- ID:
- ivo://CDS.VizieR/J/ApJ/900/125
- Title:
- Radio properties of Swift/BAT AGNs
- Short Name:
- J/ApJ/900/125
- Date:
- 02 Feb 2022 09:04:43
- Publisher:
- CDS
- Description:
- We address the very large diversity of jet production efficiency in active galactic nuclei (AGNs) by using data on low-redshift AGNs selected from the Swift/BAT catalog and having black hole (BH) masses larger than 10^8.5^M_{sun}_. Most of these AGNs accrete at intermediate rates and have bolometric luminosities dominated by mid-IR radiation. Our sample contains 14% radio-loud (RL), 6% radio-intermediate, and 80% radio-quiet (RQ) AGNs. All RL objects are found to have extended radio structures, and most of them have classical FR II morphology. Converting their radio loudness to jet production efficiency, we find that the median of this efficiency is on the order of ({epsilon}_d_/0.1)%, where {epsilon}_d_=L_bol_/(dM/dt)c^2^ is the radiation efficiency of the accretion disk. Without knowing the contribution of jets to the radio emission in RQ AGNs, we are only able to estimate their efficiencies using upper limits. Their median is found to be 0.002({epsilon}_d_/0.1)%. Our results suggest that some threshold conditions must be satisfied to allow the production of strong, relativistic jets in RL AGNs. We discuss several possible scenarios and argue that the production of collimated, relativistic jets must involve the Blandford-Znajek mechanism and can be activated only in those AGNs whose lifetime is longer than the time required to enter the magnetically arrested disk (MAD). Presuming that MAD is required to collimate relativistic jets, we expect that the weak nonrelativistic jets observed in some RQ AGNs are produced by accretion disks rather than by rotating BHs.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/466/921
- Title:
- Radio properties of z < 0.3 quasars
- Short Name:
- J/MNRAS/466/921
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To better constrain the hypotheses proposed to explain why only a few quasars are radio loud (R_L_), we compare the characteristics of 1958 nearby (z<=0.3) SDSS (Sloan Digital Sky Survey) quasars, covered by the FIRST (Faint Images of the Radio Sky at Twenty Centimeters) and NVSS (NRAO VLA Sky Survey) radio surveys. Only 22 per cent are R_L_ with log(L_1.4GHz_)>=22.5W/Hz, the majority being compact (C), weak radio sources (WRS), with log(L_1.4GHz_)<24.5W/Hz. 15 per cent of the RL quasars have extended radio morphologies: 3 per cent have a core and a jet (J), 2 per cent have a core with one lobe (L), and 10 per cent have a core with two lobes (T), the majority being powerful radio sources (PRS), with log(L_1.4GHz_)>=24.5W/Hz. In general, RL quasars have higher bolometric luminosities and ionization powers than radio-quiet (RQ) quasars. The WRS have comparable black hole (BH) masses as the RQ quasars, but higher accretion rates or radiative efficiencies. The PRS have higher BH masses than the WRS, but comparable accretion rates or radiative efficiencies. The WRS also have higher FWHM_{[OIII]} than the PRS, consistent with a coupling of the spectral characteristics of the quasars with their radio morphologies. Inspecting the SDSS images and applying a neighbour search algorithm reveal no difference between the RQ and RL quasars of their host galaxies, environments, and interaction. Our results prompt the conjecture that the phenomenon that sparks the RL phase in quasars is transient, intrinsic to the active galactic nuclei, and stochastic, due to the chaotic nature of the accretion process of matter on to the BHs.
- ID:
- ivo://CDS.VizieR/J/A+A/435/521
- Title:
- Radio Sources in Low-Luminosity AGNs. IV
- Short Name:
- J/A+A/435/521
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the completed results of a high resolution radio imaging survey of all (~200) low-luminosity active galactic nuclei (LLAGNs) and AGNs in the Palomar Spectroscopic Sample of all (~488) bright northern galaxies. The high incidences of pc-scale radio nuclei, with implied brightness temperatures >~10^7K, and sub-parsec jets argue for accreting black holes in >=50% of all LINERs and low-luminosity Seyferts; there is no evidence against all LLAGNs being mini-AGNs. The detected parsec-scale radio nuclei are preferentially found in massive ellipticals and in type 1 nuclei (i.e. nuclei with broad Halpha emission). The radio luminosity function (RLF) of Palomar Sample LLAGNs and AGNs extends three orders of magnitude below, and is continuous with, that of 'classical' AGNs. We find marginal evidence for a low-luminosity turnover in the RLF; nevertheless LLAGNs are responsible for a significant fraction of present day mass accretion.
- ID:
- ivo://CDS.VizieR/J/AN/341/703
- Title:
- Radio spectral indices of active galaxies
- Short Name:
- J/AN/341/703
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, we investigate radio properties of active galaxies taken from the reference Veron-Cetty & Veron (2010, Cat. VII/258) catalog. The galaxies are limited to magnitudes in the range of 12^m^-19^m^. We have cross-correlated the list with radio catalogs and selected those galaxies that have data on six or more radio fluxes at different wavelengths. As a result, we have 198 galaxies that satisfy these conditions. Using SDSS DR15, we have obtained 96 spectroscopic identifications of the 198 objects. After the classification, 85% of the 96 objects have changed their types. Available data on the classification of these objects and our classification showed that 56.7% of them are Seyfert galaxies. For all the objects, we have built radio spectra and estimated radio spectral indices. As a result, we obtain {alpha}>=-0.6089+/-0.056> ({alpha}_Seyfert_=-0.6013+/-0.027, {alpha}_LINER_=-0.5955+/-0.025, {alpha}_HII_=-0.6672+/-0.039, {alpha}_Comp._=-0.7128+/-0.043). We discuss the radio properties of active galaxies based on their radio spectral indices.
- ID:
- ivo://CDS.VizieR/J/AJ/142/108
- Title:
- Radio variability of compact, flat-spectrum AGNs
- Short Name:
- J/AJ/142/108
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The 4.9GHz Micro-Arcsecond Scintillation-Induced Variability (MASIV) Survey detected a drop in interstellar scintillation (ISS) for sources at redshifts z>~2, indicating an apparent increase in angular diameter or a decrease in flux density of the most compact components of these sources relative to their extended emission. This can result from intrinsic source size effects or scatter broadening in the intergalactic medium (IGM) in excess of the expected (1+z)^1/2^ angular diameter scaling of brightness temperature limited sources resulting from cosmological expansion. We report here 4.9GHz and 8.4GHz observations and data analysis for a sample of 140 compact, flat-spectrum sources which may allow us to determine the origin of this angular diameter-redshift relation by exploiting their different wavelength dependences. In addition to using ISS as a cosmological probe, the observations provide additional insight into source morphologies and the characteristics of ISS.
- ID:
- ivo://CDS.VizieR/J/A+A/654/A169
- Title:
- Radio variability to identifying changing jets
- Short Name:
- J/A+A/654/A169
- Date:
- 16 Mar 2022 00:56:46
- Publisher:
- CDS
- Description:
- Supermassive black holes can launch highly relativistic jets with velocities reaching Lorentz factors of as high as {GAMMA}>50. How the jets accelerate to such high velocities and where along the jet they reach terminal velocity are open questions that are tightly linked to their structure as well as their launching and dissipation mechanisms. Changes in the beaming factor along the jets could potentially reveal jet acceleration, deceleration, or bending. We aim to (1) quantify the relativistic effects in multiple radio frequencies and (2) study possible jet velocity-viewing angle variations at parsec scales. We used the state-of-the-art code Magnetron to model light curves from the University of Michigan Radio Observatory and the Metsahovi Radio Observatory's monitoring programs in five frequencies covering about 25 years of observations in the 4.8 to 37GHz range for 61 sources. We supplement our data set with high-frequency radio observations in the 100-340GHz range from ALMA, CARMA, and SMA. For each frequency we estimate the Doppler factor which we use to quantify possible changes in the relativistic effects along the jets. The majority of our sources do not show any statistically significant difference in their Doppler factor across frequencies. This is consistent with constant velocity in a conical jet structure, as expected at parsec scales. However, our analysis reveals 17 sources where relativistic beaming changes as a function of frequency. In the majority of cases, the Doppler factor increases towards lower frequencies. Only 1253-053 shows the opposite behavior. By exploring their jet properties we find that the jet of 0420-014 is likely bent across the 4.8-340GHz range. For 0212+735, the jet is likely parabolic, and still accelerating in the 4.8-37GHz range. We discuss possible interpretations for the trends found in the remaining sources.
- ID:
- ivo://CDS.VizieR/J/A+A/472/805
- Title:
- Radio-X-ray sources in the HDF(N) region.
- Short Name:
- J/A+A/472/805
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This catalogue lists the properties of 62 radio sources in the Hubble Deep Field (North) and Flanking Fields (HDFN) which were also detected by the Chandra X-ray satellite (see Alexander et al., 2003, Cat. <J/AJ/126/539>, file cdfn). This includes 55/92 sources brighter than 40uJy detected by MERLIN+VLA at 1.4GHz (see Muxlow et al., 2005, Cat. <J/MNRAS/358/1159>, Richards, 2000, Cat. <J/ApJ/533/611>); some were also detected by the VLA at 8.4GHz (Richards et al., 1998AJ....116.1039R) including 7 selected at this frequency. The cross-matching, derivation of properties and analysis are described fully in the paper. The radio data have a positional accuracy of 15 mas with respect to the ICRS (Muxlow et al., 2005, Cat. <J/MNRAS/358/1159>) but data using the GOODS HST ACS (Giavalisco et al., 2004, Cat. <II/261>) positions requires a shift of -342mas in Declination for alignment with the ICRS. We use measurements taken from the radio observations and from the literature to compile the flux densities, sizes and spectral/photon indices of the cross-matched radio+X-ray sources and their redshifts (where available), enabling us to derive the rest-frame luminosities. The 1.4-GHz detections are all resolved at 0.2-2arcsec resolution. The radio emission was classified using the source morphologies and radio spectral indices; optical and IR information was used as supporting evidence only. On this basis, starbursts outnumber radio AGN 3:1. The high-redshift starbursts have typical sizes of 5-10kpc and star formation rates of around 1000 Msun/yr, an order of magnitude more extended and intense than in the local universe. The X-ray sources are unresolved but their luminosity and spectral indices allows X-ray AGN and obscured (Type II) AGN to be identified (2004A&A...424..545P). In this way, we can distinguish between the origins of radio and X-ray emission from the same object. There is no obvious correlation between radio and X-ray luminosities nor spectral indices at z>1.3. About 70% of both the radio-selected AGN and the starburst samples were detected by Chandra. The X-ray luminosity indicates the presence of an AGN in at least half of the 45 cross-matched radio starbursts. Eleven of these are type-II AGN, of which 7 are at z>1.5. This distribution overlaps closely with the X-ray detected radio sources which were also detected by SCUBA. Almost all extended radio starbursts at z>1.3 host X-ray selected obscured AGN. The radio emission from most of these ultra-luminous objects is dominated by star formation although the highest redshift (z=4.424) source has a substantial AGN contribution. Star-formation appears to contribute less than 1/3 of their X-ray luminosity. Our results support the inferences from SCUBA and IR data, that at z>1.5, star formation is observably more extended and more copious, it is closely linked to AGN activity and it is triggered differently, compared with star formation at lower redshifts.
- 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.
689. RASS AGN sample
- ID:
- ivo://CDS.VizieR/J/A+AS/139/575
- Title:
- RASS AGN sample
- Short Name:
- J/A+AS/139/575
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first results of a program to identify the unknown bright active galactic nuclei (AGN) in the ROSAT All Sky Survey Bright Source Catalog (RASS-BSC). We have used logC+0.4R as an alternative expression for log(f_X_/f_opt_), where C is X-ray count rate and R stands for R magnitude. Then a high X-ray-to-optical flux ratio criterion has been used to select an AGN sample with 165 unidentified X-ray sources for optical spectroscopy. Those 165 X-ray sources have been identified in the following classes: 115 emission line AGN (QSOs and Seyferts), 2 BL Lac objects and 4 BL Lac candidates, 22 clusters of galaxies, 12 Galactic stars and 10 objects remain unidentified. This represent a success rate of about 73% for detecting AGN using our selection criteria. Plausibility is based upon the optical classification and X-ray characteristics of the sources.
690. RASS AGN sample. II.
- ID:
- ivo://CDS.VizieR/J/ApJ/590/73
- Title:
- RASS AGN sample. II.
- Short Name:
- J/ApJ/590/73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This work studies the optical emission line properties of a sample of 155 low-redshift bright X-ray-selected ROSAT Seyfert 1-type active galactic nuclei for which adequate signal-to-noise ratio spectroscopic observations are available. We measured emission-line properties by performing multicomponent fits to the emission-line profiles, covering the effect of blended iron emission. We also obtained continuum parameters, including 250eV X-ray luminosities derived from the ROSAT database. In addition, the measured properties are gathered for a correlation analysis, which confirms the well-known relations between the strengths of Fe II, [O III] emission and the X-ray slope. We also detect striking correlations between H{beta} redshift (or blueshift) and flux ratios of Fe II to H{beta} broad component and [O III] to H{beta} narrow component. These trends are most likely driven by the Eddington ratio.