15 research outputs found
Discovery of inverse-Compton X-ray emission and estimate of the volume-averaged magnetic field in a galaxy group
Observed in a significant fraction of clusters and groups of galaxies,
diffuse radio synchrotron emission reveals the presence of relativistic
electrons and magnetic fields permeating large-scale systems of galaxies.
Although these non-thermal electrons are expected to upscatter cosmic microwave
background photons up to hard X-ray energies, such inverse-Compton (IC) X-ray
emission has so far not been unambiguously detected on cluster/group scales.
Using deep, new proprietary XMM-Newton observations (200 ks of clean
exposure), we report a 4.6 detection of extended IC X-ray emission in
MRC 0116+111, an extraordinary group of galaxies at . Assuming a
spectral slope derived from low-frequency radio data, the detection remains
robust to systematic uncertainties. Together with low-frequency radio data from
GMRT, this detection provides an estimate for the volume-averaged magnetic
field of G within the central part of the group. This
value can serve as an anchor for studies of magnetic fields in the largest
gravitationally bound systems in the Universe.Comment: 11 pages, 7 figures, accepted for publication in MNRA
Extended radio emission in the galaxy cluster MS 0735.6+7421 detected with the Karl G. Jansky Very Large Array
MS 0735.6+7421 () is a massive cool core galaxy cluster hosting
one of the most powerful active galactic nuclei (AGN) outbursts known. The
radio jets of the AGN have carved out an unusually large pair of X-ray
cavities, each reaching a diameter of kpc. This makes MS 0735.6+7421 a
unique case to investigate active galactic nuclei feedback processes, as well
as other cluster astrophysics at radio wavelengths. We present new
low-radio-frequency observations of MS 0735.6+7421 taken with the Karl G.
Jansky Very Large Array (VLA): 5 hours of P-band ( MHz) and 5 hours of
L-band ( GHz) observations, both in C configuration. Our VLA P-band
( MHz) observations reveal the presence of a new diffuse radio
component reaching a scale of kpc in the direction of the jets and
of kpc in the direction perpendicular to the jets. This component
is centered on the cluster core and has a radio power scaled at GHz of
WHz. Its properties are
consistent with those expected from a radio mini-halo as seen in other massive
cool core clusters, although it may also be associated with radio plasma that
has diffused out of the X-ray cavities. Observations at higher spatial
resolution are needed to fully characterize the properties and nature of this
component. We also suggest that if radio mini-halos originate from jetted
activity, we may be witnessing the early stages of this process.Comment: 11 pages, 7 figures, submitted to MNRA
Constraints on thermal conductivity in the merging cluster Abell 2146
The cluster of galaxies Abell 2146 is undergoing a major merger and is an
ideal cluster to study ICM physics, as it has a simple geometry with the merger
axis in the plane of the sky, its distance allows us to resolve features across
the relevant scales and its temperature lies within Chandra's sensitivity. Gas
from the cool core of the subcluster has been partially stripped into a tail of
gas, which gives a unique opportunity to look at the survival of such gas and
determine the rate of conduction in the ICM. We use deep 2.4 Ms Chandra
observations of Abell 2146 to produce a high spatial resolution map of the
temperature structure along a plume in the ram-pressure stripped tail,
described by a partial cone, which is distinguishable from the hot ambient gas.
Previous studies of conduction in the ICM typically rely on estimates of the
survival time for key structures, such as cold fronts. Here we use detailed
hydrodynamical simulations of Abell 2146 to determine the flow velocities along
the stripped plume and measure the timescale of the temperature increase along
its length. We find that conduction must be highly suppressed by multiple
orders of magnitude compared to the Spitzer rate, as the energy used is about
1% of the energy available. We discuss magnetic draping around the core as a
possible mechanism for suppressing conduction.Comment: 10 pages, 3 figures, 3 tables, accepted for publication in MNRA
Constraints on thermal conductivity in the merging cluster Abell 2146
The cluster of galaxies Abell 2146 is undergoing a major merger and is an ideal cluster to study ICM physics, as it has a simple geometry with the merger axis in the plane of the sky, its distance allows us to resolve features across the relevant scales and its temperature lies within Chandra's sensitivity. Gas from the cool core of the subcluster has been partially stripped into a tail of gas, which gives a unique opportunity to look at the survival of such gas and determine the rate of conduction in the ICM. We use deep 2.4 Ms Chandra observations of Abell 2146 to produce a high spatial resolution map of the temperature structure along a plume in the ram-pressure stripped tail, described by a partial cone, which is distinguishable from the hot ambient gas. Previous studies of conduction in the ICM typically rely on estimates of the survival time for key structures, such as cold fronts. Here we use detailed hydrodynamical simulations of Abell 2146 to determine the flow velocities along the stripped plume and measure the timescale of the temperature increase along its length. We find that conduction must be highly suppressed by multiple orders of magnitude compared to the Spitzer rate, as the energy used is about 1% of the energy available. We discuss magnetic draping around the core as a possible mechanism for suppressing conduction
VLA resolves unexpected radio structures in the Perseus Cluster of galaxies
High Energy Astrophysic
The structure of cluster merger shocks: turbulent width and the electron heating time-scale
We present a new 2 Ms Chandra observation of the cluster merger Abell 2146, which hosts two huge M∼2 shock fronts each ∼500 kpc across. For the first time, we resolve and measure the width of cluster merger shocks. The best-fit width for the bow shock is 17 ± 1 kpc and for the upstream shock is 10.7 ± 0.3 kpc. A narrow collisionless shock will appear broader in projection if its smooth shape is warped by local gas motions. We show that both shock widths are consistent with collisionless shocks blurred by local gas motions of 290 ± 30 km s −1. The upstream shock forms later on in the merger than the bow shock and is therefore expected to be significantly narrower. From the electron temperature profile behind the bow shock, we measure the timescale for the electrons and ions to come back into thermal equilibrium. We rule out rapid thermal equilibration of the electrons with the shock-heated ions at the 6σ level. The observed temperature profile instead favours collisional equilibration. We find no evidence for electron heating over that produced by adiabatic compression. This supports the existing picture from collisionless shocks in the solar wind and supernova remnants. The upstream shock is consistent with this result but has a more complex structure, including a ∼ 2 keV increase in temperature ∼50 kpc ahead of the shock
A Multiwavelength Study of the Cool Core Cluster MACS J1447.4+0827
Clusters of galaxies are outstanding laboratories for understanding the physics of supermassive black hole (SMBH) feedback. Here we present the first Chandra, Karl G. Jansky Very Large Array, and Hubble Space Telescope analysis of MACS J1447.4+0827 (z = 0.3755), one of the strongest cool core clusters known, in which extreme feedback from its central SMBH is needed to prevent the hot intracluster gas from cooling. Using this multiwavelength approach, including 70 ks of Chandra X-ray observations, we detect the presence of collimated jetted outflows that coincide with a southern and a northern X-ray cavity. The total mechanical power associated with these outflows (Pcav ≈ 6 × 1044 erg s−1) is roughly consistent with the energy required to prevent catastrophic cooling of the hot intracluster gas (Lcool = 1.71 ± 0.01 × 1045 erg s−1 for tcool = 7.7 Gyr), implying that powerful SMBH feedback was in place several Gyr ago in MACS J1447.7+0827. In addition, we detect the presence of a radio minihalo that extends over 300 kpc in diameter (P1.4GHz = 3.0 ± 0.3 × 1024 W Hz−1). The X-ray observations also reveal an ~20 kpc plumelike structure that coincides with optical dusty filaments that surround the central galaxy. Overall, this study demonstrates that the various physical phenomena occurring in the most nearby clusters of galaxies are also occurring in their more distant analogs
On the relation between mini-halos and AGN feedback in clusters of galaxies
A variety of large-scale diffuse radio structures have been identified in
many clusters with the advent of new state-of-the-art facilities in radio
astronomy. Among these diffuse radio structures, radio mini-halos are found in
the central regions of cool core clusters. Their origin is still unknown and
they are challenging to discover; less than thirty have been published to date.
Based on new VLA observations, we confirmed the mini-halo in the massive strong
cool core cluster PKS 0745191 () and discovered one in the massive
cool core cluster MACS J1447.4+0827 (). Furthermore, using a detailed
analysis of all known mini-halos, we explore the relation between mini-halos
and AGN feedback processes from the central galaxy. We find evidence of strong,
previously unknown correlations between mini-halo radio power and X-ray cavity
power, and between mini-halo and the central galaxy radio power related to the
relativistic jets when spectrally decomposing the AGN radio emission into a
component for past outbursts and one for on-going accretion. Overall, our study
indicates that mini-halos are directly connected to the central AGN in
clusters, following previous suppositions. We hypothesize that AGN feedback may
be one of the dominant mechanisms giving rise to mini-halos by injecting energy
into the intra-cluster medium and reaccelerating an old population of
particles, while sloshing motion may drive the overall shape of mini-halos
inside cold fronts. AGN feedback may therefore not only play a vital role in
offsetting cooling in cool core clusters, but may also play a fundamental role
in re-energizing non-thermal particles in clusters.Comment: 26 pages, 9 figures, 8 tables, accepted for publication in MNRA