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321. 43GHz observation of the blazar Mrk 421
ID:
ivo://CDS.VizieR/J/A+A/559/A75
Title:
43GHz observation of the blazar Mrk 421
Short Name:
J/A+A/559/A75
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report the results obtained for the AGN Markarian 421 by model-fitting the data in the visibility plane, studing the proper motion of jet components, the light curve, and the spectral index of the jet features. We compare the radio data with optical light curves obtained at the Steward Observatory, considering also the optical polarization information. Mrk 421 has a bright nucleus and a one-sided jet extending towards the north-west for a few parsecs. The model-fits show that brightness distribution is well described using 6-7 circular Gaussian components, four of which are reliably identified at all epochs; all components are effectively stationary except for component D, at ~0.4mas from the core, whose motion is however subluminal. The analysis of the light curve shows two different states, with the source being brighter and more variable in the first half of 2011 than in the second half. The highest flux density is reached in February. A comparison with the optical data reveals an increase of the V magnitude and of the fractional polarization simultaneous with the enhancement of the radio activity.
322. 37GHz observations of BL Lac objects
ID:
ivo://CDS.VizieR/J/AJ/133/1947
Title:
37GHz observations of BL Lac objects
Short Name:
J/AJ/133/1947
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present 37GHz data obtained at Metsahovi Radio Observatory in 2001 December-2005 April for a large sample of BL Lacertae objects. Metsahovi radio telescope is a radome enclosed antenna with a diameter of 13.7 metres. The 37 GHz receiver is a dual horn, Dicke-switched receiver with a HEMT preamplifier, and is operated at room temperature. The observations are ON-ON observations, alternating the source and the sky in each feed horn. A typical integration time to obtain one flux density data point is 1200-1600s, and the detection limit under optimal weather conditions is about 0.2Jy.
323. 37 GHz observations of NLS1 galaxies
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.
324. 164 GHz-peaked spectrum sources
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.
325. 31GHz survey of low-frequency radio sources
ID:
ivo://CDS.VizieR/J/ApJ/704/1433
Title:
31GHz survey of low-frequency radio sources
Short Name:
J/ApJ/704/1433
Date:
21 Oct 2021
Publisher:
CDS
Description:
The 100m Robert C. Byrd Green Bank Telescope and the 40m Owens Valley Radio Observatory telescope have been used to conduct a 31GHz survey of 3165 known extragalactic radio sources over 143deg^2^ of the sky. Target sources were selected from the NRAO VLA Sky Survey in fields observed by the Cosmic Background Imager (CBI); most are extragalactic active galactic nuclei (AGNs) with 1.4GHz flux densities of 3-10mJy. The resulting 31GHz catalogs are presented in full online. Using a maximum-likelihood analysis to obtain an unbiased estimate of the distribution of the 1.4-31GHz spectral indices of these sources, we find a mean 31-1.4GHz flux ratio of 0.110+/-0.003 corresponding to a spectral index of {alpha}=-0.71+/-0.01 (S_{nu}_{prop.to}{nu}^{alpha}^); 9.0%+/-0.8% of sources have {alpha}>-0.5 and 1.2%+/-0.2% have {alpha}>0. By combining this spectral-index distribution with 1.4GHz source counts, we predict 31GHz source counts in the range 1mJy<S_31_<4mJy, N(>S_31_)=(16.7+/-1.7)deg^-2^(S_31_/1mJy)^-0.80+/-0.07^.
326. 28-40GHz variability and polarimetry
ID:
ivo://CDS.VizieR/J/MNRAS/502/4779
Title:
28-40GHz variability and polarimetry
Short Name:
J/MNRAS/502/4779
Date:
21 Oct 2021
Publisher:
CDS
Description:
We observed 51 sources in the Q-U-I JOint TEnerife (QUIJOTE) cosmological fields which were brighter than 1Jy at 30GHz in the Planck Point Source Catalogue (version 1), with the Very Large Array at 28-40GHz, in order to characterise their high-radio-frequency variability and polarization properties. We find a roughly log-normal distribution of polarization fractions with a median of 2%, in agreement with previous studies, and a median rotation measure (RM) of ~1110rad/m^2^ with one outlier up to ~64000rad/m^2^ which is among the highest RMs measured in quasar cores. We find hints of a correlation between the total intensity flux density and median polarization fraction. We find 59% of sources are variable in total intensity, and 100% in polarization at 3{sigma} level, with no apparent correlation between total intensity variability and polarization variability. This indicates that it will be difficult to model these sources without simultaneous polarimetric monitoring observations and they will need to be masked for cosmological analysis.
327. 230GHz VLBI observations of M87
ID:
ivo://CDS.VizieR/J/ApJ/807/150
Title:
230GHz VLBI observations of M87
Short Name:
J/ApJ/807/150
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report on 230GHz (1.3mm) very long baseline interferometry (VLBI) observations of M87 with the Event Horizon Telescope using antennas on Mauna Kea in Hawaii, Mt. Graham in Arizona, and Cedar Flat in California. For the first time, we have acquired 230GHz VLBI interferometric phase information on M87 through measurement of the closure phase on the triangle of long baselines. Most of the measured closure phases are consistent with 0{deg} as expected by physically motivated models for 230GHz structure such as jet models and accretion disk models. The brightness temperature of the event-horizon-scale structure is ~1x10^10^K derived from the compact flux density of ~1Jy and the angular size of ~40{mu}as~5.5R_s_, which is broadly consistent with the peak brightness of the radio cores at 1-86GHz located within ~10^2^R_s_. Our observations occurred in the middle of an enhancement in very-high-energy (VHE) {gamma}-ray flux, presumably originating in the vicinity of the central black hole. Our measurements, combined with results of multi-wavelength observations, favor a scenario in which the VHE region has an extended size of ~20-60R_s_.
328. 8.4GHz VLBI observations of Southern ICRF sources
ID:
ivo://CDS.VizieR/J/AJ/130/2529
Title:
8.4GHz VLBI observations of Southern ICRF sources
Short Name:
J/AJ/130/2529
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present 8.4GHz very long baseline interferometry (VLBI) observations of 48 southern hemisphere extragalactic sources from the International Celestial Reference Frame. These are the second in a series of observations intended to image all such sources in the southern hemisphere at milliarcsecond resolution and bring the total number of observed sources to 111. We use these data, together with previously published data, to quantify the magnitude of the expected effect of intrinsic source structure on astrometric bandwidth synthesis VLBI observations by calculating a "structure index" for the sources; the structure index yields an estimate of their astrometric quality.
329. Giant Radio Galaxies in RACS
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.
330. GLEAM 200MHz local radio luminosity function
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.