2,189 research outputs found
Constraining from X-ray properties of Clusters of Galaxies at high redshift
Properties of high redshift clusters are a fundamental source of information
for cosmology. It has been shown by Oukbir and Blanchard (1997) that the
combined knowledge of the redshift distribution of X-ray clusters of galaxies
and the luminosity-temperature correlation, , provides a powerful test
of the mean density of the Universe. In this paper, we address the question of
the possible evolution of this relation from an observational point of view and
its cosmological significance. We introduce a new indicator in order to measure
the evolution of the X-ray luminosity-temperature relation with redshift and
take advantage of the recent availability of temperature information for a
significant number of high and intermediate redshift X-ray clusters of
galaxies. From our analysis, we find a slightly positive evolution in the
relation. This implies a high value of the density parameter of
. However, because the selection of clusters included inour sample
is unknown, this can be considered only as a tentative result. A
well-controlled X-ray selected survey would provide a more robust answer. XMM
will be ideal for such a program.Comment: 10 pages, LaTeX, 4 figures,5 tables, accepted by A&
Galaxy Modelling -- I. Spectral Energy Distributions from Far-UV to Sub-mm Wavelengths
(abridged) We present STARDUST, a new self-consistent modelling of the
spectral energy distributions (SEDs) of galaxies from far-UV to radio
wavelengths. In order to derive the SEDs in this broad spectral range, we first
couple spectrophotometric and (closed-box) chemical evolutions to account for
metallicity effects on the spectra of synthetic stellar populations. We then
use a phenomenological fit for the metal-dependent extinction curve and a
simple geometric distribution of the dust to compute the optical depth of
galaxies and the corresponding obscuration curve. This enables us to calculate
the fraction of stellar light reprocessed in the infrared range. In a final
step, we define a dust model with various components and we fix the weights of
these components in order to reproduce the IRAS correlation of IR colours with
total IR luminosities. This allows us to compute far-IR SEDs that
phenomenologically mimic observed trends. We are able to predict the spectral
evolution of galaxies in a broad wavelength range, and we can reproduce the
observed SEDs of local spirals, starbursts, luminous infrared galaxies (LIRGs)
and ultra luminous infrared galaxies (ULIRGs). This modelling is so far kept as
simple as possible and depends on a small number of free parameters, namely the
initial mass function (IMF), star formation rate (SFR) time scale, gas density,
and galaxy age, as well as on more refined assumptions on dust properties and
the presence (or absence) of gas inflows/outflows.Comment: 20 pages, 23 figures, Accepted for publication in Astronomy and
Astrophysics Main Journa
A New Local Temperature Distribution Function for X-ray Clusters: Cosmological Applications
(abridged) We present a new determination of the local temperature function
of X-ray clusters. We use a new sample comprising fifty clusters for which
temperature information is now available, making it the largest complete sample
of its kind. It is therefore expected to significantly improve the estimation
of the temperature distribution function of moderately hot clusters. We find
that the resulting temperature function is higher than previous estimations,
but agrees well with the temperature distribution function inferred from the
BCS and RASS luminosity function. We have used this sample to constrain the
amplitude of the matter fluctuations on cluster's scale of
Mpc, assuming a mass-temperature relation based
on recent numerical simulations. We find for an
model. Our sample provides an ideal reference at to
use in the application of the cosmological test based on the evolution of X-ray
cluster abundance (Oukbir & Blanchard 1992, 1997). Using Henry's sample, we
find that the abundance of clusters at is significantly smaller, by
a factor larger than 2, which shows that the EMSS sample provides strong
evidence for evolution of the cluster abundance. A likelihood analysis leads to
a rather high value of the mean density parameter of the universe: (open case) and (flat case), which is
consistent with a previous, independent estimation based on the full EMSS
sample by Sadat et al.(1998). Some systematic uncertainties which could alter
this result are briefly discussed.Comment: 31 pages, 12 figures, mathches the version published in Astronomy and
Astrophysic
On Source Density Evolution of Gamma-ray Bursts
Recent optical afterglow observations of gamma-ray bursts indicate a setting
and distance scale that many relate to star-formation regions. In this paper,
we use and a set of artificial trigger thresholds to probe
several potential GRB source density evolutionary scenarios. In particular, we
compare a uniform subset of BATSE 4B data to cosmological scenarios where GRBs
evolve as the comoving density, the star formation rate, the QSO rate, and the
SN Type Ic rate. Standard candle bursts with power-law spectra and a universe
without vacuum energy were assumed. Our results significantly favor a comoving
density model, implying that GRB source density evolution is weaker than
expected in these evolutionary scenarios. GRB density might still follow
star-formation rates given proper concurrent GRB luminosity evolution,
significant beaming, significant error in standard candle assumptions, or were
a significant modification of star formation rate estimates to occur.Comment: 12 pages, 4 figures, accepted by Ap
The Evolution of the Galaxy Cluster Luminosity-Temperature Relation
We analyzed the luminosity-temperature (L-T) relation for 2 samples of galaxy
clusters which have all been observed by the ASCA satellite. We used 32 high
redshift clusters (0.3<z<0.6), 53 low redshift clusters (z<0.3), and also the
combination of the low and high redshift datasets. We assumed a power law
relation between the bolometric luminosity of the galaxy cluster and its
integrated temperature and redshift (L_{bol,44}=C*T^alpha*(1+z)^A). The results
are consistent, independent of cosmology, with previous estimates of
LT found by other authors. We observed weak or zero evolution.Comment: 20 pages, Latex, 11 figures, GIF forma
project: III. Gas mass fraction shape in high redshift clusters
We study the gas mass fraction, behavior in
project. The typical shape of high redshift galaxy
clusters follows the global shape inferred at low redshift quite well. This
result is consistent with the gravitational instability picture leading to self
similar structures for both the dark and baryonic matter. However, the mean
XMM$ clusters, the apparent gas
fraction at the virial radius is consistent with a non-evolving universal value
in a high matter density model and not with a concordance.Comment: Accepted, A&A, in pres
The Expected Rate of Gamma-Ray Burst Afterglows In Supernova Searches
We predict the rate at which Gamma-Ray Burst (GRB) afterglows should be
detected in supernova searches as a function of limiting flux. Although GRB
afterglows are rarer than supernovae, they are detectable at greater distances
because of their higher intrinsic luminosity. Assuming that GRBs trace the
cosmic star formation history and that every GRB gives rise to a bright
afterglow, we find that the average detection rate of supernovae and afterglows
should be comparable at limiting magnitudes brighter than K=18. The actual rate
of afterglows is expected to be somewhat lower since only a fraction of all
gamma-ray selected GRBs were observed to have associated afterglows. However,
the rate could also be higher if the initial gamma-ray emission from GRB
sources is more beamed than their late afterglow emission. Hence, current and
future supernova searches can place strong constraints on the afterglow
appearance fraction and the initial beaming angle of GRB sources.Comment: 13 pages, submitted to ApJ
The cluster M-T relation from temperature profiles observed with ASCA and ROSAT
We calibrate the galaxy cluster mass - temperature relation using the
temperature profiles of intracluster gas observed with ASCA (for hot clusters)
and ROSAT (for cool groups). Our sample consists of apparently relaxed clusters
for which the total masses are derived assuming hydrostatic equilibrium. The
sample provides data on cluster X-ray emission-weighted cooling flow-corrected
temperatures and total masses up to r_1000. The resulting M-T scaling in the
1-10 keV temperature range is M_1000 = (1.23 +- 0.20)/h_50 10^15 Msun (T/10
keV)^{1.79 +- 0.14} with 90% confidence errors, or significantly (99.99%
confidence) steeper than the self-similar relation M propto T^{3/2}. For any
given temperature, our measured mass values are significantly smaller compared
to the simulation results of Evrard et al. (1996) that are frequently used for
mass-temperature scaling. The higher-temperature subsample (kT > 4 keV) is
consistent with M propto T^{3/2}, allowing the possibility that the
self-similar scaling breaks down at low temperatures, perhaps due to heating by
supernovae that is more important for low-temperature groups and galaxies as
suggested by earlier works.Comment: 8 pages, 2 figures, accepted by Ap
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