- 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/A+A/644/A104
- Title:
- Auriga bright stars BRITE phot. and RV
- Short Name:
- J/A+A/644/A104
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We aim to determine periods for bright stars in the Auriga field that are otherwise not easily accessible for ground-based photometry. Continuous photometry with up to three BRITE satellites was obtained for 12 targets and subjected to a period search. Contemporaneous high-resolution optical spectroscopy with STELLA was used to obtain radial velocities through cross correlation with template spectra as well as to determine astrophysical parameters through a comparison with model spectra.
- ID:
- ivo://CDS.VizieR/J/ApJ/764/133
- Title:
- Auriga-California giant molecular cloud
- Short Name:
- J/ApJ/764/133
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have mapped the Auriga/California molecular cloud with the Herschel PACS and SPIRE cameras and the Bolocam 1.1mm camera on the Caltech Submillimeter Observatory with the eventual goal of quantifying the star formation and cloud structure in this giant molecular cloud (GMC) that is comparable in size and mass to the Orion GMC, but which appears to be forming far fewer stars. We have tabulated 60 compact 70/160 {mu}m sources that are likely pre-main-sequence objects and correlated those with Spitzer and WISE mid-IR sources. At 1.1 mm, we find 18 cold, compact sources and discuss their properties. The most important result from this part of our study is that we find a modest number of additional compact young objects beyond those identified at shorter wavelengths with Spitzer.
- ID:
- ivo://CDS.VizieR/J/AJ/153/107
- Title:
- Australian Dark Energy Survey (OzDES) quasar catalog
- Short Name:
- J/AJ/153/107
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of quasar selection using the supernova fields of the Dark Energy Survey (DES). We used a quasar catalog from an overlapping portion of the SDSS Stripe 82 region to quantify the completeness and efficiency of selection methods involving color, probabilistic modeling, variability, and combinations of color/probabilistic modeling with variability. In all cases, we considered only objects that appear as point sources in the DES images. We examine color selection methods based on the Wide-field Infrared Survey Explorer (WISE) (Wright et al. 2010AJ....140.1868W) mid-IR W1-W2 color, a mixture of WISE and DES colors (g-i and i-W1), and a mixture of Vista Hemisphere Survey (McMahon et al. 2013Msngr.154...35M) and DES colors (g-i and i-K). For probabilistic quasar selection, we used XDQSO, an algorithm that employs an empirical multi-wavelength flux model of quasars to assign quasar probabilities. Our variability selection uses the multi-band {chi}^2^-probability that sources are constant in the DES Year 1 griz-band light curves. The completeness and efficiency are calculated relative to an underlying sample of point sources that are detected in the required selection bands and pass our data quality and photometric error cuts. We conduct our analyses at two magnitude limits, i<19.8 mag and i<22 mag. For the subset of sources with W1 and W2 detections, the W1-W2 color or XDQSOz method combined with variability gives the highest completenesses of >85% for both i-band magnitude limits and efficiencies of >80% to the bright limit and >60% to the faint limit; however, the giW1 and giW1+variability methods give the highest quasar surface densities. The XDQSOz method and combinations of W1W2/giW1/XDQSOz with variability are among the better selection methods when both high completeness and high efficiency are desired. We also present the OzDES Quasar Catalog of 1263 spectroscopically confirmed quasars from three years of OzDES observation in the 30 deg^2^ of the DES supernova fields. The catalog includes quasars with redshifts up to z~4 and brighter than i=22 mag, although the catalog is not complete up to this magnitude limit.
- 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/MNRAS/426/3334
- Title:
- Australia Telescope Large Area Survey
- Short Name:
- J/MNRAS/426/3334
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Australia Telescope Large Area Survey (ATLAS) has surveyed 7 square degrees of sky around the Chandra Deep Field South and the European Large Area ISO Survey-South 1 fields at 1.4GHz. ATLAS aims to reach a uniform sensitivity of 10uJy/beam rms over the entire region with first data release currently reaching ~30uJy/beam rms. Here we present 466 new spectroscopic redshifts for radio sources in ATLAS as part of our optical follow-up programme. Of the 466 radio sources with new spectroscopic redshifts, 142 have star-forming optical spectra, 282 show evidence for active galactic nuclei (AGN) in their optical spectra, 10 have stellar spectra and 32 have spectra revealing redshifts, but with insufficient features to classify.
- ID:
- ivo://CDS.VizieR/J/ApJ/762/16
- Title:
- Australia Telescope Low-brightness Survey (ATLBS)
- Short Name:
- J/ApJ/762/16
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Australia Telescope Low-brightness Survey (ATLBS) regions have been mosaic imaged at a radio frequency of 1.4GHz with 6" angular resolution and 72{mu}Jy/beam rms noise. The images (centered at RAJ2000=00:35:00, DEJ2000=-67:00:00 and RAJ2000=00:59:17, DEJ2000=-67:00:00) cover 8.42deg^2^ sky area and have no artifacts or imaging errors above the image thermal noise. Multi-resolution radio and optical r-band images (made using the 4m CTIO Blanco telescope) were used to recognize multi-component sources and prepare a source list; the detection threshold was 0.38mJy in a low-resolution radio image made with beam FWHM of 50". Radio source counts in the flux density range 0.4-8.7mJy are estimated, with corrections applied for noise bias, effective area correction, and resolution bias. The resolution bias is mitigated using low-resolution radio images, while effects of source confusion are removed by using high-resolution images for identifying blended sources. Below 1mJy the ATLBS counts are systematically lower than the previous estimates. Showing no evidence for an upturn down to 0.4mJy, they do not require any changes in the radio source population down to the limit of the survey. The work suggests that automated image analysis for counts may be dependent on the ability of the imaging to reproduce connecting emission with low surface brightness and on the ability of the algorithm to recognize sources, which may require that source finding algorithms effectively work with multi-resolution and multi-wavelength data. The work underscores the importance of using source lists --as opposed to component lists-- and correcting for the noise bias in order to precisely estimate counts close to the image noise and determine the upturn at sub-mJy flux density.
- ID:
- ivo://CDS.VizieR/J/MNRAS/422/1527
- Title:
- Australia Telescope PMN follow-up survey
- Short Name:
- J/MNRAS/422/1527
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a source catalogue derived from high-resolution observations of a selection of PMN sources with the Australia Telescope Compact Array (ATCA). The catalogue lists 8385 sources with flux-density measurements at 4.8 and 8.6GHz, derived from observations of all fields in the declination range -87{deg}<DE<-38.5{deg} (exclusive of galactic latitudes |b|<2{deg{) with PMN flux-density S_4850_>70mJy (50mJy south of DE=-73{deg}). We assess the quality of the data, which was gathered in 1992-1994, and the resulting source parameters. We describe the population of catalogued sources, and compare it to samples from complementary catalogues. In particular we find 126 radio sources with probable association with gamma-ray sources observed by the orbiting Fermi Large Area Telescope.
- ID:
- ivo://CDS.VizieR/J/ApJ/813/28
- Title:
- Autoclassification of the variable 3XMM sources
- Short Name:
- J/ApJ/813/28
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In the current era of large surveys and massive data sets, autoclassification of astrophysical sources using intelligent algorithms is becoming increasingly important. In this paper we present the catalog of variable sources in the Third XMM-Newton Serendipitous Source catalog (3XMM) autoclassified using the Random Forest machine learning algorithm (RF). We used a sample of manually classified variable sources from the second data release of the XMM-Newton catalogs (2XMMi-DR2) to train the classifier, obtaining an accuracy of ~92%. We also evaluated the effectiveness of identifying spurious detections using a sample of spurious sources, achieving an accuracy of ~95%. Manual investigation of a random sample of classified sources confirmed these accuracy levels and showed that the Random Forest machine learning algorithm is highly effective at automatically classifying 3XMM sources. Here we present the catalog of classified 3XMM variable sources. We also present three previously unidentified unusual sources that were flagged as outlier sources by the algorithm: a new candidate supergiant fast X-ray transient, a 400s X-ray pulsar, and an eclipsing 5hr binary system coincident with a known Cepheid.
- ID:
- ivo://CDS.VizieR/J/MNRAS/358/30
- Title:
- Automated classification of ASAS variables
- Short Name:
- J/MNRAS/358/30
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- With the advent of surveys generating multi-epoch photometry and the discovery of large numbers of variable stars, the classification of these stars has to be automatic. We have developed such a classification procedure for about 1700 stars from the variable star catalogue of the All-Sky Automated Survey 1-2 (ASAS 1-2) by selecting the periodic stars and by applying an unsupervised Bayesian classifier using parameters obtained through a Fourier decomposition of the light curve. For irregular light curves we used the period and moments of the magnitude distribution for the classification. In the case of ASAS 1-2, 83 per cent of variable objects are red giants. A general relation between the period and amplitude is found for a large fraction of those stars. The selection led to 302 periodic and 1429 semiperiodic stars, which are classified in six major groups: eclipsing binaries, 'sinusoidal curves', Cepheids, small amplitude red variables, SR and Mira stars. The type classification error level is estimated to be about 7 per cent.
