- ID:
- ivo://CDS.VizieR/J/ApJS/221/12
- Title:
- AGNs in the MIR using AllWISE data
- Short Name:
- J/ApJS/221/12
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an all-sky sample of ~1.4 million active galactic nuclei (AGNs) meeting a two-color infrared photometric selection criteria for AGNs as applied to sources from the Wide-field Infrared Survey Explorer final catalog release (AllWISE). We assess the spatial distribution and optical properties of our sample and find that the results are consistent with expectations for AGNs. These sources have a mean density of ~38 AGNs per square degree on the sky, and their apparent magnitude distribution peaks at g~20, extending to objects as faint as g~26. We test the AGN selection criteria against a large sample of optically identified stars and determine the "leakage" (that is, the probability that a star detected in an optical survey will be misidentified as a quasi-stellar object (QSO) in our sample) rate to be <=4.0x10^-5^. We conclude that our sample contains almost no optically identified stars (<=0.041%), making this sample highly promising for future celestial reference frame work as it significantly increases the number of all-sky, compact extragalactic objects. We further compare our sample to catalogs of known AGNs/QSOs and find a completeness value of >~84% (that is, the probability of correctly identifying a known AGN/QSO is at least 84%) for AGNs brighter than a limiting magnitude of R<~19. Our sample includes approximately 1.1 million previously uncataloged AGNs.
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Search Results
- 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/ApJ/705/L76
- Title:
- AGNs with double-peaked [OIII] lines
- Short Name:
- J/ApJ/705/L76
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Double-peaked [OIII] profiles in active galactic nuclei (AGNs) may provide evidence for the existence of dual AGNs, but a good diagnostic for selecting them is currently lacking. Starting from ~7000 active galaxies in Sloan Digital Sky Survey DR7, we assemble a sample of 87 type 2 AGNs with double-peaked [OIII] profiles. The nuclear obscuration in the type 2 AGNs allows us to determine redshifts of host galaxies through stellar absorption lines. We typically find that one peak is redshifted and another is blueshifted relative to the host galaxy. We find a strong correlation between the ratios of the shifts and the double peak fluxes. The correlation can be naturally explained by the Keplerian relation predicted by models of co-rotating dual AGNs. The current sample statistically favors that most of the [OIII] double-peaked sources are dual AGNs and disfavors other explanations, such as rotating disk and outflows. These dual AGNs have a separation distance at ~1kpc scale, showing an intermediate phase of merging systems. The appearance of dual AGNs is about ~10^-2^, impacting on the current observational deficit of binary supermassive black holes with a probability of ~10^-4^ (Boroson & Lauer, 2009Natur.458...53B).
- ID:
- ivo://CDS.VizieR/J/A+A/564/A125
- Title:
- AGN Torus model comparison of AGN in the CDFS
- Short Name:
- J/A+A/564/A125
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Active Galactic Nuclei are known to have complex X-ray spectra that depend on both the properties of the accreting supermassive black hole (e.g. mass, accretion rate) and the distribution of obscuring material in its vicinity (i.e. the "torus"). Often however, simple and even unphysical models are adopted to represent the X-ray spectra of AGN, which do not capture the complexity and diversity of the observations. In the case of blank field surveys in particular, this should have an impact on e.g. the determination of the AGN luminosity function, the inferred accretion history of the Universe and also on our understanding of the relation between AGN and their host galaxies. We develop a Bayesian framework for model comparison and parameter estimation of X-ray spectra. We take into account uncertainties associated with both the Poisson nature of X-ray data and the determination of source redshift using photometric methods. We also demonstrate how Bayesian model comparison can be used to select among ten different physically motivated X-ray spectral models the one that provides a better representation of the observations. This methodology is applied to X-ray AGN in the 4 Ms Chandra Deep Field South. For the ~350 AGN in that field, our analysis identifies four components needed to represent the diversity of the observed X-ray spectra: (1) an intrinsic power law, (2) a cold obscurer which reprocesses the radiation due to photo-electric absorption, Compton scattering and Fe-K fluorescence, (3) an unabsorbed power law associated with Thomson scattering off ionised clouds, and (4) Compton reflection, most noticeable from a stronger-than-expected Fe-K line. Simpler models, such as a photo-electrically absorbed power law with a Thomson scattering component, are ruled out with decisive evidence (B>100). We also find that ignoring the Thomson scattering component results in underestimation of the inferred column density, N_H_, of the obscurer. Regarding the geometry of the obscurer, there is strong evidence against both a completely closed (e.g. sphere), or entirely open (e.g. blob of material along the line of sight), toroidal geometry in favour of an intermediate case. Despite the use of low-count spectra, our methodology is able to draw strong inferences on the geometry of the torus. Simpler models are ruled out in favour of a geometrically extended structure with significant Compton scattering. We confirm the presence of a soft component, possibly associated with Thomson scattering off ionised clouds in the opening angle of the torus. The additional Compton reflection required by data over that predicted by toroidal geometry models, may be a sign of a density gradient in the torus or reflection off the accretion disk. Finally, we release a catalogue of AGN in the CDFS with estimated parameters such as the accretion luminosity in the 2-10keV band and the column density, N_H_, of the obscurer.
- ID:
- ivo://CDS.VizieR/J/A+A/602/A123
- Title:
- AGN vs. host galaxy properties in COSMOS field
- Short Name:
- J/A+A/602/A123
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The coeval AGN and galaxy evolution and the observed local relations between SMBHs and galaxy properties suggest some connection or feedback between SMBH growth and galaxy build-up. We looked for correlations between properties of X-ray detected AGN and their FIR detected host galaxies, to find quantitative evidences for this connection, highly debated in the latest years. We exploit the rich multi-wavelength data set available in the COSMOS field for a large sample (692 sources) of AGN and their hosts, in the redshift range 0.1<z<4. We use X-ray data to select AGN and determine their properties (intrinsic luminosity and nuclear obscuration), and broad-band SED fitting to derive host galaxy properties (stellar mass M* and star formation rate SFR). We find that the AGN 2-10keV luminosity (LX) and the host 8-1000um star formation luminosity (LSFIR) are significantly correlated. However, the average host LSFIR has a flat distribution in bins of AGN LX, while the average AGN LX increases in bins of host LSFIR, with logarithmic slope of ~0.7, in the redshifts range 0.4<z<1.2. We also discuss the comparison between the distribution of these two quantities and the predictions from hydro-dynamical simulations. Finally we find that the average column density (NH) shows a positive correlation with the host M*, at all redshifts, but not with the SFR (or LSFIR). This translates into a negative correlation with specific SFR. Our results are in agreement with the idea that BH accretion and SF rates are correlated, but occur with different variability time scales. The presence of a positive correlation between NH and host M* suggests that the X-ray NH is not entirely due to the circum-nuclear obscuring torus, but may also include a contribution from the host galaxy.
- ID:
- ivo://CDS.VizieR/J/ApJ/772/26
- Title:
- AGN with WISE. II. The NDWFS Bootes field
- Short Name:
- J/ApJ/772/26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Stern et al. (2012ApJ...753...30S, Paper I) presented a study of Wide-field Infrared Survey Explorer (WISE) selection of active galactic nuclei (AGNs) in the 2deg^2^ COSMOS field, finding that a simple criterion W1-W2>=0.8 provides a highly reliable and complete AGN sample for W2<15.05, where the W1 and W2 passbands are centered at 3.4{mu}m and 4.6{mu}m, respectively. Here we extend this study using the larger 9deg^2^ NOAO Deep Wide-Field Survey Bootes field which also has considerably deeper WISE observations than the COSMOS field, and find that this simple color cut significantly loses reliability at fainter fluxes. We define a modified selection criterion combining the W1-W2 color and the W2 magnitude to provide highly reliable or highly complete AGN samples for fainter WISE sources. In particular, we define a color-magnitude cut that finds 130+/-4deg^-2^ AGN candidates for W2<17.11 with 90% reliability. Using the extensive UV through mid-IR broadband photometry available in this field, we study the spectral energy distributions of WISE AGN candidates. We find that, as expected, the WISE AGN selection can identify highly obscured AGNs, but that it is biased toward objects where the AGN dominates the bolometric luminosity output. We study the distribution of reddening in the AGN sample and discuss a formalism to account for sample incompleteness based on the step-wise maximum-likelihood method of Efstathiou et al. The resulting dust obscuration distributions depend strongly on AGN luminosity, consistent with the trend expected for a receding torus. At L_AGN_~3x10^44^erg/s, 29%+/-7% of AGNs are observed as Type 1, while at ~4x10^45^erg/s the fraction is 64%+/-13%. The distribution of obscuration values suggests that dust in the torus is present as both a diffuse medium and in optically thick clouds.
- 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/ApJ/748/124
- Title:
- AGN X-ray variability in the 4Ms catalog
- Short Name:
- J/ApJ/748/124
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The 4 Ms Chandra Deep Field-South (CDF-S) and other deep X-ray surveys have been highly effective at selecting active galactic nuclei (AGNs). However, cosmologically distant low-luminosity AGNs (LLAGNs) have remained a challenge to identify due to significant contribution from the host galaxy. We identify long-term X-ray variability (~month-years, observed frame) in 20 of 92 CDF-S galaxies spanning redshifts z{approx}0.08-1.02 that do not meet other AGN selection criteria. We show that the observed variability cannot be explained by X-ray binary populations or ultraluminous X-ray sources, so the variability is most likely caused by accretion onto a supermassive black hole (SMBH). The variable galaxies are not heavily obscured in general, with a stacked effective power-law photon index of {Gamma}_stack_{approx}1.93+/-0.13, and are therefore likely LLAGNs. The LLAGNs tend to lie a factor of {approx}6-80 below the extrapolated linear variability-luminosity relation measured for luminous AGNs.
- ID:
- ivo://CDS.VizieR/J/A+A/601/A10
- Title:
- A grid of MARCS model atmospheres for S stars
- Short Name:
- J/A+A/601/A10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- S-type stars are late-type giants whose atmospheres are enriched in carbon and s-process elements because of either extrinsic pollution by a binary companion or intrinsic nucleosynthesis and dredge-up on the thermally-pulsing asymptotic giant branch. A grid of MARCS model atmospheres has been computed for S stars, covering the range 2700<=Teff(K)<=4000, 0.50<=C/O<0.99, 0<=logg<=5, [Fe/H]=0., -0.5dex, and [s/Fe]= 0, 1, and 2 dex (where the latter quantity refers to the global overabundance of s-process elements). The MARCS models make use of a new ZrO line list. Synthetic spectra computed from these models are used to derive photometric indices in the Johnson and Geneva systems, as well as TiO and ZrO band strengths. A method is proposed to select the model best matching any given S star, a non-trivial operation since the grid contains more than 3500 models covering a five-dimensional parameter space. The method is based on the comparison between observed and synthetic photometric indices and spectral band strengths, and has been applied on a vast subsample of the Henize sample of S stars. Our results confirm the old claim by Piccirillo (1980MNRAS.190..441P) that ZrO bands in warm S stars (Teff > 3200K) are not caused by the C/O ratio being close to unity, as traditionally believed, but rather by some Zr overabundance. The TiO and ZrO band strengths, combined with V-K and J-K photometric indices, are used to select Teff, C/O, [Fe/H] and [s/Fe]. The Geneva U-B_1 and B_2-V_1 indices (or any equivalent) are good at selecting the gravity. The defining spectral features of dwarf S stars are outlined, but none is found among the Henize S stars. More generally, it is found that, at Teff=3200K, a change of C/O from 0.5 to 0.99 has a strong impact on V-K (2mag). Conversely, a range of 2 mag in V-K corresponds to a 200K shift along the (Teff, V-K) relationship (for a fixed C/O value). Hence, the use of a (Teff, V-K) calibration established for M stars will yield large errors for S stars, so that a specific calibration must be used, as provided in the present paper. Using the atmospheric parameters derived by our method for the sample of Henize S stars, we show that the extrinsic-intrinsic dichotomy among S stars reveals itself very clearly as a bimodal distribution in the effective temperatures. Moreover, the increase of s-process element abundances with increasing C/O ratios and decreasing temperatures is apparent among intrinsic stars, confirming theoretical expectations.
570. A-G star metallicity
- ID:
- ivo://CDS.VizieR/J/MNRAS/320/451
- Title:
- A-G star metallicity
- Short Name:
- J/MNRAS/320/451
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Edinburgh-Cape Blue Object Survey is an ongoing project to identify and analyse a large sample of hot stars selected initially on the basis of photographic colours (down to a magnitude limit (B~18.0) over the entire high-Galactic-latitude southern sky, and then studied with broad-band UBV photometry and medium-resolution spectroscopy. Due to unavoidable errors in the initial candidate selection, stars that are likely metal-deficient dwarfs and giants of the halo and thick-disc populations are inadvertently included, yet are of interest in their own right. In this paper we discuss a total of 206 candidate metal-deficient dwarfs, subgiants, giants, and horizontal-branch stars with photoelectric colours redder than (B-V)_0_=0.3, and with available spectroscopy. Radial velocities, accurate to ~10-15km/s, are presented for all of these stars. Spectroscopic metallicity estimates for these stars are obtained using a recently recalibrated relation between Ca II K-line strength and (B-V)_0_ colour. The identification of metal-poor stars from this colour-selection technique is remarkably efficient, and competitive with previous survey methods. An additional sample of 186 EC stars with photoelectric colours in the range -0.4<=(B-V)_0_<0.3, photoelectric colours in the range composed primarily of field horizontal-branch stars and other, higher gravity, A- and B-type stars, is also analysed. Estimates of the physical parameters T_eff_, log g and [Fe/H] are obtained for cooler members of this subsample, and a number of candidate RR Lyrae variables are identified.
