- ID:
- ivo://CDS.VizieR/J/A+A/649/A94
- Title:
- A universal pattern in halo magnetic fields
- Short Name:
- J/A+A/649/A94
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Magnetic fields in galaxy halos are in general very difficult to observe. Most recently, the Continuum HAlos in Nearby Galaxies - an EVLA Survey (CHANG-ES) collaboration investigated the radio halos of 35 nearby edge-on spiral galaxies in detail and detected large-scale magnetic fields in 16 of them. We used the CHANG-ES radio polarization data to create rotation measure (RM) maps for all galaxies in the sample and stack them with the aim of amplifying any underlying universal toroidal magnetic field pattern in the halo above and below the disk of the galaxy. We discovered a large-scale magnetic field in the central region of the stacked galaxy profile, which is attributable to an axial electric current that universally outflows from the center, both above and below the plane of the disk. A similar symmetry-breaking has also been observed in astrophysical jets, but never before in galaxy halos. This is an indication that galaxy halo magnetic fields are probably not generated by pure magnetohydrodynamic (MHD) processes in the central regions of galaxies. One such promising physical mechanism is the Cosmic Battery operating in the innermost accretion disk around the central supermassive black hole. We anticipate that our discovery will stimulate a more general discussion on the origin of astrophysical magnetic fields.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/402/2403
- Title:
- Australia Telescope 20GHz Survey Catalog, AT20G
- Short Name:
- J/MNRAS/402/2403
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Australia Telescope 20GHz Survey (AT20G) is a blind radio survey carried out at 20GHz with the Australia Telescope Compact Array (ATCA) from 2004 to 2008, and covers the whole sky south of declination 0{deg}. The AT20G source catalogue presented here is an order of magnitude larger than any previous catalogue of high-frequency radio sources, and includes 5890 sources above a 20GHz flux-density limit of 40mJy. All AT20G sources have total intensity and polarisation measured at 20GHz, and most sources south of declination -15{deg} also have near-simultaneous flux-density measurements at 5 and 8GHz. A total of 1559 sources were detected in polarised total intensity at one or more of the three frequencies.
- ID:
- ivo://CDS.VizieR/J/ApJS/208/14
- Title:
- BGPS. IX. Data release 2.
- Short Name:
- J/ApJS/208/14
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a re-reduction and expansion of the Bolocam Galactic Plane Survey (BGPS), first presented by Aguirre+ (2011ApJS..192....4A) and Rosolowsky+ (2011, J/ApJS/188/123). The BGPS is a 1.1mm survey of dust emission in the Northern galactic plane, covering longitudes -10{deg}<{ell}<90{deg} and latitudes |b|<0.5{deg} with a typical 1{sigma} rms sensitivity of 30-100mJy in a ~33" beam. Version 2 of the survey includes an additional ~20deg^2^ of coverage in the third and fourth quadrants and ~2deg^2^ in the first quadrant. The new data release has improved angular recovery, with complete recovery out to ~80" and partial recovery to ~300", and reduced negative bowls around bright sources resulting from the atmospheric subtraction process. We resolve the factor of 1.5 flux calibration offset between the v1.0 data release and other data sets and determine that there is no offset between v2.0 and other data sets. The v2.0 pointing accuracy is tested against other surveys and is demonstrated to be accurate and an improvement over v1.0. We present simulations and tests of the pipeline and its properties, including measurements of the pipeline's angular transfer function. The Bolocat cataloging tool was used to extract a new catalog, which includes 8594 sources, with 591 in the expanded regions. We have demonstrated that the Bolocat 40" and 80" apertures are accurate even in the presence of strong extended background emission. The number of sources is lower than in v1.0, but the amount of flux and area included in identified sources is larger.
- ID:
- ivo://CDS.VizieR/J/ApJ/799/72
- Title:
- Binary AGNs from the VLA Stripe 82 survey
- Short Name:
- J/ApJ/799/72
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Galaxy mergers play an important role in the growth of galaxies and their supermassive black holes. Simulations suggest that tidal interactions could enhance black hole accretion, which can be tested by the fraction of binary active galactic nuclei (AGNs) among galaxy mergers. However, determining the fraction requires a statistical sample of binaries. We have identified kiloparsec-scale binary AGNs directly from high-resolution radio imaging. Inside the 92deg^2^ covered by the high-resolution Very Large Array survey of the Sloan Digital Sky Survey (SDSS) Stripe 82 field, we identified 22 grade A and 30 grade B candidates of binary radio AGNs with angular separations less than 5" (10kpc at z=0.1). Eight of the candidates have optical spectra for both components from the SDSS spectroscopic surveys and our Keck program. Two grade B candidates are projected pairs, but the remaining six candidates are all compelling cases of binary AGNs based on either emission line ratios or the excess in radio power compared to the H{alpha}-traced star formation rate. Only two of the six binaries were previously discovered by an optical spectroscopic search. Based on these results, we estimate that ~60% of our binary candidates would be confirmed once we obtain complete spectroscopic information. We conclude that wide-area high-resolution radio surveys offer an efficient method to identify large samples of binary AGNs. These radio-selected binary AGNs complement binaries identified at other wavelengths and are useful for understanding the triggering mechanisms of black hole accretion.
- ID:
- ivo://CDS.VizieR/J/A+A/600/A65
- Title:
- B2 0924+30 LOFAR HBA and WSRT maps
- Short Name:
- J/A+A/600/A65
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using LOFAR (LOw Frequency ARray), Westerbork telescope and survey data, we map the spectral index and age of the remnant radio galaxy by using different ageing models.
- ID:
- ivo://CDS.VizieR/J/A+A/620/A74
- Title:
- Bootes field deep LOFAR 150MHz imaging
- Short Name:
- J/A+A/620/A74
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have conducted a deep survey (with a central rms of 55uJy) with the LOw Frequency ARray (LOFAR) at 120-168MHz of the Bootes field, with an angular resolution of 3.98"x6.45", and obtained a sample of 10091 radio sources (5{sigma} limit) over an area of 20deg^2^. The astrometry and flux scale accuracy of our source catalog is investigated. The resolution bias, incompleteness and other systematic effects that could affect our source counts are discussed and accounted for. The derived 150MHz source counts present a flattening below sub-mJy flux densities, that is in agreement with previous results from high- and low- frequency surveys. This flattening has been argued to be due to an increasing contribution of star-forming galaxies and faint active galactic nuclei. Additionally, we use our observations to evaluate the contribution of cosmic variance to the scatter in source counts measurements. The latter is achieved by dividing our Bootes mosaic into 10 non-overlapping circular sectors, each one with an approximate area of 2deg^2^. The counts in each sector are computed in the same way as done for the entire mosaic. By comparing the induced scatter with that of counts obtained from depth observations scaled to 150MHz, we find that the 1{sigma} scatter due to cosmic variance is larger than the Poissonian errors of the source counts, and it may explain the dispersion from previously reported depth source counts at flux densities S<1mJy. This work demonstrates the feasibility of achieving deep radio imaging at low-frequencies with LOFAR.
- ID:
- ivo://CDS.VizieR/J/MNRAS/460/2385
- Title:
- Bootes field LOFAR 150-MHz observations
- Short Name:
- J/MNRAS/460/2385
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first wide area (19 deg^2^), deep (~=120-150 {mu}Jy/beam), high-resolution (5.6x7.4-arcsec) LOFAR High Band Antenna image of the Bootes field made at 130-169MHz. This image is at least an order of magnitude deeper and 3-5 times higher in angular resolution than previously achieved for this field at low frequencies. The observations and data reduction, which includes full direction-dependent calibration, are described here. We present a radio source catalogue containing 6276 sources detected over an area of 19deg^2^, with a peak flux density threshold of 5{sigma}. As the first thorough test of the facet calibration strategy, introduced by van Weeren et al. (2016ApJS..223....2V), we investigate the flux and positional accuracy of the catalogue. We present differential source counts that reach an order of magnitude deeper in flux density than previously achieved at these low frequencies, and show flattening at 150-MHz flux densities below 10 mJy associated with the rise of the low flux density star-forming galaxies and radio-quiet AGN.
- ID:
- ivo://CDS.VizieR/J/MNRAS/216/173
- Title:
- Bright extragalactic radio sources at 2.7 GHz
- Short Name:
- J/MNRAS/216/173
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The brightest extragalactic radio sources at 2.7 GHz are catalogued. The complete sample comprises 233 sources found in the major centimeter wavelength surveys carried out at ANRAO/Parkes, NNRAO/Greenbank, and MPIfR/Bonn: the sample covers 9.81 sr and has limits S(27) = 2.0 Jy and |b| > 10{deg}. A critical reanalysis of the data shows that 227 (97 percent) have optical identifications and 171 (73 percent) have measured redshifts. The implications of the catalogue statistics for the luminosity functions of different radio-source populations are considered.
- ID:
- ivo://CDS.VizieR/J/A+A/549/A133
- Title:
- Bright northern radio sources with VLA/JVLA
- Short Name:
- J/A+A/549/A133
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report multiple epoch VLA/JVLA observations of 89 northern hemisphere sources, most with 37GHz flux density >1Jy, observed at 4.8, 8.5, 33.5, and 43.3GHz. The high frequency selection leads to a predominantly flat spectrum sample, with 85% of our sources being in the Planck Early Release Compact Source Catalog (ERCSC, Cat. VIII/88). These observations allow us to: 1) validate Planck's 30 and 44GHz flux density scale; 2) extend the radio spectral energy distributions of Planck sources to lower frequencies allowing for the full 5-857GHz regime to be studied; and 3) characterize the variability of these sources. At 30GHz and 44GHz, the JVLA and Planck flux densities agree to within ~3%. On timescales of less than two months the median variability of our sources is 2%. On timescales of about a year the median variability increases to 14%. Using the WMAP 7-year data, the 30GHz median variability on a 1-6 years timescale is 16%.
- ID:
- ivo://CDS.VizieR/J/MNRAS/204/151
- Title:
- Bright radio sources at 178 MHz (3CRR)
- Short Name:
- J/MNRAS/204/151
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A revised sample of bright radio sources at 178MHz is defined in order to correct the biases introduced into the 3CR catalog by confusion and partial resolution. The sample is shown to be 96 percent complete to a flux-density limit of 10Jy for sources smaller than 10arcmin. The bias of the 3CR catalog against objects of larger angular size is also reduced. Optical identifications are presented for 96 percent of the sources, 71 percent with galaxies and 25 percent with quasars. The radio-galaxy population is found to show strong space-density evolution for luminosities in excess of approximately 10^26.5^W/Hz/sr at 178MHz (redshifts greater than or approximately equal to 0.2), while the evolutionary properties of galaxies and quasars of the same luminosity and redshift are very similar.
