scholarly journals uGMRT HI 21-cm absorption observations of two extremely inverted spectrum sources

2020 ◽  
Vol 643 ◽  
pp. A174
Author(s):  
Mukul Mhaskey ◽  
Surajit Paul ◽  
Neeraj Gupta ◽  
Dipanjan Mukherjee ◽  
Gopal-Krishna
Keyword(s):  
Optical Depth ◽  
Column Density ◽  
Radio Galaxies ◽  
Radio Spectrum ◽  
Absorption Feature ◽  
Radio Sources ◽  
Spin Temperature ◽  
Inverted Spectrum ◽  
Spectrum Radio ◽  
Thick Part

We report the detection of HI 21-cm absorption in a member of the rare and recently discovered class of compact radio sources: extremely inverted spectrum extragalactic radio sources (EISERS). The EISERS conceivably form a special subclass of the inverted spectrum radio galaxies since the spectral index of the optically thick part of the spectrum for these sources crosses the synchrotron self-absorption limit of α = +2.5 (S(ν) ∝ να). We searched for HI absorption in two EISERS using the recently upgraded Giant Metrewave Radio Telescope (uGMRT) and detected an absorption feature in one of them. The strong associated HI absorption detected against the source J1209−2032 (z = 0.4040) implies an optical depth of 0.178 ± 0.02, corresponding to an HI column density of 34.8 ± 2.9 × 1020 cm−2, for an assumed HI spin temperature of 100 K and covering factor of 1. This is among the highest known optical depth and HI column densities found for compact radio sources of peaked spectrum type and supports the free-free absorption model for the steeply inverted radio spectrum of this source. For the other source, J1549+5038 (z = 2.171), no HI absorption was detected in our observations.

Steep-Spectrum Radio Sources in Clusters of Galaxies—The Southern Sample

1984 ◽  
Vol 5 (4) ◽  
pp. 516-529 ◽  
Author(s):  
O. B. Slee ◽  
J. E. Reynolds
Keyword(s):  
Radio Galaxies ◽  
High Energy ◽  
Radio Spectrum ◽  
Radio Sources ◽  
Clusters Of Galaxies ◽  
Detailed Review ◽  
X Ray ◽  
High Energy Electrons ◽  
Spectrum Radio ◽  
Inverse Compton

It is well established (e.g. Slee et al. 1983) that radio galaxies near the centres of rich clusters of galaxies tend to have steeper radio spectra than field radio galaxies. The fact that the sources with the steepest spectra occur in clusters that are highly luminous X-ray emitters has generally been interpreted in terms of the confining influence of a hot (~108 K), relatively dense (10-2 to 10-3 electrons cm-3) intra-cluster gas; the confined relativistic plasma then preferentially loses its high-energy electrons through synchrotron and inverse Compton losses, resulting in a steepening of the radio spectrum. A more detailed review of the evidence for this process is given by Robertson (1983).

scholarly journals Spatially resolved studies of extragalactic jets in high redshift radio galaxies

2014 ◽  
Vol 10 (S313) ◽  
pp. 231-235
Author(s):  
Leah K. Morabito ◽  
Adam Deller ◽  
J. B. R. Oonk ◽  
Huub Röttgering ◽  
George Miley
Keyword(s):  
High Redshift ◽  
Low Frequency ◽  
Radio Galaxies ◽  
Radio Sources ◽  
Spatially Resolved ◽  
Long Baseline ◽  
Early Results ◽  
Spectrum Radio ◽  
Extragalactic Jets ◽  
Frequency Survey

AbstractThe correlation between radio spectral steepness and redshift has been successfully used to find high redshift (z ⩾ 2) radio galaxies, but the origin of this relation is unknown. The ultra-steep spectra of high-z radio sources make them ideally suited for studies with the Low Band Antenna of the new Low Frequency Array, which covers 10–80 MHz and has baselines up to about 1300 km. As part of an ongoing survey, we use the longest baselines to map the low-frequency (< 70 MHz) spatial distributions along the jets of 5 bright extended steep spectrum high-z radio sources. From this, we will determine whether the spectra change over these spatially resolved sources, thereby constraining particle acceleration processes. We present early results from our low-frequency survey of ultra-steep spectrum radio galaxies. The first low frequency long baseline images of these objects are presented.

Four Southern Intraday Variable Radio Sources

1998 ◽  
Vol 164 ◽  
pp. 271-272 ◽  
Author(s):  
L. L. Kedziora-Chudczer ◽  
D. L. Jauncey ◽  
M. H. Wieringa ◽  
J. E. Reynolds ◽  
A. K. Tzioumis
Keyword(s):  
Flux Density ◽  
Progress Report ◽  
Radio Sources ◽  
High Flux ◽  
Inverted Spectrum ◽  
Spectrum Radio ◽  
Variable Radio

AbstractThis is a progress report on the ATCA IDV survey of compact, flat or inverted spectrum radio sources. We found that four sources: PKS 0405–385, PKS 1034–293, PKS 1144–397, and PKS 1519–273 out of the sample of 125 show high flux density variability on the daily timescale. The characteristics of observed IDV are discussed and we reflect on its possible origin.

scholarly journals FLASH early science – discovery of an intervening H i 21-cm absorber from an ASKAP survey of the GAMA 23 field

2020 ◽  
Vol 494 (3) ◽  
pp. 3627-3641 ◽  
Author(s):  
J R Allison ◽  
E M Sadler ◽  
S Bellstedt ◽  
L J M Davies ◽  
S P Driver ◽  
...  
Keyword(s):  
Path Length ◽  
Column Density ◽  
Radio Sources ◽  
Early Type ◽  
Absorption Path Length ◽  
Spin Temperature ◽  
Upper Limits ◽  
Blind Search ◽  
Cross Matching ◽  
Early Type Galaxy

ABSTRACT We present early science results from the First Large Absorption Survey in H i (FLASH), a spectroscopically blind survey for 21-cm absorption lines in cold hydrogen (H i) gas at cosmological distances using the Australian Square Kilometre Array Pathfinder (ASKAP). We have searched for H i absorption towards 1253 radio sources in the GAMA 23 field, covering redshifts between z = 0.34 and 0.79 over a sky area of approximately 50 deg2. In a purely blind search, we did not obtain any detections of 21-cm absorbers above our reliability threshold. Assuming a fiducial value for the H i spin temperature of Tspin = 100 K and source covering fraction cf = 1, the total comoving absorption path-length sensitive to all Damped Lyman α Absorbers (DLAs; NH i ≥ 2 × 1020 cm−2) is ΔX = 6.6 ± 0.3 (Δz = 3.7 ± 0.2) and super-DLAs (NH i ≥ 2 × 1021 cm−2) is ΔX = 111 ± 6 (Δz= 63 ± 3). We estimate upper limits on the H i column density frequency distribution function that are consistent with measurements from prior surveys for redshifted optical DLAs, and nearby 21-cm emission and absorption. By cross-matching our sample of radio sources with optical spectroscopic identifications of galaxies in the GAMA 23 field, we were able to detect 21-cm absorption at z = 0.3562 towards NVSS J224500−343030, with a column density of $N_{\rm H\,\small{I}} = (1.2 \pm 0.1) \times 10^{20}\, (T_{\rm spin}/100\, \mathrm{K})$ cm−2. The absorber is associated with GAMA J22450.05−343031.7, a massive early-type galaxy at an impact parameter of 17 kpc with respect to the radio source and which may contain a massive (MH i ≳ 3 × 109 M⊙) gas disc. Such gas-rich early types are rare, but have been detected in the nearby Universe.

scholarly journals VLBI Morphology of GHz-Peaked Spectrum Radio Galaxies

1994 ◽  
Vol 159 ◽  
pp. 425-425
Author(s):  
D. Dallacasa ◽  
C. Fanti ◽  
R. Fanti
Keyword(s):  
Radio Galaxies ◽  
Radio Sources ◽  
Complete Sample ◽  
Spectrum Radio ◽  
5 Ghz

GHz-Peaked Spectrum (GPS) radio sources are intrinsically small (< 1 kpc) and unbeamed objects. The galaxies considered here (0316+161, 0404+768, 0428+205, 1323+321, 1358+624, 1819+39, 1829+29) have been selected from the Peacock and Wall (1981) catalogue, and belong to a complete sample of Compact Steep-Spectrum (CSS) radio sources (Fanti et al., 1990). Their radio spectra show a turnover which could be explained in terms of synchrotron self-absorption. It occurs at frequencies ranging from about 100 MHz to 5 GHz and for this reason they do not appear in the 3CR catalogue.

scholarly journals A sample of 669 ultra steep spectrum radio sources to find high redshift radio galaxies

2000 ◽  
Vol 143 (2) ◽  
pp. 303-333 ◽  
Author(s):  
C. De Breuck ◽  
W. van Breugel ◽  
H. J.A. Röttgering ◽  
G. Miley
Keyword(s):  
High Redshift ◽  
Radio Galaxies ◽  
Radio Sources ◽  
Spectrum Radio

scholarly journals 3.21. Atomic ISM in the nuclear starburst regions of M82 & NGC 253

1998 ◽  
Vol 184 ◽  
pp. 131-132
Author(s):  
M. S. Yun ◽  
P. T. P. Ho ◽  
K. Y. Lo
Keyword(s):  
Radio Source ◽  
Optical Depth ◽  
Column Density ◽  
Radio Continuum ◽  
Starburst Galaxy ◽  
Spin Temperature ◽  
Integrated Optical ◽  
Density Map ◽  
Starburst Regions

M82 (NGC 3034) is a nearby (D = 3.3 Mpc) “prototypical” starburst galaxy which emits most of its luminosity in the infrared (LIR = 3×1010L⊙, see Rieke et al. 1980). M82 is also a strong radio source 3C 231, with numerous compact knots which are thought to be young SNR's (Kronberg et al., 1981; Muxlow et al., 1994). Its strong 1.4 GHz radio continuum is extended over the entire 500 pc nuclear starburst region, and the HI absorption is easily mapped at 2″ (30 pc) resolution using the VLA. The resulting velocity integrated optical depth (τΔV) map can be converted to HI column density map if HI spin temperature (Tsp) is known.

scholarly journals Evolution of low-frequency contribution in emission of steep-spectrum radio sources

2014 ◽  
Vol 11 (S308) ◽  
pp. 631-635
Author(s):  
Alla P. Miroshnichenko
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Radio Spectrum ◽  
Unified Model ◽  
Linear Size ◽  
Radio Sources ◽  
Mean Values ◽  
Spectrum Radio ◽  
Size Characteristic ◽  
The Mean

AbstractWe consider evolution properties of galaxies and quasars with steep radio spectrum at the decametre band from the UTR-2 catalogue. The ratios of source's monochromatic luminosities at the decametre and high-frequency bands display the dependence on the redshift, linear size, characteristic age of examined objects. At that, the mean values of corresponding ratios for considered galaxies and quasars have enough close quantities,testifying on the unified model of sources. We analyse obtained relations for two types of steep-spectrum sources (with linear steep spectrum (S) and low-frequency steepness after a break (C+)) from the UTR-2 catalogue.

scholarly journals Radio-optical Identification of Very-Steep Spectrum Radio Sources from the UTR-2 Catalogue

2002 ◽  
Vol 199 ◽  
pp. 217-218 ◽  
Author(s):  
H. Andernach ◽  
O.V. Verkhodanov ◽  
N.V. Verkhodanova
Keyword(s):  
Radio Source ◽  
High Redshift ◽  
Radio Galaxies ◽  
Image Databases ◽  
Radio Continuum ◽  
Radio Sources ◽  
Optical Identification ◽  
X Ray ◽  
Spectrum Radio

We used radio source catalogues accessible from the CATS database to establish radio continuum spectra for decametric radio sources in the UTR-2 catalogue. In an attempt to find further candidates for high-redshift radio galaxies, we searched the FIRST and NVSS surveys for counterparts of a sample of UTR sources with ultra-steep radio spectra (USS, α ≤ −1.2, S ∼ vα). We derived accurate positions and sizes for 23 of these USS sources. The search for optical counterparts from the APM (object) and DSS (image) databases, as well as infrared and X—ray identifications of these UTR sources are in progress.

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