- ID:
- ivo://CDS.VizieR/J/ApJ/378/65
- Title:
- 8.4GHz observations of compact starbursts
- Short Name:
- J/ApJ/378/65
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The 40 ultraluminous (log(LFIR/L_{sun}_>=11.25) galaxies in the IRAS Bright Galaxy Sample of sources stronger than S=5.24Jy at {lambda}=60{mu}m were mapped with approximately 0.25-arcsec resolution at 8.44GHz. Twenty-five contain diffuse radio sources obeying the FIR-radio correlation; these are almost certainly starburst galaxies. Fourteen other galaxies have nearly blackbody FIR spectra with color temperatures between 60 and 80K so their (unmeasured) FIR angular sizes must exceed approximately 0.25-arcsec, yet they contain compact (but usually resolved) radio sources smaller than this limit. The unique radio and FIR properties of these galaxies can be modeled by ultraluminous nuclear starbursts so dense that they are optically thick to free-free absorption at {nu}~1.49GHz and dust absorption at {lambda}~25{mu}m. Only one galaxy (UGC 08058 = Mrk 231) is a dominated by a variable radio source too compact to be an ultraluminous starburst; it must be powered by a 'monster'.
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- ID:
- ivo://CDS.VizieR/J/A+A/603/A100
- Title:
- 37 GHz observations of NLS1 galaxies
- Short Name:
- J/A+A/603/A100
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Observations performed at Metsahovi Radio Observatory at 37GHz are presented for a sample of 78 radio-loud and radio-quiet narrow-line Seyfert 1 (NLS1) galaxies, together with additional lower and higher frequency radio data from RATAN-600, Owens Valley Radio Observatory, and the Planck satellite. Most of the data have been gathered between February 2012 and April 2015 but for some sources even longer light curves exist. The detection rate at 37GHz is around 19%, which is comparable to other populations of active galactic nuclei presumed to be faint at radio frequencies, such as BL Lac objects. Variability and spectral indices are determined for sources with enough detections. Based on the radio data, many NLS1 galaxies show a blazar-like radio spectra exhibiting significant variability. The spectra at a given time are often inverted or convex. The source of the high-frequency radio emission in NLS1 galaxies, detected at 37GHz, is most probably a relativistic jet rather than star formation. Jets in NLS1 galaxies are therefore expected to be a much more common phenomenon than earlier assumed.
- ID:
- ivo://CDS.VizieR/J/other/AstBu/74.348
- Title:
- 164 GHz-peaked spectrum sources
- Short Name:
- J/other/AstBu/74
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Gigahertz-Peaked spectrum (GPS) sources are compact active galactic nuclei, presumably young precursors of bright radio sources. The study of GPS radio properties provides information about the features of synchrotron radiation in extragalactic sources. Also in applied research, GPS sources are useful as compact stationary radio sources in the sky for astrometric purposes. This paper presents the results of a multifrequency GPS study based on quasi-simultaneous measurements with the RATAN-600 radio telescope during the 2006-2017 period. A catalog of GPS spectral flux densities at six frequencies - 1.1, 2.3, 4.8, 7.7/8.2, 11.2, and 21.7GHz - is obtained. In addition, for the analysis of radio spectra, data from low-frequency surveysGLEAM(GaLactic and Extragalactic AllskyMurchisonwidefield array survey) and TGSS (Tata institute for fundamental research GMRT Sky Survey) and high-frequency measurements from Planck survey are used. A total number of 164 GPS and candidates have been identified (17 of them are new discoveries), which makes up a small fraction of GPS in the initial sample of bright AGNs - about 2%. The physical properties and formation conditions of synchrotron radiation is found to be quite different in GPS of different AGNs types. The deficit of distant GPS (z>2) with low maximum frequencies (less than 1GHz) has been confirmed. The existing "size-peak frequency" anticorrelation is continuous. The continuum radio spectra are found to become statistically steeper with increasing redshift.
- ID:
- ivo://CDS.VizieR/J/ApJ/769/125
- Title:
- 1.4GHz radio variability in FIRST & SDSS Stripe 82
- Short Name:
- J/ApJ/769/125
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on a blind survey for extragalactic radio variability that was carried out by comparing two epochs of data from the Faint Images of the Radio Sky at Twenty centimeters survey with a third epoch from a new 1.4GHz survey of SDSS Stripe 82. The three epochs are spaced seven years apart and have an overlapping area of 60deg^2^. We uncover 89 variable sources down to the millijansky level, 75 of which are newly identified, and we find no evidence for transient phenomena. This new sample of variable sources allows us to infer an upper limit to the mean characteristic timescale of active galactic nucleus radio variability of 14yr. We find that only 1% of extragalactic sources have fractional variability f_var_>3, while 44% of Galactic sources vary by this much. The variable sample contains a larger fraction of quasars than a comparable non-variable control sample, though the majority of the variable sources appear to be extended galaxies in the optical. This implies that either quasars are not the dominant contributor to the variability of the sample, or that the deep optical data allow us to detect the host galaxies of some low-z quasars. We use the new, higher resolution data to report on the morphology of the variable sources. Finally, we show that the fraction of sources that are variable remains constant or increases at low flux densities. This may imply that next generation radio surveys with telescopes like Australian Square Kilometer Array Pathfinder and MeerKAT will see a constant or even increasing fraction of variable sources down into the sub-millijansky regime.
- ID:
- ivo://CDS.VizieR/J/AJ/99/1071
- Title:
- 1.4 GHz source survey
- Short Name:
- J/AJ/99/1071
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on 1.4GHz continuum observations for 56 contiguous VLA fields, using the D configuration, in a region devoid of nearby, rich galaxy clusters (at z<0.4). 354 continuum sources are tabulated, with fluxes down to about 1.5mJy, in an area of about 12degres^+2^. Only about seven of the 354 radio sources are associated with known rich galaxy clusters at z>0.4 (tabulated by Gunn, Hoessel, and Oke, 1986ApJ...306...30G). We compare source positions with those from an optical catalog (generated from a POSS plate with the use of the Minnesota Automated Plate Scanner) and find mild correlations on angular scales of order 1arcmin. This suggests some association of radio sources with galaxy groups (sizes of order 200 kpc) at redshifts of order z~0.1, even though there are no rich galaxy clusters in this redshift range.
- ID:
- ivo://CDS.VizieR/J/ApJ/533/611
- Title:
- 1.4GHz survey in HDF region
- Short Name:
- J/ApJ/533/611
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have conducted a deep radio survey with the Very Large Array at 1.4GHz of a region containing the Hubble Deep Field (HDF). This survey overlaps previous observations at 8.5GHz allowing us to investigate the radio spectral properties of microJansky sources to flux densities greater than 40{mu}Jy at 1.4GHz and greater than 8{mu}Jy at 8.5GHz. A total of 371 sources have been catalogued at 1.4GHz as part of a complete sample within 20 of the HDF.
- ID:
- ivo://CDS.VizieR/J/other/Galax/9.99
- Title:
- Giant Radio Galaxies in RACS
- Short Name:
- J/other/Galax/9.
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- We report the results of a visual inspection of images of the Rapid ASKAP Continuum Survey (RACS) in search of extended radio galaxies (ERG) that reach or exceed linear sizes on the order of one Megaparsec. We searched a contiguous area of 1059deg^2^ from RA=20h20m to 06h20m, and -50{deg}<Dec<-40{deg} which is covered by deep multi-band optical images of the Dark Energy Survey (DES), and in which previously only three ERGs larger than 1Mpc had been reported. For over 1800 radio galaxy candidates inspected, our search in optical and infrared images resulted in hosts for 1440 ERG, for which spectroscopic and photometric redshifts from various references were used to convert their largest angular size (LAS) to projected linear size (LLS). This resulted in 178 newly discovered giant radio sources (GRS) with LLS>1Mpc, of which 18 exceed 2Mpc and the largest one is 3.4Mpc. Their redshifts range from 0.02 to about 2.0, but only 10 of the 178 new GRS have spectroscopic redshifts. For the 146 host galaxies the median r-band magnitude and redshift are 20.9 and 0.64, while for the 32 quasars or candidates these are 19.7 and 0.75. Merging the six most recent large compilations of GRS results in 458 GRS larger than 1Mpc, so we were able to increase this number by about 39 per cent to now 636.
- ID:
- ivo://CDS.VizieR/J/other/PASA/38.41
- Title:
- GLEAM 200MHz local radio luminosity function
- Short Name:
- J/other/PASA/38.
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) is a radio continuum survey at 76-227MHz of the entire southern sky (Declination <+30{deg}) with an angular resolution of ~2arcmin. In this paper, we combine GLEAM data with optical spectroscopy from the 6dF Galaxy Survey to construct a sample of 1,590 local (median z~0.064) radio sources with S_200MHz_>55mJy across an area of ~16700deg^2^. From the optical spectra, we identify the dominant physical process responsible for the radio emission from each galaxy: 73 per cent are fuelled by an active galactic nucleus (AGN) and 27 per cent by star formation. We present the local radio luminosity function for AGN and star-forming galaxies at 200MHz and characterise the typical radio spectra of these two populations between 76MHz and ~1GHz. For the AGN, the median spectral index between 200MHz and ~1GHz, {alpha}, is -0.600+/-0.010 (where S proportional to {nu}^{alpha}^) and the median spectral index within the GLEAM band, {alpha}_low_, is -0.704+/-0.011. For the star-forming galaxies, the median value of {alpha}_high_ is -0.650+/-0.010 and the median value of {alpha}_low_ is -0.596+/-0.015. Among the AGN population, flat-spectrum sources are more common at lower radio luminosity, suggesting the existence of a significant population of weak radio AGN that remain core-dominated even at low frequencies. However, around 4 per cent of local radio AGN have ultra-steep radio spectra at low frequencies ({alpha}_low_<-1.2). These ultra-steep-spectrum sources span a wide range in radio luminosity, and further work is needed to clarify their nature.
- ID:
- ivo://CDS.VizieR/J/A+A/549/A55
- Title:
- GMRT 153MHz (2m) Radio Mini Survey I.
- Short Name:
- J/A+A/549/A55
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present wide area, deep, high-resolution 153MHz GMRT observations of the NOAO Bootes field, adding to the extensive, multi-wavelength data of this region. The observations, data reduction, and catalogue construction and description are described here. The seven pointings produced a final mosaic covering 30 square degrees with a resolution of 25". The rms noise is 2mJy/beam in the centre of the image, rising to 4-5mJy/beam on the edges, with an average of 3mJy/beam. Seventy-five per cent of the area has an rms <4mJy/beam. The extracted source catalogue contains 1289 sources detected at 5{sigma}, of which 453 are resolved. We estimate the catalogue to be 92 per cent reliable and 95 per cent complete at an integrated flux density limit of 14mJy. The flux densities and astrometry have been corrected for systematic errors. We calculate the differential source counts which are in good agreement with those in the literature and provide an important step forward in quantifying the source counts at these low frequencies and low flux densities. The GMRT 153MHz sources have been matched to the 1.4GHz NVSS and 327MHz WENSS catalogues and spectral indices were derived.
- ID:
- ivo://CDS.VizieR/J/AJ/154/169
- Title:
- GMRT observations of head-tail radio galaxies
- Short Name:
- J/AJ/154/169
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from a study of seven large known head-tail radio galaxies based on observations using the Giant Metrewave Radio Telescope at 240 and 610 MHz. These observations are used to study the radio morphologies and distribution of the spectral indices across the sources. The overall morphology of the radio tails of these sources is suggestive of random motions of the optical host around the cluster potential. The presence of multiple bends and wiggles in several head-tail sources is possibly due to the precessing radio jets. We find steepening of the spectral index along the radio tails. The prevailing equipartition magnetic field also decreases along the radio tails of these sources. These steepening trends are attributed to the synchrotron aging of plasma toward the ends of the tails. The dynamical ages of these sample sources have been estimated to be ~10^8^ yr, which is a factor of six more than the age estimates from the radiative losses due to synchrotron cooling.
