80 research outputs found
The merging galaxy cluster A520 --- a broken-up cool core, a dark subcluster, and an X-ray channel
We present results from a deep Chandra X-ray observation of a merging galaxy
cluster A520. A high-resolution gas temperature map, after the subtraction of
the cluster-scale emission, reveals a long trail of dense, cool clumps ---
apparently the fragments of a cool core that has been completely stripped from
the infalling subcluster by ram pressure. In this scenario, we can assume that
the clumps are still connected by the magnetic field lines. The observed
temperature variations imply that thermal conductivity is suppressed by a
factor >100 across the presumed direction of the magnetic field (as found in
other clusters), and is also suppressed -along- the field lines by a factor of
several. Two massive clumps in the periphery of A520, visible in the weak
lensing mass map and the X-ray image, have apparently been completely stripped
of gas during the merger, but then re-accreted the surrounding high-entropy gas
upon exit from the cluster. An X-ray hydrostatic mass estimate for one of the
clumps (that has simple geometry) agrees with the lensing mass. Its current gas
mass to total mass ratio is very low, 1.5-3%, which makes it a "dark
subcluster". We also found a curious low X-ray brightness channel (likely a
low-density sheet in projection) going across the cluster along the direction
of an apparent secondary merger. The channel may be caused by plasma depletion
in a region of an amplified magnetic field (with plasma ). The
shock in A520 will be studied in a separate paper.Comment: Accepted for publication in ApJ. 13 pages, 7 figures. (Author
affiliation updated (v2), updated with final revisions prior to publication
(v3).
Do radio core-halos and cold fronts in non major merging clusters originate from the same gas sloshing?
We show an interesting correlation between the surface brightness and
temperature structure of the relaxed clusters RXJ1720.1+2638 and MS1455.0+2232,
hosting a pair of cold fronts, and their central core--halo radio source. We
discuss the possibility that the origin of this diffuse radio emission may be
strictly connected with the gas sloshing mechanism suggested to explain the
formation of cold fronts in non major merging clusters. We show that the
radiative lifetime of the relativistic electrons is much shorter than the
timescale on which they can be transported from the central galaxy up to the
radius of the outermost cold front. This strongly indicates that the observed
diffuse radio emission is likely produced by electrons re--accelerated via some
kind of turbulence generated within the cluster volume limited by the cold
fronts during the gas sloshing.Comment: 4 pages inc. 6 figures (2color). Accepted for publication in ApJ
Heated Intracluster Gas and Radio Connections: the Singular case of MKW3s
Similarly to other cluster of galaxies previously classified as cooling flow
systems, the Chandra observation of MKW3s reveals that this object has a
complex X-ray structure hosting both a X-ray cavity and a X-ray filament.
Unlike the other clusters, however, the temperature map of the core of MKW3s
shows the presence of extended regions of gas heated above the radially
averaged gas temperature at any radius.
As the cluster does not show evidences for ongoing major mergers Mazzotta et
al. suggest a connection between the heated gas and the activity of the central
AGN. Nevertheless, due to the lack of high quality radio maps, this
interpretation was controversial.
In this paper we present the results of two new radio observations of MKW3s
at 1.28GHz and 604MHz obtained at the GMRT. Together with the Chandra
observation and a separate VLA observation at 327MHz from Young, we show
unequivocal evidences for a close connection between the heated gas region and
the AGN activity and we briefly summarize possible implications.Comment: To appear in a special issue of the "Journal of the Korean
Astronomical Society" (JKAS). Proceedings of the International conference on
Cosmic Rays and Magnetic Fields in Large Scale Structure, Busan, Korea, 200
Discovery of a giant radio halo in a new Planck galaxy cluster PLCKG171.9-40.7
We report the discovery of a giant radio halo in a new, hot, X-ray luminous
galaxy cluster recently found by Planck, PLCKG171.9-40.7. The radio halo was
found using Giant Metrewave Radio Telescope observations at 235 MHz and 610
MHz, and in the 1.4 GHz data from a NRAO Very Large Array Sky Survey pointing
that we have reanalyzed. The diffuse radio emission is coincident with the
cluster X-ray emission, has an extent of ~1 Mpc and a radio power of ~5x 10^24
W/Hz at 1.4 GHz. Its integrated radio spectrum has a slope of alpha~1.8 between
235 MHz and 1.4 GHz, steeper than that of a typical giant halo. The analysis of
the archival XMM-Newton X-ray data shows that the cluster is hot (~10 keV) and
disturbed, consistent with X-ray selected clusters hosting radio halos. This is
the first giant radio halo discovered in one of the new clusters found by
Planck.Comment: 9 pages, 8 figures and 4 tables. Corrected Figure 7. Matches ApJ
published versio
The Complete Local Volume Groups Sample - II. A study of the Central Radio Galaxies in the HighRichness Sub-sample
We present a study of the radio properties of the dominant early-type
galaxies in 26 galaxy groups, the high-richness sub-sample of the Complete
Local-volume Groups Sample (CLoGS). Combining new 610 MHz and 235 MHz
observations of 21 groups from the Giant Metrewave Radio Telescope (GMRT) with
archival GMRT and Very Large Array (VLA) survey data, we find a high detection
rate, with 92% of the dominant galaxies hosting radio sources. The sources have
a wide range of luminosities, 10 10 W/Hz in the 235 and 610
MHz bands. The majority (54%) are point-like, but 23% have radio jets, and
another 15% are diffuse radio sources with no clear jet/lobe morphology. The
spectral index of the detected radio sources ranges from very flat values of
~0.2 to typical radio synchrotron spectra of ~0.9 with only two presenting
steep radio spectra with > 1. We find that jet sources are
more common in X-ray bright groups, with radio non-detections found only in
X-ray faint systems. Radio point sources appear in all group environments
irrespective of their X-ray properties or spiral fraction. We estimate the
mechanical power (Pcav) of the jet sources in the X-ray bright groups to be
10 10 erg/s, with the two large-scale jet systems (NGC 193
and NGC 4261) showing jet powers two orders of magnitude greater than the
radiative losses from the cool cores of their groups. This suggests that
central AGN are not always in balance with cooling, but may instead produce
powerful periodical bursts of feedback heating.Comment: Accepted for publication by MNRAS, 19 Manuscript pages with 8 tables
and 8 figures, plus 13 pages of appendice
Occurrence of radio minihalos in a mass-limited sample of galaxy clusters
We investigate the occurrence of radio minihalos --- diffuse radio sources of
unknown origin observed in the cores of some galaxy clusters --- in a
statistical sample of 58 clusters drawn from the Planck Sunyaev-Zel'dovich
cluster catalog using a mass cut (). We
supplement our statistical sample with a similarly-sized non-statistical sample
mostly consisting of clusters in the ACCEPT X-ray catalog with suitable X-ray
and radio data, which includes lower-mass clusters. Where necessary (for 9
clusters), we reanalyzed the Very Large Array archival radio data to determine
if a mihinalo is present. Our total sample includes all 28 currently known and
recently discovered radio minihalos, including 6 candidates. We classify
clusters as cool-core or non-cool core according to the value of the specific
entropy floor in the cluster center, rederived or newly derived from the
Chandra X-ray density and temperature profiles where necessary (for 27
clusters). Contrary to the common wisdom that minihalos are rare, we find that
almost all cool cores - at least 12 out of 15 (80%) - in our complete sample of
massive clusters exhibit minihalos. The supplementary sample shows that the
occurrence of minihalos may be lower in lower-mass cool-core clusters. No
minihalos are found in non-cool-cores or "warm cores". These findings will help
test theories of the origin of minihalos and provide information on the
physical processes and energetics of the cluster cores.Comment: 34 pages, accepted for publication in ApJ. Added a section
"Definition of a minihalo" and an appendix "Radio size and average surface
brigthtness of minihalos and halos
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