9 research outputs found
A Multi-Frequency View of the Radio Phoenix in the Abell 85 Cluster
Radio phoenices are complex and filamentary diffuse radio sources found in
both merging and relaxed clusters. The formation of these sources was proposed
to be adiabatic compression of old Active Galactic Nucleus (AGN) plasma in
shock waves. Most of the previous spectral studies of these sources were
limited to integrated spectral indices, which were found to be very steep as
well as show a curved spectrum. Here, we have performed a multi-frequency
investigation of the radio phoenix in the Abell 85 cluster. Owing to the
sensitive high-resolution observations, we found some of the finer filamentary
structures that were previously undetected. We produced resolved spectral index
maps of the radio phoenix between 148, 323, 700, and 1280 MHz. The orientation
of the filaments, as well as the gradient across the spectral index maps
suggest the possible direction of the shock motion from northeast to southwest.
The integrated spectral index of the radio phoenix was found to be very steep
with a break at around 700 MHz, indicating the re-energization of fossil
electrons being recent. Furthermore, the spectral index of the filaments was
found to be less steep compared to the non-filamentary regions, implying
greater energy injection in the filaments. The observed features in the radio
phoenix in the Abell 85 cluster seem to be in support of the adiabatic shock
compression mechanism.Comment: 17 pages, 12 figures, 3 tables, submitted to AAS journa
A radio bridge connecting the minihalo and phoenix in the Abell 85 cluster
Galaxy clusters are located at the nodes of cosmic filaments and therefore
host a lot of hydrodynamical activity. However, cool core clusters are
considered to be relatively relaxed systems without much merging activity. The
Abell 85 cluster is a unique example where the cluster hosts both a cool core
and multiple ongoing merging processes. In this work, we used 700 MHz uGMRT as
well as MeerKAT L-band observations, carried out as part of the MGCLS, of the
Abell 85. We reconfirm the presence of a minihalo in the cluster centre at
700MHz that was recently discovered in MGCLS. Furthermore, we discovered a
radio bridge connecting the central minihalo and the peripheral radio phoenix.
The mean surface brightness, size and flux density of the bridge at 700 MHz is
found to be Jy/arcsec, kpc and mJy,
respectively, with a spectral index of . Although
the origin of the seed relativistic electrons is still unknown, turbulent
re-acceleration caused by both the spiralling sloshing gas in the intracluster
medium (ICM) and the post-shock turbulence from the outgoing merging shock
associated with the phoenix formation may be responsible for the bridge.Comment: 7 pages, 6 Figures, 2 Tables. Accepted for publication in MNRAS-
On the Origin of Diffuse Radio Emission in Abell 85 -- Insights from new GMRT Observations
Extended, steep, and ultra-steep spectrum radio emission in a galaxy cluster
is usually associated with recent mergers. Simulations show that radio
phoenixes are aged radio galaxy lobes whose emission reactivates when a low
Mach shock compresses it. A85 hosts a textbook example of a radio phoenix at
about 320 kpc southwest of the cluster center. We present a new high resolution
325 MHz GMRT radio map illustrating this radio phoenix's complex and
filamentary structure. The full extent of the radio structure is revealed for
the first time from these radio images of A85. Using archival \textit{Chandra}
X-ray observations, we applied an automated 2-D shock finder to the X-ray
surface brightness and Adaptive Circular Binning (ACB) temperature maps which
confirmed a bow shock at the location of the radio phoenix. We also compared
the Mach number from the X-ray data with the radio-derived Mach number in the
same region using multi-frequency radio observations and find that they are
consistent within the 1 error level.Comment: Accepted for publication in MNRAS (11 Pages, 6 Figures, 4 Tables
Diffuse radio emission in the galaxy cluster SPT-CL J2031-4037: a steep spectrum intermediate radio halo?
The advent of sensitive low frequency radio observations has revealed a
number of diffuse radio objects with peculiar properties that are challenging
our understanding about the physics of the intracluster medium. Here, we report
the discovery of a steep spectrum radio halo surrounding the central Brightest
Cluster Galaxy (BCG) in the galaxy cluster SPT-CL J2031-4037. This cluster is
morphologically disturbed yet has a weak cool core, an example of cool
core/non-cool core transition system, which harbours a radio halo of
Mpc in size. The halo emission detected at 1.7 GHz is less extended compared to
that in the 325 MHz observation, and the spectral index of the part of the halo
visible at 325 MHz to 1.7 GHz frequencies was found to be .
Also, was found to be W Hz
which falls in the region where radio mini-halos, halo upper limits and
ultra-steep spectrum (USS) halos are found in the plane. Additionally, simulations presented in the paper provide
support to the scenario of the steep spectrum. The diffuse radio emission found
in this cluster may be a steep spectrum "intermediate" or "hybrid" radio halo
which is transitioning into a mini-halo.Comment: 6 pages, 3 figures; Accepted for publication in MNRAS Lette
Exploring diffuse radio emission in galaxy clusters and groups with the uGMRT and the SKA
Diffuse radio emission has been detected in a considerable number of galaxy
clusters and groups, revealing the presence of pervasive cosmic magnetic
fields, and of relativistic particles in the large-scale structure (LSS) of the
Universe. Since cluster radio emission is faint and steep spectrum, its
observations are largely limited by the instrument sensitivity and frequency of
observation, leading to a dearth of information, more so for lower-mass
systems. The unprecedented sensitivity of recently commissioned low-frequency
radio telescope arrays, aided by the development of advanced calibration and
imaging techniques, have helped in achieving unparalleled image quality. At the
same time, the development of sophisticated numerical simulations and the
availability of supercomputing facilities have paved the way for
high-resolution numerical modeling of radio emission, and the structure of the
cosmic magnetic fields in LSS, leading to predictions matching the capabilities
of observational facilities. In view of these rapidly-evolving scenerio in
modeling and observations, in this review, we summarise the role of the new
telescope arrays and the development of advanced imaging techniques and discuss
the detections of various kinds of cluster radio sources. In particular, we
discuss observations of the cosmic web in the form of supercluster filaments,
studies of emission in poor clusters and groups of galaxies, and of ultra-steep
spectrum sources. We also review the current theoretical understanding of
various diffuse cluster radio sources and the associated magnetic field and
polarization. As the statistics of detections improve along with our
theoretical understanding, we update the source classification schemes based on
their intrinsic properties. We conclude by summarising the role of the upgraded
GMRT and our expectations from the upcoming Square Kilometre Array (SKA)
observatories.Comment: 32 pages, 10 figures, accepted for publication in the Journal of
Astrophysics and Astronomy (JoAA) (to appear in the special issue on "Indian
participation in the SKA"
Exploring diffuse radio emission in galaxy clusters and groups with the uGMRT and the SKA
Diffuse radio emission has been detected in a considerable number of galaxy clusters and groups, revealing the presence of pervasive cosmic magnetic fields, and of relativistic particles in the large-scale structure (LSS) of the Universe. Since cluster radio emission is faint and steep spectrum, its observations are largely limited by the instrument sensitivity and frequency of observation, leading to a dearth of information, more so for lower-mass systems. The unprecedented sensitivity of recently commissioned low-frequency radio telescope arrays, aided by the development of advanced calibration and imaging techniques, have helped in achieving unparalleled image quality. At the same time, the development of sophisticated numerical simulations and the availability of supercomputing facilities have paved the way for high-resolution numerical modeling of radio emission, and the structure of the cosmic magnetic fields in LSS, leading to predictions matching the capabilities of observational facilities. In view of these rapidly-evolving scenerio in modeling and observations, in this review, we summarise the role of the new telescope arrays and the development of advanced imaging techniques and discuss the detections of various kinds of cluster radio sources. In particular, we discuss observations of the cosmic web in the form of supercluster filaments, studies of emission in poor clusters and groups of galaxies, and of ultra-steep spectrum sources. We also review the current theoretical understanding of various diffuse cluster radio sources and the associated magnetic field and polarization. As the statistics of detections improve along with our theoretical understanding, we update the source classification schemes based on their intrinsic properties. We conclude by summarising the role of the upgraded GMRT and our expectations from the upcoming Square Kilometre Array (SKA) observatories
Exploring diffuse radio emission in galaxy clusters and groups with the uGMRT and the SKA
Diffuse radio emission has been detected in a considerable number of galaxy clusters and groups, revealing the presence of pervasive cosmic magnetic fields, and of relativistic particles in the large-scale structure (LSS) of the Universe. Since cluster radio emission is faint and steep spectrum, its observations are largely limited by the instrument sensitivity and frequency of observation, leading to a dearth of information, more so for lower-mass systems. The unprecedented sensitivity of recently commissioned low-frequency radio telescope arrays, aided by the development of advanced calibration and imaging techniques, have helped in achieving unparalleled image quality. At the same time, the development of sophisticated numerical simulations and the availability of supercomputing facilities have paved the way for high-resolution numerical modeling of radio emission, and the structure of the cosmic magnetic fields in LSS, leading to predictions matching the capabilities of observational facilities. In view of these rapidly-evolving scenerio in modeling and observations, in this review, we summarise the role of the new telescope arrays and the development of advanced imaging techniques and discuss the detections of various kinds of cluster radio sources. In particular, we discuss observations of the cosmic web in the form of supercluster filaments, studies of emission in poor clusters and groups of galaxies, and of ultra-steep spectrum sources. We also review the current theoretical understanding of various diffuse cluster radio sources and the associated magnetic field and polarization. As the statistics of detections improve along with our theoretical understanding, we update the source classification schemes based on their intrinsic properties. We conclude by summarising the role of the upgraded GMRT and our expectations from the upcoming Square Kilometre Array (SKA) observatories
Exploring diffuse radio emission in galaxy clusters and groups with the uGMRT and the SKA
Diffuse radio emission has been detected in a considerable number of galaxy clusters and groups, revealing the presence of pervasive cosmic magnetic fields, and of relativistic particles in the large-scale structure (LSS) of the Universe. Since cluster radio emission is faint and steep spectrum, its observations are largely limited by the instrument sensitivity and frequency of observation, leading to a dearth of information, more so for lower-mass systems. The unprecedented sensitivity of recently commissioned low-frequency radio telescope arrays, aided by the development of advanced calibration and imaging techniques, have helped in achieving unparalleled image quality. At the same time, the development of sophisticated numerical simulations and the availability of supercomputing facilities have paved the way for high-resolution numerical modeling of radio emission, and the structure of the cosmic magnetic fields in LSS, leading to predictions matching the capabilities of observational facilities. In view of these rapidly-evolving scenerio in modeling and observations, in this review, we summarise the role of the new telescope arrays and the development of advanced imaging techniques and discuss the detections of various kinds of cluster radio sources. In particular, we discuss observations of the cosmic web in the form of supercluster filaments, studies of emission in poor clusters and groups of galaxies, and of ultra-steep spectrum sources. We also review the current theoretical understanding of various diffuse cluster radio sources and the associated magnetic field and polarization. As the statistics of detections improve along with our theoretical understanding, we update the source classification schemes based on their intrinsic properties. We conclude by summarising the role of the upgraded GMRT and our expectations from the upcoming Square Kilometre Array (SKA) observatories