7,387 research outputs found
Evolution in the iron abundance of the ICM
We present a Chandra analysis of the X-ray spectra of 56 clusters of galaxies
at , which cover a temperature range of keV. Our analysis
is aimed at measuring the iron abundance in the ICM out to the highest redshift
probed to date. We find that the emission-weighted iron abundance measured
within in clusters below 5 keV is, on average, a factor of
higher than in hotter clusters, following , which confirms the trend seen in local samples. We made use of
combined spectral analysis performed over five redshift bins at
to estimate the average emission weighted iron abundance. We find a constant
average iron abundance as a function of redshift,
but only for clusters at . The emission-weighted iron abundance is
significantly higher () in the redshift range
, approaching the value measured locally in the inner radii for a mix of cool-core and non cool-core clusters in the
redshift range . The decrease in with can be
parametrized by a power law of the form . The observed
evolution implies that the average iron content of the ICM at the present epoch
is a factor of larger than at . We confirm that the ICM is
already significantly enriched () at a look-back time
of 9 Gyr. Our data provide significant constraints on the time scales and
physical processes that drive the chemical enrichment of the ICM.Comment: 4 pages, 4 figures, to appear in the Proceedings of "The Extreme
Universe in the Suzaku Era", Dicember 2006, Kyoto (Japan
A FIRST DETERMINATION OF THE SURFACE DENSITY OF GALAXY CLUSTERS AT VERY LOW X--RAY FLUXES
We present the first results of a serendipitous search for clusters of
galaxies in deep ROSAT-PSPC pointed observations at high galactic latitude. The
survey is being carried out using a Wavelet based Detection Algorithm which is
not biased against extended, low surface brightness sources. A new
flux--diameter limited sample of 10 cluster candidates has been created from
surveyed area. Preliminary CCD observations have revealed
that a large fraction of these candidates correspond to a visible enhancement
in the galaxy surface density, and several others have been identified from
other surveys. We believe these sources to be either low--moderate redshift
groups or intermediate to high redshift clusters. We show X-ray and optical
images of some of the clusters identified to date. We present, for the first
time, the derived number density of the galaxy clusters to a flux limit of (0.5--2.0 keV). This extends the -- of previous cluster surveys by more than one decade in flux.
Results are compared to theoretical predictions for cluster number counts.Comment: uuencoded compressed Postscript, 7 pages including 4 figures.
Accepted for publication in Ap. J. Letters
Enforcement Questions of the International Whaling Commission: Are Exclusive Economic Zones The Solution?
The micro-Jy Radio Source Population: the VLA-CDFS View
We analyse the 267 radio sources from our deep (flux limit of 42 microJy at
the field center at 1.4 GHz) Chandra Deep Field South 1.4 and 5 GHz VLA survey.
The radio population is studied by using a wealth of multi-wavelength
information, including morphology and spectral types, in the radio, optical,
and X-ray bands. The availability of redshifts for ~ 70% of our sources allows
us to derive reliable luminosity estimates for the majority of the objects.
Contrary to some previous results, we find that star-forming galaxies make up
only a minority (~ 1/3) of sub-mJy sources, the bulk of which are faint radio
galaxies, mostly of the Fanaroff-Riley I type.Comment: 6 pages, 3 figures, to appear in the proceedings of "At the Edge of
the Universe", Sintra, Portugal, Oct. 9 - 13, 200
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