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Start Over Subject active galactic nuclei
1011. X-ray detection of radio-selected SF galaxies
ID:
ivo://CDS.VizieR/J/A+A/542/A16
Title:
X-ray detection of radio-selected SF galaxies
Short Name:
J/A+A/542/A16
Date:
21 Oct 2021
Publisher:
CDS
Description:
X-ray surveys contain sizable numbers of star forming galaxies, beyond the AGN which usually make the majority of detections. Many methods to separate the two populations are used in the literature, based on X-ray and multiwavelength properties. We aim at a detailed test of the classification schemes and to study the X-ray properties of the resulting samples. We build on a sample of galaxies selected at 1.4GHz in the VLA-COSMOS survey, classified by Smolcic et al. (2008ApJS..177...14S) according to their optical colours and observed with Chandra. A similarly selected control sample of AGN is also used for comparison. We review some X-ray based classification criteria and check how they affect the sample composition. The efficiency of the classification scheme devised by Smolcic et al. (2008ApJS..177...14S) is such that ~30% of composite/misclassified objects are expected because of the higher X-ray brightness of AGN with respect to galaxies. The latter fraction is actually 50% in the X-ray detected sources, while it is expected to be much lower among X-ray undetected sources. Indeed, the analysis of the stacked spectrum of undetected sources shows, consistently, strongly different properties between the AGN and galaxy samples. X-ray based selection criteria are then used to refine both samples. The radio/X-ray luminosity correlation for star forming (SF) galaxies is found to hold with the same X-ray/radio ratio valid for nearby galaxies. Some evolution of the ratio may be possible for sources at high redshift or high luminosity, tough it is likely explained by a bias arising from the radio selection. Finally, we discuss the X-ray number counts of star forming galaxies from the VLA- and C-COSMOS surveys according to different selection criteria, and compare them to the similar determination from the Chandra Deep Fields. The classification scheme proposed here may find application in future works and surveys.
1012. X-ray flux variability of AGN
ID:
ivo://CDS.VizieR/J/MNRAS/466/3309
Title:
X-ray flux variability of AGN
Short Name:
J/MNRAS/466/3309
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present results of a systematic study of flux variability on hourly time-scales in a large sample of active galactic nuclei (AGN) in the 3-79keV band using data from Nuclear Spectroscopic Telescope Array. Our sample consists of four BL Lac objects (BL Lacs), three flat spectrum radio quasars (FSRQs) 24 Seyfert 1, 42 Seyfert 2 and eight narrow line Seyfert 1 (NLSy1) galaxies. We find that in the 3-79keV band, about 65 per cent of the sources in our sample show significant variations on hourly time-scales. Using the Mann-Whitney U-test and the Kolmogorov-Smirnov test, we find no difference in the variability behaviour between Seyfert 1 and 2 galaxies. The blazar sources (FSRQs and BL Lacs) in our sample are more variable than Seyfert galaxies that include Seyfert 1 and Seyfert 2 in the soft (3-10keV), hard (10-79keV) and total (3-79keV) bands. NLSy1 galaxies show the highest duty cycle of variability (87 per cent), followed by BL Lacs (82 per cent), Seyfert galaxies (56 per cent) and FSRQs (23 per cent). We obtained flux doubling/halving time in the hard X-ray band less than 10 min in 11 sources. The flux variations between the hard and soft bands in all the sources in our sample are consistent with zero lag.
1013. X-ray measurements of ChaMP-SDSS galaxies
ID:
ivo://CDS.VizieR/J/ApJ/705/1336
Title:
X-ray measurements of ChaMP-SDSS galaxies
Short Name:
J/ApJ/705/1336
Date:
21 Oct 2021
Publisher:
CDS
Description:
The combination of the Sloan Digital Sky Survey (SDSS) and the Chandra Multiwavelength Project (ChaMP; Green et al. 2004ApJS..150...43G) currently offers the largest and most homogeneously selected sample of nearby galaxies for investigating the relation between X-ray nuclear emission, nebular line emission, black hole masses, and properties of the associated stellar populations. We provide X-ray spectral fits and valid uncertainties for all the galaxies with counts ranging from 2 to 1325 (mean 76, median 19). We present here novel constraints that both X-ray luminosity L_X_ and X-ray spectral energy distribution bring to the galaxy evolutionary sequence HII->Seyfert/Transition Object->LINER->Passive suggested by optical data.
1014. X-ray & MIR AGNs in Stripe 82 with eBOSS spectra
ID:
ivo://CDS.VizieR/J/ApJ/876/50
Title:
X-ray & MIR AGNs in Stripe 82 with eBOSS spectra
Short Name:
J/ApJ/876/50
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report the results of a Sloan Digital Sky Survey IV eBOSS program to target X-ray sources and mid-infrared-selected Wide-field Infrared Survey Explorer (WISE) active galactic nucleus (AGN) candidates in a 36.8deg^2^ region of Stripe 82. About half this survey (15.6deg^2^) covers the largest contiguous portion of the Stripe 82 X-ray survey. This program represents the largest spectroscopic survey of AGN candidates selected solely by their WISE colors. We combine this sample with X-ray and WISE AGNs in the field identified via other sources of spectroscopy, producing a catalog of 4847 sources that is 82% complete to r~22. Based on X-ray luminosities or WISE colors, 4730 of these sources are AGNs, with a median sample redshift of z~1. About 30% of the AGNs are optically obscured (i.e., lack broad lines in their optical spectra). BPT analysis, however, indicates that 50% of the WISE AGNs at z<0.5 have emission line ratios consistent with star-forming galaxies, so whether they are buried AGNs or star-forming galaxy contaminants is currently unclear. We find that 61% of X-ray AGNs are not selected as mid-infrared AGNs, with 22% of X-ray AGNs undetected by WISE. Most of these latter AGNs have high X-ray luminosities (Lx>10^44^erg/s), indicating that mid-infrared selection misses a sizable fraction of the highest luminosity AGNs, as well as lower luminosity sources where AGN-heated dust is not dominating the mid-infrared emission. Conversely, ~58% of WISE AGNs are undetected by X-rays, though we do not find that they are preferentially redder than the X-ray-detected WISE AGNs.
1015. X-ray & MIR luminosities of the GBT galaxies
ID:
ivo://CDS.VizieR/J/ApJ/892/18
Title:
X-ray & MIR luminosities of the GBT galaxies
Short Name:
J/ApJ/892/18
Date:
19 Jan 2022 08:55:44
Publisher:
CDS
Description:
We present an investigation of the dependence of H_2_O maser detection rates and properties on the mid-IR active galactic nucleus (AGN) luminosity, L_AGN_, and the obscuring column density, N_H_, based on mid-IR and hard X-ray photometry. Based on spectral energy distribution fitting that allows for decomposition of the black hole accretion and star formation components in the mid-infrared, we show that the megamaser (disk maser) detection rate increases sharply for galaxies with 12{mu}m AGN luminosity L_12um_^AGN^ greater than 10^42^erg/s, from <~3% (<~2%) to ~12% (~5%). By using the ratio of the observed X-ray to mid-IR AGN luminosity as an indicator of N_H_, we also find that megamaser (disk maser) detection rates are boosted to 15% (7%) and 20% (9%) for galaxies with N_H_>=10^23^/cm^2^ and N_H_>=10^24^cm^-2^, respectively. Combining these column density cuts with a constraint for high L_12um_^AGN^ (>=10^42^erg/s) predicts further increases in the megamaser (disk maser) detection rates to 19% (8%) and 27% (14%), revealing unprecedented potential increases of the megamaser and disk maser detection rates by a factor of 7-15 relative to the current rates, depending on the chosen sample selection criteria. A noteworthy aspect of these new predictions is that the completeness rates are only compromised mildly, with the rates remaining at the level of ~95% (~50%) for sources with N_H_>=10^23^/cm^2^ (N_H_>=10^24^/cm^2^). Applying these selection methods to current X-ray AGN surveys predicts the detection of >~15 new megamaser disks.
1016. X-ray monitoring of 1ES 1927+654
ID:
ivo://CDS.VizieR/J/ApJS/255/7
Title:
X-ray monitoring of 1ES 1927+654
Short Name:
J/ApJS/255/7
Date:
06 Dec 2021 19:56:23
Publisher:
CDS
Description:
1ES 1927+654 is a nearby active galactic nucleus (AGN) that underwent a changing-look event in early 2018, developing prominent broad Balmer lines that were absent in previous observations. We have followed up this object in the X-rays with an ongoing campaign that started in 2018 May and that includes 265 NICER (for a total of 678ks) and 14 Swift/XRT (26ks) observations, as well as three simultaneous XMM-Newton/NuSTAR (158/169ks) exposures. In the X-rays, 1ES 1927+654 shows a behavior unlike any previously known AGN. The source is extremely variable both in spectral shape and flux and does not show any correlation between X-ray and UV flux on timescales of hours or weeks/months. After the outburst, the power-law component almost completely disappeared, and the source showed an extremely soft continuum dominated by a blackbody component. The temperature of the blackbody increases with the luminosity, going from kT~80eV (for a 0.3-2keV luminosity of L_0.3-2_~10^41.5^erg/s) to ~200eV (for L_0.3-2_~10^44^erg/s). The spectra show evidence of ionized outflows and of a prominent feature at ~1keV, which can be reproduced by a broad emission line. The unique characteristics of 1ES 1927+654 in the X-ray band suggest that it belongs to a new type of changing-look AGN. Future X-ray surveys might detect several more objects with similar properties.
1017. X-ray observations of Stripe 82
ID:
ivo://CDS.VizieR/J/MNRAS/436/3581
Title:
X-ray observations of Stripe 82
Short Name:
J/MNRAS/436/3581
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have analysed the XMM-Newton and Chandra data overlapping ~16.5deg^2^ of Sloan Digital Sky Survey Stripe 82, including ~4.6deg^2^ of proprietary XMM-Newton data that we present here. In total, 3362 unique X-ray sources are detected at high significance. We derive the XMM-Newton number counts and compare them with our previously reported Chandra logN-logS relations and other X-ray surveys. The Stripe 82 X-ray source lists have been matched to multiwavelength catalogues using a maximum likelihood estimator algorithm. We discovered the highest redshift (z=5.86) quasar yet identified in an X-ray survey. We find 2.5 times more high-luminosity (L_X_>10^45erg/s) AGN than the smaller area Chandra and XMM-Newton survey of COSMOS and 1.3 times as many identified by XBootes. Comparing the high-luminosity active galactic nuclei (AGN) we have identified with those predicted by population synthesis models, our results suggest that this AGN population is a more important component of cosmic black hole growth than previously appreciated. Approximately a third of the X-ray sources not detected in the optical are identified in the infrared, making them candidates for the elusive population of obscured high-luminosity AGN in the early universe.
1018. X-ray Observations of Stripe 82
ID:
ivo://CDS.VizieR/J/ApJ/817/172
Title:
X-ray Observations of Stripe 82
Short Name:
J/ApJ/817/172
Date:
21 Oct 2021
Publisher:
CDS
Description:
We release the next installment of the Stripe 82 X-ray survey point-source catalog, which currently covers 31.3deg^2^ of the Sloan Digital Sky Survey (SDSS) Stripe 82 Legacy field. In total, 6181 unique X-ray sources are significantly detected with XMM-Newton (>5{sigma}) and Chandra (>4.5{sigma}). This catalog release includes data from XMM-Newton cycle AO 13, which approximately doubled the Stripe 82X survey area. The flux limits of the Stripe 82X survey are 8.7x10^-16^erg/s/cm2, 4.7x10^-15^erg/s/cm2, and 2.1x10^-15^erg/s/cm2 in the soft (0.5-2keV), hard (2-10keV), and full bands (0.5-10keV), respectively, with approximate half-area survey flux limits of 5.4x10^-15^erg/s/cm2, 2.9x10^-14^erg/s/cm2, and 1.7x10^-14^erg/s/cm2. We matched the X-ray source lists to available multi-wavelength catalogs, including updated matches to the previous release of the Stripe 82X survey; 88% of the sample is matched to a multi-wavelength counterpart. Due to the wide area of Stripe 82X and rich ancillary multi-wavelength data, including coadded SDSS photometry, mid-infrared WISE coverage, near-infrared coverage from UKIDSS and VISTA Hemisphere Survey, ultraviolet coverage from GALEX, radio coverage from FIRST, and far-infrared coverage from Herschel, as well as existing ~30% optical spectroscopic completeness, we are beginning to uncover rare objects, such as obscured high-luminosity active galactic nuclei at high-redshift. The Stripe 82X point source catalog is a valuable data set for constraining how this population grows and evolves, as well as for studying how they interact with the galaxies in which they live.
1019. X-ray of active galaxies and nuclei
ID:
ivo://CDS.VizieR/VII/181
Title:
X-ray of active galaxies and nuclei
Short Name:
VII/181
Date:
21 Oct 2021
Publisher:
CDS
Description:
(no description available)
1020. X-ray properties of AGN
ID:
ivo://CDS.VizieR/J/A+A/309/81
Title:
X-ray properties of AGN
Short Name:
J/A+A/309/81
Date:
21 Oct 2021
Publisher:
CDS
Description:
ROSAT spectra of 86 Active Galactic Nuclei (AGN) with a broad range of optical FeII strengths have been analyzed. The results of the spectral analysis have been combined with optical and radio data as well as with optical emission line properties collected from the literature to understand the origin of the strong FeII emission and the nature of the soft X-ray excess.