- ID:
- ivo://CDS.VizieR/J/MNRAS/453/2682
- Title:
- Observation & modelling for radio-loud AGN
- Short Name:
- J/MNRAS/453/2682
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The interactions between radio-loud AGN and their environments play an important role in galaxy and cluster evolution. Recent work has demonstrated fundamental differences between high- and low-excitation radio galaxies (HERGs and LERGs), and shown that they may have different relationships with their environments. In the Chandra Large Project ERA (Environments of Radio-loud AGN), we made the first systematic X-ray environmental study of the cluster environments of radio galaxies at a single epoch (z~0.5), and found tentative evidence for a correlation between radio luminosity and cluster X-ray luminosity. We also found that this relationship appeared to be driven by the LERG subpopulation. We have now repeated the analysis with a low-redshift sample (z~0.1), and found strong correlations between radio luminosity and environment richness and between radio luminosity and central density for the LERGs but not for the HERGs. These results are consistent with models in which the HERGs are fuelled from accretion discs maintained from local reservoirs of gas, while LERGs are fuelled more directly by gas ingested from the intracluster medium. Comparing the samples, we found that although the maximum environment richness of the HERG environments is similar in both samples, there are poorer HERG environments in the z~0.1 sample than in the z~0.5 sample. We have therefore tentative evidence of evolution of the HERG environments. We found no differences between the LERG subsamples for the two epochs, as would be expected if radio and cluster luminosities are related.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJS/194/29
- Title:
- Observations of blazars at 15GHz
- Short Name:
- J/ApJS/194/29
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space Telescope provides an unprecedented opportunity to study gamma-ray blazars. To capitalize on this opportunity, beginning in late 2007, about a year before the start of LAT science operations, we began a large-scale, fast-cadence 15GHz radio monitoring program with the 40m telescope at the Owens Valley Radio Observatory (OVRO). This program began with the 1158 northern ({delta}>-20{deg}) sources from the Candidate Gamma-ray Blazar Survey and now encompasses over 1500 sources, each observed twice per week with about 4mJy (minimum) and 3% (typical) uncertainty. Here, we describe this monitoring program and our methods, and present radio light curves from the first two years (2008 and 2009). As a first application, we combine these data with a novel measure of light curve variability amplitude, the intrinsic modulation index, through a likelihood analysis to examine the variability properties of subpopulations of our sample.
- ID:
- ivo://CDS.VizieR/J/A+A/535/A38
- Title:
- Observations of NOAO Bootes field at 153MHz
- Short Name:
- J/A+A/535/A38
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present deep, high-resolution radio interferometric observations at 153MHz to complement the extensively studied NOAO Bootes field. We provide a description of the observations, data reduction and source catalog construction. From our single pointing GMRT observation of ~12 hours we obtain a high-resolution (26"x22") image of ~11.3 square degrees, fully covering the Bootes field region and beyond.
564. OCSVM anomalies
- ID:
- ivo://CDS.VizieR/J/A+A/606/A39
- Title:
- OCSVM anomalies
- Short Name:
- J/A+A/606/A39
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Wide-angle photometric surveys of previously uncharted sky areas or wavelength regimes will always bring in unexpected sources - novelties or even anomalies - whose existence and properties cannot be easily predicted from earlier observations. Such objects can be efficiently located with novelty detection algorithms. Here we present an application of such a method, called one-class support vector machines (OCSVM), to search for anomalous patterns among sources preselected from the mid-infrared AllWISE catalogue covering the whole sky. To create a model of expected data we train the algorithm on a set of objects with spectroscopic identifications from the SDSS DR13 database, present also in AllWISE. The OCSVM method detects as anomalous those sources whose patterns - WISE photometric measurements in this case - are inconsistent with the model. Among the detected anomalies we find artefacts, such as objects with spurious photometry due to blending, but more importantly also real sources of genuine astrophysical interest. Among the latter, OCSVM has identified a sample of heavily reddened AGN/quasar candidates distributed uniformly over the sky and in a large part absent from other WISE-based AGN catalogues. It also allowed us to find a specific group of sources of mixed types, mostly stars and compact galaxies. By combining the semi-supervised OCSVM algorithm with standard classification methods it will be possible to improve the latter by accounting for sources which are not present in the training sample, but are otherwise well-represented in the target set. Anomaly detection adds flexibility to automated source separation procedures and helps verify the reliability and representativeness of the training samples. It should be thus considered as an essential step in supervised classification schemes to ensure completeness and purity of produced catalogues.
- ID:
- ivo://CDS.VizieR/J/ApJ/789/112
- Title:
- Offset AGN Candidates
- Short Name:
- J/ApJ/789/112
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Offset active galactic nuclei (AGNs) are AGNs that are in ongoing galaxy mergers, which produce kinematic offsets in the AGNs relative to their host galaxies. Offset AGNs are also close relatives of dual AGNs. We conduct a systematic search for offset AGNs in the Sloan Digital Sky Survey by selecting AGN emission lines that exhibit statistically significant line-of-sight velocity offsets relative to systemic. From a parent sample of 18,314 Type 2 AGNs at z < 0.21, we identify 351 offset AGN candidates with velocity offsets of 50 km/s <|{Delta}v| < 410 km/s. When we account for projection effects in the observed velocities, we estimate that 4%-8% of AGNs are offset AGNs. We designed our selection criteria to bypass velocity offsets produced by rotating gas disks, AGN outflows, and gravitational recoil of supermassive black holes, but follow-up observations are still required to confirm our candidates as offset AGNs. We find that the fraction of AGNs that are offset candidates increases with AGN bolometric luminosity, from 0.7% to 6% over the luminosity range 43 < log (L_bol_) [erg/s] <46. If these candidates are shown to be bona fide offset AGNs, then this would be direct observational evidence that galaxy mergers preferentially trigger high-luminosity AGNs. Finally, we find that the fraction of AGNs that are offset AGN candidates increases from 1.9% at z = 0.1 to 32% at z = 0.7, in step with the growth in the galaxy merger fraction over the same redshift range.
- ID:
- ivo://CDS.VizieR/J/MNRAS/465/L114
- Title:
- OGLE16aaa UVOT light curves
- Short Name:
- J/MNRAS/465/L114
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the discovery and first three months of follow-up observations of a currently on-going unusual transient detected by the Optical Gravitational Lensing Experiment (OGLE-IV) survey, located in the centre of a galaxy at redshift z=0.1655. The long rise to absolute magnitude of -20.5mag, slow decline, very broad He and H spectral features make OGLE16aaa similar to other optical/UV tidal disruption events (TDEs). Weak narrow emission lines in the spectrum and archival photometric observations suggest the host galaxy is a weak-line active galactic nucleus, which has been accreting at higher rate in the past. OGLE16aaa, along with SDSS J0748, seems to form a sub-class of TDEs by weakly or recently active supermassive black holes (SMBHs). This class might bridge the TDEs by quiescent SMBHs and flares observed as "changing-look quasars", if we interpret the latter as TDEs. If this picture is true, the previously applied requirement for identifying a flare as a TDE that it had to come from an inactive nucleus, could be leading to observational bias in TDE selection, thus affecting TDE-rate estimations.
- ID:
- ivo://CDS.VizieR/J/AJ/133/496
- Title:
- OH megamasers infrared photometry
- Short Name:
- J/AJ/133/496
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- OH megamasers are the most luminous masers in the universe. The total of 109 OH megamaser (OHM) galaxies known so far have been collected, and cross-identifications of those OHM galaxies with Two Micron All Sky Survey (2MASS) sources are made in this paper. Using 2MASS (Cat. II/246) and IRAS (Cat. II/125, II/156) data, the infrared properties of OHM-detected and non-detected sources are compared.
- ID:
- ivo://CDS.VizieR/J/ApJ/549/155
- Title:
- [OIII] emission in a sample of AGNs
- Short Name:
- J/ApJ/549/155
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The emission-line flux ratio of [OIII]4363/[OIII]5007 (R_OIII_) is a useful diagnostic for the ionization mechanism and physical properties of emission-line regions in active galactic nuclei (AGNs). However, it is known that simple photoionization models underpredict the [OIII]4363 intensity, being inconsistent with observations. In this paper we report on several pieces of evidence that a large fraction of the [OIII]4363 emission arises from the dense gas obscured by putative tori: (1) the visibility of high-R_OIII_ regions is correlated to that of broad-line regions, (2) higher R_OIII_ objects show hotter mid-infrared colors, (3) higher R_OIII_ objects show stronger highly ionized emission lines such as [FeVII] 6087 and [FeX]6374, and (4) higher R_OIII_ objects have broader line width of [OIII]4363 normalized by that of [OIII]5007.
- ID:
- ivo://CDS.VizieR/J/ApJ/883/94
- Title:
- Optical and UV follow-up of 1ES 1927+654
- Short Name:
- J/ApJ/883/94
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the sudden optical and ultraviolet (UV) brightening of 1ES1927+654, which until now was known as a narrow-line active galactic nucleus (AGN). 1ES 1927+654 was part of the small and peculiar class of "true Type-2" AGNs that lack broad emission lines and line-of-sight obscuration. Our high-cadence spectroscopic monitoring captures the appearance of a blue, featureless continuum, followed several weeks later by the appearance of broad Balmer emission lines. This timescale is generally consistent with the expected light travel time between the central engine and the broadline emission region in (persistent) broadline AGN. Hubble Space Telescope spectroscopy reveals no evidence for broad UV emission lines (e.g., CIV{lambda}1549, CIII]{lambda}1909, MgII{lambda}2798), probably owing to dust in the broadline emission region. To the best of our knowledge, this is the first case where the lag between the change in continuum and in broadline emission of a "changing look" AGN has been temporally resolved. The nature and timescales of the photometric and spectral evolution disfavor both a change in line-of-sight obscuration and a change of the overall rate of gas inflow as driving the drastic spectral transformations seen in this AGN. Although the peak luminosity and timescales are consistent with those of tidal disruption events seen in inactive galaxies, the spectral properties are not. The X-ray emission displays a markedly different behavior, with frequent flares on timescales of hours to days, and will be presented in a companion publication.
- ID:
- ivo://CDS.VizieR/J/A+A/310/384
- Title:
- Optical brightness of 3 ROSAT Seyfert galaxies
- Short Name:
- J/A+A/310/384
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The printed version of this paper describes the X-ray and optical properties of four new active galaxies discovered in the ROSAT All-Sky Survey. While one object (RX J1257.5+2412) is identified as a BL Lac object, the other three (RX J1239.3+2431, RX J1225.7+2055, and RX J1250.2+1923) are narrow line Seyfert 1 galaxies. Three of these four objects are bright enough to be studied on archival photographic plates of Sonneberg Observatory. The present list contains the individual brightness measurements of these objects all of which turned out to be variable on timescales of weeks to years. Some lightcurves (long-term as well as short-term) are given in the printed version.
