7,705 research outputs found
The X-ray Luminosity Function of Bright Clusters in the Local Universe
We present the X-ray luminosity function (XLF) for clusters of galaxies
derived from the RASS1 Bright Sample. The sample, selected from the ROSAT
All-Sky Survey in a region of 2.5 sr within the southern Galactic cap, contains
130 clusters with flux limits in the range ~ 3-4 x 10^-12 ergs/cm^2/s in the
0.5-2.0 keV band. A maximum-likelihood fit with a Schechter function of the XLF
over the entire range of luminosities (0.045 - 28. x 10^44 ergs/s), gives alpha
= 1.52 +/- 0.11, L_* = 3.80 +0.70 -0.55 x 10^44 ergs/s, and A = 5.07 +/- 0.45 x
10^-7 Mpc^-3 (10^44 ergs/s)^(\alpha-1). We investigate possible evolutionary
effects within the sample, out to our redshift limit (z ~ 0.3), finding no
evidence for evolution. Our results are in good agreement with other local
estimates of the XLF, implying that this statistic for the local universe is
now well determined. Comparison with XLFs for distant clusters (0.3 < z < 0.6),
shows that no evolution is present for L_X < 10^{44} ergs/s. However, we detect
differences at the 3 sigma level, between our local XLF and the distant one
estimated by Henry et al. for the EMSS sample. This difference is still present
when considering the EMSS sample revised by Nichol et al.Comment: 13 pages with 3 figures included, LaTex, aaspp4.sty and epsf.sty,
accepted for publication in ApJ Letters, only minor changes, added reference
CHANDRA reveals galaxy cluster with the most massive nearby cooling core, RXCJ1504.1-0248
A CHANDRA follow-up observation of an X-ray luminous galaxy cluster with a
compact appearance, RXCJ1504.1-0248 discovered in our REFLEX Cluster Survey,
reveals an object with one of the most prominent cluster cooling cores. With a
core radius of ~30 kpc smaller than the cooling radius with ~140 kpc more than
70% of the high X-ray luminosity of Lbol = 4.3 10e45 erg s-1 of this cluster is
radiated inside the cooling radius. A simple modeling of the X-ray morphology
of the cluster leads to a formal mass deposition rate within the classical
cooling flow model of 1500 - 1900 Msun yr-1 (for h=0.7), and 2300 - 3000 Msun
yr-1 (for h=0.5). The center of the cluster is marked by a giant elliptical
galaxy which is also a known radio source. Thus it is very likely that we
observe one of the interaction systems where the central cluster AGN is heating
the cooling core region in a self-regulated way to prevent a massive cooling of
the gas, similar to several such cases studied in detail in more nearby
clusters. The interest raised by this system is then due to the high power
recycled in RXCJ1504-0248 over cooling time scales which is about one order of
magnitude higher than what occurs in the studied, nearby cooling core clusters.
The cluster is also found to be very massive, with a global X-ray temperature
of about 10.5 keV and a total mass of about 1.7 10e15 Msun inside 3 Mpc.Comment: accepted for publication in Astrophys. Journal, 10 figure
Chandra Observations of the A3266 Galaxy Cluster Merger
Analysis of a 30,000 s X-ray observation of the Abell 3266 galaxy cluster
with the ACIS on board the Chandra Observatory has produced several new
insights into the cluster merger. The intracluster medium has a
non-monotonically decreasing radial abundance profile. We argue that the most
plausible origin for the abundance enhancement is unmixed, high abundance
subcluster gas from the merger. The enrichment consists of two stages:
off-center deposition of a higher abundance material during a subcluster merger
followed by a strong, localized intracluster wind that acts to drive out the
light elements, producing the observed abundance enhancement. The wind is
needed to account for both an increase in the heavy element abundance and the
lack of an enhancement in the gas density. Dynamical evidence for the wind
includes: (1) a large scale, low surface brightness feature perpendicular to
the merger axis that appears to be an asymmetric pattern of gas flow to the
northwest, away from the center of the main cluster, (2) compressed gas in the
opposite direction (toward the cluster center), and (3), the hottest regions
visible in the temperature map coincide with the proposed merger geometry and
the resultant gas flow. The Chandra data for the central region of the main
cluster shows a slightly cooler, filamentary region that is centered on the
central cD galaxy and is aligned with the merger axis directly linking the
dynamical state of the cD to the merger. Overall, the high spectral/spatial
resolution Chandra observations support our earlier hypothesis (Henriksen,
Donnelly, & Davis 1999) that we are viewing a minor merger in the plane of the
sky.Comment: Accepted to ApJ. 13 pages, 4 tables, 11 figure
Cosmological Effects of Powerful AGN Outbursts in Galaxy Clusters: Insights from an XMM-Newton Observation of MS0735+7421
We report on the results of an analysis of XMM-Newton observations of
MS0735+7421, the galaxy cluster which hosts the most energetic AGN outburst
currently known. The previous Chandra image shows twin giant X-ray cavities
(~200 kpc diameter) filled with radio emission and surrounded by a weak shock
front. XMM data are consistent with these findings. The total energy in
cavities and shock (~6 \times 10^{61} erg) is enough to quench the cooling flow
and, since most of the energy is deposited outside the cooling region (~100
kpc), to heat the gas within 1 Mpc by ~1/4 keV per particle. The cluster
exhibits an upward departure (factor ~2) from the mean L-T relation. The boost
in emissivity produced by the ICM compression in the bright shells due to the
cavity expansion may contribute to explain the high luminosity and high central
gas mass fraction that we measure. The scaled temperature and metallicity
profiles are in general agreement with those observed in relaxed clusters.
Also, the quantities we measure are consistent with the observed M-T relation.
We conclude that violent outbursts such as the one in MS0735+7421 do not cause
dramatic instantaneous departures from cluster scaling relations (other than
the L-T relation). However, if they are relatively common they may play a role
in creating the global cluster properties.Comment: 69 pages, 30 figures, accepted for publication in ApJ Main Journa
A Flux-limited Sample of Bright Clusters of Galaxies from the Southern Part of the ROSAT All-Sky Survey: the Catalog and the LogN-LogS
We describe the selection of an X-ray flux-limited sample of bright clusters
of galaxies in the southern hemisphere, based on the first analysis of the
ROSAT All-Sky Survey data (RASS1). The sample is constructed starting from an
identification of candidate clusters in RASS1, and their X-ray fluxes are
remeasured using the Steepness Ratio Technique. This method is better suited
than the RASS1 standard algorithm for measuring flux from extended sources. The
final sample is count-rate-limited in the ROSAT hard band (0.5-2.0 keV), so
that due to the distribution of NH, its effective flux limit varies between
about 3-4 x 10**-12 ergs cm**-2 s**-1 over the selected area. This covers the
Decl<2.5 deg part of the south Galactic cap region (b<-20 deg) - with the
exclusion of patches of low RASS1 exposure time and of the Magellanic Clouds
area - for a total of 8235 deg**2. 130 candidate sources fulfill our selection
criteria for bonafide clusters of galaxies in this area. Of these, 101 are
Abell/ACO clusters, while 29 do not have a counterpart in these catalogs. Of
these clusters, 126 (97%) clusters have a redshift and for these we compute an
X-ray luminosity. 20% of the cluster redshifts come from new observations, as
part of the ESO Key Program REFLEX Cluster Survey that is under completion.
Considering the intrinsic biases and incompletenesses introduced by the flux
selection and source identification processes, we estimate the overall
completeness to be better than 90%. The observed number count distribution,
LogN-LogS, is well fitted by a power law with slope alpha = 1.34 +/- 0.15 and
normalization A = 11.87 +/- 1.04 sr**-1 (10**-11 ergs cm**-2 s**-1)**alpha, in
good agreement with other measurements.Comment: 27 pages, 8 figures and 3 tables included, LaTex, emulateapj.sty and
epsf.sty, accepted for publication in ApJ: scheduled for the March 20, 1999,
Vol.514. The cluster catalog is available at
http://www.merate.mi.astro.it/~degrand
Chandra Observation of the Cluster of Galaxies MS 0839.9+2938 at z=0.194: the Central Excess Iron and SN Ia Enrichment
We present the Chandra study of the intermediately distant cluster of
galaxies MS 0839.9+2938. By performing both the projected and deprojected
spectral analyses, we find that the gas temperature is approximately constant
at about 4 keV in 130-444h_70^-1 kpc. In the inner regions, the gas temperature
descends towards the center, reaching <~ 3 keV in the central 37h_70^-1 kpc.
This infers that the lower and upper limits of the mass deposit rate are 9-34
M_sun yr^-1 and 96-126 M_sun yr^-1, respectively within 74h_70^-1 kpc where the
gas is significantly colder. Along with the temperature drop, we detect a
significant inward iron abundance increase from about 0.4 solar in the outer
regions to about 1 solar within the central 37h_70^-1 kpc. Thus MS 0839.9+2938
is the cluster showing the most significant central iron excess at z>~ 0.2. We
argue that most of the excess iron should have been contributed by SNe Ia. By
utilizing the observed SN Ia rate and stellar mass loss rate, we estimate that
the time needed to enrich the central region with excess iron is 6.4-7.9 Gyr,
which is similar to those found for the nearby clusters. Coinciding with the
optical extension of the cD galaxy (up to about 30h_70^-1 kpc), the observed
X-ray surface brightness profile exhibits an excess beyond the distribution
expected by either the beta model or the NFW model, and can be well fitted with
an empirical two-beta model that leads to a relatively flatter mass profile in
the innermost region.Comment: Accepted for publication in Ap
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