1,495 research outputs found
Active galactic nucleus feedback in clusters of galaxies
Observations made during the last ten years with the Chandra X-ray
Observatory have shed much light on the cooling gas in the centers of clusters
of galaxies and the role of active galactic nucleus (AGN) heating. Cooling of
the hot intracluster medium in cluster centers can feed the supermassive black
holes found in the nuclei of the dominant cluster galaxies leading to AGN
outbursts which can reheat the gas, suppressing cooling and large amounts of
star formation. AGN heating can come in the form of shocks, buoyantly rising
bubbles that have been inflated by radio lobes, and the dissipation of sound
waves.Comment: Refereed review article published in Chandra's First Decade of
Discovery Special Feature edition of the Proceedings of the National Academy
of Science
Chandra Observation of the Cluster Environment of a WAT Radio Source in Abell 1446
Wide-angle tail (WAT) radio sources are often found in the centers of galaxy
clusters where intracluster medium (ICM) ram pressure may bend the lobes into
their characteristic C-shape. We examine the low redshift (z=0.1035) cluster
Abell 1446, host to the WAT radio source 1159+583. The cluster exhibits
possible evidence for a small-scale cluster-subcluster merger as a cause of the
WAT radio source morphology. This evidence includes the presence of temperature
and pressure substructure along the line that bisects the WAT as well as a
possible wake of stripped interstellar material or a disrupted cool core to the
southeast of the host galaxy. A filament to the north may represent cool,
infalling gas that's contributing to the WAT bending while spectroscopically
determined redshifts of member galaxies may indicate some component of a merger
occurring along the line-of-sight. The WAT model of high flow velocity and low
lobe density is examined as another scenario for the bending of 1159+583. It
has been argued that such a model would allow the ram pressure due to the
galaxy's slow motion through the ICM to shape the WAT source. A temperature
profile shows that the cluster is isothermal (kT= 4.0 keV) in a series of
annuli reaching a radius of 400 kpc. There is no evidence of an ongoing cooling
flow. Temperature, abundance, pressure, density, and mass profiles, as well as
two-dimensional maps of temperature and pressure are presented.Comment: 40 AASTeX pages including 15 postscript figures; accepted for
publication in Ap
Low Frequency Radio Observations of X-ray Ghost Bubbles in Abell 2597: A History of Radio Activity in the Core
A previous analysis of the Chandra X-ray image of the center of the cooling
core cluster Abell 2597 showed two ``ghost holes'' in the X-ray emission to the
west and northeast of the central radio galaxy PKS 2322-123. Previous radio
observations did not detect any radio emission coming from the interior of the
X-ray holes. We present new low frequency radio observations of Abell 2597. At
330 MHz, radio emission extends into the interior of the western ghost bubble,
but not the northeast one. Our re-analysis of the archival Chandra data shows
evidence for an X-ray tunnel (elongated region of reduced X-ray emission)
extending from near the center of the cD out to the west ghost bubble. We also
detect a smaller X-ray hole to the northeast of the center of the cD and closer
than the outer ghost bubbles. Radio observations at 1.3 GHz show extensions to
the west along the X-ray tunnel toward the west ghost bubble, to the northeast
into the new X-ray hole, and to the northwest. All of these structures are much
larger than the two inner radio lobes seen previously at 8 GHz. The X-ray
tunnel suggests that the west ghost bubble is part of a continuous flow of
radio plasma out from the active galactic nucleus, rather than a detached
buoyant old radio lobe, and thus it may be an intermediate case between an
active radio galaxy and a buoyant lobe.Comment: ApJ accepted, 5 page
THE RADIO/X-RAY CONNECTION IN ABELL 2029
Abstract We present results of an analysis of the central regions of Abell 2029 and discuss the connections between the radio and X-ray components of the cluster. Despite the very relaxed appearance of the thermal gas in the outer cluster regions, the Chandra observations reveal significant structure in the cluster core. There are a number of bright X-ray filaments as well as a spiral "excess". Several of the filaments appear to be connected to the steep-spectrum cluster-center radio source PKS 1508+059. An analysis of the temperature structure in the cluster shows that the southern extension of PKS 1508+059 is surrounded by cool X-ray gas, while the northern lobe apparently lies in a region of average temperature. We also discuss the inner regions of the radio source which show two oppositelydirected, collimated jets that disrupt as the jets apparently encounter a drop in the confining thermal plasma
Cosmological Constraints from Galaxy Clustering and the Mass-to-Number Ratio of Galaxy Clusters
We place constraints on the average density (Omega_m) and clustering
amplitude (sigma_8) of matter using a combination of two measurements from the
Sloan Digital Sky Survey: the galaxy two-point correlation function, w_p, and
the mass-to-galaxy-number ratio within galaxy clusters, M/N, analogous to
cluster M/L ratios. Our w_p measurements are obtained from DR7 while the sample
of clusters is the maxBCG sample, with cluster masses derived from weak
gravitational lensing. We construct non-linear galaxy bias models using the
Halo Occupation Distribution (HOD) to fit both w_p and M/N for different
cosmological parameters. HOD models that match the same two-point clustering
predict different numbers of galaxies in massive halos when Omega_m or sigma_8
is varied, thereby breaking the degeneracy between cosmology and bias. We
demonstrate that this technique yields constraints that are consistent and
competitive with current results from cluster abundance studies, even though
this technique does not use abundance information. Using w_p and M/N alone, we
find Omega_m^0.5*sigma_8=0.465+/-0.026, with individual constraints of
Omega_m=0.29+/-0.03 and sigma_8=0.85+/-0.06. Combined with current CMB data,
these constraints are Omega_m=0.290+/-0.016 and sigma_8=0.826+/-0.020. All
errors are 1-sigma. The systematic uncertainties that the M/N technique are
most sensitive to are the amplitude of the bias function of dark matter halos
and the possibility of redshift evolution between the SDSS Main sample and the
maxBCG sample. Our derived constraints are insensitive to the current level of
uncertainties in the halo mass function and in the mass-richness relation of
clusters and its scatter, making the M/N technique complementary to cluster
abundances as a method for constraining cosmology with future galaxy surveys.Comment: 23 pages, submitted to Ap
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