Remnant radio galaxies discovered in a multi-frequency survey

2021 ◽  
Vol 38 ◽  
Author(s):  
Benjamin Quici ◽  
Natasha Hurley-Walker ◽  
Nicholas Seymour ◽  
Ross J. Turner ◽  
Stanislav S. Shabala ◽  
...  
Keyword(s):  
Surface Brightness ◽  
Radio Galaxy ◽  
Radio Galaxies ◽  
Low Surface Brightness ◽  
Show Evidence ◽  
Frequency Survey ◽  
Square Kilometer Array ◽  
Murchison Widefield Array ◽  
Limiting Case ◽  
Compact Array

Abstract The remnant phase of a radio galaxy begins when the jets launched from an active galactic nucleus are switched off. To study the fraction of radio galaxies in a remnant phase, we take advantage of a $8.31$ deg $^2$ subregion of the GAMA 23 field which comprises of surveys covering the frequency range 0.1–9 GHz. We present a sample of 104 radio galaxies compiled from observations conducted by the Murchison Widefield Array (216 MHz), the Australia Square Kilometer Array Pathfinder (887 MHz), and the Australia Telescope Compact Array (5.5 GHz). We adopt an ‘absent radio core’ criterion to identify 10 radio galaxies showing no evidence for an active nucleus. We classify these as new candidate remnant radio galaxies. Seven of these objects still display compact emitting regions within the lobes at 5.5 GHz; at this frequency the emission is short-lived, implying a recent jet switch off. On the other hand, only three show evidence of aged lobe plasma by the presence of an ultra-steep-spectrum ( $\alpha<-1.2$ ) and a diffuse, low surface brightness radio morphology. The predominant fraction of young remnants is consistent with a rapid fading during the remnant phase. Within our sample of radio galaxies, our observations constrain the remnant fraction to $4\%\lesssim f_{\mathrm{rem}} \lesssim 10\%$ ; the lower limit comes from the limiting case in which all remnant candidates with hotspots are simply active radio galaxies with faint, undetected radio cores. Finally, we model the synchrotron spectrum arising from a hotspot to show they can persist for 5–10 Myr at 5.5 GHz after the jets switch of—radio emission arising from such hotspots can therefore be expected in an appreciable fraction of genuine remnants.

scholarly journals The 6C Survey

1977 ◽  
Vol 74 ◽  
pp. 3-7
Author(s):  
J. E. Baldwin
Keyword(s):  
Surface Brightness ◽  
Low Frequency ◽  
Radio Galaxies ◽  
Aperture Synthesis ◽  
Radio Sources ◽  
Source Density ◽  
The North ◽  
Low Surface Brightness ◽  
Celestial Pole ◽  
Frequency Survey

A new survey of radio sources at 151 MHz, which has not been described previously, is in progress at Cambridge. There are several of us working on it including Warner, Kenderdine, Waggett, Masson and Mayer. The results of the first observations are at present in a preliminary state but we hope that in time they will form the first part of the 6C survey. The purpose of the survey is not to reach the faintest sources detected so far in aperture synthesis observations but to study moderately faint sources at a low observing frequency and to cover a large part of the northern sky rapidly. The deepest survey made so far at a low frequency is that of Ryle and Neville (1962) at 178 MHz over a region of 50 square degrees near the north celestial pole. The faintest sources detected had flux densities of 0.25 Jy, corresponding to a source density of 104 sr−1. It is already 15 years since that survey, which was the first trial of aperture synthesis using the earth's rotation, and much more is now technically possible. One of the most interesting features of a low frequency survey is its ability to detect preferentially sources with steep radio spectra and to be sensitive to sources of very low surface brightness. We know that in many cases these two properties go together and are associated with old radio sources, or at least with those parts of sources which are old. Many of the weak radio galaxies in nearby clusters are obvious examples of this type of source while the final, and so far unidentified, stages of the development of the most powerful double sources may be exciting candidates for discovery.

scholarly journals Giant low surface brightness haloes in distant radio galaxies: USS0828+193

2002 ◽  
Vol 336 (2) ◽  
pp. 436-444 ◽  
Author(s):  
M. Villar-Martín ◽  
J. Vernet ◽  
S. Di Serego Alighieri ◽  
R. Fosbury ◽  
L. Pentericci ◽  
...  
Keyword(s):  
Surface Brightness ◽  
Radio Galaxies ◽  
Low Surface Brightness

scholarly journals Diffuse Cluster Radio Sources

1996 ◽  
Vol 175 ◽  
pp. 333-338 ◽  
Author(s):  
L. Feretti ◽  
G. Giovannini
Keyword(s):  
Surface Brightness ◽  
Radio Galaxy ◽  
Radio Sources ◽  
Clusters Of Galaxies ◽  
Rare Phenomenon ◽  
Low Surface Brightness ◽  
Extended Sources ◽  
Formation And Evolution

Diffuse radio sources in clusters remain a poorly understood phenomenon. They are very extended sources (0.4-0.6 Mpc), of low surface brightness and steep spectrum, which cannot be identified with any active radio galaxy. They are a rare phenomenon, as they have been found so far in few clusters of galaxies. This paper reviews the current findings about this kind of sources, and the suggestions about their formation and evolution.

scholarly journals HI in Karachentsev Objects Properties of new nearby Dwarf Galaxies

1999 ◽  
Vol 171 ◽  
pp. 299-306
Author(s):  
W.K. Huchtmeier
Keyword(s):  
Column Density ◽  
Detection Rate ◽  
Surface Brightness ◽  
Dwarf Galaxies ◽  
Disk Galaxies ◽  
Local Volume ◽  
Low Surface Brightness ◽  
Compact Array

AbstractThis is a report on HI observations of newly discovered nearby dwarf galaxies, most of which of low surface brightness, from the first section of the Karachentsev catalog. Observations were performed using the 100-m radiotelescope at Effelsberg, the Nançay radiotelescope, and the compact array of the Australia Telescope. We observed 220 galaxies with a detection rate of about 60%. 35 of the observed galaxies are located within the Local Volume (i.e., within 10 Mpc). The smallest detected galaxies have diameters around 0.3 kpc and HI-masses of a few times 106 solar masses. We confirm a correlation between HI column density and surface brightness of gas-rich disk galaxies.

scholarly journals MIGHTEE: Are giant radio galaxies more common than we thought?

2020 ◽  
Author(s):  
J Delhaize ◽  
I Heywood ◽  
M Prescott ◽  
M J Jarvis ◽  
I Delvecchio ◽  
...  
Keyword(s):  
Surface Brightness ◽  
Radio Galaxies ◽  
Number Density ◽  
Diffuse Emission ◽  
The Past ◽  
Recent Estimate ◽  
Low Surface Brightness ◽  
Extended Emission ◽  
Radio Power ◽  
Limited Sensitivity

Abstract We report the discovery of two new giant radio galaxies (GRGs) using the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) survey. Both GRGs were found within a ∼1 deg2 region inside the COSMOS field. They have redshifts of z = 0.1656 and z = 0.3363 and physical sizes of 2.4 Mpc and 2.0 Mpc, respectively. Only the cores of these GRGs were clearly visible in previous high resolution VLA observations, since the diffuse emission of the lobes was resolved out. However, the excellent sensitivity and uv coverage of the new MeerKAT telescope allowed this diffuse emission to be detected. The GRGs occupy an unpopulated region of radio power – size parameter space. Based on a recent estimate of the GRG number density, the probability of finding two or more GRGs with such large sizes at z &lt; 0.4 in a ∼1 deg2 field is only 2.7 × 10−6, assuming Poisson statistics. This supports the hypothesis that the prevalence of GRGs has been significantly underestimated in the past due to limited sensitivity to low surface brightness emission. The two GRGs presented here may be the first of a new population to be revealed through surveys like MIGHTEE which provide exquisite sensitivity to diffuse, extended emission.

scholarly journals Morphology and Stellar Populations in the Gas-Rich, Giant LSBGs

1999 ◽  
Vol 171 ◽  
pp. 191-195 ◽  
Author(s):  
P. Knezek
Keyword(s):  
Entire Range ◽  
Surface Brightness ◽  
Spiral Galaxies ◽  
High Surface ◽  
Nuclear Spectroscopy ◽  
Nuclear Activity ◽  
High Surface Brightness ◽  
Low Surface Brightness ◽  
Show Evidence ◽  
Low Surface Brightness Galaxies

AbstractAn unexpected characteristic of low surface brightness galaxies (LSBGs) is that a significant number are massive and possess substantial amounts of atomic gas. We present preliminary results of an ongoing program to obtain BVRIJHK imaging, along with some nuclear spectroscopy, of a well-defined sample of LSBGs which are gas-rich and of similar size to giant, high surface brightness spiral galaxies (HSBGs). These LSBGs span the entire range of Hubble disk morphologies. While their disks are bluer, on average, than comparable HSBGs, the optical morphology of massive LSBGs indicates that many of these systems have undergone previous star formation episodes. They typically have long disk scale lengths, and range from MB = −16 to −22 (H0 = 75 km s−1 Mpc−1). About half of the LSBGs with bulges show evidence of nuclear activity, and ~30% appear to be barred. These massive, gas-rich LSBGs apparently have varied, and often complex, evolutionary histories.

scholarly journals Duty cycle of the radio galaxy B2 0258+35

2018 ◽  
Vol 618 ◽  
pp. A45 ◽  
Author(s):  
M. Brienza ◽  
R. Morganti ◽  
M. Murgia ◽  
N. Vilchez ◽  
B. Adebahr ◽  
...  
Keyword(s):  
Galaxy Evolution ◽  
Duty Cycle ◽  
Spectral Properties ◽  
Surface Brightness ◽  
Large Scale ◽  
Radio Galaxy ◽  
Low Frequency ◽  
Evolutionary Stage ◽  
Low Surface Brightness ◽  
Frequency Coverage

Context. Radio loud active galactic nuclei (AGN) are episodic in nature, cycling through periods of activity and quiescence. The study of this duty cycle has recently gained new relevance because of the importance of AGN feedback for galaxy evolution. Aims. In this work we investigate the duty cycle of the radio galaxy B2 0258+35, which was previously suggested to be a restarted radio galaxy based on its morphology. The radio source consists of a pair of kpc-scale jets embedded in two large-scale lobes (∼240 kpc) with relaxed shape and very low surface brightness, which resemble remnants of a past AGN activity. Methods. We have combined new LOFAR data at 145 MHz and new Sardinia Radio Telescope data at 6600 MHz with available WSRT data at 1400 MHz to investigate the spectral properties of the outer lobes and derive their age. Results. Interestingly, the spectrum of both the outer northern and southern lobes is not ultra-steep as expected for an old ageing plasma with spectral index values equal to α1451400 = 0.48 ± 0.11 and α14006600 = 0.69 ± 0.20 in the outer northern lobe, and α1451400 = 0.73 ± 0.07 in the outer southern lobe. Moreover, despite the wide frequency coverage available for the outer northern lobe (145–6600 MHz), we do not identify a significant spectral curvature (SPC ≃ 0.2 ± 0.2). Conclusions. While mechanisms such as in-situ particle reacceleration, mixing or compression can temporarily play a role in preventing the spectrum from steepening, in no case seem the outer lobes to be compatible with being very old remnants of past activity as previously suggested (with age ≳ 80 Myr). We conclude that either the large-scale lobes are still fuelled by the nuclear engine or the jets have switched off no more than a few tens of Myr ago, allowing us to observe both the inner and outer structure simultaneously. Our study shows the importance of combining morphological and spectral properties to reliably classify the evolutionary stage of low surface brightness, diffuse emission that low frequency observations are revealing around a growing number of radio sources.

scholarly journals The Discovery of Red Low Surface Brightness Galaxies

1999 ◽  
Vol 171 ◽  
pp. 145-153
Author(s):  
Karen O’Neil
Keyword(s):  
Surface Brightness ◽  
Brightness Distribution ◽  
Actual Surface ◽  
Wide Range ◽  
Low Surface Brightness ◽  
Show Evidence ◽  
Low Surface Brightness Galaxies ◽  
Lsb Galaxies ◽  
Digital Survey ◽  
Density Regime

AbstractWe have performed a digital survey for Low Surface Brightness (LSB) galaxies in the spiral-rich Cancer and Pegasus clusters as well as the low density regime defined by the Great Wall. A total of 127 galaxies were found with μB(0) > 22.0 mag arcsec‒2, 119 of which were previously unidentified.Consistent with other surveys, we find a significant number of galaxies with μB(0) > 23.0 mag arcsec‒2 which suggests that the space density of galaxies as a function of μB(0) is not strongly peaked. To more rigorously test this hypothesis we compare the actual surface brightness distribution from our survey with that from two different types of Monte-Carlo based sky images and show that it is not possible to distinguish between the flat distribution and the Gaussian one as the proper description of the underlying surface brightness distribution for this survey beyond 24.0 mag arcsec−2.The colors of the survey galaxies range continuously from very blue to the first discovery of very red LSB galaxies. It also includes a group of old galaxies which show evidence for recent star formation. This continuous range of colors clearly shows that LSB galaxies at the present epoch define a wide range of evolutionary states.

scholarly journals PKS 2250–351: A giant radio galaxy in Abell 3936

2020 ◽  
Vol 37 ◽  
Author(s):  
N. Seymour ◽  
M. Huynh ◽  
S. S. Shabala ◽  
J. Rogers ◽  
L. J. M. Davies ◽  
...  
Keyword(s):  
Radio Galaxy ◽  
Elliptical Galaxy ◽  
Host Galaxy ◽  
The Galaxy ◽  
Order Of Magnitude ◽  
Mass Assembly ◽  
Murchison Widefield Array ◽  
Ir Emission ◽  
Jet Power ◽  
Compact Array

Abstract We present a detailed analysis of the radio galaxy PKS $2250{-}351$ , a giant of 1.2 Mpc projected size, its host galaxy, and its environment. We use radio data from the Murchison Widefield Array, the upgraded Giant Metre-wavelength Radio Telescope, the Australian Square Kilometre Array Pathfinder, and the Australia Telescope Compact Array to model the jet power and age. Optical and IR data come from the Galaxy And Mass Assembly (GAMA) survey and provide information on the host galaxy and environment. GAMA spectroscopy confirms that PKS $2250{-}351$ lies at $z=0.2115$ in the irregular, and likely unrelaxed, cluster Abell 3936. We find its host is a massive, ‘red and dead’ elliptical galaxy with negligible star formation but with a highly obscured active galactic nucleus dominating the mid-IR emission. Assuming it lies on the local M– $\sigma$ relation, it has an Eddington accretion rate of $\lambda_{\rm EDD}\sim 0.014$ . We find that the lobe-derived jet power (a time-averaged measure) is an order of magnitude greater than the hotspot-derived jet power (an instantaneous measure). We propose that over the lifetime of the observed radio emission ( ${\sim} 300\,$ Myr), the accretion has switched from an inefficient advection-dominated mode to a thin disc efficient mode, consistent with the decrease in jet power. We also suggest that the asymmetric radio morphology is due to its environment, with the host of PKS $2250{-}351$ lying to the west of the densest concentration of galaxies in Abell 3936.

The Jets in Radio Galaxy B1308–441

1996 ◽  
Vol 13 (3) ◽  
pp. 218-226 ◽  
Author(s):  
Paul A. Jones
Keyword(s):  
Radio Galaxy ◽  
Radio Galaxies ◽  
Class I ◽  
Bright Spot ◽  
The Core ◽  
Compact Array

AbstractThe giant radio galaxy B1308–441 has prominent two-sided jets, typical of Fanaroff–Riley class I radio galaxies, but there is an unusual bright spot in the SE jet 2 arcmin from the core that gives a marked asymmetry to the source. Observations at 1·37 and 2·37 GHz with the Australia Telescope Compact Array show that the bright spot has a flattened spectrum and high polarisation, and changes the direction of the SE jet. There is a diffuse optical object close to the bright spot which may be related to a shock in the jet.

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