- ID:
- ivo://CDS.VizieR/J/A+A/574/A4
- Title:
- Radio image of Luminous Infrared Galaxies
- Short Name:
- J/A+A/574/A4
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Luminous Infrared Galaxies (LIRGs) are systems enshrouded in dust, which absorbs most of their optical/UV emission and radiates it again in the mid- and far-infrared. Radio observations are largely unaffected by dust obscuration, enabling us to study the central regions of LIRGs in an unbiased manner. The main goal of this project is to examine how the radio properties of local LIRGs relate to their infrared spectral characteristics. Here we present an analysis of the radio continuum properties of a subset of the Great Observatories All-sky LIRG Survey (GOALS), which consists of 202 nearby systems (z<0.088). Our radio sample consists of 35 systems, containing 46 individual galaxies, that were observed at both 1.49 and 8.44GHz with the VLA with a resolution of about 1-arcsec (FWHM). The aim of the project is to use the radio imagery to probe the central kpc of these LIRGs in search of Active Galactic Nuclei (AGN). We used the archival data at 1.49 and 8.44GHz to create radio-spectral-index maps using the standard relation between flux density S{nu} and frequency {nu}, S{nu}~{nu}^-{alpha}^, where {alpha} is the radio spectral index. By studying the spatial variations in {alpha}, we classified the objects as radio-AGN, radio-SB, and AGN/SB (a mixture). We identified the presence of an active nucleus using the radio morphology, deviations from the radio/infrared correlation, and spatially resolved spectral index maps, and then correlated this to the usual mid-infrared ([NeV]/[NeII] and [OIV]/[NeII] line ratios and equivalent width of the 6.2um PAH feature) and optical (BPT diagram) AGN diagnostics. We find that 21 out of the 46 objects in our sample (~45%) are radio-AGN, 9 out of the 46 (~20%) are classified as starbursts (SB) based on the radio analysis, and 16 (~35%) are AGN/SB. After comparing to other AGN diagnostics we find 3 objects out of the 46 (~7%) that are identified as AGN based on the radio analysis, but are not classified as such based on the mid-infrared and optical AGN diagnostics presented in this study.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/555/A110
- Title:
- Radio images of CIZA J2242.8+5301
- Short Name:
- J/A+A/555/A110
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Giant cluster radio relics are thought to form at shock fronts in the course of collisions between galaxy clusters. Via processes that are still poorly understood, these shocks accelerate or re-accelerate cosmic-ray electrons and might amplify magnetic fields. The best object to study this phenomenon is the galaxy cluster CIZA J2242.8+5301 as it shows the most undisturbed relic. By means of Giant Metrewave Radio Telescope (GMRT) and Westerbork Synthesis Radio Telescope (WSRT) data at seven frequencies spanning from 153MHz to 2272MHz, we study the synchrotron emission in this cluster. We aim at distinguishing between theoretical injection and acceleration models proposed for the formation of radio relics. We also study the head-tail radio sources to reveal the interplay between the merger and the cluster galaxies. We produced spectral index, curvature maps, and radio colour-colour plots and compared our data with predictions from models. We present one of the deepest 153MHz maps of a cluster ever produced, reaching a noise level of 1.5mJy/beam. We derive integrated spectra for four relics in the cluster, discovering extremely steep spectrum diffuse emission concentrated in multiple patches. We find a possible radio phoenix embedded in the relic to the south of the cluster. The spectral index of the northern relic retains signs of steepening from the front towards the back of the shock also at the radio frequencies below 600MHz. The spectral curvature in the same relic also increases in the downstream area. The data is consistent with the Komissarov-Gubanov injection models, meaning that the emission we observe is produced by a single burst of spectrally-aged accelerated radio electrons.
1353. Radio images of NGC 4631
- ID:
- ivo://CDS.VizieR/J/A+A/632/A11
- Title:
- Radio images of NGC 4631
- Short Name:
- J/A+A/632/A11
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NGC 4631 is an interacting galaxy which exhibits one of the largest gaseous halos observed among edge-on galaxies. We aim to examine the synchrotron and polarization properties of its disk and halo emission with new radio continuum data. Radio continuum observations of NGC 4631 were performed with the Karl G. Jansky Very Large Array at C-band (5.99GHz) in the C & D array configurations, and at L-band (1.57GHz) in the B, C, & D array configurations. The Rotation Measure Synthesis algorithm was utilized to derive the polarization properties. We detected linearly polarized emission at C-band and L-band. The magnetic field in the halo is characterized by strong vertical components above and below the central region of the galaxy. The magnetic field in the disk is only clearly seen in the eastern side of NGC 4631, where it is parallel to the plane of the major axis of the galaxy. We detected for the first time a large-scale, smooth Faraday depth pattern in a halo of an external spiral galaxy, which implies the existence of a regular (coherent) magnetic field. A quasi-periodic pattern in Faraday depth with field reversals was found in the northern halo of the galaxy. The field reversals in the northern halo of NGC 4631, together with the observed polarization angles, indicate giant magnetic ropes (GMRs) with alternating directions. To our knowledge, this is the first time such reversals are observed in an external galaxy.
- ID:
- ivo://CDS.VizieR/J/ApJ/701/1922
- Title:
- Radio interferometric planet search. I.
- Short Name:
- J/ApJ/701/1922
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Radio astrometry of nearby, low-mass stars has the potential to be a powerful tool for the discovery and characterization of planetary companions. We present a Very Large Array survey of 172 active M dwarfs at distances of less than 10pc. Twenty-nine stars were detected with flux densities greater than 100uJy. We observed seven of these stars with the Very Long Baseline Array at milliarcsecond resolution in three separate epochs. With a detection threshold of 500uJy in images of sensitivity 1{sigma}~100uJy, we detected three stars three times (GJ 65B, GJ 896A, GJ 4247), one star twice (GJ 285), and one star once (GJ 803). Two stars were undetected (GJ 412B and GJ 1224). For the four stars detected in multiple epochs, residuals from the optically determined apparent motions have an root-mean-square deviation of ~0.2 milliarcseconds, consistent with statistical noise limits. Combined with previous optical astrometry, these residuals provide acceleration upper limits that allow us to exclude planetary companions more massive than 3-6M_Jup_ at a distance of ~1AU with a 99% confidence level.
- ID:
- ivo://CDS.VizieR/J/A+A/575/A55
- Title:
- Radio jet emission from GeV-emitting NLSy1
- Short Name:
- J/A+A/575/A55
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- With the current study we aim at gaining understanding on the properties of radio emission and the assumed jet from four radio loud and {gamma}-ray loud Narrow Line Seyfert 1 galaxies i.e. Seyfert 1 galaxies with emission lines at the low-end of the FWHM distribution. The ultimate goal is twofold; first, the investigation whether a relativistic jet is operating at the source giving out the radio output observed and second, the quantification of the jet characteristics in order to understand possible similarities and differences with the jets found in typical blazars. The current study relies on the most systematic monitoring of radio loud and {gamma}-ray detected Narrow Line Seyfert 1 galaxies in the cm and mm radio bands conducted with the Effelsberg 100-m and IRAM 30-m telescopes. It covers the longest time baselines and the most radio frequencies, to date. This dataset of multi- wavelength, long-term radio light curves is analysed from a number of perspectives. A novel algorithm is introduced in order to extract sensible variability parameters (mainly amplitudes and timescales) which are then used for the computation of variability brightness temperatures and the corresponding Doppler factors. The jet powers are computed from the light curves to estimate the energy output and compare it with typical blazars. The dynamics of radio Spectra Energy Distributions are examined for understanding the mechanism causing the variability. The length of the available light curves for 3 of the 4 sources in the sample allowed a firm understanding of the general behaviour of the sources. They all display intensive variability which seems to be happening at a pace rather faster than what is generally seen in blazars. The flaring events become progressively more prominent as the frequency increases and show intensive spectral evolution indicative of shock evolution. The variability brightness temperatures and the associated Doppler factors are rather moderate implying a mildly relativistic jet. The computed jet powers show very energetic flows. The radio polarisation in one case, clearly implies the presence of a quiescent jet underlying recursive flaring activity. Finally, in one case, the sudden disappearance of a {gamma}-ray flare below some critical frequency in our band, urges for further investigation of the possible mechanism causing the evolution of broadband events. Despite the generally lower flux densities the sources appear to show all typical characteristics seen in blazars powered by relativistic jets. Intensive variability, spectral evolution across the different bands following evolutionary paths explained by traveling shocks, Doppler factors indicating mildly relativistic speeds.
- ID:
- ivo://CDS.VizieR/J/MNRAS/461/2346
- Title:
- Radio-loud and radio-quiet quasars sample
- Short Name:
- J/MNRAS/461/2346
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We compare covering factors of circumnuclear dusty obscurers in radio-loud and radio-quiet quasars. The radio-loud quasars are represented by a sample of FR II quasars obtained by cross-matching a catalog of the FR II radio sources selected by van Velzen et al. with the SDSS DR7 catalog of quasars. Covering factors of FR II quasars are compared with covering factors of the radio-quiet quasars matched with them in redshift, black hole mass, and Eddington-ratio. We found that covering factors, proxied by the infrared-to-bolometric luminosity ratio, are on average slightly smaller in FR II quasars than in radio-quiet quasars, however, this difference is statistically significant only for the highest Eddington ratios. For both samples, no statistically significant dependence of a median covering factor on Eddington ratio, black hole mass, nor redshift can be claimed.
- ID:
- ivo://CDS.VizieR/J/ApJ/658/815
- Title:
- Radio loudness of active galactic nuclei
- Short Name:
- J/ApJ/658/815
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate how the total radio luminosity of AGN-powered radio sources depends on their accretion luminosity and the central black hole mass. Our studies cover about 7 orders of magnitude in accretion luminosity (expressed in Eddington units, i.e., as Eddington ratios) and the full range of AGN black hole masses.
1358. Radio-loud QSOs at z~4
- ID:
- ivo://CDS.VizieR/J/MNRAS/348/857
- Title:
- Radio-loud QSOs at z~4
- Short Name:
- J/MNRAS/348/857
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We obtained spectra of 60 red, star-like objects (m_E_<18.8) identified with FIRST radio sources, S_1.4GHz_>1mJy. Eight are quasi-stellar objects (QSOs) with redshift z>3.6. Combined with our earlier pilot search, our sample of 121 candidates yields a total of 18 z>3.6 QSOs (10 of these with z>4.0). 8 per cent of candidates with S_1.4GHz_<10mJy and 37 per cent of candidates with S_1.4GHz_>10mJy are QSOs with z>3.6. The surface density of m_E_<18.8, S_1.4GHz_>1mJy, z>4 QSOs is 0.003deg^-2^. This is currently the only well-defined sample of radio-loud QSOs at z~4 selected independently of radio spectral index. The QSOs are highly luminous in the optical (eight have M_B_<28, q_0_=0.5, H_0_=50km/s/Mpc). The SEDs are as varied as those seen in optical searches for high-redshift QSOs, but the fraction of objects with weak (strongly self-absorbed) Ly emission is marginally higher (3 out of 18) than for high-redshift QSOs from SDSS (5 out of 96).
- ID:
- ivo://CDS.VizieR/J/MNRAS/449/2818
- Title:
- 87 radio loud quasars (RLS) with 3.6<=z<=4.4
- Short Name:
- J/MNRAS/449/2818
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We obtain a sample of 87 radio-loud quasi-stellar objects (QSOs) in the redshift range 3.6<=z<=4.4 by cross-correlating sources in the Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) radio survey (S_1.4GHz_>1mJy) with star-like objects having r<20.2 in Sloan Digital Sky Survey (SDSS) Data Release 7. Of these 87 QSOs, 80 are spectroscopically classified in previous work (mainly SDSS), and form the training set for a search for additional such sources. We apply our selection to 2916 FIRST-DR7 pairs and find 15 likely candidates. Seven of these are confirmed as high-redshift quasars, bringing the total to 87. The candidates were selected using a neural-network, which yields 97 percent completeness (fraction of actual high-z QSOs selected as such) and an efficiency (fraction of candidates which are high-z QSOs) in the range of 47-60 percent. We use this sample to estimate the binned optical luminosity function (LF) of radio-loud QSOs at z~4, and also the LF of the total QSO population and its comoving density. Our results suggest that the radio-loud fraction at high z is similar to that at low z and that other authors may be underestimating the fraction at high z. Finally, we determine the slope of the optical LF and obtain results consistent with previous studies of radio-loud QSOs and of the whole population of QSOs. The evolution of the LF with redshift was for many years interpreted as a flattening of the bright-end slope, but has recently been re-interpreted as strong evolution of the break luminosity for high-z QSOs, and our results, for the radio-loud population, are consistent with this.
- ID:
- ivo://CDS.VizieR/J/A+AS/134/221
- Title:
- Radio-loud ROSAT sources near NEP
- Short Name:
- J/A+AS/134/221
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A deep and large-area survey of the North Ecliptic Pole region was made with the ROSAT All-Sky Survey and the VLA to elucidate the population of radio-loud extragalactic objects. A region of 29.3 square degrees was surveyed with sensitivities around 5x10^-14^erg/s/cm^2^ in the soft X-ray band and 1mJy at 1.5GHz. Optical counterparts were sought on digitized Schmidt plates from POSS-I and II. Seventy-four reliable RASS-VLA sources were found. The sample is a heterogeneous mixture of Seyfert galaxies, quasars, BL Lac objects, galaxy clusters and groups containing a radio galaxy. Optical magnitudes range from B=~14 to B>22. Three results are noteworthy: (1) the bimodality in the ratio of radio to optical emission seen in optically- and X-ray-selected AGN samples is also evident in the ROSAT-VLA objects; (2) X-ray and radio selection is an effective method for locating poor galaxy clusters and groups; and (3) a considerable population of optically faint but X-ray/radio-bright objects is present. This last group may be either distant clusters with radio galaxies or "red quasars".