- ID:
- ivo://CDS.VizieR/J/AJ/131/2426
- Title:
- Optical and radio study of Abell 2111
- Short Name:
- J/AJ/131/2426
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an in-depth analysis of the Butcher-Oemler cluster A2111, including new optical spectroscopy plus a deep Very Large Array (VLA) radio continuum observation. These are combined with optical imaging from the Sloan Digital Sky Survey (SDSS) to assess the activity and properties of member galaxies. Prior X-ray studies have suggested A2111 to be a head-on cluster merger, a dynamical state that might be connected to the high level of activity inferred from its blue fraction. We are able to directly assess this claim, using our spectroscopic data to identify 95 cluster members among 196 total galaxy spectra. We are able to detect 175 optical sources from the SDSS in our VLA radio data, of which 35 have redshift information.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/596/768
- Title:
- Optical depths in 19 QSOs
- Short Name:
- J/ApJ/596/768
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We measure the distribution of carbon in the intergalactic medium as a function of redshift z and overdensity {delta}. Using a hydrodynamical simulation to link the H I absorption to the density and temperature of the absorbing gas, and a model for the UV background radiation, we convert ratios of C IV to H I pixel optical depths into carbon abundances. For the median metallicity this technique was described and tested in Paper I (Aguirre et al., 2002ApJ...576....1A) of this series. Here we generalize it to reconstruct the full probability distribution of the carbon abundance and apply it to 19 high-quality quasar absorption spectra.
- ID:
- ivo://CDS.VizieR/J/ApJ/880/32
- Title:
- Optical/{gamma}-ray flares for Fermi-LAT blazars
- Short Name:
- J/ApJ/880/32
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Even with several thousand Fermi-Large Area Telescope (LAT) blazar detections, the {gamma}-ray emission mechanism is poorly understood. We explore correlated optical/{gamma}-ray flux variations for 178 Fermi-LAT blazars regularly monitored by the Katzman Automatic Imaging Telescope, the Small and Moderate Aperture Research Telescope System, and the Steward Observatory. Out of the 178 sources, 121 show a measurable (>1{sigma}) discrete correlation function peak. Using the derived time lags and Bayesian block light-curve decompositions, we measure the fraction of common and orphan flares between the two bands. After accounting for sampling and sensitivity limitations we quantify for the first time the true orphan flare rates of optical and {gamma}-ray flares: 54.5% of optical and 20% of {gamma}-ray flares are orphan events. Both the intraband temporal relation and the small orphan {gamma}-ray flare fraction point toward leptonic processes as the likely mechanisms for the high-energy emission. Motivated to discriminate between synchrotron self-Compton (SSC) and external-Compton dominance in individual sources, we use the flux-flux variations to determine the slope m of the log fopt-log f{gamma} dependence. The slope distribution suggests a bimodal population with high and intermediate synchrotron peak objects showing larger m than low synchrotron peak objects. We find that m is naturally decreased through pollution from the orphan (typically optical) flares and develop a method to statistically recover, given the sources' measured orphan flare rate, the intrinsic m. While source classes show composite behavior, the majority of BL Lac objects favor m=2, indicating an SSC origin for the {gamma}-rays. No preference for either m is found in flat spectrum radio quasars.
- ID:
- ivo://CDS.VizieR/J/A+A/586/A139
- Title:
- Optical ident. and redshifts of Planck SZ sources
- Short Name:
- J/A+A/586/A139
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of approximately three years of observations of Planck Sunyaev-Zeldovich (SZ) sources with telescopes at the Canary Islands observatories as part of the general optical follow-up programme undertaken by the Planck Collaboration. In total, 78 SZ sources are discussed. Deep-imaging observations were obtained for most of these sources; spectroscopic observations in either in long-slit or multi-object modes were obtained for many. We effectively used 37.5 clear nights. We found optical counterparts for 73 of the 78 candidates. This sample includes 53 spectroscopic redshift determinations, 20 of them obtained with a multi-object spectroscopic mode. The sample contains new redshifts for 27 Planck clusters that were not included in the first Planck SZ source catalogue (PSZ1).
- ID:
- ivo://CDS.VizieR/J/AJ/130/1345
- Title:
- Optical-infrared colors of CORALS QSOs
- Short Name:
- J/AJ/130/1345
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The presence of dust in quasar absorbers, such as damped Ly{alpha} (DLA) systems, may cause the background QSO to appear reddened. We investigate the extent of this potential reddening by comparing the optical-to-infrared colors of QSOs with and without intervening absorbers. Our QSO sample is based on the Complete Optical and Radio Absorption Line System (CORALS) survey of Ellison and coworkers. The CORALS data set consists of 66 radio-selected QSOs at z_em_>=2.2 with complete optical identifications. We have obtained near-simultaneous B- and K-band magnitudes for a subset of the CORALS sample and supplemented our observations with further measurements published in the literature. In total, we have B-K colors for 42 of the 66 QSOs, of which 14 have intervening DLA systems. To account for redshift-related color changes, the B-K colors are normalized using the Sloan Digital Sky Survey QSO composite.
- ID:
- ivo://CDS.VizieR/J/A+A/414/487
- Title:
- Optically bright AGN in ROSAT-FSC
- Short Name:
- J/A+A/414/487
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To build a large, optically bright, X-ray selected AGN sample we have correlated the ROSAT-FSC (<IX/29>) catalogue of X-ray sources with the USNO (<I/252>) catalogue limited to objects brighter than O=16.5 and then with the APS (<VII/214>) database. Each of the 3212 coincidences was classified using the slitless Hamburg spectra. 493 objects were found to be extended and 2719 starlike. Using both the extended objects and the galaxies known from published catalogues we built up a sample of 185 galaxies with O(APS)<17.0mag, which are high-probability counterparts of RASS-FSC X-ray sources. 130 galaxies have a redshift from the literature and for another 34 we obtained new spectra. The fraction of Seyfert galaxies in this sample is 20%. To select a corresponding sample of 144 high-probability counterparts among the starlike sources we searched for very blue objects in an APS-based color-magnitude diagram. Forty-one were already known AGN and for another 91 objects we obtained new spectra, yielding 42 new AGN, increasing their number in the sample to 83. This confirms that surveys of bright QSOs are still significantly incomplete. On the other hand we find that, at a flux limit of 0.02ct/s and at this magnitude, only 40% of all QSOs are detected by ROSAT.
- ID:
- ivo://CDS.VizieR/J/AJ/139/390
- Title:
- Optically selected BL Lac objects from SDSS-DR7
- Short Name:
- J/AJ/139/390
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a sample of 723 optically selected BL Lac candidates from the Sloan Digital Sky Survey Data Release 7 (SDSS DR7) spectroscopic database encompassing 8250deg^2^ of sky; our sample constitutes one of the largest uniform BL Lac samples yet derived. Each BL Lac candidate has a high-quality SDSS spectrum from which we determine spectroscopic redshifts for ~60% of the objects. Redshift lower limits are estimated for the remaining objects utilizing the lack of host galaxy flux contamination in their optical spectra; we find that objects lacking spectroscopic redshifts are likely at systematically higher redshifts.
- ID:
- ivo://CDS.VizieR/J/ApJ/651/61
- Title:
- Optically thick absorbers near luminous quasars
- Short Name:
- J/ApJ/651/61
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- With close pairs of quasars at different redshifts, a background quasar sight line can be used to study a foreground quasar's environment in absorption. We search 149 moderate-resolution background quasar spectra from Gemini, Keck, the MMT, and the SDSS to survey Lyman limit systems (LLSs) and damped Ly{alpha} systems (DLAs) in the vicinity of 1.8<z<4.0 luminous foreground quasars. A sample of 27 new quasar-absorber pairs is uncovered with column densities 10^17.2^cm^-2^<NH<10^20.9^cm^-2^ and transverse (proper) distances of 22h^-1^kpc<R<1.7h^-1^Mpc from the foreground quasars.
- ID:
- ivo://CDS.VizieR/J/A+A/627/A33
- Title:
- Optically variable AGN in COSMOS field
- Short Name:
- J/A+A/627/A33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The analysis of the variability of active galactic nuclei (AGNs) at different wavelengths and the study of possible correlations among different spectral windows are nowadays a major field of inquiry. Optical variability has been largely used to identify AGNs in multivisit surveys. The strength of a selection based on optical variability lies in the chance to analyze data from surveys of large sky areas by ground-based telescopes. However the effectiveness of optical variability selection, with respect to other multiwavelength techniques, has been poorly studied down to the depth expected from next generation surveys. Here we present the results of our r-band analysis of a sample of 299 optically variable AGN candidates in the VST survey of the COSMOS field, counting 54 visits spread over three observing seasons spanning >3yr. This dataset is >3 times larger in size than the one presented in our previous analysis (De Cicco et al., 2015, Cat. J/A+A/574/A112), and the observing baseline is 8 times longer. We push towards deeper magnitudes (r(AB)~23.5mag) compared to past studies; we make wide use of ancillary multiwavelength catalogs in order to confirm the nature of our AGN candidates, and constrain the accuracy of the method based on spectroscopic and photometric diagnostics. We also perform tests aimed at assessing the relevance of dense sampling in view of future wide-field surveys. We demonstrate that the method allows the selection of high-purity (>86%) samples. We take advantage of the longer observing baseline to achieve great improvement in the completeness of our sample with respect to X-ray and spectroscopically confirmed samples of AGNs (59%, vs. ~15% in our previous work), as well as in the completeness of unobscured and obscured AGNs. The effectiveness of the method confirms the importance to develop future, more refined techniques for the automated analysis of larger datasets.
- ID:
- ivo://CDS.VizieR/J/A+A/634/A50
- Title:
- Optically variable AGN in the VST/CDF-S
- Short Name:
- J/A+A/634/A50
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Variability has proven to be a powerful tool to detect active galactic nuclei (AGN) in multi-epoch surveys. The new-generation facilities expected to become operational in the next few years will mark a new era in time-domain astronomy and their wide-field multi-epoch campaigns will favor extensive variability studies. We present our analysis of AGN variability in the second half of the VST survey of the Wide Chandra Deep Field South (W-CDF-S), performed in the r band and covering a 2 sq. deg. area. The analysis complements a previous work, in which the first half of the area was investigated. We provide a reliable catalog of variable AGN candidates, which will be critical targets in future variability studies. We selected a sample of optically variable sources , and made use of infrared data from the Spitzer mission to validate their nature by means of color-based diagnostics. We obtain a sample of 782 AGN candidates among which 12 are classified as supernovae, 54 as stars, and 232 as AGN. We estimate a contamination <~ 20% and a completeness ~38% with respect to mid-infrared selected samples.
