We present the mid-infrared colors of X-ray-detected AGNs and explore mid-infrared selection criteria. Using a statistical matching technique, the likelihood ratio, over 900 IRAC counterparts were ...identified with a new MUSYC X-ray source catalog that includes image1000 published X-ray sources in the Chandra Deep Field-South and Extended Chandra Deep Field-South. Most X-ray- selected AGNs have IRAC spectral shapes consistent with power-law slopes, image, and display a wide range of colors, image. Although X-ray sources typically fit to redder (more negative alpha ) power laws than non-X-ray-detected galaxies, more than 50% do have flat or blue (galaxy-like) spectral shapes in the observed 3-8 mum band. Only a quarter of the X-ray-selected AGNs detected at 24 mum are well fit by featureless red power laws in the observed 3.6-24 mum, likely the subset of our sample whose infrared spectra are dominated by emission from the central AGN region. Most IRAC color selection criteria fail to identify the majority of X-ray-selected AGNs, finding only the more luminous AGNs, the majority of which have broad emission lines. In deep surveys, these color selection criteria select 10%- 20% of the entire galaxy population and miss many moderate-luminosity AGNs.
The dust covering factor in active galactic nuclei Stalevski, Marko; Ricci, Claudio; Ueda, Yoshihiro ...
Monthly Notices of the Royal Astronomical Society,
05/2016, Letnik:
458, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The primary source of emission of active galactic nuclei (AGNs), the accretion disc, is surrounded by an optically and geometrically thick dusty structure (‘the so-called dusty torus’). The infrared ...radiation emitted by the dust is nothing but a reprocessed fraction of the accretion disc emission, so the ratio of the torus to the AGN luminosity (L
torus/L
AGN) should corresponds to the fraction of the sky obscured by dust, i.e. the covering factor. We undertook a critical investigation of the L
torus/L
AGN as the dust covering factor proxy. Using state-of-the-art 3D Monte Carlo radiative transfer code, we calculated a grid of spectral energy distributions (SEDs) emitted by the clumpy two-phase dusty structure. With this grid of SEDs, we studied the relation between L
torus/L
AGN and the dust covering factor for different parameters of the torus. We found that in the case of type 1 AGNs the torus anisotropy makes L
torus/L
AGN underestimate low covering factors and overestimate high covering factors. In type 2 AGNs L
torus/L
AGN always underestimates covering factors. Our results provide a novel easy-to-use method to account for anisotropy and obtain correct covering factors. Using two samples from the literature, we demonstrated the importance of our result for inferring the obscured AGN fraction. We found that after the anisotropy is properly accounted for, the dust covering factors show very weak dependence on L
AGN, with values in the range of ≈0.6–0.7. Our results also suggest a higher fraction of obscured AGNs at high luminosities than those found by X-ray surveys, in part owing to the presence of a Compton-thick AGN population predicted by population synthesis models.
We present deep near-infrared JHK imaging of four 10' X 10' fields. The observations were carried out as part of the Multiwavelength Survey by Yale-Chile (MUSYC) with ISPI on the CTIO 4 m telescope. ...The typical point-source limiting depths are J ~ 22.5, H ~ 21.5, and K ~ 21 (5 s; Vega). The effective seeing in the final images is ~1.0''. We combine these data with MUSYC UBVRIz imaging to create K-selected catalogs that are unique for their uniform size, depth, filter coverage, and image quality. We investigate the rest-frame optical colors and photometric redshifts of galaxies that are selected using common color selection techniques, including distant red galaxies (DRGs), star-forming and passive BzKs, and the rest-frame UV-selected BM, BX, and Lyman break galaxies (LBGs). These techniques are effective at isolating large samples of high-redshift galaxies, but none provide complete or uniform samples across the targeted redshift ranges. The DRG and BM/BX/LBG criteria identify populations of red and blue galaxies, respectively, as they were designed to do. The star-forming BzKs have a very wide redshift distribution, extending down to z ~ 1, a wide range of colors, and may include galaxies with very low specific star formation rates. In comparison, the passive BzKs are fewer in number, have a different distribution of K magnitudes, and have a somewhat different redshift distribution. By combining either the DRG and BM/BX/LBG criteria, or the star-forming and passive BzK criteria, it appears possible to define a reasonably complete sample of galaxies to our flux limit over specific redshift ranges. However, the redshift dependence of both the completeness and sampled range of rest-frame colors poses an ultimate limit to the usefulness of these techniques.
We present a long-term, multi-wavelength project to understand the epoch of fastest growth of the most massive black holes by using a sample of 40 luminous quasars at z ≃ 4.8. These quasars have ...rather uniform properties, with typical accretion rates and black hole masses of L/LEdd ≃ 0.7 and MBH ≃ 109M⊙. The sample consists of “FIR-bright” sources with a previous Herschel/SPIRE detection, suggesting SFR > 1,000 M⊙ yr−1, as well as of “FIR-faint” sources for which Herschel stacking analysis implies a typical SFR of ~400 M⊙ yr−1. Six of the quasars have been observed by ALMA in C ii λ157.74μm line emission and adjacent rest-frame 150μm continuum, to study the dusty cold ISM. ALMA detected companion, spectroscopically confirmed sub-mm galaxies (SMGs) for three sources—one FIR-bright and two FIR-faint. The companions are separated by ~14–45 kpc from the quasar hosts, and we interpret them as major galaxy interactions. Our ALMA data therefore clearly support the idea that major mergers may be important drivers for rapid, early SMBH growth. However, the fact that not all high-SFR quasar hosts are accompanied by interacting SMGs, and their ordered gas kinematics observed by ALMA, suggest that other processes may be fueling these systems. Our analysis thus demonstrates the diversity of host galaxy properties and gas accretion mechanisms associated with early and rapid SMBH growth.
Accurately determining the masses of supermassive black holes is crucial to understand their evolution and the establishment of their relationship with their host galaxy properties. Beyond the local ...universe, the single epoch mass estimation method provides a simple procedure to estimate black hole masses in large spectroscopic samples of type-1 active galactic nuclei. The method assumes virialized motion of gas in the close vicinity to the active black holes, traced through broad emission lines. However, because of the assumption of a universal virial factor, this procedure has uncertainties associated with the unknown distribution of the gas clouds. Here, using a sample of 39 quasars observed with the VLT/X-shooter spectrograph, we compare alternative estimations of black hole masses determined from the properties of the accretion disk emission around the black hole with the single epoch virial mass estimations. We find that the virial factor is inversely proportional to the observed width of the broad emission lines. This result implies that current virial masses can be miss-estimated by up to a factor of 6. Our analysis indicates that either the effect of line-of-sight inclination in a planar distribution of the broad line emitting gas or the radiation pressure perturbations to the distribution of gas can reproduce our findings.
We present new H-band spectroscopy for a flux-limited sample of 40 z 4.8 active galactic nuclei, selected from the Sloan Digital Sky Survey. The sample probably contains the most massive active black ...holes (BHs) at this redshift and spans a broad range in bolometric luminosity, 2.7 X 1046 erg s--1 < L bol < 2.4 X 1047 erg s--1. The high-quality observations and the accurate fitting of the Mg II Delta *l2798 line enable us to study, systematically, the distribution of BH mass (M BH) and normalized accretion rate (L/L Edd) at z 4.8. We find that 108 M M BH 6.6 X 109 M with a median of ~8.4 X 108 M . We also find that 0.2 L/L Edd 3.9 with a median of ~0.6. Most of these sources had enough time to grow to their observed mass at z 4.8 from z = 20, assuming a range of seed BH masses, with ~40% that are small enough to be stellar remnants. Compared to previously studied samples at z 2.4 and 3.3, the masses of the z 4.8 BHs are typically lower by ~0.5 dex and their L/L Edd is higher by a similar factor. The new z 4.8 sample can be considered as the progenitor population of the most massive BHs at z 2.4 and 3.3. Such an evolutionary interpretation requires that the growth of the BHs from z 4.8 to z 3.3 and z 2.4 proceeds with short duty cycles, of about 10%-20%, depending on the particular growth scenario.
We report Herschel/SPIRE, Spitzer and Wide-field Infrared Survey Explorer observations of 44 z Asymptotically = to 4.8 optically selected active galactic nuclei (AGNs). This flux-limited sample ...contains the highest mass black holes (BHs) at this redshift. Ten of the objects were detected by Herschel and five show emission that is not clearly associated with the AGNs. The mean BH mass (M sub(BH)) and AGN luminosity (L sub(AGN)) of the detected sources are significantly higher than those of the undetected ones. The spectral differences are seen all the way from UV to far infrared wavelengths. We compare our L sub(SF) and L sub(AGN) to lower redshift samples and show a new correlation between L sub(SF) and M sub(BH). We also examine several rather speculative ideas about the host galaxy properties including the possibility that the detected sources are above the SF mass sequence (MS) at z Asymptotically = to 4.8, perhaps in mergers, and most of the undetected sources are on the MS.
ALMA Observations of Quasar Host Galaxies at z 4.8 Nguyen, Nathen H.; Lira, Paulina; Trakhtenbrot, Benny ...
Astrophysical journal/The Astrophysical journal,
05/2020, Letnik:
895, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We present ALMA Band 7 data of the C ii emission line and underlying far-IR (FIR) continuum for 12 luminous quasars at powered by fast-growing supermassive black holes (SMBHs). Our total sample ...consists of 18 quasars, 12 of which are presented here for the first time. The new sources consist of six Herschel/SPIRE-detected systems, which we define as "FIR-bright" sources, and six Herschel/SPIRE-undetected systems, which we define as "FIR-faint" sources. We determine dust masses for the quasars hosts of , implying interstellar medium gas masses comparable to the dynamical masses derived from the C ii kinematics. It is found that, on average, the Mg ii line is blueshifted by with respect to the C ii emission line, which is also observed when complementing our observations with data from the literature. We find that all of our FIR-bright subsample and most of the FIR-faint objects lie above the main sequence of star-forming galaxies at . We detect companion submillimeter galaxies for two sources, both FIR-faint, with a range of projected distances of kpc and typical velocity shifts of from the quasar hosts. Of our total sample of 18 quasars, 5/18 are found to have dust-obscured star-forming companions.
Intermediate-mass black holes (IMBHs) have masses between 102 and 106 M and are key to our understanding of the formation of massive black holes. The known population of IMBHs remains small, with a ...few hundred candidates and only a handful of them confirmed as bona fide IMBHs. Until now, the most widely used selection method is based on spectral analysis. Here we present a methodology to select IMBH candidates via optical variability analysis of the nuclear region of local galaxies ( ). Active IMBHs accreting at low rates show small amplitude variability with timescales of hours, as is seen in one of the known IMBHs, NGC 4395. We found a sample of ∼500 galaxies demonstrating fast and small amplitude variation in their week-based light curves. We estimate an average occupancy fraction of 4% and a surface density of ∼3 deg−2, which represent an increase by a factor of ∼40 compared to previous searches. A large fraction (78%) of the candidates are in spiral galaxies. We preliminarily confirm the active galactic nucleus nature of 22 sources via Baldwin, Phillips, and Terlevich diagrams using Sloan Digital Sky Survey legacy spectra. Further confirmation of these candidates will require multiwavelength observations, especially in X-ray and radio bands.
We release the next installment of the Stripe 82 X-ray survey point-source catalog, which currently covers 31.3 deg{sup 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 (>5σ) and Chandra (>4.5σ). 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 8.7 × 10{sup −16} erg s{sup −1} cm{sup −2}, 4.7 × 10{sup −15} erg s{sup −1} cm{sup −2}, and 2.1 × 10{sup −15} erg s{sup −1} cm{sup −2} in the soft (0.5–2 keV), hard (2–10 keV), and full bands (0.5–10 keV), respectively, with approximate half-area survey flux limits of 5.4 × 10{sup −15} erg s{sup −1} cm{sup −2}, 2.9 × 10{sup −14} erg s{sup −1} cm{sup −2}, and 1.7 × 10{sup −14} erg s{sup −1} cm{sup −2}. 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.
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