30 research outputs found
Radio properties of a complete sample of nearby groups of galaxies
Much of the evolution of galaxies takes place in groups where feedback has the greatest impact on galaxy formation. By using an optically selected, statistically complete sample of 53 nearby groups (CLoGS), observed at radio (GMRT) and X-ray (Chandra and XMM-Newton) frequencies, we aim to characterise the radio-AGN population in groups and examine their impact on the intra-group gas and member galaxies. In this dissertation, low-frequency GMRT radio images of the nearby (<80 Mpc) central brightest group ellipticals from the high richness CLoGS sub-sample are presented for the first time at 235 and 610 MHz. Using the sensitivity to older electron populations at 235 MHz and the resolution of 610 MHz as a key to identify past and current AGN activity, a detailed analysis of the radio properties for each of the central group radio sources is performed, with the results being in addition combined with findings from the X-ray observations
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
New insights into the evolution of the FR I radio galaxy 3C 270 (NGC 4261) from VLA and GMRT radio observations
We present Giant Metrewave Radio Telescope (GMRT) 240 MHz observations of the
nearby luminous FR I radio source 3C 270, in the group-central elliptical NGC
4261. Combining these data with reprocessed Very Large Array (VLA) 1.55 and 4.8
GHz observations, we produce spectral index maps that reveal a constant
spectral index along the jets and a gradual steepening from the ends of the
jets through the lobes towards the nucleus. A Jaffe & Perola (JP) model fitted
to the integrated spectrum of the source gives an asymptotic low-frequency
index of , while JP models fitted to the
observed spectral index trend along the lobes allow us to estimate radiative
ages of Myr and Myr for the west and east lobes respectively.
Our age estimates are a factor of two lower than the 75-Myr upper limit derived
from X-ray data (O'Sullivan et al. 2011). We find unlikely the scenario of an
early supersonic phase in which the lobe expanded into the ISM at approximately
Mach 6 (3500 km s), and suggest that either the source underwent
multiple AGN outbursts with possible large changes in jet power, or possibly
that the source age that we find is due to a backflow that transports young
electrons from the jet tips through the lobes toward the nucleus relatively
quickly. We calculate that in the lobes the energy ratio of non-radiating to
radiating particles is indicating significant gas entrainment. If
the lobes are in pressure balance with their surroundings, the total energy
required to heat the entrained material is erg, 40% of the
total enthalpy of the lobes.Comment: 14 pages, 11 figures, 8 tables. Accepted for publication by MNRAS.
Revised throughout in response to referee's comment
The Complete Local Volume Groups Sample -- III. Characteristics of group central radio galaxies in the Local Universe
Using new 610 MHz and 235 MHz observations from the Giant Metrewave Radio
Telescope (GMRT) in combination with archival GMRT and Very Large Array (VLA)
survey data we present the radio properties of the dominant early-type galaxies
in the lowrichness sub-sample of the Complete Local-volume Groups Sample
(CLoGS; 27 galaxy groups) and provide results for the radio properties of the
full CLoGS sample for the first time. We find a high radio detection rate in
the dominant galaxies of the low-richness sub-sample of 82% (22/27); for the
full CLoGS sample, the detection rate is 87% (46/53). The group-dominant
galaxies exhibit a wide range of radio power, 10 10 W
Hz in the 235 and 610 MHz bands, with the majority (53%) presenting
point-like radio emission, 19% hosting currently active radio jets, 6% having
remnant jets, 9% being diffuse and 13% having no detected radio emission. The
mean spectral index of the detected radio sources in the 235610 MHz
frequency range is found to be 0.68, and
0.59 in the 2351400 MHz one. In agreement with
earlier studies, we find that the fraction of ultra-steep spectrum sources
(1.3) is 4%, mostly dependent on the detection limit at 235 MHz.
The majority of point-like systems are found to reside in dynamically young
groups, whereas jet systems show no preference between spiral-rich and
spiral-poor group environments. The mechanical power of the jet sources in the
lowrichness sample groups is estimated to be 10 10
erg s with their black hole masses ranging between 210
510 M. We confirm previous findings that, while radio
jet sources tend to be associated with more massive black holes, black hole
mass is not the decisive factor in determining jet activity or power.Comment: Accepted for publication in MNRAS, 48 pages of which 18 Manuscript
pages with 10 tables and 8 figures, plus 30 pages of appendices with 25
figures and 1 tabl
The Complete Local Volume Groups Sample - I. Sample Selection and X-ray Properties of the High-Richness Subsample
We present the Complete Local-Volume Groups Sample (CLoGS), a statistically
complete optically-selected sample of 53 groups within 80 Mpc. Our goal is to
combine X-ray, radio and optical data to investigate the relationship between
member galaxies, their active nuclei, and the hot intra-group medium (IGM). We
describe sample selection, define a 26-group high-richness subsample of groups
containing at least 4 optically bright (log L_B>=10.2 LBsol) galaxies, and
report the results of XMM-Newton and Chandra observations of these systems. We
find that 14 of the 26 groups are X-ray bright, possessing a group-scale IGM
extending at least 65kpc and with luminosity >10^41 erg/s, while a further 3
groups host smaller galaxy-scale gas halos. The X-ray bright groups have masses
in the range M_500=0.5-5x10^13 Msol, based on system temperatures of 0.4-1.4
keV, and X-ray luminosities in the range 2-200x10^41 erg/s. We find that
~53-65% of the X-ray bright groups have cool cores, a somewhat lower fraction
than found by previous archival surveys. Approximately 30% of the X-ray bright
groups show evidence of recent dynamical interactions (mergers or sloshing),
and ~35% of their dominant early-type galaxies host AGN with radio jets. We
find no groups with unusually high central entropies, as predicted by some
simulations, and confirm that CLoGS is in principle capable of detecting such
systems. We identify three previously unrecognized groups, and find that they
are either faint (L_X,R500<10^42 erg/s) with no concentrated cool core, or
highly disturbed. This leads us to suggest that ~20% of X-ray bright groups in
the local universe may still be unidentified.Comment: Accepted for publication by MNRAS, 25 Manuscript pages with 6 tables
and 10 figures, plus 30 pages of appendices. v2 corrects minor typographical
errors identified at proof stag
Evidence of AGN feedback and sloshing in the X-ray luminous NGC 1550 galaxy group
We present results from GMRT and Chandra observations of the NGC 1550 galaxy
group. Although previously thought of as relaxed, we show evidence that gas
sloshing and active galactic nucleus (AGN) heating have affected the structure
of the system. The 610 and 235 MHz radio images show an asymmetric jet-lobe
structure with a total size of 33 kpc, with a sharp kink at the base of
the more extended western jet, and bending of the shorter eastern jet as it
enters the lobe. The 235610 MHz spectral index map shows that both radio
lobes have steep spectral indices () indicating the
presence of an old electron population. The X-ray images reveal an asymmetric
structure in the hot gas correlated with the radio structure, as well as
potential cavities coincident with the radio lobes, with rims and arms of gas
that may have been uplifted by the cavity expansion. The X-ray residual map
reveals an arc shaped structure to the east that resembles a sloshing cold
front. Radio spectral analysis suggests a radiative age of about 33 Myr for the
source, comparable to the sloshing timescale and dynamical estimates of the age
of the lobes. An estimate of the mechanical energy required to inflate the
cavities suggests that the AGN of NGC 1550 is capable of balancing radiative
losses from the intragroup medium (IGM) and preventing excessive cooling,
providing that the AGN jets are efficiently coupled to the IGM gas. In
conclusion, we find evidence of sloshing motions from both radio and X-ray
structures, suggesting that NGC 1550 was perturbed by a minor merger or
infalling galaxy about 33 Myr ago.Comment: Accepted for publication in MNRAS, 17 pages with 13 figures and 10
table
The XXL Survey: : XXIX. GMRT 610 MHz continuum observations
Accepted for publication in a forthcoming issue of Astronomy & Astrophysics. Reproduced with permission from Astronomy & Astrophysics. © 2018 ESO.We present the 25 square-degree GMRT-XXL-N 610 MHz radio continuum survey, conducted at 50 cm wavelength with the Giant Metrewave Radio Telescope (GMRT) towards the XXL Northern field (XXL-N). We combined previously published observations of the XMM-Large Scale Structure (XMM-LSS) field, located in the central part of XXL-N, with newly conducted observations towards the remaining XXL-N area, and imaged the combined data-set using the Source Peeling and Atmospheric Modeling (SPAM) pipeline. The final mosaic encompasses a total area of 30:4 square degrees, with rms <150 μJy beam -1 over 60% of the area. The rms achieved in the inner 9.6 square degree area, enclosing the XMM-LSS field, is about 200 μJy beam -1, while that over the outer 12.66 square degree area (which excludes the noisy edges) is about 45 μJy beam -1. The resolution of the final mosaic is 6.5 arcsec. We present a catalogue of 5434 sources detected at ≥7 × rms. We verify, and correct the reliability of, the catalog in terms of astrometry, flux, and false detection rate. Making use of the (to date) deepest radio continuum survey over a relatively large (2 square degree) field, complete at the flux levels probed by the GMRT-XXL-N survey, we also assess the survey's incompleteness as a function of flux density. The radio continuum sensitivity reached over a large field with a wealth of multi-wavelength data available makes the GMRTXXL- N 610 MHz survey an important asset for studying the physical properties, environments and cosmic evolution of radio sources, in particular radio-selected active galactic nuclei (AGN).Peer reviewedFinal Accepted Versio