261 research outputs found
Images, structural properties and metal abundances of galaxy clusters observed with Chandra ACIS-I at 0.1<z<1.3
We have assembled a sample of 115 galaxy clusters at 0.1<z<1.3 with archived
Chandra ACIS-I observations. We present X-ray images of the clusters and make
available region files containing contours of the smoothed X-ray emission. The
structural properties of the clusters were investigated and we found a
significant absence of relaxed clusters (as determined by centroid shift
measurements) at z>0.5. The slope of the surface brightness profiles at large
radii were steeper on average by 15% than the slope obtained by fitting a
simple beta-model to the emission. This slope was also found to be correlated
with cluster temperature, with some indication that the correlation is weaker
for the clusters at z>0.5. We measured the mean metal abundance of the cluster
gas as a function of redshift and found significant evolution, with the
abundances dropping by 50% between z=0.1 and z~1. This evolution was still
present (although less significant) when the cluster cores were excluded from
the abundance measurements, indicating that the evolution is not solely due to
the disappearance of relaxed, cool core clusters (which are known to have
enhanced core metal abundances) from the population at z>0.5.Comment: 23 pages, 12 figures. Accepted for publication in ApJS. Updated to
match published version. Redshifts of two clusters (RXJ1701 and CL0848)
corrected and two observations of MACSJ0744.8 have been combined into one.
Conclusions unchanged. A version with images of all of the clusters is
available at http://hea-www.harvard.edu/~bmaughan/clusters.htm
Deep XMM and Chandra observations of ClJ1226.9+3332: A detailed X-ray mass analysis of a z=0.89 galaxy cluster
Deep XMM and Chandra observations of ClJ1226.9+3332 at z=0.89 have enabled
the most detailed X-ray mass analysis of any such high-redshift galaxy cluster.
The XMM temperature profile of the system shows no sign of central cooling,
with a hot core and a radially declining profile. A temperature map shows
asymmetry with a hot region that appears to be associated with a subclump of
galaxies at the cluster redshift, but is not visible in the X-ray surface
brightness. This is likely to be result of a merger event in the cluster, but
does not appear to significantly affect the overall temperature profile. The
XMM temperature profile, and combined Chandra and XMM emissivity profile
allowed precise measurements of the global properties of ClJ1226.9+3332; we
find kT=10.4+/-0.6keV, Z=0.16+/-0.05\Zsol, and M=5.2^{+1.0}_{-0.8}x10^{14}Msol.
We obtain profiles of the metallicity, entropy, cooling time and gas fraction,
and find a high concentration parameter for the total density profile of the
system. The global properties are compared with the local LT and MT relations,
and we are able to make the first observational test of the predicted evolution
of the YM relation. We find that departures from these scaling relations are
most likely caused by an underestimate of the total mass by ~30% in the X-ray
hydrostatic mass analysis due to the apparent recent or ongoing merger
activity.Comment: 14 pages, 19 figures. To be submitted to Ap
A First Look at the Nuclear Region of M31 with Chandra
We report on the first observation of the nuclear region of M31 with the
Chandra X-ray Observatory. The nuclear source seen with the Einstein and ROSAT
HRIs is resolved into five point sources. One of these sources is within 1'' of
the M31 central super-massive black hole. As compared to the other point
sources in M31, this nuclear source has an unusual x-ray spectrum. Based on the
spatial coincidence we identify this source with the central black hole, and
note that the unusual spectrum is a challenge to current theories. A bright
transient is detected ~26'' to the west of the nucleus, which may be associated
with a stellar mass black hole.Comment: Submitted to ApJ Letters, 4 pages, 4 figures. email:
garcia,ssm,fap,wrf,jem,cjf, @head-cfa.harvard.ed
A breathing zirconium metal-organic framework with reversible loss of crystallinity by correlated nanodomain formation
The isoreticular analogue of the metal-organic framework UiO-66(Zr), synthesized with the flexible trans-1,4-cyclohexanedicarboxylic acid as linker, shows a peculiar breathing behavior by reversibly losing long-range crystalline order upon evacuation. The underlying flexibility is attributed to a concerted conformational contraction of up to two thirds of the linkers, which breaks the local lattice symmetry. X-ray scattering data are described well by a nanodomain model in which differently oriented tetragonal-type distortions propagate over about 7-10 unit cells
Chandra temperature profiles for a sample of nearby relaxed galaxy clusters
We present Chandra gas temperature profiles at large radii for a sample of 13
nearby, relaxed galaxy clusters and groups, which includes A133, A262, A383,
A478, A907, A1413, A1795, A1991, A2029, A2390, MKW4, RXJ1159+5531, and USGC
S152. The sample covers a range of average temperatures from 1 to 10 keV. The
clusters are selected from the archive or observed by us to have sufficient
exposures and off-center area coverage to enable accurate background
subtraction and reach the temperature accuracy of better than 20-30% at least
to r=0.4-0.5 r_180, and for the three best clusters, to 0.6-0.7 r_180. For all
clusters, we find cool gas in the cores, outside of which the temperature
reaches a peak at r =~ 0.15 r_180 and then declines to ~0.5 of its peak value
at r =~ 0.5 r_180. When the profiles are scaled by the cluster average
temperature (excluding cool cores) and the estimated virial radius, they show
large scatter at small radii, but remarkable similarity at r>0.1-0.2 r_180 for
all but one cluster (A2390). Our results are in good agreement with previous
measurements from ASCA by Markevitch et al. and from Beppo-SAX by DeGrandi &
Molendi. Four clusters have recent XMM-Newton temperature profiles, two of
which agree with our results, and we discuss reasons for disagreement for the
other two. The overall shape of temperature profiles at large radii is
reproduced in recent cosmological simulations.Comment: ApJ in press. Replaced to synchronize with accepted version. Analysis
for two clusters (A2029 and RXJ1159) adde
A comparison of the strong lensing properties of the Sersic and the NFW profiles
We investigate the strong lensing properties of the Sersic profile as an
alternative to the NFW profile, focusing on applications to lens modelling of
clusters. Given an underlying Sersic dark matter profile, we study whether an
NFW profile can provide an acceptable fit to strong lensing constraints in the
form of single or multiple measured Einstein radii. We conclude that although
an NFW profile that fits the lensing constraints can be found in many cases,
the derived parameters may be biased. In particular, we find that for n~2,
which corresponds to massive clusters, the mass at r_200 of the best fit NFW is
overestimated (by a factor of ~2) and the concentration is very low (c~2). The
differences are important enough to warrant the inclusion of Sersic profile for
future analysis of strong lensing clusters.Comment: 19 pages (single column format), 11 figures. Accepted for publication
by JCA
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