scaleheight.
Dynamical simulations: waiting for VLT-GIRAFFE observations of distant galaxies
Laurent Chemin and Veronique Cayatte
OBSPM, FRANCE
Laurent.Chemin@obspm.fr
()
The VLT-GIRAFFE instrument is a soonly released optical (370 nm $ \leq
\lambda_{obs} \leq$ 900 nm) multifibre spectrograph working at medium or high
resolution (9000 $\leq R \leq$ 29000). Two of the three observational modes
will be integral field : 15 deployable \textbf{I}ntegral \textbf{F}ield
\textbf{U}nits (2.1"$\times$3.1") in the 25'
field of view and 1 large array \textbf{ARGUS} (11.5" $\times$ 7.3" or 6.6"
$\times$ 4.2"). \par With these modes, spectroscopy of disks at redshifts up
to $z\sim$ 1 will allow to do kinematical
and dynamical studies of galaxies. In particular, the \textbf{IFU} mode is
well adapted to map distant galaxies because the size and the number of its
arrays are consistent with those expected
for objects in a redshift range in such a field of view. \par To understand
the future GIRAFFE data, we need an analysis tool based on simulations which
results will be directly compared to the
observations. The main inputs of the simulations are the luminosity
distribution of objects through high angular resolution imaging and
the velocities distribution. We will be able to see which
kinematical model can account for the observations and so to evaluate
fundamental parameters of the objects (for instance the maximum rotational
velocity useful for the Tully-Fisher relation, the mass...) or the
rate of interacting galaxies. We present here the results of different
simulations.
On the stellar mass density within spiral galaxy disks
Thilo Kranz*, Adrianne Slyz**, Hans-Walter Rix*
* MPI Astronomie, Heidelberg, Germany
** University of Oxford, UK
kranz@mpia.de
()
We study the mass density within spiral galaxies on the
basis of NIR photometry and gas kinematics from observations
and simulations. Although K-band images provide a quite
reliable estimate of the stellar mass distribution within
the disks of spiral galaxies, we demonstrate that correcting
the color to a constant stellar M/L leads to shorter disk
scale lengths and has a notable effect on the disk-halo
decomposition. In most sub-maximal disk decompositions,
good fits to a galaxy's measured rotation curve cannot be
achieved by axisymmetric disk and halo models but require
non-circular velocity components to be taken into account.
We accomplish this by performing 2D hydrodynamical gas
simulations.
Furthermore, in comparison with the galaxy's measured
kinematics, the simulated velocity fields allow us to
constrain the contribution of a smooth dark matter component
to the total mass in the inner few exponential disk scale
lengths in spiral galaxies. We show for a sample of
galaxies that the simulations overpredict the non-circular
gas motions for a strictly maximal stellar disk
contribution.
Our data sample will be made available for public use.
On the spiral Structure of NGC 2915
M. Bureau and F. Masset
Columbia University
Saclay
fmasset@cea.fr
()
Eulerian numerical simulation of the HI disk gas of the
galaxy NGC2915 are presented, and the results are used to
infer the properties of this disk and the surrounding
halo (HI surface density, dark matter content, etc.)
Bar Wings
Maria Sundin
Mikael Lerner
Magnus Thomasson
Gothenburg University, Sweden
SEST, Chile
Onsala Space Observatory, Sweden
tfams@fy.chalmers.se
()
In galaxies with short bars, i.e. bars not extending out to
the co-rotation radius, there may be an extra dynamical
component located between the bar and a spiral arm pattern
starting at the co-rotation radius. We call this component
"the bar wings". The appearance of a galaxy with bar wings
changes dramatically on timescales shorter than a bar
rotation period. The bar wings will periodically appear as
leading or trailing arm fragments. In between, it may show
up as an outer envelope surrounding the bar or as a theta-
galaxy. The bar wings is a bar-like component in the sense
that the phase of the m=2 Fourier component of the surface
is roughly constant within it. The bar and the bar wings are
involved in a continous and alternating exchange of angular
momentum between them. The result is that the pattern speeds
of both the components show strong oscillations that are 180
degrees out of phase. A simple orbit analysis reveals that
the 3:1 resonance orbits are a major constituent of the
bar wings. Also 4:1 orbits and orbits around Lagrange points
L4 and L5 are important.
Spiral shape and mass distribution in five grand design galaxies
Magnus Thomasson
Karl Johan Donner
Onsala, Sweden
Helsinki Univ. Observatory, Finland
magnus@oso.chalmers.se
()
From N-body simulations of disc galaxies, we have found
that the shape of the spiral arms corresponds to Toomre's
critical wavenumber (which depends on the rotation curve,
through the epicyclic frequency, and on the disc surface
density). For real galaxies, the disc surface density can
thus be determined from observations of the rotation curve
and the shape of the arms.
We have applied the method to five grand design spiral
galaxies with inclinations large enough that the rotations
curve can be determined, but small enough for the spiral
structure to be clearly visible: M51, M100, NGC1357,
NGC1566, and NGC2997. Using published rotation curves
and images, we first determine the disk surface density.
From published disk/bulge decompositions of the observed
luminosity distribution, we then calculate the
mass-to-luminosity ratio for the disc. The M/L-ratios we
obtain in this way are relatively low.
This method of determining the disc surface denstity is
independent of additional assumptions, and the results
show that there cannot be large amounts of dark matter in
the discs of the five studied galaxies.
Multi-Wavelength Study of NGC 1784
Douglas L. Ratay
Stephen T. Gottesman
University of Florida, USA
doug@astro.ufl.edu
()
NGC 1784 is a flocculent, barred, late type spiral galaxy.
We present HI, optical(narrow and broad band), and NIR images
of this galaxy. NGC 1784 seems to be undergoing an interaction
with a small companion galaxy. This was undiscovered before
our HI observations were made. A link from this galaxy to a
large sample studying the properties of barred and flocculent
galaxies will also be made.
Dynamical Evolution of Central Kpc in Barred Galaxies
Isaac Shlosman
JILA, University of Colorado at Boulder, USA
shlosman@jila.colorado.edu
()
Recent progress in ground-based instruments and the
availability of the
Hubble Space Telescope allows for the first time a meaningful analysis
of central morphology and kinematics, both stellar and gaseous, in disk
galaxies. I will discuss implications for dynamics and evolution of
this region and for its coupling with smaller and larger spatial scales.
3D modeling of the vertical structure of the galaxy
Gilberto C. Gomez
Donald P. Cox
UW - Madison, USA
gomez@wisp.physics.wisc.edu
()
We present the results of our 3-dimensional modeling of a
MHD flow into a spiral gravitational potential, extending
the work done by Martos \& Cox (1998). We pay particular
attention to the similarities of the resulting structures
to hydraulic bores, generation of substructure, and
secondary gaseous arms.
wwall@inaoep.mx
()
Eccentric Equilibria for Keplerian Fluid Disks
T. S. Statler
Ohio University, Athens, OH, USA
tss@coma.phy.ohiou.edu
()
In the idealization of a razor-thin Keplerian disk, flow along aligned,
elliptical streamlines of constant eccentricity creates a density that
is constant on streamlines. In such a configuration there will be no
compression of the fluid, and therefore no dissipation due to bulk viscosity.
For most density profiles, the pressure gradient will drive a differential
precession which will destroy the alignment; however, there is a family of
simple equilibria in which the precession frequency is the same at all radii.
These disks could therefore be long-lived at significant eccentricities if the
shear viscosity is negligible. In the limit of small eccentricity, the models
can be seen as axisymmetric disks perturbed by a traveling acoustic wave
similar to an ocean wave, in which the fluid rises and falls epicyclically in
the gravitational field of the central mass. The expected emission line
profiles from the eccentric disks are strongly asymmetric in general, and,
in extreme cases, prone to misinterpretation as single narrow lines with
significant velocity offsets.
A new look at the holes of dwarf galaxies (POSTER)
F. Javier Sanchez-Salcedo
IA-UNAM
jsanchez@astroscu.unam.mx
()
New stastitiscal tests are proposed to discriminate
between the different scenarios proposed for
the formation of HI holes in gas-rich dwarf galxies.
Although conclusions are still premature, the
standard scenario of expanding shells by powerful
energy injection by winds and supernova explosions
is favoured.
Disk Galaxy Evolution
Roberto Abraham
Dept. of Astronomy & Astrophysics, University of Toronto, Canada
abraham@astro.utoronto.ca
()
Recent progress in constraining the evolution
of disk galaxies will be
reviewed. I will focus in turn on evidence for evolution in the size,
luminosity, morphological and dynamical characteristics of luminous disks.
At least *some* of these characteristics are well constrained to z=1. Some
characteristics (such as detailed morphology) change quickly with
redshift, but there is little evidence that other characteristics (such as
size) change at all. I will touch upon the implications of these
observations for theories of galaxy formation, and conclude that the
redshift range 1$<$z$<$2 is critical for testing such theories. This is also
the redshift range over which we know the least about luminous disk
galaxies. The severe observational selection effects inherent in studying
disk evolution at z$>$1 will then be described, and a summary given of what
little is known about disk galaxies at 1$<$z$<$2 in spite these selection
effects. I will conclude by showing how the Advanced Camera for Surveys
coupled with technical advances in ground-based spectroscopy (such as the
nod and shuffle technique) will open up the 1$<$z$<$2 redshift range for study
in the next couple of years.
dhuos@inaoep.mx
()
Simulations of the Eccentric Nuclear Disk in M31
Robert M. Salow
Ohio University
salow@helios.phy.ohiou.edu
()
We have constructed approximate self-consistent models of eccentric
stellar disks around central black holes. These models include a
finite-dispersion, weakly self-gravitating disk in a frame rotating at a
constant precession speed. The disks are built by an iteration scheme in
which the disk is populated by quasi-periodic orbits using a distribution
function written in terms of the Kepler integrals of motion. Properties
of these models will be discussed, particularly those that are relevant to
the double nucleus of M31. We have also developed an n-body code which is
well suited for stability studies of disk systems with high-eccentricity
orbits. Preliminary results on the use of this code to study the
stability of our disk models will be discussed.
omartin@fcfm.buap.mx
()
Magnetohydrodynamic Density Waves in Spiral Galaxies
Yu-Qing Lou
Department of Astronomy and Astrophysics, University of Chicago, USA
lou@oddjob.uchicago.edu
()
Relativistic cosmic-ray electrons interact with galactic magnetic fields
and give rise to synchrotron radio emissions that reveal well-organized
large-scale spiral patterns in good correspondence to large-scale optical
structures of spiral galaxies. The system of a spiral galaxy involves
a massive dark-matter halo, a thin stellar disk, a magnetized gas disk
of interstellar medium (ISM) and a spheroid of cosmic-ray gas. We here
describe a physical scenario for magnetized spiral galaxies on the basis
of magnetohydrodynamic (MHD) density waves which involve self-gravity,
differential rotation, epicyclic oscillations, Lorentz force, pressure
force and velocity dispersions. The basic results of our analyses on fast
and slow MHD density waves since 1996 (Fan & Lou, Nature, 383, 800) are
summarized. For multiwavelength observations of spiral galaxies, we
emphasize the perspective that large-scale magnetic fields of MHD density
waves play the key role in organizing correlated structures of the various
underlying ISM components. In particular, the magnetized neutral hydrogen
disk is an integral component in the overall MHD density wave scenario
(Lou et al. ApJ, 2002). Possible wave excitation mechanisms are mentioned
and diagnostic features of magnetized ISM are emphasized. Applications to
nearby spiral galaxies NGC6946, M51 (NGC 5194), M31 (NGC 224) and NGC2997
will be discussed. Based on recent magnetic field observations of NGC1097
and NGC2997, it becomes evident that MHD density waves also play important
roles in the circumnuclear regions and may be responsible for the
appearance of luminous starburst rings (Lou et al. 2001, ApJL, 553, 35).
It would be extremely important to map out in details magnetic field
patterns in the circumnuclear regions of spiral galaxies. With proper
adaptations, the physics of spiral MHD density waves may be relevant
to the dynamics of accretion disks in various astrophysical contexts,
especially in terms of transporting angular momentum.
Asymmetries in the disk of the Milky Way
Drimmel, R. and Smart, R.
Osservatorio Astronomico di Torino, Italy
drimmel@to.astro.it
()
Asymmetries in the stellar disk of the Milky Way, manifested by the
Galactic warp and spiral arms, are investigated using Galactic diffuse NIR
emission and optical star counts from the recently released
Guide Star Catalogue II. Star counts for approximately 150
lines-of-sight within 25 degrees of the Galactic poles, covering nearly
4000 square degrees of sky, are analyzed
using a model independent method to assess the amplitude of a
local tilt in the stellar disk. Such a tilt is consistent with a
Galactic warp starting within the Solar Circle, and as seen in the
diffuse NIR emission as measured by COBE (Drimmel & Spergel 2001,
Freudenreich 1998). Finally, various spiral arm geometries,
including one based on the dynamical model of Amaral and Lepine
(1997), are incorporated in a model of the Galactic diffuse NIR
emission that is then fit to observations made by the COBE satellite.
The favored models have a four arm pattern, with two arms dominating.
WIYN Integral-Field Kinematics of Disk Galaxies
Matthew A. Bershady
U. of Wisconsin, USA
mab@astro.wisc.edu
()
We present results on medium spectral resolution, 2D kinematic studies
of disks with DensePak and the newly-commissioned SparsePak fiber
array on the WIYN telescope: A Tully-Fisher relation for nearly
face-on galaxies; H-alpha velocity fields of low-surface-brightness
disks; and the stellar velocity fields and dispersions of normal
disks. These data permit us to explore the detailed mass
distributions, mass-to-light ratios, and asymmetries of a wide range
of spiral galaxies. We discuss the implications of these studies in
the context of comparable measurements at higher redshift.
pochoas@inaoep.mx
()
ahtramop@inaoep.mx
()
yamil@inaoep.mx
()
1. Neutral Hydrogen Observations in Isolated Triple Systems of Galaxies. 2. BVRIJHK Surface Photometry and Halpha Fabry-Perot Interferometry in Mixed Morphology (E+S) Pairs of Galaxies.
1.H.M.Hernandez-Toledo, W.K. Huchtmeier, V.Karachentseva and E. Brinks. 2. H.M. Hernandez-Toledo, M. Rosado, I.Cruz-Gonzalez, and A. Franco
1. Instituto de Astronomia, UNAM, Mexico. Max-Planck-Institute fur Radioastronomie, Bonn, Germany. Astronomical Observatory of Kiev. Departameno de Astronomia, Universidad de Guanajuato, Mexico. 2. Instituto de Astronomia, UNAM, Mexico
hector@astroscu.unam.mx
()
1. We report single-dish HI (Effelsberg 100m Telescope) observations of a sample of 26 Isolated Triple Systems of Galaxies in the Northern Hemisphere , Karachentseva (1979;1988).
2. We report some preliminary results of an Optical/NIR photometric and Interferometric study in a sample of Mixed Morphology (E+S) Pairs of Galaxies from the Catalogue of Isolated Pairs of Galaxies, Karachentsev (1972).
Kinematic response of the outer stellar disk to a central bar
Gerhard M\"uhlbauer, Walter Dehnen
Gerhard M\"uhlbauer: MPIA Heidelberg, Germany
Walter Dehnen: MPIA Heidelberg, Germany
muehlbau@mpia-hd.mpg.de
()
We performed numerical 2D simulations in order to estimate the influence of a central
bar-like perturbation on the velocity distribution in the outer parts of
a disk galaxy. To get reasonable statistics, priority was not on a self-consistent
calculation but rather on a high particle number of $10^7$. Therefore a fixed
potential for the galaxy together with a rotating perturbation with m=2-symmetry
was assumed. After completion of adiabatic growth of the perturbation
and some further rotation periods for the disk to re-settle into equilibrium,
the first and second moments of the resulting velocity distribution have been
analysed, giving information on assymetric drift, vertex deviation and Oort constants.
Results are presented best as azimuthal Fourier components with
focus on the m=2-components corresponding to the perturbation symmetry. Several
resonance patterns are discernible.
Secular evolution of barred galaxies : theory
E. Athanassoula
Observatoire de Marseille
lia@paxi.cnrs-mrs.fr
()
Dark matter in spiral galaxies
A. Bosma
Observatoire de Marseille
bosma@batis.cnrs-mrs.fr
()
I will explain why we still do not have a "standard" model
for the mass distribution of spiral galaxies, and describe
various methods which might help to get us there. I will
also describe ongoing work on declining rotation curves
and other topics based on HI observations.
toa@inaoep.mx
()
pepe@astroscu.unam.mx
()
Formation of Galaxy Discs by merger of sub-galaxies
Williams, P.R. & Nelson, A.H.
Tohoku University (Japan) and Cardiff University (UK)
nelsona@cf.ac.uk
()
Computer Simulations of galaxy formation show that an
important mechanism for the formation of galaxy discs is the tidal
disruption of smaller satellite galaxies which are an integral part of
the formation process. A star-forming Tree SPH simulation of this process
will be analysed.
Warped galaxies and the dark matter connection
Yves Revaz
Geneva Observatory, SWITZERLAND
yves.revaz@obs.unige.ch
()
50 years have passed since the first HI observation
of the Milky Way
warp. If during this time, numerous hypothesis have been proposed to
explain this galactic common phenomenon, none of them was able to
clearly satisfying all the constraints provided by the observations.
Most of the works on the topic are based on the assumption of a
spherical or triaxial dark matter halo as predicted by the CDM theory.
In this poster, we point out some problems arising with a dynamically
hot dark matter halo and explore
the hypothesis of a heavy self-gravitating warped disk.
For such a model, periodic orbits which form the backbone of
the galaxy are described and are confronted with N-body simulations.
Interaction of HVCs with Galactic Disk.
Alfredo Santillan(1) & Jose Franco(2)
(1) CA-DGSCA, UNAM, Mexico.
(2) IA, UNAM, Mexico
alfredo@astroscu.unam.mx
()
The role of the magnetic field in the lopsided structures in the Galactic Center region
Michel Tagger
Service d'Astrophysique, CEA Saclay (France)
tagger@cea.fr
()
I will describe how recent results on a spiral instability of magnetized accretion disks could shed light on the structures observed in the Galactic Center region. There, on a scale of $\sim 100$ pc, the distribution and velocity field of the gas is strongly lopsided, while the magnetic field is highly anomalous: it is vertical (rather than mostly horizontal in the Glactic disk), and measured in milligauss (rather than microgauss). The magnetized structures observed above the disk provide a natural diagnostic of the complex dynamics in this region.
Off-plane gas and galaxy discs
Linda Sparke
Astronomy Deaprtment, University of Wisconsin-Madison
sparke@astro.wisc.edu
()
Gas that orbits a disk galaxy, but does not
lie in the plane of the
disk, has probably been perturbed or excited out of that plane, or
has fallen in from outside. Recent work shows no easy path to
exciting galactic warps of the amplitude that we observe; in polar
ring galaxies, the outer, mainly gaseous, ring appears to be 'younger'
than the inner stellar body. This talk reviews the idea that both
warps and polar rings represent the relics of earlier infall or
interaction.
yjuarez@inaoep.mx
()
Disk Formation in CDM: Crises and Resolutions
Avishai Dekel
Hebrew University of Jerusalem
dekel@phys.huji.ac.il
()
The spin problem and the cusp problem of galaxy formation
in CDM cosmology are addressed in terms of tidal effects
during halo buidup by mergers. It is argued that feedback
processes provide possible resolution to these problems.
The coupling between the baryonic and dark matter components in galaxies
Amr El-Zant, Isaac Shlosman
University of Kentucky and CASA, University of Colorado at
Boulder, USA
elzant@origins.colorado.edu
()
We examine the effect of dark matter distribution on the
evolution of baryonic component in galaxies and vice versa.
In particular we study the effect of halo central
concentration and (a)symmetry on disk formation and
oribital stability.
Circumnuclear structures in the interacting
active galaxy NGC 1241: kinematics and optical/IR morphology
Diaz R.J. (1), Dottori H. (2), Villamizar N. (2), Carranza G. (1)
(1) Observatorio Astronomico de Cordoba, UNC, Argentina
(2) Instituto de Fisica, UFRGS, Brasil
diaz@oac.uncor.edu
()
We have studied the central regions of NGC 1241, an interacting galaxy with
an active nucleus. We used high resolution Gemini North Telescope K, J
images (~ 0.3" resolution), HST Pa alpha and (V+R) images (~ 0.2" and ~
0.1") to analyze the spiral pattern in the inner 7" (1" = 257 pc).
The complete set of data allowed us to unveil the
presence of peculiar features in the nuclear region of this
galaxy: a trailing spiral structure inside a star formation ring
with dimensions 2.8" x 1.7", a mini-bar (1.4") and what appears to be a pair
of leading nuclear spiral arms. The circumnuclear ring appears clumpy in Pa
alpha emission, it has a mean diameter ~ 1400 pc and harbours a N-S aligned
~ 500 pc long, central bar.
The morphological scenario is complex and the structural
parameters are different in each band. Gemini-Hokupa'a images show
a smooth, inclined disk, with approximately elliptical
isodensities of varying position angle. Ellipses fits indicate
that the disk inclination is similar to that of the star forming
ring. The overall reddening to the southwest of the nucleus is
stronger, implying that this is the near side of the galaxy. The
Pa alpha nuclear bar, almost perpendicular to the global one,
was not detected in a previously published HST color map.
We have applied 2D and 1D Fourier analysis for the first time at
circumnuclear scales in the optical and IR bands simultaneously.
Fast Fourier Transform shows that a barred m=2 mode is dominant
in K and J bands. The bar in K and J bands is counterclockwise rotated by
30º with regard to the Pa alpha one. (V+R) band presents a more complex
structure
with a strong m=1 mode. The position of the m=2 mode
corotation is clearly defined by our analysis and approximately
coincides with the extreme of the Pa alpha bar. The leading
spiral pattern ends in the Pa alpha ring. Our kinematical data
yield a trailing pattern angular speed Omega_p = 230+-20 km/sec/kpc.
Published numerically modelled galactic disks indicate a pattern age of the
order of tens of millions years. Nevertheless, considering its
high angular speed, the pattern has done several
revolutions since the perturbation origin.
The study of the rotation curve, with a lower angular resolution, indicates
that the circumnuclear ring would be just inside the Inner Lindblad
Resonance (r ~ 1 kpc) of the global pattern.
Magnetic Fields in Southern Barred Spiral Galaxies
J.I. Harnett,
R. Beck, M. Thierbach, M. Ehle, R.F. Haynes & R. Wielebinski
UTS
Max-Planck_Institut fuer Radioastronomie
Max-Planck_Institut fuer Radioastronomie
University of Tasmania
Max-Planck_Institut fuer Radioastronomie
jules@eng.uts.edu.au
()
Polarized radio emission from southern barred spiral galaxies.
Magnetic fields in normal spiral galaxies follow, in the main, optical spiral
arm patterns, but are often of maximum intensity between the arms. In barred
galaxies however, the conditions are somewhat different; the gas and dust
move in highly non-circular orbits and streamlines are strongly deflected in
the bar region along shock fronts, behind which the gas is compressed in a
fast-shearing flow. The gas in the bar region rotates faster than the bar so
compression regions traced by massive dust lanes develop along the edge of
the bar that is leading with respect to the galaxy's rotation. Gas inflow
along the compression region may fuel starburst activity in a dense
circum-nuclear ring although this inflow is difficult to measure
observationally and the dynamics are not understood. In order to investigate
the role of the magnetic field in the bar with respect to the gas flow and
star formation, we have observed 19 nearby barred galaxies. We present our
results for some southern galaxies here.
Gas Kinematics in Barred and Spiral Galaxies
Michael Regan
Space Telescope Science Institute
mregan@stsci.edu
()
The kinematics of the interstellar medium in disk galaxies
influences many processes in galaxy evolution.
For example, since the gas in dissipative it can lose angular momentum and thus increase the central mass concentration in the galaxy.
In addition, the interstellar medium is the fuel for star formation and star formation can be influenced by a variety of kinematic processes such as spiral density waves, shocks in bars, and bar driven mass inflow.
In this talk I will review the state of the art in various type of kinematic observations of the atomic, molecular and ionized interstellar medium. I will concentrate on observations that produce full two-dimensional maps of the kinematics since these provide us with the most information to compare to other observations and models.
Global Interstear Gas Masses and Gas Surface Densities in Spiral Galaxies
Judith S. Young
U.Mass., Amherst, USA
young@astro.umass.edu
()
The observations made as a part of the FCRAO Extragalactic
CO Survey (Young et al. 1995) are used to examine the
molecular gas distributions, the global H$_2$ masses, the
star formation efficiency, the H$_2$/HI ratio, and the gas
to dust ratio, within and among 300 galaxies in the local
universe as a function of morphology, luminosity, and
environment. Significant global trends in the gas-to-dynamical
mass ratio, the molecular gas-to-warm dust mass ratio, and
the H$_2$/HI ratio are found as a function of morphology for
spiral galaxies along the Hubble sequence. Globally in these
systems, the luminosity of high mass stars per unit mass of
molecular gas (also called the star formation efficiency)
does not vary in the mean as a function of morphology, while
the star formation efficiency does show significant variations
as a function of environment. The star formation efficiency
also shows a marked tendency to be elevated in smaller spiral
galaxies. All of these results are presented, and used to
provide insight into the processes of star formation and galaxy
evolution, as well as placing constraints on current models
of galaxy evolution.
The effect of minor mergers on spiral galaxies
Rodrigo Ibata
Observatoire de Strasbourg
ibata@astro.u-strasbg.fr
()
We know that spiral galaxies are continually accreting mass even at the
present day, as we observe many of them, including the Milky Way, in the
process of swallowing up itheir smaller companions. I will review the
recent observations and the recent numerical experiments, which suggest that
repeated accetions have a significant impact on the dynamical and chemical
evolution of the primary galaxy.
DYNAMICAL AND CHEMICAL EVOLUTION OF THE LMC DISK
HORACIO A. DOTTORI
INSTITUTO DE FÍSICA, UNIVERSIDADE FEDERAL DO RIO GRANDE DO SUL, PORTO ALEGRE, BRAZIL
dottori@if.ufrgs.br, dottori@voyager.com.br
()
The LMC present us with a unique case to study the connection between the process of star formation and the structure and dynamics of disks. Its study is important to bridge the gap between the study of small scale structures in the Milky Way and that of global processes in distant galaxies.
In this talk we revise kinematical observations at different wavelenghts as well as the kinematical implications of stars and mainly of star-clusters ages and distribution.
We also discuss the possible effect of the interaction with the Milky Way and with the Small Magellanic Cloud and the imprints left by these interactions in the process of star formation as well as in the present disk structure.
Evolution of galaxy bulges
Balcells, M.
Instituto de Astrofisica de Canarias, Spain
balcells@ll.iac.es
()
I present recent results of our ongoing study of galaxy bulges.
We have determined the Fundamental Plane (FP) of bulges in B and K.
The FP closely follows that of ellipticals and S0 in Coma, adding to the
evidence that early-to-intermediate bulges are old. I then emphasize the
suitability of S\'ersic's law to model the surface brightness profiles of bulges,
and use N body simulations to show that bulges may evolve by accretion of
dense satellites. Such accretion explains the growth of thick disks in early-type
galaxies. Last, I discuss recent HST/NICMOS imaging of bulge cores and compare bulge
profiles and central densities to those of ellipticals at HST resolutions.
Formation of Galactic Disks
S. Michael Fall
STScI
fall@stsci.edu
()
This contribution will review the theory of the formation
of galactic disks. The emphasis will be on understanding
the origin and evolution of the angular momentum of galaxies,
which determines the most basic properties of the disks.
Some of the problems the theory has encountered will be
reviewed, as well as some of the most likely solutions.
Pulsars Spin-Down History
Cesar Alvarez Ochoa
Alberto Carrami\~nana Alonso
INAOE, Mexico
calvarez@inaoep.mx
()
Most pulsars are concentrated around (P~log -0.3,Pdot~log -14.7) in
the $\dot{P}-P$ diagram. It is believed that pulsars arrive to that
region of the diagram through spin-down evolution from region of short
periods and large period derivatives. However, there is no clear correlation
between $\dot{P}$ and $P$ in the $\dot{P}-P$ diagram. The details of the
spin-down mechanisms remain unclear, despite the many models
proposed to describe them.
In this work, we present a multipole spin-down equation directly
derived from the general model, $\dot{\nu}=-f(\nu,t)$. We test this model
against the $\dot{P}-P$ diagram using four young pulsars with good timing
history: the Crab, Vela, PSR B1509-58 and PSR B0540-69.
We found that if pulsars do not change their parameters with time,
the evolutionary model is inconsistent with observations. By assuming
that magnetic fields decay significantly during the pulsar life time, we
found that a decay law of the form $B(t)=1/(1+t/t_c)$ with timescales
of around $10^4$ years fits the observations.
Kinematics and massive star formation in the disk of the MW.
Abraham Luna
Luis Carrasco
Leonardo Bronfman
William Wall
INAOE, Mexico
INAOE, Mexico
U. de Chile
INAOE, Mexico
aluna@inaoep.mx
()
We test the Schmidt`s Law in the disk of the Milky Way, using the most complete data sets of CO and massive star formation regions. We confirm that star formation is enhanced in regions with high gas density. Preliminary results show the connection between high gas density, rigid-body kinematics with small shear, and arms regions.
aleonl@inaoep.mx
()
kraan@astro.ugto.mx
()
alfred@astroscu.unam.mx
()
gergim@oac.uncor.edu
()
nelson@inaoep.mx
()