69 research outputs found
The cluster of galaxies Abell 376
We present a dynamical analysis of the galaxy cluster Abell 376 based on a
set of 73 velocities, most of them measured at Pic du Midi and Haute-Provence
observatories and completed with data from the literature. Data on individual
galaxies are presented and the accuracy of the determined velocities is
discussed as well as some properties of the cluster. We obtained an improved
mean redshift value z=0.0478^{+0.005}_{-0.006} and velocity dispersion
sigma=852^{+120}_{-76}km/s. Our analysis indicates that inside a radius of
900h_{70}^{-1}kpc (15 arcmin) the cluster is well relaxed without any
remarkable feature and the X-ray emission traces fairly well the galaxy
distribution. A possible substructure is seen at 20 arcmin from the centre
towards the Southwest direction, but is not confirmed by the velocity field.
This SW clump is, however, kinematically bound to the main structure of Abell
376. A dense condensation of galaxies is detected at 46 arcmin (projected
distance 2.6h_{70}^{-1}Mpc) from the centre towards the Northwest and analysis
of the apparent luminosity distribution of its galaxies suggests that this
clump is part of the large scale structure of Abell 376. X-ray spectroscopic
analysis of ASCA data resulted in a temperature kT = 4.3+/-0.4 keV and metal
abundance Z = 0.32+/-0.08 Z_solar. The velocity dispersion corresponding to
this temperature using the T_X-sigma scaling relation is in agreement with the
measured galaxies velocities.Comment: 11 pages, 10 figures, accepted for publication in A&
Exact solutions for the spatial de Vaucouleurs and Sersic laws and related quantities
Using the Mathematica package, we find exact analytical expressions for the
so-called de-projected De Vaucouleurs and Sersic laws as well as for related
spatial (3D) quantities, such the mass, gravitational potential, the total
energy and the central velocity dispersion, generally involved in astronomical
calculations expressed in terms of the Meijer G functions.Comment: 11 pages, accepted in A
Dissipationless Collapse of Spherical Protogalaxies and the Fundamental Plane
Following on from the numerical work of Capelato, de Carvalho & Carlberg
(1995, 1997), where dissipationless merger simulations were shown to reproduce
the "Fundamental Plane" (FP) of elliptical galaxies, we investigate whether the
end products of pure, spherically symmetric, one-component dissipationless {\it
collapses} could also reproduce the FP. Past numerical work on collisionless
collapses have addressed important issues on the dynamical/structural
characteristics of collapsed equilibrium systems. However, the study of
collisionless collapse in the context of the nature of the FP has not been
satisfactorily addressed yet. Our aim in this paper is to focus our attention
on the resulting collapse of simple one-component spherical models with a range
of different initial virial coefficients. We find that the characteristic
correlations of the models are compatible with virialized, centrally homologous
systems. Our results strengthen the idea that merging may be a fundamental
ingredient in forming non-homologous objects.Comment: 9 pages, 4 Postscript figures, Astronomy & Astrophysics in press
(2002). Abstract placement correcte
Gravo-thermal properties and formation of elliptical galaxies
We have analyzed a sample of galaxies belonging to three clusters: Coma, Abell 85, and Abell 496 (real galaxies) and a sample of simulated elliptical galaxies formed in a hierarchical merging scheme (virtual galaxies). We use the Sersic law to describe their light profile. The specific entropy (Boltzmann-Gibbs definition) is then calculated supposing that the galaxies behave as spherical, isotropic, one-component systems. We find that, to a good approximation (about 10%), both real and virtual galaxies have an almost unique specific entropy. Within this approximation the galaxies are distributed in a thin plane in the space defined by the three Sersic law parameters, which we call the Entropic Plane. A further analysis shows that both real and virtual galaxies are in fact located on a thin line, therefore indicating the existence of another - and yet unknown - physical property, besides the uniqueness of the specific entropy. A more careful examination of the virtual galaxies sample indicates a very small increase of their specific entropy with merging generation. In a hierarchical scenario, this implies a correlation between the specific entropy and the total mass, which is indeed seen in our data. The scatter and tilt of the Entropic Line, defined by Lima Neto et al. (1999a), are reduced when this correlation is taken into account. Although one cannot distinguish between various generations for real galaxies, the distribution of their specific entropy is similar to that in the virtual sample, suggesting that hierarchical merging processes could be an important mechanism in the building of elliptical galaxies
Merging of Low-Mass Systems and the Origin of the Fundamental Plane
We present a new set of dissipationless N-body simulations to examine the
feasibility of creating bright ellipticals (following the Kormendy relation) by
hierarchically merging present-day early-type dwarf galaxies, and to study how
the encounter parameters affect the location of the end-product in the
plane. We investigate the merging of one-component
galaxies of both equal and different masses, the merging of two-component
galaxy models to explore the effect of dark halos on the final galaxy
characteristics, and the merging of ultracompact dwarf galaxies. We find that
the increase of with is attributable to an increase in the
initial orbital energy. The merger remnants shift down in the plane and fail to reach the KR. Thus, the KR is not reproducable by
mergers of dwarf early-type systems, rendering untenable the theory that
present-day dwarfs are responsible for even a small fraction of the present-day
ellipticals, unless a considerable amount of dissipation is invoked. However,
we do find that present-day dwarfs can be formed by the merger of ultra-compact
dwarfs.Comment: 10 pages, 8 figures. Accepted for publication in MNRA
The Cluster of Galaxies Abell 970
We present a dynamical analysis of the galaxy cluster Abell 970 based on a
new set of radial velocities measured at ESO, Pic du Midi and Haute-Provence
observatories. Our analysis indicates that this cluster has a substructure and
is out of dynamical equilibrium. This conclusion is also supported by
differences in the positions of the peaks of the surface density distribution
and X-ray emission, as well as by the evidence of a large scale velocity
gradient in the cluster. We also found a discrepancy between the masses
inferred with the virial theorem and with the X-ray emission, what is expected
if the galaxies and the gas inside the cluster are not in hydrostatic
equilibrium. Abell 970 has a modest cooling flow, as is expected if it is out
of equilibrium as suggested by Allen (1998). We propose that cooling flows may
have an intermittent behavior, with phases of massive cooling flows being
followed by phases without significant cooling flows after the acretion of a
galaxy group massive enough to disrupt the dynamical equilibrium in the center
of the clusters. A massive cooling flow will be established again, after a new
equilibrium is achieved.Comment: 24 pages, 9 figures, submitted to A&
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