- ID:
- ivo://CDS.VizieR/J/A+A/618/A92
- Title:
- Radio-loud NLSy1 galaxies optical polarisation
- Short Name:
- J/A+A/618/A92
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We quantify the temporal behaviour of the optical polarisation fraction and angle for a selected sample of radio-loud NLSy1s. We also search for rotations of the polarisation plane similar to those commonly observed in blazars. The dataset was obtained with the RoboPol polarimeter of the Skinakas observatory as well as the KANATA, Perkins, and Steward observatories. We carried out numerical simulations to assess the probability that long rotations of the polarisation plane were caused by intrinsically evolving electric vector position angles (EVPAs) instead of observational noise. We conclude that it is much more likely that intrinsic rotations are responsible for the observed phenomenology.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/842/87
- Title:
- Radio luminosity function of FSRQs
- Short Name:
- J/ApJ/842/87
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the radio luminosity function (LF) of flat-spectrum radio quasars (FSRQ), using the largest and most complete sample to date. Cross-matching between the FIRST 20cm and GB6 6cm radio surveys, we find 638 flat-spectrum radio sources above 220mJy at 1.4GHz; of these, 327 are classified and verified using optical spectroscopy data, mainly from Sloan Digital Sky Survey Data Release 12. We also considered flat-spectrum radio sources that lack both literature references and optical spectroscopy, and we identified 12 out of the 43 such sources to potentially be FSRQs, using their WISE colors. From the fully identified sample of 242 FSRQs, we derived the radio LF and cosmic evolution of blazars at 1.4GHz, finding good agreement with previous work at 5GHz. The number density of FSRQs increases dramatically to a redshift of z~2 and then declines for higher redshifts. Furthermore, the redshift at which the quasar density peaks is clearly dependent on luminosity, with more luminous sources peaking at higher redshifts. The approximate best-fit LF for a luminosity-dependent evolutionary model is a broken power-law with slopes ~0.7 and ~1.7 below and above the break luminosity, logL_1.4_~43.8erg/s, respectively.
- ID:
- ivo://CDS.VizieR/J/MNRAS/390/289
- Title:
- Radio observations of A3158
- Short Name:
- J/MNRAS/390/289
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 1.4- and 2.5-GHz Australia Telescope Compact Array (ATCA) observations of the galaxy cluster A3158 (z=0.0597) which is located within the central part of the Horologium-Reticulum supercluster (HRS). Spectroscopic data for the central part of the HRS suggest that A3158 is in a dynamically important position within the supercluster and that it is moving toward the double cluster system A3125/A3128 which marks the centre of the HRS. A total of 110 radio galaxies are detected in a 35-arcmin radius about the cluster at 1.4GHz, of which 30 are also detected at 2.5GHz.
- ID:
- ivo://CDS.VizieR/J/AJ/135/2470
- Title:
- Radio observations of the HDFS region. IV.
- Short Name:
- J/AJ/135/2470
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Australia Telescope Hubble Deep Field-South (ATHDF-S) survey of the Hubble Deep Field-South (HDF-S) reaches sensitivities of ~10uJy at 1.4, 2.5, 5.2, and 8.7GHz, making the ATHDF-S one of the deepest surveys ever performed with the Australia Telescope Compact Array (ATCA). Here, we present the optical identifications of the ATHDF-S radio sources using data from the literature. We find that ~66% of the radio sources have optical counterparts to I=23.5mag. Deep Hubble Space Telescope (HST) imaging of the area identifies a further 12% of radio sources. We present new spectroscopic observations for 98 of the radio sources and supplement these spectroscopic redshifts with photometric ones calculated from five-band optical imaging.
- ID:
- ivo://CDS.VizieR/J/ApJS/167/103
- Title:
- Radio/Optical catalog of the SSA 13 field
- Short Name:
- J/ApJS/167/103
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a 1.4GHz catalog of 810 radio sources (560 sources in the complete sample) found in the SSA 13 field (RA=13:12, DE=42:38). The 1.4GHz radio image was obtained from a 91hr VLA integration with an rms noise level of 4.82uJy/beam at the field center. Optical images in the R band (6300{AA}) and z band (9200{AA}) with 3{sigma} detection magnitudes of 26.1 and 24.9, respectively, were obtained from three observing nights on the 8m Subaru Telescope. We find that 88%+/-2% of the radio sources are identified with an optical counterpart.
- ID:
- ivo://CDS.VizieR/J/A+A/520/A62
- Title:
- Radio-optical scrutiny of compact AGN
- Short Name:
- J/A+A/520/A62
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the correlations between the VLBA (Very Long Baseline Array) radio emission at 15GHz, extended emission at 151MHz, and optical nuclear emission at 5100{AA} for a complete sample of 135 compact jets. We use the partial Kendall's tau correlation analysis to check the link between radio properties of parsec-scale jets and optical nuclear luminosities of host active galactic nuclei (AGN).
- ID:
- ivo://CDS.VizieR/J/ApJS/185/124
- Title:
- 58 radio sources near BNGSs
- Short Name:
- J/ApJS/185/124
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a preliminary survey of 58 radio sources within the isoplanatic patches (r<25") of bright (11<R<12) stars suitable for use as natural guide stars with high-order adaptive optics (AO). An optical and near-infrared imaging survey was conducted utilizing tip-tilt corrections in the optical and AO in the near-infrared. Spectral energy distributions were fit to the multi-band data for the purpose of obtaining photometric redshifts using the Hyperz code. Several of these photometric redshifts were confirmed with spectroscopy, a result that gives more confidence to the redshift distribution for the whole sample. Additional long-wavelength data from Spitzer, SCUBA, SHARC2, and VLA supplement the optical and near-infrared data. We find the sample generally follows and extends the magnitude-redshift relation found for more powerful local radio galaxies. The survey has identified several reasonably bright (H=19-20) objects at significant redshifts (z>1) that are now within the capabilities of the current generation of AO-fed integral-field spectrographs. These objects constitute a unique sample that can be used for detailed ground-based AO studies of galactic structure, evolution, and active galactic nucleus formation at high redshift.
- ID:
- ivo://CDS.VizieR/J/MNRAS/391/297
- Title:
- Radio Survey of 7 X-ray Clusters of Galaxies
- Short Name:
- J/MNRAS/391/297
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Australia Telescope Compact Array (ATCA) has been used at 1.38 and 2.38GHz to survey seven southern Abell clusters of galaxies with high X-ray luminosities: A2746, A2837, A3126, A3216, A3230, A3827 and A3836. The clusters have also been surveyed at 0.843GHz with the Molonglo Observatory Synthesis Telescope (MOST). We have listed a complete 1.38-GHz sample of 149 radio sources within the Abell circles centred on their X-ray centroids. We compare their identification fractions, emitted 1.38-GHz and optical powers, radio spectral indices and radial variation in projected source density with those of the radio-selected samples of Slee et al. (1998AuJPh..51..971S). We compare our fractional radio luminosity function with that of the radio-selected samples of Ledlow and Owen (1996AJ....112....9L) and Slee et al. (1998AuJPh..51..971S). Three significant differences are noted between X-ray and radio-selected samples of clusters; (1) the X-ray sample has an excess of flat-spectrum radio sources; (2) the fractional radio luminosity function for the FR I sources in the X-ray selected sample is much steeper, implying that fewer of their cluster galaxies become hosts for the stronger FR I radio galaxies; (3) a complete absence of FR II radio galaxies in the X-ray selected sample. The average excess projected density of radio sources near our cluster centres is approx. 5 times the background source density.
- ID:
- ivo://CDS.VizieR/J/AJ/157/63
- Title:
- Radius relations for low-metallicity M-dwarf stars
- Short Name:
- J/AJ/157/63
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- M subdwarfs are low-metallicity M dwarfs that typically inhabit the halo population of the Galaxy. Metallicity controls the opacity of stellar atmospheres; in metal-poor stars, hydrostatic equilibrium is reached at a smaller radius, leading to smaller radii for a given effective temperature. We compile a sample of 88 stars that span spectral classes K7 to M6 and include stars with metallicity classes from solar-metallicity dwarf stars to the lowest metallicity ultra subdwarfs to test how metallicity changes the stellar radius. We fit models to Palomar Double Spectrograph (DBSP) optical spectra to derive effective temperatures (T_eff_) and we measure bolometric luminosities (L_bol_) by combining broad wavelength-coverage photometry with Gaia parallaxes. Radii are then computed by combining the T_eff_ and L_bol_ using the Stefan-Boltzman law. We find that for a given temperature, ultra subdwarfs can be as much as five times smaller than their solar-metallicity counterparts. We present color-radius and color-surface brightness relations that extend down to [Fe/H] of -2.0 dex, in order to aid the radius determination of M subdwarfs, which will be especially important for the WFIRST exoplanetary microlensing survey.
- ID:
- ivo://CDS.VizieR/J/AJ/162/72
- Title:
- Random forests method to discover high-redshift QSOs
- Short Name:
- J/AJ/162/72
- Date:
- 14 Mar 2022 07:01:17
- Publisher:
- CDS
- Description:
- We present a method of selecting quasars up to redshift ~6 with random forests, a supervised machine-learning method, applied to Pan-STARRS1 and WISE data. We find that, thanks to the increasing set of known quasars, we can assemble a training set that enables supervised machine-learning algorithms to become a competitive alternative to other methods up to this redshift. We present a candidate set for the redshift range 4.8-6.3, which includes the region around z=5.5 where selecting quasars is difficult due to their photometric similarity to red and brown dwarfs. We demonstrate that, under our survey restrictions, we can reach a high completeness (66%{+/-}7% below redshift 5.6/83_-9_^+6^% above redshift 5.6) while maintaining a high selection efficiency (78_-8_^+10^%/94_-8_^+5^% ). Our selection efficiency is estimated via a novel method based on the different distributions of quasars and contaminants on the sky. The final catalog of 515 candidates includes 225 known quasars. We predict the candidate catalog to contain additional 148_-33_^+41^ new quasars below redshift 5.6 and 45_-8_^+5^ above, and we make the catalog publicly available. Spectroscopic follow-up observations of 37 candidates led us to discover 20 new high redshift quasars (18 at 4.6<~z<~5.5, 2z~5.7). These observations are consistent with our predictions on efficiency. We argue that random forests can lead to higher completeness because our candidate set contains a number of objects that would be rejected by common color cuts, including one of the newly discovered redshift 5.7 quasars.
