- 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^.
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Search Results
- 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.
- 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_.
- ID:
- ivo://CDS.VizieR/VIII/109
- Title:
- GLEAM III. South Galactic Pole
- Short Name:
- VIII/109
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the South Galactic Pole (SGP) data release from the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey. These data combine both years of GLEAM observations at 72-231MHz conducted with the Murchison Widefield Array (MWA) and cover an area of 5,113 deg^2^ centred on the SGP at 20h40m<RA<05h04m and -48{deg}<Dec<-2{deg}. At 216MHz, the typical rms noise is ~5mJy/beam and the angular resolution ~2 arcmin. The source catalogue contains a total of 108851 components above 5{sigma}, of which 77 per cent have measured spectral indices between 72 and 231MHz. Improvements to the data reduction in this release include the use of the GLEAM Extragalactic catalogue as a sky model to calibrate the data, a more efficient and automated algorithm to deconvolve the snapshot images, and a more accurate primary beam model to correct the flux scale. This data release enables more sensitive large-scale studies of extragalactic source populations as well as spectral variability studies on a one-year timescale.
- 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/MNRAS/464/3357
- Title:
- GMRT 610-MHz observations of the AMI001 field
- Short Name:
- J/MNRAS/464/3357
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 610-MHz Giant Metrewave Radio Telescope observations of 0.84deg^2^ of the AMI001 field (centred on 00h23m10s, +31d53') with an rms noise of 18microJy/beam in the centre of the field. A total of 955 sources are detected, and 814 are included in the source count analysis. The source counts from these observations are consistent with previous work. We have used these data to study the spectral index distribution of a sample of sources selected at 15.7GHz from the recent deep extension to the Tenth Cambridge (10C) survey. The median spectral index, alpha, (where S{prop.to}nu^-alpha^^) between 0.08<S_15.7GHz/mJy<0.2 is 0.32+/-0.14, showing that star-forming galaxies, which have much steeper spectra, are not contributing significantly to this population. This is in contrast to several models, but in agreement with the results from the 10C ultra-deep source counts; the high-frequency sky therefore continues to be dominated by radio galaxies down to S_15.7GHz_=0.1mJy.
- 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.
- ID:
- ivo://CDS.VizieR/J/ApJ/801/91
- Title:
- Gould's Belt Very Large Array survey. IV. Taurus
- Short Name:
- J/ApJ/801/91
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a multi-epoch radio study of the Taurus-Auriga star-forming complex made with the Karl G. Jansky Very Large Array at frequencies of 4.5GHz and 7.5GHz. We detect a total of 610 sources, 59 of which are related to young stellar objects (YSOs) and 18 to field stars. The properties of 56% of the young stars are compatible with non-thermal radio emission. We also show that the radio emission of more evolved YSOs tends to be more non-thermal in origin and, in general, that their radio properties are compatible with those found in other star-forming regions. By comparing our results with previously reported X-ray observations, we notice that YSOs in Taurus-Auriga follow a Gudel-Benz relation with {kappa}=0.03, as we previously suggested for other regions of star formation. In general, YSOs in Taurus-Auriga and in all the previous studied regions seem to follow this relation with a dispersion of ~1dex. Finally, we propose that most of the remaining sources are related with extragalactic objects but provide a list of 46 unidentified radio sources whose radio properties are compatible with a YSO nature.
- ID:
- ivo://CDS.VizieR/J/ApJ/790/49
- Title:
- Gould's Belt VLA survey. III. Orion region
- Short Name:
- J/ApJ/790/49
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from a high-sensitivity (60{mu}Jy), large-scale (2.26deg^2^) survey obtained with the Karl G. Jansky Very Large Array as part of the Gould's Belt Survey program. We detected 374 and 354 sources at 4.5 and 7.5GHz, respectively. Of these, 148 are associated with previously known young stellar objects (YSOs). Another 86 sources previously unclassified at either optical or infrared wavelengths exhibit radio properties that are consistent with those of young stars. The overall properties of our sources at radio wavelengths such as their variability and radio to X-ray luminosity relation are consistent with previous results from the Gould's Belt Survey. Our detections provide target lists for follow-up Very Long Baseline Array radio observations to determine their distances as YSOs are located in regions of high nebulosity and extinction, making it difficult to measure optical parallaxes.
- ID:
- ivo://CDS.VizieR/J/ApJ/805/9
- Title:
- Gould's Belt VLA Survey. II. Serpens region
- Short Name:
- J/ApJ/805/9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present deep (~17{mu}Jy) radio continuum observations of the Serpens molecular cloud, the Serpens south cluster, and the W40 region obtained using the Very Large Array in its A configuration. We detect a total of 146 sources, 29 of which are young stellar objects (YSOs), 2 of which are BV stars, and 5 more of which are associated with phenomena related to YSOs. Based on their radio variability and spectral index, we propose that about 16 of the remaining 110 unclassified sources are also YSOs. For approximately 65% of the known YSOs detected here as radio sources, the emission is most likely non-thermal and related to stellar coronal activity. As also recently observed in Ophiuchus, our sample of YSOs with X-ray counterparts lies below the fiducial Guedel & Benz (1993ApJ...405L..63G) relation. Finally, we analyze the proper motions of nine sources in the W40 region. This allows us to better constrain the membership of the radio sources in the region.