26 research outputs found
The Two-Component Virial Theorem and the Physical Properties of Stellar Systems
Motivated by present indirect evidences that galaxies are surrounded by dark
matter halos, we investigate whether their physical properties can be described
by a formulation of the virial theorem which explicitly takes into account the
gravitational potential term representing the interaction of the dark halo with
the barionic or luminous component. Our analysis shows that the application of
such a ``two-component virial theorem'' not only accounts for the scaling
relations displayed, in particular, by elliptical galaxies, but also for the
observed properties of all virialized stellar systems, ranging from globular
clusters to galaxy clusters.Comment: 13 pages, 2 figures, LaTeX, corrected few typos. This version matches
the published versio
The structure and dynamics of the AC114 galaxy cluster revisited
We present a dynamical analysis of the galaxy cluster AC114 based on a
catalogue of 524 velocities. Of these, 169 (32%) are newly obtained at ESO
(Chile) with the VLT and the VIMOS spectrograph. Data on individual galaxies
are presented and the accuracy of the measured velocities is discussed.
Dynamical properties of the cluster are derived. We obtain an improved mean
redshift value z= 0.31665 +/- 0.0008 and velocity dispersion \sigma= 1893+73-82
\kms. A large velocity dispersion within the core radius and the shape of the
infall pattern suggests that this part of the cluster is in a radial phase of
relaxation with a very elongated radial filament spanning 12000 \kms. A radial
foreground structure is detected within the central 0.5/h Mpc radius,
recognizable as a redshift group at the same central redshift value. We analyze
the color distribution for this archetype Butcher-Oemler galaxy cluster and
identify the separate red and blue galaxy sequences. The latter subset contains
44% of confirmed members of the cluster, reaching magnitudes as faint as R_{f}=
21.1 (1.0 magnitude fainter than previous studies). We derive a mass M_{200}=
(4.3 \pm 0.7) x 10^15 Msun/h. In a subsequent paper we will utilize the
spectral data presented here to explore the mass-metallicity relation for this
intermediate redshift cluster.Comment: 17 pages, 11 figures, 4 tables, accepted for publication in MNRA
"Fundamental-Plane"-Like Relations From Collisionless Stellar Dynamics: A Comparison of Mergers and Collapses
We present a new set of dissipationless N-body simulations aiming to better
understand the pure dynamical aspects of the ``Fundamental Plane'' (FP) of
elliptical galaxies. We have extended our previous hierarchical merger scheme
by considering the Hernquist profile for the initial galaxy model.
Two-component Hernquist galaxy models were also used to study the effect of
massive dark halos on the end-products characteristics. We have also performed
new collapse simulations including initial spin. We found that the
one-component Hernquist mergers give results similar to those found for the
one-component King models, namely both were able to build-up small scatter
FP-like correlations with slopes consistent with what is found for the
near-infrared FP of nearby galaxies. The two-component models also reproduce a
FP-like correlation, but with a significantly steeper slope. This is in
agreement with what has been found for elliptical galaxies at higher redshift
(0.1 z 0.6). We discuss some structural properties of the simulated
galaxies and their ability to build-up FP-like correlations. We confirm that
collapses generally do not follow a FP-like correlation regardless of the
initial spin. We suggest that the evolution of gradients in the gravitational
field of the merging galaxies may be the main ingredient dictating the final
non-homology property of the end products.Comment: 15 pages, 11 figures, uses mn2e.cls. Accepted for publication in
MNRA
The Nature of the Activity in Hickson Compact Groups of Galaxies
We present the results of the spectral classification of the 82 brightest
galaxies in a sample of 17 compact groups. We verify that the AGNs are
preferentially located in the most early-type and luminous galaxies of the
groups, as is usually observed in the field. But these AGNs also appear to be
systematically concentrated towards the central parts of the groups. Our
observations suggest a correlation between activity types, morphologies and
densities of galaxies in the compact groups. This is consistent with a scenario
in which galaxies of compact groups evolve by interacting with their
environment and are currently in a quiet phase of their activityComment: 22 pages, LaTeX (aasms4.sty) + 7 figures; accepted for publication in
the Astrophysical Journa
Evidence of Substructure in the Cluster of Galaxies A3558
We investigate the dynamical properties of the cluster of galaxies A3558
(Shapley 8). Studying a region of one square degree ( 3 Mpc) centered
on the cluster cD galaxy, we have obtained a statistically complete photometric
catalog with positions and magnitudes of 1421 galaxies (down to a limiting
magnitude of ). This catalog has been matched to the recent velocity
data obtained by Mazure et al. (1997) and from the literature, yielding a
radial velocity catalog containing 322 galaxies. Our analysis shows that the
position/velocity space distribution of galaxies shows significant
substructure. A central bimodal core detected previously in preliminary studies
is confirmed by using the Adaptive Kernel Technique and Wavelet Analysis. We
show that this central bimodal subtructure is nevertheless composed of a
projected feature, kinematically unrelated to the cluster, plus a group of
galaxies probably in its initial merging phase into a relaxed core. The cD
velocity offset with respect to the average cluster redshift, reported earlier
by several authors, is completely eliminated as a result of our dynamical
analysis. The untangling of the relaxed core component also allows a better,
more reliable determination of the central velocity dispersion, which in turn
eliminates the ``-problem'' for A3558. The cluster also shows a
``preferential'' distribution of subclumps coinciding with the direction of the
major axis position angle of the cD galaxy and of the central X-ray emission
ellipsoidal distribution, in agreement with an anisotropic merger scenario.Comment: 35 pages in latex, 17 figures in Postscript, accepted for publication
in the Astrophysical Journa
The Velocity Field in the Neighbourhood of Clusters of Galaxies: a Study Based on Photometric Redshifts
International audienceWe present a preliminary study of the velocity field in the neighbourhood of the Abell 1942 cluster of galaxies (z ≈ 0.22), for which both photometric and spectroscopic redshifts are available. Besides characterizing the dynamical stage of this particular cluster, the aim of this work is to search for efficient tools capable to provide reliable representations of the infall velocity fields for samples of clusters of galaxies, based solely on photometric redshifts