- ID:
- ivo://CDS.VizieR/J/A+A/423/469
- Title:
- AGNs from RXTE 3-20keV All-Sky Survey
- Short Name:
- J/A+A/423/469
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We compiled a sample of 95 AGNs serendipitously detected in the 3-20keV band at Galactic latitude |b|>10deg during the RXTE slew survey (XSS, Revnivtsev et al., Cat. <J/A+A/418/927>), and utilize it to study the statistical properties of the local population of AGNs, including the X-ray luminosity function and absorption distribution. We find that among low X-ray luminosity (LX<10^43.5^erg/s) AGNs, the ratio of absorbed (characterized by intrinsic absorption in the range 10^22^cm^-2^<NH<10^24^cm^-2^) and unabsorbed (NH<10^22^cm^-2^) objects is 2:1, while this ratio drops to less than 1:5 for higher luminosity AGNs. The summed X-ray output of AGNs with LX>10^41^erg/s estimated here is smaller than the earlier estimated total X-ray volume emissivity in the local Universe, suggesting that a comparable X-ray flux may be produced together by lower luminosity AGNs, non-active galaxies and clusters of galaxies. Finally, we present a sample of 35 AGN candidates, composed of unidentified XSS sources.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/476/2501
- Title:
- AGN short time-scale optical variability
- Short Name:
- J/MNRAS/476/2501
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first short time-scale (~ hours to days) optical variability study of a large sample of active galactic nuclei (AGNs) observed with the Kepler/K2 mission. The sample contains 252 AGN observed over four campaigns with ~30 min cadence selected from the Million Quasar Catalogue with R magnitude <19. We performed time series analysis to determine their variability properties by means of the power spectral densities (PSDs) and applied Monte Carlo techniques to find the best model parameters that fit the observed power spectra. A power-law model is sufficient to describe all the PSDs of our sample. A variety of power-law slopes were found indicating that there is not a universal slope for all AGNs. We find that the rest-frame amplitude variability in the frequency range of 6x10^-6^-10^-4^Hz varies from 1 to 10 per cent with an average of 1.7 per cent. We explore correlations between the variability amplitude and key parameters of the AGN, finding a significant correlation of rest-frame short-term variability amplitude with redshift. We attribute this effect to the known 'bluer when brighter' variability of quasars combined with the fixed bandpass of Kepler data. This study also enables us to distinguish between Seyferts and blazars and confirm AGN candidates. For our study, we have compared results obtained from light curves extracted using different aperture sizes and with and without detrending. We find that limited detrending of the optimal photometric precision light curve is the best approach, although some systematic effects still remain present.
- ID:
- ivo://CDS.VizieR/J/ApJ/815/128
- Title:
- AGNs rest-frame UV and optical parameters
- Short Name:
- J/ApJ/815/128
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The ability to accurately derive black hole (BH) masses at progressively higher redshifts and over a wide range of continuum luminosities has become indispensable in the era of large-area extragalactic spectroscopic surveys. In this paper, we present an extension of existing comparisons between rest-frame UV and optical virial BH mass estimators to intermediate redshifts and luminosities comparable to the local H{beta} reverberation-mapped active galactic nuclei (AGNs). We focus on the Mg II, C IV, and C III] broad emission lines and compare them to both H{alpha} and H{beta}. We use newly acquired near-infrared spectra from the Fiber-fed Multi-object Spectrograph instrument on the Subaru telescope for 89 broad-lined AGNs at redshifts between 0.3 and 3.5, complemented by data from the AGES survey. We employ two different prescriptions for measuring the emission line widths and compare the results. We confirm that Mg II shows a tight correlation with H{alpha} and H{beta}, with a scatter of ~0.25 dex. The C IV and C III] estimators, while showing larger scatter, are viable virial mass estimators after accounting for a trend with the UV-to-optical luminosity ratio. We find an intrinsic scatter of ~0.37 dex between Balmer and carbon virial estimators by combining our data set with previous high redshift measurements. This updated comparison spans a total of three decades in BH mass. We calculate a virial factor for C IV/C III] logf_C IV/C III]_=0.87 with an estimated systematic uncertainty of ~0.4 dex and find excellent agreement between the local reverberation mapped AGN sample and our high-z sample.
- ID:
- ivo://CDS.VizieR/J/MNRAS/488/1035
- Title:
- AGN UV luminosity function
- Short Name:
- J/MNRAS/488/1035
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present lists of more than 80000 mostly UV-optical colour-selected AGN from 12 data sets, homogenised with respect to the assumed cosmology, magnitude system, and bandpass correction (if possible). We also present the selection functions for each of the 12 data sets, similarly homogenised. The total sample spans redshifts from z=0 to 7.5. The paper presents a detailed description of the combined sample and determinations of the AGN UV luminosity function throughout this redshift range. The code for developing and analysing AGN luminosity functions is available on GitHub (https://github.com/gkulkarni/QLF). The inferred UV luminosity functions can also be used to derive the contribution of AGN to the cosmic UV background and its effect on the intergalactic medium (IGM). The GitHub repository also includes code for this. Here we also present the luminosity functions in redshift bins, luminosity function evolution models from the paper, the 912{AA} and 1450{AA} volume emissivity of AGN from z=0 to 15, and the hydrogen photoionization rate contribution by AGN in this redshift range.
- ID:
- ivo://CDS.VizieR/J/ApJS/176/355
- Title:
- AGN X-Ray emission and black holes
- Short Name:
- J/ApJS/176/355
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work we use a sample of 318 radio-quiet quasars (RQQs) to investigate the dependence of the ratio of optical/UV flux to X-ray flux, {alpha}_ox_, and the X-ray photon index, {Gamma}_X_, on black hole mass, UV relative to Eddington luminosity, and X-ray relative to Eddington luminosity. Our sample is drawn from the literature, with X-ray data from ROSAT and Chandra, and optical data mostly from the SDSS; 153 of these sources have estimates of {Gamma}_X_ from Chandra. We estimate M_BH_ using standard estimates derived from the H{beta}, MgII, and CIV broad emission lines. To date, this is the largest study of the dependence of RQQ X-ray parameters on black hole mass and related quantities, and the first to attempt to correct for the large statistical uncertainty in the broad-line mass estimates.
- ID:
- ivo://CDS.VizieR/J/A+AS/112/347
- Title:
- A Homogeneous Bright QSO Survey
- Short Name:
- J/A+AS/112/347
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This is the first paper in a series aimed at defining a statistically significant sample of QSOs in the range 15<B<18.75 and 0.3<z<2.2. The selection is carried out using direct plates obtained at the ESO and UK Schmidt Telescopes, scanned with the COSMOS facility and searched for objects with an ultraviolet excess. Follow-up spectroscopy, carried out at ESO La Silla, is used to classify each candidate. In this initial paper, we describe the scientific objectives of the survey; the selection and observing techniques used. We present the first sample of 285 QSOs (M_B_<-23) in a 153 sq.deg area, covered by the six "deep" fields, intended to obtain significant statistics down B=~18.75 with unprecedented photometric accuracy. From this database, QSO counts are determined in the magnitude range 17<B<18.75.
- ID:
- ivo://CDS.VizieR/J/ApJ/815/33
- Title:
- A Hubble diagram for quasars
- Short Name:
- J/ApJ/815/33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new method to test the {Lambda}CDM cosmological model and to estimate cosmological parameters based on the nonlinear relation between the ultraviolet and X-ray luminosities of quasars. We built a data set of 1138 quasars by merging several samples from the literature with X-ray measurements at 2keV and SDSS photometry, which was used to estimate the extinction-corrected 2500{AA} flux. We obtained three main results: (1) we checked the nonlinear relation between X-ray and UV luminosities in small redshift bins up to z~6, confirming that the relation holds at all redshifts with the same slope; (2) we built a Hubble diagram for quasars up to z~6, which is well matched to that of supernovae in the common z=0-1.4 redshift interval and extends the test of the cosmological model up to z~6; and (3) we showed that this nonlinear relation is a powerful tool for estimating cosmological parameters. Using the present data and assuming a {Lambda}CDM model, we obtain {Omega}_M_=0.22_-0.08_^+0.10^ and {Omega}_{Lambda}_=0.92-0.30_^+0.18^ ({Omega}=0.28+/-0.04 and {Omega}_{Lambda}_=0.73+/-0.08 from a joint quasar-SNe fit). Much more precise measurements will be achieved with future surveys. A few thousand SDSS quasars already have serendipitous X-ray observations from Chandra or XMM-Newton, and at least 100000 quasars with UV and X-ray data will be made available by the extended ROentgen Survey with an Imaging Telescope Array all-sky survey in a few years. The Euclid, Large Synoptic Survey Telescope, and Advanced Telescope for High ENergy Astrophysics surveys will further increase the sample size to at least several hundred thousand. Our simulations show that these samples will provide tight constraints on the cosmological parameters and will allow us to test for possible deviations from the standard model with higher precision than is possible today.
- ID:
- ivo://CDS.VizieR/J/MNRAS/472/2085
- Title:
- ALHAMBRA fields type-I AGN with ELDAR
- Short Name:
- J/MNRAS/472/2085
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present ELDAR, a new method that exploits the potential of medium- and narrow-band filter surveys to securely identify active galactic nuclei (AGN) and determine their redshifts. Our methodology improves on traditional approaches by looking for AGN emission lines expected to be identified against the continuum, thanks to the width of the filters. To assess its performance, we apply ELDAR to the data of the ALHAMBRA survey, which covered an effective area of 2.38deg^2^ with 20 contiguous medium-band optical filters down to F814W=24.5. Using two different configurations of ELDAR in which we require the detection of at least 2 and 3 emission lines, respectively, we extract two catalogues of type-I AGN. The first is composed of 585 sources (79% of them spectroscopically-unknown) down to F814W=22.5 at z_phot_>1, which corresponds to a surface density of 209 deg-2. In the second, the 494 selected sources (83% of them spectroscopically-unknown) reach F814W=23 at z_phot_>1.5, for a corresponding number density of 176deg^-2^. Then, using samples of spectroscopically-known AGN in the ALHAMBRA fields, for the two catalogues we estimate a completeness of 73% and 67%, and a redshift precision of 1.01% and 0.86% (with outliers fractions of 8.1% and 5.8%). At z>2, where our selection performs best, we reach 85% and 77% completeness and we find no contamination from galaxies.
- ID:
- ivo://CDS.VizieR/J/MNRAS/380/162
- Title:
- Aligned radio polarizations of quasars
- Short Name:
- J/MNRAS/380/162
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used the very large Jodrell Bank VLA Astrometric Survey/Cosmic Lens All-Sky Survey 8.4-GHz surveys of flat-spectrum radio sources to test the hypothesis that there is a systematic alignment of polarization position angle vectors on cosmological scales of the type claimed by Hutsemekers et al. (2005, Cat. <J/A+A/441/915>). The polarization position angles of 4290 sources with polarized flux density 1mJy have been examined. They do not reveal large-scale alignments either as a whole or when split in half into high-redshift (z>=1.24) and low-redshift subsamples. Nor do the radio sources which lie in the specific areas covered by Hutsemekers et al. (<J/A+A/441/915>) show any significant effect. We have also looked at the position angles of parsec-scale jets derived from very long baseline interferometry observations and again find no evidence for systematic alignments. Finally, we have investigated the correlation between the polarization position angle and those of the parsec-scale jets. As expected, we find that there is a tendency for the polarization angles to be perpendicular to the jet angles. However, the difference in jet and polarization position angles does not show any systematic trend in different parts of the sky.
- ID:
- ivo://CDS.VizieR/J/A+A/441/915
- Title:
- Alignments of quasar polarization vectors
- Short Name:
- J/A+A/441/915
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Based on a new sample of 355 quasars with significant optical polarization and using complementary statistical methods, we confirm that quasar polarization vectors are not randomly oriented over the sky with a probability often in excess of 99.9%.