- 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.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/767/94
- Title:
- 1.1-1.9GHz SETI survey of KOIs. I.
- Short Name:
- J/ApJ/767/94
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a targeted search for narrow-band (<5Hz) drifting sinusoidal radio emission from 86 stars in the Kepler field hosting confirmed or candidate exoplanets. Radio emission less than 5Hz in spectral extent is currently known to only arise from artificial sources. The stars searched were chosen based on the properties of their putative exoplanets, including stars hosting candidates with 380K>T_eq_>230K, stars with five or more detected candidates or stars with a super-Earth (R_p_<3R_{earth}_) in a >50 day orbit. Baseband voltage data across the entire band between 1.1 and 1.9GHz were recorded at the Robert C. Byrd Green Bank Telescope between 2011 February and April and subsequently searched offline. No signals of extraterrestrial origin were found. We estimate that fewer than ~1% of transiting exoplanet systems host technological civilizations that are radio loud in narrow-band emission between 1 and 2GHz at an equivalent isotropically radiated power (EIRP) of ~1.5x10^21^erg/s, approximately eight times the peak EIRP of the Arecibo Planetary Radar, and we limit the number of 1-2GHz narrow-band-radio-loud Kardashev type II civilizations in the Milky Way to be <10^-6^/M_{sun}_. Here we describe our observations, data reduction procedures and results.
- ID:
- ivo://CDS.VizieR/J/ApJ/716/521
- Title:
- 31GHz sky survey with the SZA
- Short Name:
- J/ApJ/716/521
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first sample of 31GHz selected sources to flux levels of 1mJy. From late 2005 to mid-2007, the Sunyaev-Zel'dovich Array observed 7.7deg^2^ of the sky at 31GHz to a median rms of 0.18mJy/beam. We identify 209 sources at greater than 5{sigma} significance in the 31GHz maps, ranging in flux from 0.7mJy to ~200mJy. Archival NVSS data at 1.4GHz and observations at 5GHz with the Very Large Array are used to characterize the sources. We determine the maximum-likelihood integrated source count to be N(>S)=(27.2+/-2.5)deg^-2^x(S_mJy_)^-1.18+/-0.12^ over the flux range 0.7-15mJy. This result is significantly higher than predictions based on 1.4GHz selected samples, a discrepancy which can be explained by a small shift in the spectral index distribution for faint 1.4GHz sources. From comparison with previous measurements of sources within the central arcminute of massive clusters, we derive an overdensity of 6.8+/-4.4, relative to field sources.
- 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/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^.
- 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/ApJ/835/254
- Title:
- GLASS. IX. Structural param. from HFF & GLASS
- Short Name:
- J/ApJ/835/254
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using deep Hubble Frontier Fields imaging and slitless spectroscopy from the Grism Survey from Space, we study 2200 cluster and 1748 field galaxies at 0.2<=z<=0.7 to determine the impact of environment on galaxy size and structure at stellar masses logM_*_/M_{sun}_>7.8, an unprecedented limit at these redshifts. Based on simple assumptions-r_e_=f(M_*_)-we find no significant differences in half-light radii (r_e_) between equal-mass cluster or field systems. More complex analyses --r_e_=f(M_*_,U-V,n,z,{Sigma})-- reveal local density ({Sigma}) to induce only a 7%+/-3% (95% confidence) reduction in r_e_ beyond what can be accounted for by U-V color, Sersic index (n), and redshift (z) effects. Almost any size difference between galaxies in high- and low-density regions is thus attributable to their different distributions in properties other than environment. Indeed, we find a clear color-r_e_ correlation in low-mass passive cluster galaxies (logM_*_/M_{sun}_<9.8) such that bluer systems have larger radii, with the bluest having sizes consistent with equal-mass star-forming galaxies. We take this as evidence that large-r_e_ low-mass passive cluster galaxies are recently acquired systems that have been environmentally quenched without significant structural transformation (e.g., by ram pressure stripping or starvation). Conversely, ~20% of small-r_e_ low-mass passive cluster galaxies appear to have been in place since z>~3. Given the consistency of the small-r_e_ galaxies' stellar surface densities (and even colors) with those of systems more than ten times as massive, our findings suggest that clusters mark places where galaxy evolution is accelerated for an ancient base population spanning most masses, with late-time additions quenched by environment-specific mechanisms mainly restricted to the lowest masses.
- ID:
- ivo://CDS.VizieR/VIII/102
- Title:
- GLEAM II. Galactic plane
- Short Name:
- VIII/102
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This work makes available a further of the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey, covering half of the accessible galactic plane, across 20 frequency bands sampling 72-231MHz, with resolution 4-2arcmin. Unlike previous GLEAM data releases, we used multi-scale CLEAN to better deconvolve large-scale galactic structure. For the galactic longitude ranges 345{deg}<l<67{deg}, 180{deg}<l<240{deg}, we provide a compact source catalogue of 22037 components selected from a 60-MHz bandwidth image centred at 200MHz, with RMS noise ~-10-20mJy/beam and position accuracy better than 2-arcsec. The catalogue has a completeness of 50% at ~120mJy, and a reliability of 99.86%. It covers galactic latitudes 1{deg}<=|b|<=10{deg} towards the galactic centre and |b|<=10{deg} for other regions, and is available from Vizier; images covering |b|<=10{deg} for all longitudes are made available on the GLEAM Virtual Observatory (VO).server and SkyView.
- 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/VIII/107
- Title:
- GLEAM sources ionospheric position shifts
- Short Name:
- VIII/107
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Nearly 200 hours of observing with the Murchison Widefield Array (MWA) radio telescope during the Galactic and Extra-galactic All-sky MWA (GLEAM) survey were used to assemble images of ionospheric structure. These images cover a nearly 50 degree-wide area on the sky at a cadence of 10 minutes over many 5-7 hours-long observing runs. They are generated by tracking the apparent motions of ~200-800 cosmic radio sources caused by changes in the transverse gradient of the ionospheric total electron content. Spectral analysis of these images revealed that the dataset was dominated by three distinct signatures. The first is consistent with field-aligned structures within the topside ionosphere/lower plasmasphere previously imaged with the MWA. The second are structures that are relatively large and aligned nearly east/west. Regional weather data implies that these are preferentially detected when there is a noticeable shear within the sub- tropical jet stream, which passes near the MWA. This suggests that this signature may be related to gravity waves launched by jet stream shear. The final signature is consistent with the properties of so-call electro-buoyancy waves that are known to occur at midlatitudes at night. Detections of these were more common when regional sporadic-E was present, supporting a proposed connection between these waves and polarization electric fields that may arise within sporadic-E. We discuss the implications for future observations with the Square Kilometer Array.
