Search

Start Over Subject active galactic nuclei
981. Xinglong optical spectra of UGC3223 in 4 epochs
ID:
ivo://CDS.VizieR/J/AJ/159/245
Title:
Xinglong optical spectra of UGC3223 in 4 epochs
Short Name:
J/AJ/159/245
Date:
21 Oct 2021
Publisher:
CDS
Description:
The discovery of spectral type transition of active galactic nuclei (AGNs), the so-called "changing-look" (CL) phenomenon, challenges the widely accepted AGN paradigm, not only in the orientation-based unified model, but also in the standard disk model. In past decades, only a couple of nearby repeat changing-look active galactic nuclei (CL-AGNs) have been identified. Here we report spectroscopic observations of UGC3223 over the course of 18yr, from 2001 onwards. Combining the spectrum taken in 1987 by Stirpe, we have witnessed its type transitions from 1.5 to 2.0 to 1.8 over 32yr, and captured a long-lived (at least 10 yr) thorough "turn-off" state with a spectrum typical of a Seyfert 2 galaxy. The long-term thorough turn-off state probably suggests a once-dormant and an awakening central engine in UGC3223. We argue that the (dis)appearance of the broad Balmer emission lines can be explained by the disk-wind broad-line region model given the evolution of the calculated Eddington ratio of accretion of the supermassive black hole.
982. Xinglong spectra of two changing-look SDSS AGNs
ID:
ivo://CDS.VizieR/J/ApJ/887/15
Title:
Xinglong spectra of two changing-look SDSS AGNs
Short Name:
J/ApJ/887/15
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report a spectroscopic identification of two new changing-look active galactic nuclei (CL-AGNs): SDSSJ104705.16+544405.8 and SDSSJ120447.91+170256.8, both with a "turn-off" type transition from type-1 to type-1.8/1.9. The identification is arrived at through a follow-up spectroscopic observation of the five CL-AGNs candidates that are extracted from the sample recently released in MacLeod+ (2019, J/ApJ/874/8). The candidates are extracted by the authors from the Sloan Digit Sky Survey Data Release 7, and are spectroscopically confirmed quasars with large amplitude variability. By compiling a sample of 26 previously identified CL-AGNs, we confirm the claim by MacLeod+ that CL-AGNs tend to be biased against a low Eddington ratio, and identify an overlap between the CL-AGNs at their dim state and the so-called intermediate-type AGNs. The overlap implies that there two populations of the intermediate-type AGNs with different origins. One is due to the torus orientation effect, and the other to the intrinsic change of the accretion rate of the central supermassive black holes.
983. XMM AGN optical-UV luminosities
ID:
ivo://CDS.VizieR/J/A+A/539/A48
Title:
XMM AGN optical-UV luminosities
Short Name:
J/A+A/539/A48
Date:
21 Oct 2021
Publisher:
CDS
Description:
Active galactic nuclei (AGN) emit radiation over a wide range of wavelengths, with a peak of emission in the far-UV region of the electromagnetic spectrum, a spectral region that is historically difficult to observe. Using optical, GALEX UV, and XMM-Newton data we derive the spectral energy distribution (SED) from the optical/UV to X-ray regime of a sizeable sample of AGN. The principal motivation is to investigate the relationship between the optical/UV emission and the X-ray emission and provide bolometric corrections to the hard X-ray (2-10keV) energy range, k_bol_, the latter being a fundamental parameter in current physical cosmology.
984. 2XMM AGN X-ray and mid-IR luminosities
ID:
ivo://CDS.VizieR/J/MNRAS/449/1422
Title:
2XMM AGN X-ray and mid-IR luminosities
Short Name:
J/MNRAS/449/1422
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have determined the relation between the AGN luminosities at rest-frame 6{mu}m associated with the dusty torus emission and at 2-10keV energies using a complete, X-ray-flux-limited sample of 232 AGN drawn from the Bright Ultra-hard XMM-Newton Survey. The objects have intrinsic X-ray luminosities between 10^42^ and 10^46^erg/s and redshifts from 0.05 to 2.8. The rest-frame 6{mu}m luminosities were computed using data from the Wide-field Infrared Survey Explorer and are based on a spectral energy distribution decomposition into AGN and galaxy emission. The best-fitting relationship for the full sample is consistent with being linear, L_6{mu}m_{prop.to}L_2-10keV_^0.99+/-0.03^, with intrinsic scatter, {Delta}logL_6{mu}m_~0.35dex. The L_6{mu}m_/L_2-10keV_ luminosity ratio is largely independent of the line-of-sight X-ray absorption. Assuming a constant X-ray bolometric correction, the fraction of AGN bolometric luminosity reprocessed in the mid-IR decreases weakly, if at all, with the AGN luminosity, a finding at odds with simple receding torus models. Type 2 AGN have redder mid-IR continua at rest-frame wavelengths <12{mu}m and are overall ~1.3-2 times fainter at 6{mu}m than type 1 AGN at a given X-ray luminosity. Regardless of whether type 1 and type 2 AGN have the same or different nuclear dusty toroidal structures, our results imply that the AGN emission at rest-frame 6{mu}m is not isotropic due to self-absorption in the dusty torus, as predicted by AGN torus models. Thus, AGN surveys at rest-frame ~6{mu}m are subject to modest dust obscuration biases.
985. XMM/CDFS AGN intrinsic absorption
ID:
ivo://CDS.VizieR/J/A+A/459/693
Title:
XMM/CDFS AGN intrinsic absorption
Short Name:
J/A+A/459/693
Date:
21 Oct 2021
Publisher:
CDS
Description:
We combine bright XMM-Newton data with the Chandra Deep Field South observations to explore the behavior of the intrinsic AGN absorption, as a function of redshift and luminosity. Our sample consists of 359 sources selected in the hard 2-8keV band, spanning the flux range 6x10^-16^-3x10^-13^erg/cm^2^/s with a high rate of spectroscopic or photometric redshift completeness (100 and 85 per cent respectively for the Chandra and XMM-Newton data). We derive the column density values using X-ray spectral fits. We find that the fraction of obscured AGN falls with increasing luminosity in agreement with previous findings. The fraction of obscured AGN shows an apparent increase at high redshifts (z>2). Simulations show that this effect can most probably be attributed to the fact that at high redshifts the column densities are overestimated.
986. XMM-COSMOS Type 1 AGNs
ID:
ivo://CDS.VizieR/J/A+A/512/A34
Title:
XMM-COSMOS Type 1 AGNs
Short Name:
J/A+A/512/A34
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a study of the X-ray to optical properties of a sample of 545 X-ray selected Type 1 AGN, from the XMM-COSMOS survey, over a wide range of redshifts (0.04<z<4.25) and X-ray luminosities (40.6<=LogL[2-10]keV<=45.3). About 60% of them are spectroscopically identified Type 1 AGN, while the others have a reliable photometric redshift and are classified as Type 1 AGN on the basis of their multi-band Spectral Energy Distributions. We discuss the relationship between UV and X-ray luminosity, as parameterized by the alpha_ox_ spectral slope, and its dependence on redshift and luminosity.
987. XMM-LSS at 240MHz and 610MHz
ID:
ivo://CDS.VizieR/J/A+A/471/1105
Title:
XMM-LSS at 240MHz and 610MHz
Short Name:
J/A+A/471/1105
Date:
21 Oct 2021
Publisher:
CDS
Description:
The low-frequency radio survey of the XMM-Large Scale Structure (XMM-LSS) field aims to study the connection between the extragalactic radio source populations and their environment as traced by X-ray and optical emission. In this paper we present new radio observations of the XMM-LSS field carried out using the Giant Meterwave Radio Telescope at 240 and 610MHz. These observations complement the observations presented by Cohen at al. (2003, Cat. <J/ApJ/591/640>) and Tasse et al. (2006, Cat. <J/A+A/456/791>) at 74 and 325MHz with the Very Large Array. At 240 and 610MHz, we reach noise levels of ~2.5 and ~0.3mJy/beam, leading to the detection of 466 and 769 sources over 18.0 and 12.7 degree^2^ with resolutions of 14.7arcsec and 6.5arcsec respectively. Combining these data with the available source lists at 74, 325 (Tasse et al., 2006, Cat. <J/A+A/456/791>) and 1400MHz (NVSS), we build a multifrequency catalogue containing 1611 radio sources. We check for consistency of the astrometry and flux density estimates. We fit a simple synchrotron radiation model to the flux density measurements of the 318 radio sources being detected in at least 4 bands. While ~26% of them show signature of spectral ageing, ~6% show self absorption.
988. XMM-LSS field X-ray sources classification
ID:
ivo://CDS.VizieR/J/A+A/557/A81
Title:
XMM-LSS field X-ray sources classification
Short Name:
J/A+A/557/A81
Date:
21 Oct 2021
Publisher:
CDS
Description:
The XMM-Large Scale Structure survey (XMM-LSS), covering an area of 11.1 sq. deg., contains more than 6000 X-ray point-like sources detected with XMM-Newton to a flux of 3x10^-15^erg/s/cm^2^ in the [0.5-2]keV band. The vast majority of these sources have optical (CFHTLS), infrared (SWIRE IRAC and MIPS), near-infrared (UKIDSS) and/or ultraviolet (GALEX) counterparts. We wish to investigate the environmental properties of the different types of the XMM-LSS X-ray sources by defining their environment using the i'-band CFHTLS W1 catalog of optical galaxies to a magnitude limit of 23.5mag. We have classified 4435 X-ray selected sources on the basis of their spectra, SEDs, and X-ray luminosity, and estimated their photometric redshifts, which have a 4-11 band photometry with an accuracy of sigma_dz_/(1+z_sp_)=0.076 with 22.6% outliers for i'<26mag. We estimated the local overdensities of 777 X-ray sources that have spectro-z or photo-z calculated by using more than seven bands (accuracy of sigma_dz_/(1+z_sp_)=0.061 with 13.8% outliers) within the volume-limited region defined by 0.1<z<0.85 and -23.5<M_i'_<-20. Although X-ray sources may be found in variety of environments, a high fraction (~55-60%), as verified by comparing with the random expectations, reside in overdense regions. The galaxy overdensities within which X-ray sources reside show a positive recent redshift evolution (at least for the range studied; z<0.85). We also find that X-ray selected galaxies, when compared to AGN, inhabit significantly higher galaxy overdensities, although their spatial extent appear to be smaller than that of AGN. Hard AGN (HR>-0.2) are located in more overdense regions than soft AGN (HR<-0.2), which is clearly seen in both redshift ranges, although it appears to be stronger in the higher redshift range (0.55<z<0.85). Furthermore, the galaxy overdensities (with {delta}>1.5) within which soft AGN are embedded appear to evolve more rapidly compared to the corresponding overdensities around hard AGN.
989. XMM-LSS survey: AGN classifications
ID:
ivo://CDS.VizieR/J/A+A/474/473
Title:
XMM-LSS survey: AGN classifications
Short Name:
J/A+A/474/473
Date:
21 Oct 2021
Publisher:
CDS
Description:
Our goal is to characterize AGN populations by comparing their X-ray and optical classifications within the framework of the standard orientation-based unified scheme. We present a sample of 99 spectroscopically identified (R<=22mag) X-ray selected point sources in the XMM-LSS survey which are significantly detected (>=3{sigma}) in the [2-10]keV band with fluxes between 8x10^-15^ and 8x10^-14^erg/s/cm^2^, and which have more than 80 counts. We have compared their X-ray and optical classifications. To this end, we performed an X-ray spectral analysis for all of these 99 X-ray sources in order to assess whether they are intrinsically absorbed or not. The X-ray classification is based on the measured intrinsic column density. The optical classification is based on the measured FWHM of the permitted emission lines, the absence of broad lines being due to obscuration within the framework of the standard AGN unified scheme.
990. XMM-Newton/2dF survey. IV.
ID:
ivo://CDS.VizieR/J/MNRAS/352/91
Title:
XMM-Newton/2dF survey. IV.
Short Name:
J/MNRAS/352/91
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present an analysis of the X-ray spectral properties of 61 hard X-ray (2-8keV) selected sources from the bright XMM-Newton/2dF (f(2-8keV)>10^-14^erg/cm^2^/s) survey. This comprises nine XMMNewton pointings in the North Galactic Pole region (~1.6deg^2^) and overlaps with the SDSS, 2QZ and 2dFGRS surveys. Our sources contribute about 50 per cent of the 2-10keV X-ray background down to the flux limit of 10^-14^erg/cm^2^/s. The hardness ratio distribution of the sample suggests a deficit of heavily absorbed sources. Spectroscopic identifications exist for 34 sources.