9,723 research outputs found
The specific entropy of elliptical galaxies: an explanation for profile-shape distance indicators?
Dynamical systems in equilibrium have a stationary entropy; we suggest that
elliptical galaxies, as stellar systems in a stage of quasi-equilibrium, may
have a unique specific entropy. This uniqueness, a priori unknown, should be
reflected in correlations between the parameters describing the mass (light)
distribution in galaxies. Following recent photometrical work (Caon et al.
1993; Graham & Colless 1997; Prugniel & Simien 1997), we use the Sersic law to
describe the light profile of elliptical galaxies and an analytical
approximation to its three dimensional deprojection. The specific entropy is
calculated supposing that the galaxy behaves as a spherical, isotropic,
one-component system in hydrostatic equilibrium, obeying the ideal gas state
equations. We predict a relation between the 3 parameters of the Sersic,
defining a surface in the parameter space, an `Entropic Plane', by analogy with
the well-known Fundamental Plane. We have analysed elliptical galaxies in Coma
and ABCG 85 clusters and a group of galaxies (associated with NGC 4839). We
show that the galaxies in clusters follow closely a relation predicted by the
constant specific entropy hypothesis with a one-sigma dispersion of 9.5% around
the mean value of the specific entropy. Assuming that the specific entropy is
also the same for galaxies of different clusters, we are able to derive
relative distances between the studied clusters. If the errors are only due to
the determination of the specific entropy (about 10%), then the error in the
relative distance determination should be less than 20% for rich clusters. We
suggest that the unique specific entropy may provide a physical explanation for
the distance indicators based on the Sersic profile put forward by Young &
Currie (1994, 1995) and discussed by Binggeli & Jerjen (1998).Comment: Submitted to MNRAS (05/05/99), 15 pages, 10 figure
Mass formula for T=0 and T=1 ground states of N=Z nuclei
An algebraic model is developed to calculate the T=0 and T=1 ground state
binding energies for N=Z nuclei. The method is tested in the sd shell and is
then extended to 28-50 shell which is currently the object of many experimental
studies.Comment: 5 figure
Free-floating molecular clumps and gas mixing: hydrodynamic aftermaths of the intraclusterinterstellar medium interaction
The interaction of gas-rich galaxies with the intra-cluster medium (ICM) of
galaxy clusters has a remarkable impact on their evolution, mainly due to the
gas loss associated with this process. In this work, we use an idealised,
high-resolution simulation of a Virgo-like cluster, run with RAMSES and with
dynamics reproducing that of a zoom cosmological simulation, to investigate the
interaction of infalling galaxies with the ICM. We find that the tails of ram
pressure stripped galaxies give rise to a population of up to more than a
hundred clumps of molecular gas lurking in the cluster. The number count of
those clumps varies a lot over time -- they are preferably generated when a
large galaxy crosses the cluster (M M), and their
lifetime ( Myr) is small compared to the age of the cluster. We
compute the intracluster luminosity associated with the star formation which
takes place within those clumps, finding that the stars formed in all of the
galaxy tails combined amount to an irrelevant contribution to the intracluster
light. Surprisingly, we also find in our simulation that the ICM gas
significantly changes the composition of the gaseous disks of the galaxies:
after crossing the cluster once, typically 20% of the cold gas still in those
disks comes from the ICM.Comment: 9 pages, 6 figures. Accepted for publication in MNRA
Giant Ringlike Radio Structures Around Galaxy Cluster Abell 3376
In the current paradigm of cold dark matter cosmology, large-scale structures
are assembling through hierarchical clustering of matter. In this process, an
important role is played by megaparsec (Mpc)-scale cosmic shock waves, arising
in gravity-driven supersonic flows of intergalactic matter onto dark
matter-dominated collapsing structures such as pancakes, filaments, and
clusters of galaxies. Here, we report Very Large Array telescope observations
of giant (~2 Mpc by 1.6 Mpc), ring-shaped nonthermal radio-emitting structures,
found at the outskirts of the rich cluster of galaxies Abell 3376. These
structures may trace the elusive shock waves of cosmological large-scale matter
flows, which are energetic enough to power them. These radio sources may also
be the acceleration sites where magnetic shocks are possibly boosting
cosmic-ray particles with energies of up to 10^18 to 10^19 electron volts.Comment: Published on Science, 3 November 2006. Main paper and Supporting
Online Materia
The entropy of elliptical galaxies in Coma: a clue for a distance indicator
We have fitted the surface brightness of a sample of 79 elliptical galaxies
pertaining to the Coma cluster of galaxies using the Sersic profile. This model
is defined through three primary parameters: scale length (a), intensity
(\Sigma_0), and a shape parameter (\nu); physical and astrophysical quantities
may be computed from these parameters. We show that correlations are stronger
among primary parameters than the classical astrophysical ones. In particular,
the galaxies follow a high correlation in \nu and a parameters. We show that
the \nu and a correlation satisfies a constant specific entropy condition. We
propose to use this entropy relation as distance indicator for clusters.Comment: 5 pages, 3 figures, submitted to MNRAS Letter
An XMM-Newton view of the cluster of galaxies Abell 85
We have observed the cluster of galaxies Abell 85 with XMM-Newton. These data
have allowed us to confirm in a previous paper the existence of the extended 4
Mpc filament detected by the ROSAT PSPC in the neighbourhood of this cluster,
and to determine an X-ray temperature of about about 2 keV. We now present a
thorough analysis of the properties of the X-ray gas in the cluster itself,
including temperature and metallicity maps for the entire cluster. These
results show that Abell 85 had intense merging activity in the past and is not
fully relaxed, even in the central region. We have also determined the
individual abundances for some iron-group metals and alpha-elements in various
regions; the ratios of these metallicities to the iron abundance show that both
supernova types Ia and II must be involved in the intra-cluster gas enrichment.
Spectral analysis of the central region suggests a different redshift of the
X-ray emitting gas compared to the mean cluster velocity derived from galaxy
member redshifts. We discuss the implications of the difference between the cD
galaxy redshift, the mean galaxy redshift and the hot gas redshift, as well as
the possibility of several groups being accreted on to Abell 85. Finally, we
obtain the dynamical mass profile and baryon fraction taking into account the
new determined temperature profile. The dynamical mass in Abell 85 has a steep
density profile, similar to the ones found in N-body simulations.Comment: Accepted for publication in Astronomy & Astrophysic
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