Turku, Finland, 13th-18th June 1999
ABSTRACTS
A Numerical Study of a Triple Merger of Spirals
Presentation Type : Poster
ABSTRACT
We present the results of a numerical simulation of a triplet of spiral
galaxies leading to a merger. We investigate, using a test-particle approach,
the evolution of the gas in the system.
Galaxy interactions in triplets
Presentation Type : Talk
ABSTRACT
A set of numerical simulations are used to study some of the rich dynamics of
galaxy triplets. A comparison of our results with the observed properties of
Karachentsev triples is made, and conclusions will be provided.
Authors: Sahar Said Allam & D. Tucker
Compact Groups of Galaxies in the Las Campanas Redshift Survey
Presentation Type : Talk
ABSTRACT
Compact groups of galaxies -- relatively poor groups of galaxies in which the
typical separations between members is of the order of a galaxy diameter --
offer an exceptional laboratory for the study of dense galaxian environments.
Here, we present first results from a new catalogue of compact groups, based
upon the Las Campanas Redshift Survey, which contains 78 compact groups having
3 or more members.
The three body problem and nuclear structures in barred galaxies
Presentation Type : Talk
ABSTRACT
We construct models of a galaxy in order to provide a possible identification
of the dynamical processes that lead to the formation of structure observed in
galactic nuclei. We assume that the center of our model contains a very massive
double black hole, surrounded by relatively low-mass particles - star clusters,
gas, and dust complexes. Our previous work (Anosova et al. 1994, 1995) showed
that the dynamical evolution of such a model produces many structures similar
to those observed in the nuclei of galaxies, including rings and various types
of flows and jets. In such models the 'gravitational slingshot' effect
frequently occurs.
We consider a number of such models with different initial parameters.
Comparison of our models with the observed structure of NGC 4314 shows good
agreement at one stage of the evolution for certain combinations of initial
parameters. The model predicts also the velocity field observed in NGC 4314.
N-body simulations of interactions and mergings in small galaxy groups
Presentation Type : Talk
ABSTRACT
Not yet available
Authors: B.Babic, R.M.Price, K.Jones
HI Imaging of Southern Compact Groups
Presentation Type : Poster
ABSTRACT
The HI synthesis imaging of four Southern Compact Groups using the Australia
Telescope Compact Array is presented. Two of the groups are comprised of 3
member galaxies, while the other two Hickson Compact Groups, HCG22 and HCG 26
are slightly larger in population. Signs of activity such as HI bridges and
distortions in the HI disk are quite visible for two of the four groups, while
the other two are not so active dynamically it seems. The poster will show HI
velocity maps, along with various moment maps,and other relevant graphs and
information pertaining to the four groups.
Note: An MPEG video file of the HI cloud for one of the 'groups' is also
available.
Authors: Peter Berczik & Sergei G. Kravchuk
Evolution of dwarf galaxy in strong tidal field.
Presentation Type : Talk
ABSTRACT
We consider the evolution of dwarf galaxy in the external gravity field of
Milky Way -- like disk galaxy. The host galaxy potential is taken as a rigidly
fixed one which defined as three component potential distribution proposed by
Douphole B. & Colin J., 1995, A&A, 300, 117. The mass of the first
bulge--component is taken to be approx 1.4E10 solar masses, the mass of the
disk one is approx 7.9E10 solar masses and the halo mass is approx 7E11 solar
masses.
Initially the dwarf satellite is modeled as a cold gas cloud 10^4 K of radius
2 kpc and total mass of 2.0E8 solar masses. The satellite initial orbit is
resides in the YZ plane and maximal distance from the center of host galaxy
doesn't exceed 50 kpc. The velocity field of the satellite is defined by its
initial solid body rotation of around its own Z axis and by orbital motion
around host galaxy.
The evolution of this system is described using the our Chemo -- Dynamical
Smoothed Particle Hydrodynamic (CD -- SPH) code. The star formation (SF)
process, SNII, SNIa and PN events as well as chemical enrichment of gas is
considered within the framework of model proposed in Berczik P., 1998,
(astro-ph/9807059) and Berczik P., 1999, A&A, submitted.
The developed model provide a realistic description of dynamics and chemical
evolution of typical dwarf satellite galaxy.
Isolated galaxy triplets in the Las Campanas redshift Survey
Presentation Type : Poster
ABSTRACT
In this poster we present a study of isolated galaxy triplets in observed
slices of the Las Campanas Redshift Survey (hereafter LCRS; Shectman et
al. 1996). The slightly modified friends-of-friends algorithm (Huchra & Geller
1982) has been used to extract the isolated galaxy triplet candidates from the
original LCRS catalog, using the value of 1000 km/sec as a well defined gap
between groups in both redshift and sky projection directions. All together 88
galaxy group candidates have been found which makes approximately 1% of the
total galaxy number. The final catalog of the galaxy groups is reduced by
different selection criteria. The properties of the isolated galaxy triplets
are discussed.
Authors: D. Bettoni and L.M. Buson
The peculiar nature of galaxies in Hickson 67
Presentation Type : Poster
ABSTRACT
The nature of the galaxies in the Hickson Compact Group H67 is investigated.
This compact group consist of four galaxies, three of which (A, C, D) are
embedded in a common envelope. The fourth galaxy (B) is a spiral that is
detected both in radio and in IR wavebands. Kinematical data for the three
galaxies in apparent interaction are discussed. They show that the galaxies are
probably in an ongoing merger process.
Simulations of the Cartwheel group
Presentation Type : Talk
ABSTRACT
Not yet available
Photometry of dwarf galaxies within 10Mpc
Presentation Type : Talk
ABSTRACT
Multicolour CCD photometry of dwarf galaxies in and around the M81, M101 and
CVnI groups is presented. These observations are part of a project aimed at
obtaining reliable surface photometry of dwarf galaxies within 10Mpc. The
global photometric parameters derived will serve as the basis for a comparison
between different galactic environments.
Compact HI High-Velocity Clouds in the Local Group
Presentation Type : Talk
ABSTRACT
We have identified a class of high-velocity clouds which are compact and
apparently isolated (see astro-ph 9810433). The kinematic and spatial
deployment of these objects resembles that of Local Group galaxies. The CHVC's
have a net infall velocity of 100 km/s in the Local Group reference frame. The
properties of the ensemble of these clouds suggest a population which has as
yet had little interaction with the more massive Local Group members. If the
distance of 1 Mpc is typical, then the CHVC objects would have characteristic
sizes of about 15 kpc and gas masses of a few 10**7 solar masses, comparable to
(sub-)dwarf galaxies.
Authors: Gene Byrd and Mauri Valtonen
Tidal Perturbation, Dark Matter, and Active Galaxy Nuclei
Presentation Type : Talk
ABSTRACT
Theory and observation will be compared for the hypothesis that nuclear
activity in disk galaxies is caused by tidal perturbation. Observational
surveys of companions of disk galaxies as well as double galaxies will be
considered. Results of previous simulation surveys of tidal triggering of
nuclear activity will be used with analytic calculations to evaluate the
physical sufficiency of the tidal mechanism. Predictions will be compared to
observations of double galaxies. The importance and role of inert halos will
be evaluated.
This work was supported by the Academy of Finland and NSF Grant RUI980218. GB
expresses appreciation for the hospitality of Tuorla Observatory during a
winter spring 1999 visit.
Small groups at z>0 as sites for X-ray emission and AGN rekindling
Presentation Type : Talk
ABSTRACT
Not yet available
Escape With the Formation of a Binary in Two-Dimension Three-Body Problem
Presentation Type : Talk
ABSTRACT
Not yet available
Authors: V.Charmandaris & F.Combes
Minor mergers and the formation of Shell Galaxies
Presentation Type : Talk
ABSTRACT
It is widely accepted that galaxy interactions and mergers have a profound
consequences to the morphology and evolution of galaxy groups. In particular
there have been a lot of observational evidence suggesting that accretion of
small companions into more massive group members is a frequent event. We
present our numerical study on the formation of stellar and gaseous shells
often observed around early type galaxies (ie. N3656, CenA).
Taking into account dynamical friction, a proper treatment of the dissipation
of the gas and using a realistic distribution of the stellar and gaseous
component, we are able to reproduce the observed spatial distribution of
gaseous and stellar shells.
Authors: A. D. Chernin, V. P. Dolgachev, L.M. Domozhilova
Wide triple systems of galaxies: Statistical estimation of dark matter mass
Presentation Type : Talk
ABSTRACT
Triplets of galaxies provide an opportunity to measure the amount of dark
matter on the intermediate space scales between individual galaxies and
clusters. We use observational data on wide triple systems with typical
projected mean harmonic separation of approx 600 1/h kpc (h = H/75 km/s/Mpc)
and crossing time near the Hubble time from a catalogue compiled by Trofimov
and Chernin (1995). Their dynamics was studied with a set of computer
simulations, in which wide triplets are treated as systems in the
pre-virialized state of free-fall from the initial state at rest 12+/-2 Gyr
ago. In all, more than 5 000 states of the systems were calculated in a dozen
sets of simulations, and the models of several sets were found to simulate
adequately the observed states of the wide triplets; these states constitute a
general variety which was used for statistical estimations of the total mass of
a typical wide triplet. The mass proves to be about 1E13 solar masses, and the
relative dark matter content is estimated by the mass-to-light ratio (M/L)
approx (150-300) h in solar units (Msun/Lsun), which means that the mass of
dark matter is more than an order of magnitude larger than the luminous matter
in these systems.
Influence of extended gas in small groups dynamics
Presentation Type : Talk
ABSTRACT
HI observations have revealed that galaxies in small groups are deficient in
atomic gas, like in richer galaxy clusters such as Virgo, although in a lesser
extent. Galaxy interactions could be the cause of this deficiency, stripping
the gas out of galaxies and enriching the inter-cluster medium (ICM) in hot
gas, which in turn strips gas through ram pressure. Alternatively, the gas
present at the formation of the group could have been heated to its virial
temperature, and be observed now as X-rays. We will review the dynamical
processes related to this extended gas in small galaxy groups.
On the nature of Compact Groups of Galaxies
Presentation Type : Talk
ABSTRACT
We report the results of a systematic study of galaxies in the regions of
Hickson Compact Groups (HCGs). We have carried out a spectroscopic survey in
the regions of 17 HCGs from which we determined radial velocities for the faint
galaxies previously identified by de Carvalho et al (1994) in the surroundings
of the groups. Statistical methods were applied to the resulting catalog in
order to determine the kinematical structure of each observed field. We
identified three possible evolutionary phases among groups in the sample: loose
groups, [core+halo] systems, and compact groups. Besides, the study of the
luminosity function of galaxies in our sample shows that it is
indistinguishable from that found in large surveys covering a range of
environments. An investigation focusing on the nature of Compact Groups (CGs)
through the study of their elliptical galaxies has shown that, from the
dynamical viewpoint, E galaxies in CGs are essentially similar to those in
dense clusters.
Identification of Loose Groups in Redshift Surveys
Presentation Type : Talk
ABSTRACT
The combination of semi-analytic models of galaxy formation with N-body
simulations of cosmic structure formation enables us to explore both the
clustering properties of galaxies and their global properties. Two Cold Dark
Matter Universes provide redshift survey mock catalogs whose galaxy group
catalogs is in reasonable agreement with the results obtained with the Center
for Astrophysics redshift surveys. However, the internal properties of groups
of galaxies are sensitive to the galaxy formation recipe. Therefore, a better
understanding of the properties of real groups can shed light on the complexity
of galaxy formation processes.
Authors: Igor Drozdovsky and Nikolay Tikhonov
Stellar content in the nearby groups of galaxies
Presentation Type : Talk
ABSTRACT
We present the results of a detailed photometric study of the galaxies of the
two nearby group: IC342/Maffei and M81. Images have been obtained with the 6m
BTA telescope and Nordic optical telescope. The resulting colour-magnitude
diagrams reveal the morphology of different stellar populations in these
systems.
Young stellar populations in the Local Group
Presentation Type : Talk
ABSTRACT
The properties and even formation of some young star clusters in the Local
group galaxies may be connected with the interactions of these galaxies during
which the events of triggered star formation and exchange of the gas content
might occur. The young massive clusters in the LMC and SMC are often
considered to form after the interactions of these galaxies with each other
and/or the Milky Way galaxy. The giant arcs of young stars and clusters in the
LMC might formed after the infall of clouds orbiting around the Galaxy, though
another suggestion seems to be more compatible with all the data on these
features.
Authors: Jaan Einasto and Maret Einasto
Dark matter in groups and clusters of galaxies
Presentation Type : Talk
ABSTRACT
Dark matter in groups and clusters of galaxies is reviewed. Dynamical link
between galaxies and surrounding systems is discussed. This link and
morphological data suggest common evolutionary history of galaxies in systems.
Small Satellite Probes of Spiral Galaxies
Presentation Type : Poster
ABSTRACT
Small satellites provide a dynamical tool for estimating the masses of spiral
galaxies with several caveats. The satellites and spiral galaxies were observed
primary in neutral hydrogen, although visible observations from other sources
are included in the data. Estimates of halo masses surrounding the spirals are
based on the dynamical conditions of the satellites in their unknown orbits.
Dark Matter in the Milky Way
Presentation Type : Talk
ABSTRACT
I review the topics of dark matter in the disk and halo of the Milky Way. The
amount of matter in the disk is now well constrained by Hipparcos studies of
nearby stars via distances and kinematics. The mass of the local disk is now
well understood. Studies carried out with the Space Telescope show that the
putative dark matter halo of the Milky Way is unlikely to be in the form of
faint M dwarfs but might be in old, cool white dwarfs. The faint end of the
luminosity function is now being measured directly via counts of red stars with
HST: such stars are common but their total mass contribution to the Galaxy is
not dominant.
Age Estimates for Galaxies in Groups
Presentation Type : Talk
ABSTRACT
Estimating the age of elliptical galaxies from their stars has proved difficult
due to the age-metallicity degeneracy of old stellar populations. Recently
however this degeneracy has been broken by the combination of stellar
spectroscopy and new models. These luminosity-weighted central ages are now
available for many galaxies, including some in loose and compact groups. The
current situation is reviewed and future prospects discussed. As well as being
useful for determining the evolutionary history of galaxy groups, such age
estimates can explain some of the scatter in well-known galaxy scaling
relations.
Authors: Tarsh Freeman, G. Byrd, G. Purcell, R. Buta, and D. McCormick
NGC4622 versus NGC4378 Disks: Grazing vs. Plunging Encounters
Presentation Type : Poster
ABSTRACT
We simulate these galaxies' arm patterns via these two types of encounters. In
NGC4622, the perturber plunges in a retrograde sense to create an inner
long-term density wave plus outer tidal arms. We show the ring between these
two to be periodic gas cloud orbits in the lopsided disk potential, a single
fold resonance ring. NGC4378's single arm can be produced by a grazing small
perturber. We simulate observed irregularities in rotation curve. We use disk
colours to find disk orientation and to show that the arm trails. Support was
provided by NSF RUI 9802918, REU AST-9424226. We thank CTIO for use of
observational facilities.
The evolution of DM halos in high resolution cosmological N-body simulations
Presentation Type : Talk
ABSTRACT
We discuss the evolution of DM halos hosting galaxies in a cosmological
environment (LCDM cosmology with Omega = 0.3, h = 0.7) using an N-body
simulations of 60 h^-1 Mpc size with a dynamical range of 32000.
Signs of interactions in NGC 5846 and other ellipticals in poor groups
Presentation Type : Talk
ABSTRACT
We present ROSAT (PSPC,HRI) and optical imagery of NGC 5846, the dominant
elliptical (E) in a poor group of galaxies. A filamentary dust lane is
detected in the inner few kpc of NGC 5846, closely associated with H-alpha
emission and local enhancements in the X-ray emission. We discuss three
possible origins of the dusty filaments; (1) mass loss from stars within NGC
5846, (2) condensation out of a "cooling flow", and (3) material donated by a
small neighbouring galaxy. From constraints on the dust grain lifetime and
energy balance within the X-ray-emitting gas, we conclude that the dust and
ionized gas are products of a recent interaction with a small, gas-rich galaxy.
We compare the time scale of galaxy interactions (also as implied by the
properties of the dusty filaments) with the detection rate of dust features in
giant Es within poor groups.
Authors: Hanski, M., Teerikorpi, P., Theureau, G., Baryshev, Yu., Ekholm, T., Paturel, G., Lanoix, P.
Evidence for dark matter in different scales from KLUN galaxy sample
Presentation Type : Poster
ABSTRACT
KLUN sample of 6600 spirals has given information on dark matter in different
scales:
1) Type dependence of the zero-point of the Tully-Fisher relation indicates M/L
is in the range 9 to 16 on galactic scales
2) In comparison, selection effects suggest a larger M/L for the extended halos
of Karachentsev double galaxies
3) A study of the Perseus-Pisces supercluster, using Malmquist bias corrected
TF distances and Tolman-Bondi solutions, gives M/L = 200 to 600 for the
supercluster. Similar results come from our previous and new work on Virgo
supercluster.
4) Developed version of Sandage-Tammann-Hardy test of the linear Hubble law
inside the observed hierarchical (fractal) galaxy distribution up to 200 Mpc
suggests that either Omega_0 is very small (0.01) or themajor part of matter is
uniformly distributed dark matter.
Black hole ejections in mergers of small groups of galaxies
Presentation Type : Poster
ABSTRACT
The formation and evolution of a four black hole system in the center of a
galaxy has been simulated. This has been done starting from the evolutionary
model for the repeated encounters of galaxies. After a four black hole system
is formed mergers, ejections and escapes can occur. Possibility of formation of
double radio sources as a result of such evolution has been studied. Different
parameters of two-sided ejections in simulations has been compared to the
observations of two-sided radio sources. The role of selection effects and the
existence of unobserved class of radio sources has been discussed.
Effects of galaxy winds on small groups.
Presentation Type : Talk
ABSTRACT
Galaxy formation can leave its imprint in the intragalactic medium. Preheating
by galaxy winds injects energy into the gas, and should have the greatest
effect in small galaxy groups. This has already been reported in compact
groups, but these only represent a few percent of all groups. Here we present
the largest survey so far of the X-ray properties of loose groups. We derive
relations between X-ray luminosity, temperature and velocity dispersion. Also
examined are the surface brightness profiles of these systems. We report clear
evidence for the effect of galaxy winds, and we compare the properties of these
loose groups with those of compact groups.
Statistical Properties of the Emission in Mixed Morphology (E+S) Pairs. The FIR Results.
Presentation Type : Poster
ABSTRACT
This poster examines the level of MIR/FIR enhancement that can be stimulated by
galaxy-galaxy interactions and its correlation to optical morphology. It
extends over the optical results in Hern\'andez Toledo et al. (1999, Hereafter
Paper1) into the FIR which is more sensitive to the signature of interaction
induced star formation by making use of one of the most complete and
homogeneous optically-selected samples of (E+S) pairs (Catalogue of Isolated
Pairs of Galaxies in the Northern Hemisphere; hereafter CPG: Karachentsev
1972). This pair sample has the advantage of having a similarly compiled
control sample (Catalogue of Isolated Galaxies: hereafter CIG: Karachentseva
1973) over the same region of the northern sky as the (E+S) pairs. The size and
depth of both the (E+S) and CIG samples make it possible to study the
correlation of MIR and FIR emission with several other optical properties
including the component/pair morphologies and a new estimation of the FIR
luminosity function (FIRLF). We find average factors of 3 and 5 enhancement in
FIR and 25$\mu$m luminosities of the late-type pair components relative to an
isolated galaxy control sample. This is interpreted as the MIR/FIR signature of
the interaction--star formation connection. The large number of E+S pairs, the
presence of both an optical luminosity enhancement (Paper 1), the clear FIR
enhancement reported here and varying degrees of morphological distortion
suggest that most of these pairs are physical binaries. A question then arises:
How mixed pairs can exist at all in significant numbers when local
environmental conditions are thought to dictate galaxy morphology?
Collisional Ring Galaxies
Presentation Type : Talk
ABSTRACT
The probability of plunging orbits is enhanced in groups of galaxies and
indeed, observations show that ring galaxies, which are believed to form when a
galaxy passes through the center of a larger rotating disk, are often found in
small groups (e.g., the Cartwheel, VIIZw466, Arp119). The dynamics of these
galaxies may therefore be more complex than previously thought. I'll present
results of numerical simulations of both gas and stars in colliding galaxies as
well as observations of a few ring-like systems.
"HI in HCG95" and "New Dwarf Galaxies in the IC342/Maffei group"
Presentation Type : Talk
ABSTRACT
1) VLA observations of the neutral atomic hydrogen and the (21-cm) radio
continuum of the compact group HCG95 are presented. Two dwarf galaxies are
identified as members of this group by their HI velocities.
2) A number of low surface brightness dwarf irregular galaxies from the latest
Karachentsev list of "candidates for nearby dwarf galaxies" have been detected
in HI with the 100-m radiotelescope at Effelsberg. Their positions and their
radial velocities suggest membership in the IC342/Maffei group. The faintest of
these HI-rich dwarf galaxies has only 3 10**6 solar masses in HI (at a distance
of 3.6 Mpc).
Authors: Hunsberger, Charlton, & Zaritsky
The Luminosity Function of Galaxies in Compact Groups
Presentation Type : Talk
ABSTRACT
From R-band images of 39 Hickson compact groups (HCGs), we use galaxy counts to
determine a luminosity function. We find that a single Schechter function is a
poor fit to the data, so we use a composite function consisting of separate
Schechter functions for the bright and faint galaxies. The decreasing bright
end slope implies a deficit of intermediate luminosity galaxies in our sample
and the faint end slope is slightly steeper than that reported for earlier HCG
luminosity functions. Furthermore, luminosity functions of subsets of our
sample reveal more substantial dwarf populations for groups with x-ray halos,
groups with tidal dwarf candidates, and groups with a dominant elliptical or
lenticular galaxy. Collectively, these results support the hypothesis that
within compact groups, the initial dwarf galaxy population is replenished by
"subsequent generations" formed in the tidal debris of giant galaxy
interactions.
Star Formation and Environment in Compact Groups of Galaxies
Presentation Type : Talk
ABSTRACT
We present a study on the influence of the environment on the Star Formation
Rate (SFR) of a sample of galaxies in compact groups. The main tool used in
this study is a set of good quality Halpha frames of the galaxies in the
sample. By comparing the SFRs of the galaxies in the groups with those of a
sample of field galaxies, we obtained that the SFRs of the galaxies in the
groups are not affected by the environment, on average. However, there exists a
population of low SFR spirals in the groups whose presence is attributed to the
nearby passages experienced by the galaxies in the groups. Also, those groups
where merging interactions occur, show an appreciable enhancement in the SFR.
Galaxy triplets at medium redshifts from the SDSS
Presentation Type : Poster
ABSTRACT
We have identified close pairs and triplets of galaxies in the Sloan Digital
Sky Survey commissioning imaging data. The data set is from one of the SDSS
equatorial fields covering an area close to 100 square degrees. We have
estimated the angular correlation function of these objects and appear to be
appreciably more strongly clustered than single galaxies.
We have also estimated that the fraction of galaxies in close triple systems,
at a mean redshift of 0.33 (19 < r'(SDSS) < 21), is 1.26%. If account is taken
for possible triplets detected due to superposition, the fraction of galaxies
in physical triplets at z = 0.33 is 0.66%. The significance of this number is
discussed and compared to 0.5% obtained by Karachentsev et al. (1981) for
similar local sytems.
A new sample of compact groups in the southern sky
Presentation Type : Talk
ABSTRACT
A new sample of 60 groups in the southern sky, for which full spectroscopic
data are available, is presented. The sample has been obtained through an
automated search technique on galaxy catalogues, and the first results on
dynamics properties of such complete sample are presented.
Observational properties of galaxies in small groups
Presentation Type : Poster
ABSTRACT
Basic observational properties of galaxies in small systems are compared with
properties of field galaxies selected on the basis of the same isolation
criteria as the samples of system galaxies. Observational selection effects
that distort observational properties of active and normal galaxies differently
are analysed.
Observations of triple galaxies
Presentation Type : Talk
ABSTRACT
This report presents basic observational parameters for galaxy triplets
selected by a criterion of their isolation on the sky (=Catalog of Triple
Galaxies, Karachentseva et al,1979). The CTG sample is compared with a sample
of wide triple systems from Nearby Galaxies Catalog (Tully, 1988) as well from
a new whole-sky catalog of small galaxy groups in the Local Supercluster
(Makarov & Karachentsev, 2000). For all the samples their medians of virial
mass-to-luminosity ratio lie in a narrow range, 25 < Mvir/L < 40 (Mo/Lo), while
the medians of crossing time occupy a wider range, 0.04 < Tcross < 0.4 (in 1/H
units).
Southern triplets of galaxies
Presentation Type : Talk
ABSTRACT
Using the ESO/SERC and POSS-I sky surveys we selected 76 isolated triple
systems of galaxies with Dec.< -3 deg. For each triplet the equatorial
coordinates, type of configuration, angular diameters, apparent angular
separation of the components, morphological types, total magnitudes and some
other characteristics are presented. 33 of 76 triplets have the measured radial
velocities for all the components. The median values of basic dynamic
parameters: a radial velocity dispersion, mean harmonic separation, an absolute
magnitude of galaxies, mass-to-luminosity ratio are very close to ones obtained
earlier for 83 northern isolated triple systems from the list of Karachentseva
et al. (1979).
Authors: Ludmila Kiseleva and Victor Orlov
Computer statistics of catalogues of triple galaxies: internal dynamics and mass estimation
Presentation Type : Talk
ABSTRACT
The average observational properties of existing catalogues of triple galaxies
are simulated numerically in order to estimate the total mass of these systems
and the type of galaxy motions (isotropic motion, rotation or collapse) within
triplets. Results are applied to the 45 physically associated compact triplets
from the list of Karachentsev et al., as well as to wide triplets catalogued by
Huchra & Geller (sample of 40 systems) and Maia et al. (50 triplets)
Merging galaxies in compact groups analytical theory.
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Authors: Harry J Lehto, Pekka Heinamaki, Arthur D. Chernin, Mauri J. Valtonen
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Authors: D. Makarov & I. Karachentsev
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Authors: Gary A. Mamon & Sergio Dos Santos
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Authors: P. Merluzzi, A.A. Shaker, G. Longo
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Authors: I.I.Nikiforov, I.V.Petrovskaya, S.Ninkovich
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Authors: K. Nilsson, M. Valtonen, G. Byrd, J.-Q. Zheng, H. Korhonen and M.I. Andersen
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Authors: Shingo Nishiura, Masashi Shimada, and Yoshiaki Taniguchi
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Authors: Kelm B., Focardi P. Palumbo G.G.C.
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Authors: Kristian Pedersen, Jens Hjorth, Nial Tanvir and Yuzuru Yoshii.
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Authors: H. Plana, C. Mendes de Oliveira, P. Amram, C. Balkowsky
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Authors: Marcus Price, Boris Babic, Keith Jones
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Authors: T. Pursimo et. al.
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Authors: Tanvuia L., Kelm B., Focardi P., Rampazzo R., Zeilinger W.W.
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Authors: Bonfanti P., Rampazzo R., Simien F., Prugniel Ph.
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Authors: P. Rautiainen and H. Salo
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Authors: Rami Rekola and Chris Flynn
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Authors: Shaya, E.J., Peebles, P.J.E., Tully, R.B., Phelps, S.D.
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Authors: Sonia Temporin, Ronald Weinberger & Florian Kerber
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Authors: P. Tenjes, J. Einasto
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Authors: G.M. Richter, P. Boehm and J. Vennik
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Presentation Type : Talk
ABSTRACT
Authors: S.Wiren, B. Liu, and M.J. Valtonen
Presentation Type : Poster
ABSTRACT
Authors: A.V.Zasov, V.P.Arkhipova
Presentation Type : Talk
ABSTRACT
Presentation Type : Poster
ABSTRACT
Usually the galaxy merging cross-section "s" is supposed to vanish if relative
velocity v exceeds the runaway one. Actually the decrease law of s on v is very
essential as it determines the uniformity degree of merging probability.
Discuss is the way this dependence influences the galaxy mass function and the
possibility of explosive evolution. The special case of square- law decrease of
s at large v brings to a constant degree of uniformity of the coagulation
factor
Seppo Laine
NGC 7479 - the Rosetta stone of minor mergers?
The overall morphology of the barred spiral galaxy NGC 7479 was modeled
numerically in a simple minor merger scenario. I paid special attention to the
morphology and velocity field of the asymmetric spiral structure and the strong
stellar bar. The mass of the satellite galaxy was 1/30 of the total mass of the
primary. The satellite was started in a circular prograde orbit at six disk
scale lengths from the centre of the primary. I followed the evolution of the
merger until the secondary galaxy reached the nuclear region of the primary. A
comparison between the modeled and observed morphologies of the stellar and the
ionized and neutral gas distributions and velocity fields supports the
hypothesis that the transient look of NGC 7479 is a result of a minor merger. I
also discuss the effects of variations in the initial parameters of the merger.
Harry J. Lehto
Masaai Warrior shield: life time of a three body system
We have investigated the behavior of a general Newtonian three body system
using the simplest initial conditions. We calculated the evolution of about
200 000 bound three body systems. Within our resolution these cover all the
possible inital states. All these systems eventually decay with one body being
ejected from the residual binary system. The overall pattern representing the
decay timescales projected on a homology map is dominated by resonances. In
general appearance it reminds us of a traditional Masaai warrior shield.
D. I. Makarov
A new catalogue of multiple galaxies in the Local Supercluster
To reveal small galaxy groups in the Local Supercluster, a new approach is
suggested which allows for individual properties of galaxies. The criterion is
based on the assumption of closed motions of companions round the dominating
group member within a sphear of zero energy.
The criterion is applied to a sample of 5976 nearby galaxies with radial
velocities Vo < 3000 km/s. The 3333 galaxies have been assigned to 855 groups
that include 56% of the considered sample. For the groups revealed by the new
algorithm (with k > 4 members) the median velocity dispersion is 73 km/s, the
median harmonic radius is 240 kpc, the median crossing time is 0.2(1/H), and
the median virial-mass-to-light ratio is 40 Mo/Lo.
Apparently, the median M/L is roughly independant on the group radius out to
a few hundred kps giving an upper limit of the dark halo extension.
Gary Mamon
The nature of low velocity dispersion compact groups in general and of HCG 16 in particular
We show that a galaxy system in virial equilibrium must have a minimum velocity
dispersion for its total mass to be greater than the sum of the masses of its
constituent galaxies. This is also true for systems that are currently near
full cosmological collapse. Applying this argument to the lower velocity
dispersion compact groups in Hickson's sample, we argue that the great majority
of these cannot be physically dense systems. We then predict that low velocity
dispersion compact groups should not display regular and extended diffuse X-ray
emission. We analyze in detail the X-ray emission the low velocity dispersion
compact group HCG 16, and show that half of this emission is related to
foreground or background point sources, unassociated with the group. HCG 16 is
a puzzling case, because it is even less likely to be caused by a chance
alignment of galaxies. Its nature may be related to its large- scale
environment, which shows it to be at the intersection of several very long
cosmological filaments.
Claudia Mendes de Oliveira
Observations of Compact Groups
Small groups of galaxies of three to five galaxies with small projected
separations and low relative velocities are common in the nearby universe.
However, the hypothesis that a small galaxy group in projection is also a
compact configuration in 3-D is only confirmed when the group members are found
to be in interaction with one another. If so, the low relative velocity
dispersion of galaxies in the group as well as the small distances between them
will favour the formation of merger remnants (Barnes 1989).
We review the several photometric and spectroscopic indicators of galaxy
interactions in groups which have proved that catalogued systems are indeed
triplets, quartets and quintets in interaction, in an attempt to sort out, in a
one-by-one case, the systems that are real in 3-D. We will also show some new
observations on the velocity field of several small groups (Cartwheel Galaxy,
Seyfert Sextet, Stephan's Quintet and several others), which allow a
description of their dynamical state. Although the warm gas component usually
contributes only a small fraction of the total mass of a galaxy, it responds
very quickly to gravitational perturbations and therefore allows a detailed
study of the recent history of interactions/accretions of the systems. Finally
we will show some exciting new results on the velocity fields of some possible
newly-formed dwarf galaxies in one compact group.
Paola Merluzzi
Far Infrared Emission as indicator of interaction in Hickson Compact Groups
The Far Infrared (FIR) properties of galaxies in Hickson compact groups (HCG)
are investigated to study their nature. By using re-processed IRAS data, we
computed the FIR luminosity and the dust mass by adopting a temperature
distribution model. Our results are compared with those previously available
and with the FIR properties of samples of isolated, interacting and merging
galaxies. We find that in the previous work the interaction is overestimated by
a factor of two and we do not find FIR enhancement in HCGs. We discuss these
results taking into account: a) the low resolution of the IRAS data; b) the
relations between FIR, radio and CO emissions; c) the different status of
galaxies in HCGs (some of them are experimenting merging or interaction, while
other systems are quiescent and present a FIR luminosity similar to that of the
isolated galaxies); d) the influence of the environment such as the very high
density of these systems which can inhibit the star formation.
John S. Mulchaey
X-ray Observations of Groups of Galaxies
Recent ROSAT and ASCA observations of poor groups of galaxies indicate that
many of these systems are X-ray sources. The X-ray emission in groups is often
spatially extended. X-ray spectroscopy suggests the emission mechanism is most
likely thermal bremsstrahlung. This interpretation requires that the entire
volume of the group be filled with a hot, low density gas. This gas component
is known as the intragroup medium. I will review the properties of the
intragroup medium and the dynamical implications of this component. I will also
describe how the next generation of X-ray telescopes will likely advance our
understanding of the X-ray properties of poor groups.
Juan C. Muzzio
Regular and chaotic motion in a restricted three body problem of astrophysical interest
We classify the orbits of massless points moving near a body that moves in
circular orbit around a more massive one. The model corresponds to stars in a
galactic satellite (i.e., a dwarf galaxy or a globular cluster moving around a
large galaxy). There are some significant differences with the traditional
restricted three body problem of celestial mechanics (e.g., the gravitational
force is zero, rather than infinite, at the center of the satellite). The
interesting result is that chaotic orbits are very common and in several models
they are more abundant than regular orbits. We discuss how these results can
affect present ideas about the structure of galactic satellites.
A. A. Myullyari
On the stability of homographic N-body configurations
An N-body configuration is a central configuration if the gravitational force
on the bodies is proportional to distances from the center. The system is
homographic if the configuration formed by the bodies in the inertial
barycentric coordinate system stays similar to itself. Homographic
configurations are central configurations. All central configurations are
unstable. Expanding homographic configurations of equal masses on the vertices
of regular polygons and polyhedrons are used to study the instability in
detail. Perturbations growing faster than the general expansion of the system
t^(2/3) are considered to be unstable. Investigation in the linear
approximation is carried out. There is always an unstable perturbation that
divides the system into pairs of bodies.
Computer simulations are used to study the subsequent non-linear stage of the
process, confirming the results of the linear stability analysis.
I. Nikiforov
Milky Way Rotation Models from Neutral Hydrogen and Molecular Clouds: Galactic Constants, Common Details and Differences
The data on the rotation of the neutral hydrogen and molecular clouds (MC) have
been analysed to determine the main Galactic constants and the rotation curve
of the Milky Way. A difference between rotation laws of these two subsystems
was taken into account in a simple form to derive R_0 with two techniques of
comparison between HI and MC rotations. Combining these new results with
findings from the MC data only (Nikiforov, 1999), the final estimate of R_0=8.2
+/- 0.7 kpc from MC kinematics was obtained. The significant difference between
rotation curves from HI and MC at 1.1 < R/R_0 < 1.5 is found. It has a longitude
dependence and is most likely to be due to the perturbation from spiral wave
with the pitch angle close to 20 degrees. A decline of rotation velocity near
R = R_0 is confirmed from both HI and MC data.
I. Nikiforov
Interpretation of Rotation Curves of Giant Galaxies in the Local Group with the Truncated Exponential Disc Model
Each of giant spiral galaxies in the Local Group, our Galaxy and M31, have a
drop in rotation velocity which can be a 'signature' of a truncation in the
galactic disc. Considering this truncation, a multi-component mass model for
the Galaxy is constructed. The model consists of the bulge, the halo and two
disc components: the 'stellar' disc, found to be truncated at R = 0.8 R_0 (R_0
is the Galactic center distance), and the more extended 'gaseous' disc. This
model describes both a decline of velocity and the nonzero disc density in the
vicinity of the Sun. The model parameters and masses of all components are
obtained. Earlier, a similar mass modeling with truncated disc was carried out
for M31. Perhaps, the disc truncation arises from the tidal interaction with
companion galaxies.
K. Nilsson
Deducing the Orbit of the Radio Galaxy 3C129
The galaxy 3C129 possess a long radio tail shaped approximately like a segment
of an ellipse curving around a nearby giant galaxy. Byrd and Valtonen (1978,
ApJ 221, 481) used the segment to deduce the 3C129 orbit around the giant
galaxy, with and without tail buoyancy. The chief difficulty was the unknown
redshift of the giant galaxy. We have obtained with the Nordic Optical
Telescope a redshift for the giant galaxy. This redshift plus that of 3C129
gives more orbital parameters, in particular, a mass several times 10 to the
14th solar masses for the mass of the system. Because this mass is
independent of the X-ray observations and the poorly known system velocity
dispersion, the properties of the system's hot gas component as well as
processes in the radio tail can be studied.
GB expresses appreciation to the Academy of Finland for support and also for
the hospitality of Tuorla Observatory during a winter/spring 1999 visit.
Shingo Nishiura
Deep Optical Imaging of a Compact Group of Galaxies, Seyfert's Sextet
Recently, the X-ray satellite ROSAT has been used to investigate the dark
matter content in a large number of groups of galaxies because the hot gas
probed in the soft X-ray is generally believed to be gravitationally bound to
the groups. Although the majority of groups of galaxies detected by ROSAT show
round-shaped morphologies in the soft X-ray, some groups such as Seyfert's
Sextet show irregular-shaped soft X-ray morphologies. In order to understand
the origin of the irregular-shaped soft X-ray morphology of SS, we have
obtained a deep R-band optical image of this group. Our image shows that a
faint envelope down to a surface brightness mu_R ~26 mag per square arcsec
surrounds the member galaxies. Comparing this optical faint envelope with the
soft X-ray image, we find that both the images are remarkably similar in
morphology. Since the optical faint envelope should be attributed to stars
liberated from the member galaxies through historical tidal interactions, this
similarity provides direct morphological evidence that the dark matter was
originally associated with the individual galaxies and are now spreading out
around the group.
Giorgio Palumbo
Objectively selected samples of galaxy multiplets: an analysis of observed properties
Changes in the properties and in the relative number of (isolated) small groups
of galaxies are studied
a) when the search radius for group membership is allowed to increase
b) when an increasing neighbour search radius is applied.
Groups themselves are identified via an automatic algorithm running on
Zcat. Subsequent (DSS + CCD) image inspection allows a morphological group
classification. With respect to similar previous studies which apply either an
optical or an automatic identification, both, dense groups and rather loose
chains are defined.
Dynamical group parameters (and interaction stage) are presented and discussed.
Kristian Pedersen
Detection of hot plasma around M96 in the Leo-I group.
The nearby (D=11 Mpc) sparse group of galaxies, Leo-I, is in many respects
unique. It is the nearest group containing both bright spirals (M96 and M95)
and a bright elliptical (M105). A giant (diameter ca. 200 kpc) intergalactic
HI ring orbits the central M105/NGC3384 galaxy pair and appears to interact
with M96. If M96 is really in the group core, the Leo-I group provides an
unusually "clean" route to determining the Hubble constant. In our 22 ksec
ASCA SIS exposure of M96 we have detected diffuse X-ray emission extending more
than 10 arcminutes North of M96, in the direction of the HI ring. The
morphology and spectral characteristics of the diffuse emission shows that M96
has recently interacted with the HI ring, indicating that M96, the HI ring and
the central galaxy M105 are at the same distance within a few percent.
Jaime Perea
The distribution of mass in compact groups
Atomic gas is an excellent tracer of galaxy interaction when at least one of
the members is a late type galaxy. With this idea we are currently analyzing a
sample of compact groups observed with the VLA. During the data analysis stage
we noted the existence of HI clouds not connected with the main group, the
clouds were identified with dwarf and/or low surface brightness galaxies on the
POSS. Later they were observed with the 2.5m NOT telescope using ALFOSC. These
galaxies provide not only with information about the properties of the galaxies
belonging to compact groups prior to the gravitational interaction but they
constitute a satellite system for characterizing the dynamics. Our first result
are on HCG 96 and we find that for this group there is no room for a huge
amount of dark matter.
Henri Plana
The Nature of the Hickson Compact Group 18
We present the velocity field and monochromatic map of the Halpha line in
emission of the Hickson Compact group 18 (HCG 18), obtained with a Fabry Perot
system on the Canada-France-Hawaii telescope. HCG 18 was originally catalogued
as a group of four members. The brightest galaxy was later shown to be a
discordant object, unrelated to the group. The other three galaxies were
classified as magellanic irregulars. They are involved in a halo of diffuse
light. With our new data we were not able to separate the velocity fields of
each member but instead we built a combined velocity field of the three
galaxies. Our preliminary results show the following: 1) the gas distribution
is very clumpy; 2) the Halpha velocity field of HCG 18 does not show a
consistent rotation motion; 3) the overall isophote shapes and velocities are
in general agreement with the HI data, with a few important differences. These
observations allow us to investigate the nature of the group HCG 18, if it is a
real group, a merger remnant or a single normal galaxy with several
star-bursting knots.
Trevor Ponman
Galaxies and the intergalactic medium in groups
I discuss the evidence for links between the galaxies in groups and the
properties of the IGM - taking in similarity breaking, metallicity
distributions and the relationship between X-ray properties and galaxy content.
Marcus Price
Compact Galaxy Groups in the South
We have undertaken a study of Hickson Compact Groups in the southern sky. We
are also extending the list of southern compact groups using a variety of
approaches to identification of groups. Initial HI observations were made with
the 63 metre Parkes Radio Telescope. High resolution images were obtained in
follow-up observations with the ATNF Compact Array. A related poster gives
details of these observations. This is a progress report on our studies.
Following the suggestion of Williams, et al (ApJ 101, 1957, 1991) we are
studying southern groups to investigate the stages of the evolution of
interactions by means of the HI signatures. We discuss several groups in
detail. The HI distributions noted in various studies of Hickson Compact
groups begin with normal HI profiles associated with the individual galaxies in
the group--and indicating little if any signs of interaction. Other groups
(probably in a later stage of interaction) show bridges, disturbances in HI
distributions in individual galaxies, and other indications of tidal
interactions. Finally, some groups (still later stages of interaction?) share
a common HI envelope with no obvious connection to any of the individual
galaxies. Thus far we have seen no indications of dispersal or collapse of the
large scale HI envelopes that would leave a highly gas deficient elliptical
galaxy such as those predicted by numerical simulations (e.g. Barnes, Nature
338, 123, 1989). Continuum observations of the individual galaxies suggest
that nuclear continuum emission may also be a good indicator of the stage of
interaction. This can be due to induced star formation (starburst phenomenon)
or AGN activity fed by gas from the galaxy interactions.
Tapio Pursimo
BL Lac Objects in small galaxy groups.
Not yet Available
Roberto Rampazzo
Inventory of galaxy properties in small scale structures
We have obtained broad band imaging and low resolution spectroscopy using the
0.9m Dutch, WFI at 2.2m and the 1.5m ESO telescopes for a set of galaxies in 32
small groups. The groups span a wide range in density and show different
morphological mix. We have obtained systemic velocities, photometric parameters
and a preliminary spectral analysis of dominant galaxies in the groups. Our aim
is to investigate the connection between interaction and induced galaxy
activity from star formation to AGN activity.
Roberto Rampazzo
Kinematics of early-type galaxies in the compact groups HCG 67, HCG 74, and HCG 79
The compact groups HCG~67, HCG~74, and HCG~79 have been observed at the 1.93-m
telescope at OHP equipped with the CARELEC spectrograph. Rotation-velocity and
velocity-dispersion profiles have been obtained for early-type members present
in these groups. Kinematic peculiarities are discussed as function of the
morphological structure presented by galaxies in each group.
Pertti Rautiainen
Presence and Absence of Outer Rings in Barred Galaxies
Many barred galaxies have an outer ring, whose diameter is about twice that of
the bar. The most favoured explanation for the outer ring formation relates
them to the outer Lindblad resonance (OLR) of the rotating bar. The shapes of
the rings correspond to the periodic orbits near the OLR and the rings are
easily produced in gas dynamical simulations using analytical bar
potentials. However, many barred galaxies lack outer rings. There are at least
three possible explanations to the absence of an outer ring in such galaxies:
1) the time scale for outer ring formation is so long (over 1 Gyrs) that
galaxies with quite recently formed bars would naturally miss them, 2) the
outer potential is dominated by spirals arms with a lower pattern speed, which
prevents the resonance ring formation and 3) an inter- action with another
galaxy has destroyed the outer ring.
Rami Rekola
GAIA and the Local Group
The European Space Agency's GAIA satellite is currently being planned and aims
to achieve parallaxes and proper motions of a few microarcsecond (few 1E-6)
accuracy to 19th magnitude for the whole sky. Distances to all objects within
10 kpc will be accurately measured. For a large number of local group galaxies
three dimensional space velocities will be measured to accuracies of a few 10's
of km/s. The mission will significantly constrain the evolutionary history and
kinematics of local group galaxies.
R. Sancisi
HI observations of interacting triplets
Not yet available
W. Saslaw
Small galaxy groups at large redshift
Not yet available
Remco Schoenmakers
Kinematics of Sculptor Group Galaxies
An analysis of the kinematics of the five major spiral galaxies in the Sculptor
Group is presented. These galaxies are analyzed using the method of harmonic
expansion of the velocity field as described in Schoenmakers, Franx and de
Zeeuw (1997). Three different types of kinematic distortions were found: warps,
lopsidedness and elongation. All the Sculptor galaxies show kinematic
lopsidedness, two show signs of global elongation and two are kinematically
warped. These distortions are discussed in terms of their group environment.
Bernhard Schwarz
Not yet available
Ed Shaya
Least Action Orbit Calculations for Galaxies within 5 Mpc.
The Least Action Variational method is an elegant non-chaotic technique for
calculating the full trajectories of systems in a cosmological context. It has
been used extensively on the Local Group in a series of papers by Peebles. We
are now extending this analysis to include several more groups that are within
5 Mpc and totalling about 100 individual galaxies. Our repertory of tools
include code that hold present distances constant and allow the redshift to
vary, hold present redshifts fixed and directly calculate possible positions,
and one that iterates on distances until a proper redshift is found.
The sensitivity of predicted distances to variation in individual masses or
mass-to-light ratio will be presented. Typically there are a multiplicity of
orbit solutions. However, most of these solutions can be eliminated by their
distinct predicted distances.
Jack W. Sulentic
Stephan's Quintet and the Implications for Compact Groups
Stephans Quintet (SQ) is one of the best known and most studied compact groups
on the sky. We present new X-ray (ROSAT), IR (ISO) and optical (broad band,
Halpha and Fabry Perot) data that clarify the present and past evolutionary
history of this group. If SQ is typical of the compact group phenomenon then:
1) the groups evolve slowly, resisting merging, due to the injection of energy
from high velocity intruders and 2) show low levels of enhanced star formation
because the individual ISMs are quickly stripped via intruder collisions with
resultant gas either too hot or cold to form stars. Infall of residual
near-nuclear gas may stimulate the development of AGN.
Sonia Temporin
At the verge of coalescence: a dusty group of galaxies
We found a new, very compact group of galaxies characterized by a median
projected separation between galaxies of 5.2/h kpc and a very low velocity
dispersion. All the observed member galaxies show emission-line spectra and a
disturbed morphology. From these properties it emerges that this compact group
is in an extremely advanced stage of evolution.
Peeter Tenjes
Parameters of Dark Matter distribution in the Andromeda Galaxy
For most of galaxies the discrimination between the dark and visible matter
distribution is not unique. For this reason different approximations are used,
e.g. maximum disk hypothesis etc. However, in case of the nearby galaxy M31 two
additional constraints can be used in order to determine the parameters of dark
matter distribution. The first one is to take into account the motion of M31
relative to the Milky Way. The second one is to consider the thickness and
velocity dispersion measurements of the HI disk in order to calculate total
mass density in the galactic plane. Together with the surface brightness and
rotation curve data it is possible to determine the dark matter distribution
parameters without additional assumptions.
Hrant Tovmassian
The nature of compact groups
The problem of the reality of Compact Groups of galaxies (CGs) is discussed.
We separated two classes from the total lists of CGs: elongated, chain-like
groups (I), and round ones (II). It is shown that some parameters of both
classes of HCGs are quite different. The Radial Velocity Dispersions are
smaller in chain-like groups, and the interaction and merging processes are
more efficient in them. The difference of stellar magnitudes between the
brightest galaxy in the group and the second by brightness galaxy in HCGs is
larger in groups of class I. At the same time it is smaller in groups with
larger number of members. The surface distribution in round CGs is concentrated
towards the centers of groups.
The above mentioned differences allowed as to conclude that CGs are real
physical entities.
It is shown also that almost all HCGs are dynamically associated with generally
elongated loose groups of galaxies, and are the compact cores of the
latter. Mostly those loose groups, the direction of elongation of which compose
with the line of sight angles close to 45 deg, were revealed by previous
investigations.
The remote members of HCGs (the members of loose groups) are either ejected
from the corresponding groups or are gravitationally bound with them. HCGs
have, probably, longer life-times, than it has been deduced from N-body
simulations, and thus may be more stable configurations.
Ginevra Trinchieri
Peculiar X-ray features in bright early-type galaxies.
Two X--ray bright early type galaxies, selected for their unusually high X--ray
to optical flux ratio, have been observed at high spatial resolution with the
ROSAT HRI. Both sources are clearly extended, thus excluding a nuclear origin
of the high X--ray emission. In both cases, a small group of galaxies could be
the most natural explanation for the high X--ray luminosity observed. However,
at least part of the emission from IC 1262 is in a peculiar very bright
feature, shaped like an arc, and not clearly associated to a group galaxy.
This could be the signature of a recent merger, in the form of a bow shock at
the site of impact.
Douglas L. Tucker
Loose Groups of Galaxies in the Las Campanas Redshift Survey
A ``friends-of-friends'' percolation algorithm has been used to extract a
catalogue of 1495 "delta n / n = 80" density enhancements (loose groups) from
the six slices of the Las Campanas Redshift Survey (LCRS). I will describe in
this talk the peculiarities of extracting a group catalogue from the LCRS and
the general properties of the LCRS Loose Groups.
Mauri Valtonen
Evolution of multiple black hole nuclei in merged galaxies
In a group of about 30 galaxies, typically 8 mergers take place during the
redshift interval of 0 < z < 0.7 (Fang and Saslaw 1997). This high rate of
mergers means that there are also some multiple mergers. We may estimate that
typically we find in such a cluster about 22 ordinary galaxies, two single
mergers and one double merger. If every galaxy possesses one supermassive
central black hole, then the single mergers have a binary black hole each and
the double merger either a three or four black hole system. The instability of
the latter systems leads to interesting evolution which may have many different
end points. Examples of the orbits leading to different end results are shown
in a video movie.
Jaan Vennik
The fate of dwarf galaxies
Dwarf satellite galaxies and globular clusters, which are bound to luminous (in
particular early type) galaxies, can be steered by interactions to orbits
penetrating deep into the potential of their parent galaxy. Numerical
simulations have shown that the outer stars of those dwarf satellites are
eroded by dynamical friction and the dwarf galaxy is completely destroyed in a
relatively short time, resulting in very faint disturbances (soft merging) in
the form of faint rings in the halo of parent galaxy. With special image
processing methods we have found faint structures in E and S0 galaxies, which
for many reasons (mass, statistics etc.) can be interpreted as the first
observational evidence of this type of soft merging.
Lourdes Verdes-Montenegro
Tracing the interaction in HCGs through the atomic gas.
In order to understand the evolution of HCGs the atomic gas is crucial as a
privileged tracer of interactions. For this reason we have mapped with the VLA
a dozen of compact groups representative of different situations. I will show
specific results with a detailed description of the morphology and kinematics,
as well as more general conclusions for the different cases found.
Seppo Wiren
Binary galaxy spin correlations arising from mergers of galaxies
Statistics of spin orientations in binary galaxies may be used as a tool to
study the formation process of galaxies. Helou found that the spins of spiral
galaxies in binary systems are anticorrelated, and he suggested that it may
have to do with the inclination dependence of the galaxy merger process.We
study this dependence in small groups of galaxies. An N-body code is developed
which uses an inclination dependent dynamical friction law to affect mergers of
galaxies. It is found that some correlation results in this way in groups which
have initially random spin orientations.
A. V. Zasov
Vorontsov-Velyaminov's nests: what are they?
We review observational data available today related to the objects classified
by Vorontsov-Velyaminov as the 'nests' of galaxies: photometric data,
structural properties, emission spectra and gas kinematics. It is shown that
some 'nests' really present multiple systems, but in many cases they appear to
be peculiar single late type galaxies, containing bright sites of active star
formation. Some ideas about the nature of their peculiarities are discussed.
Jiaqing Zheng
Dynamics and Merging Process in Compact Galaxy Groups
Compact groups of galaxies may serve as a natural laboratory for studies of the
formation, evolution and interaction of stellar systems.
By using the traditional N-body code (Aarseth) with friction force and merging
process, we studied the dynamics of small galaxy groups. The results have been
compared with observational data by Karachentsev. The calculating results agree
well with observations.
Our conclusion is: The triplets and binaries of galaxies might be formed mainly
by merging processes.