Obscured accretion from AGN surveys

Vignali, C.

doi:10.1017/s1743921314003548

Cited by 3 publications

(2 citation statements)

References 100 publications

(96 reference statements)

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“…Besides the many observational evidences of feedback processes in terms of outflows in molecular and neutral/ionized gas, at both low and high redshift (e.g., Nesvadba et al 2008;Feruglio et al 2010;Maiolino et al 2012;Harrison et al 2012Harrison et al , 2014Cicone et al 2014;Brusa et al 2014), including signatures in the X-ray band (e.g., Chartas et al 2002;Tombesi et al 2012, and references therein), this "picture" still needs to be confirmed in most of its aspects, in particular for what concerns the key phase during which large amounts of gas are funneled to the center, thus inducing both obscured accretion and star formation (e.g., Treister et al 2010). Type 2 (obscured) AGN are witnesses and, at the same time, main actors of such phase; finding them across cosmic time is therefore crucial to place constraints on AGN vs. galaxy co-evolution models (see, e.g., the reviews by Merloni &Heinz 2013 andVignali 2014) as well as on X-ray background synthesis models (XRB; e.g., Gilli et al 2007;Ballantyne 2009;Treister et al 2009;Akylas et al 2012;Shi et al 2013; see also Moretti et al 2012).…”

Section: Introductionmentioning

confidence: 99%

The space density of Compton-thick AGN atz≈ 0.8 in the zCOSMOS-Bright Survey

Vignali

Mignoli

Gilli

et al. 2014

A&A

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Context. The obscured accretion phase in black hole growth is a crucial ingredient in many models linking the active galactic nuclei (AGN) activity with the evolution of their host galaxy. At present, a complete census of obscured AGN is still missing, although several attempts in this direction have been carried out recently, mostly in the hard X-rays and at mid-infrared wavelengths.Aims. The purpose of this work is to assess whether the [Ne v] emission line at 3426 Å can reliably pick up obscured AGN up to z ≈ 1 by assuming that it is a reliable proxy of the intrinsic AGN luminosity and using moderately deep X-ray data to characterize the amount of obscuration. Methods. A sample of 69 narrow-line (Type 2) AGN at z ≈ 0.65-1.20 were selected from the 20k-zCOSMOS Bright galaxy sample on the basis of the presence of the [Ne v]3426 Å emission. The X-ray properties of these galaxies were then derived using the Chandra-COSMOS coverage of the field; the X-ray-to-[Ne v] flux ratio, coupled with X-ray spectral and stacking analyses, was then used to infer whether Compton-thin or Compton-thick absorption is present in these sources. Then the [Ne v] luminosity function was computed to estimate the space density of Compton-thick AGN at z ≈ 0.8. Results. Twenty-three sources were detected by Chandra, and their properties are consistent with moderate obscuration (on average, ≈a few ×10 22 cm −2 ). The X-ray properties of the remaining 46 X-ray undetected Type 2 AGN (among which we expect to find the most heavily obscured objects) were derived using X-ray stacking analysis. Current data, supported by Monte Carlo simulations, indicate that a fraction as high as ≈40% of the present sample is likely to be Compton thick. The space density of Compton-thick AGN with logL 2−10 keV > 43.5 at z = 0.83 is Φ Thick = (9.1 ± 2.1) × 10 −6 Mpc −3 , in good agreement with both X-ray background model expectations and the previously measured space density for objects in a similar redshift and luminosity range. We regard our selection technique for Compton-thick AGN as clean but not complete, since even a mild extinction in the narrow-line region can suppress [Ne v] emission. Therefore, our estimate of their space density should be considered as a lower limit.

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Section: Introductionmentioning

confidence: 99%

The space density of Compton-thick AGN atz≈ 0.8 in the zCOSMOS-Bright Survey

Vignali

Mignoli

Gilli

et al. 2014

A&A

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“…Not only do X-ray surveys suffer from little quiescent galaxy contamination as stars produce little intrinsic X-ray radiation, they are further able to recover large samples of obscured AGNs due to the penetrating nature of light at these energetic wavelengths (e.g. Vignali 2014).…”

Section: Introductionmentioning

confidence: 99%

Characterizing the WISE-selected heavily obscured quasar population with optical spectroscopy from the Southern African Large Telescope

Hviding

Hickox

Hainline

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We present the results of an optical spectroscopic survey of 46 heavily obscured quasar candidates. Objects are selected using their mid-infrared (mid-IR) colours and magnitudes from the Wide-Field Infrared Survey Explorer (WISE ) and their optical magnitudes from the Sloan Digital Sky Survey (SDSS). Candidate Active Galactic Nuclei (AGNs) are selected to have mid-IR colours indicative of quasar activity and lie in a region of mid-IR colour space outside previously published X-ray based selection regions. We obtain optical spectra for our sample using the Robert Stobie Spectrograph on the Southern African Large Telescope. Thirty objects (65%) have identifiable emission lines, allowing for the determination of spectroscopic redshifts. Other than one object at z ∼ 2.6, candidates have moderate redshifts ranging from z = 0.1 to 0.8 with a median of 0.3. Twenty-one (70%) of our objects with identified redshift (46% of the whole sample) are identified as AGNs through common optical diagnostics. We model the spectral energy distributions of our sample and found that all require a strong AGN component, with an average intrinsic AGN fraction at 8 µm of 0.91. Additionally, the fits require large extinction coefficients with an average E(B − V) AGN = 17.8 (average A(V) AGN = 53.4). By focusing on the area outside traditional mid-IR photometric cuts, we are able to capture and characterise a population of deeply buried quasars that were previously unattainable through X-ray surveys alone.

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COSMOS2020: Investigating the AGN-obscured accretion phase at z ∼ 1 via [Ne V] selection

Barchiesi,

Vignali,

Pozzi

et al. 2024

A&A

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The black hole-and-galaxy (BH-galaxy) co-evolution paradigm predicts a phase where most of the star formation (SF) and BH accretion takes place in gas-rich environments, namely, in what are likely to be very obscured conditions. In the first phase of this growth, some of the galactic gas is funnelled toward the centre of the galaxy and is accreted into the supermassive BH, triggering active galactic nucleus (AGN) activity. The large quantity of gas and dust hides the emission and the AGN appears as an obscured (type 2) AGN. The degree of obscuration in type 2 AGNs may even reach values as high as $N_H>10^ $ cm$^ $ (i.e., Compton-thick, CT). Population synthesis models of the X-ray background (XRB) suggest that a large population of CT-AGN is, in fact, needed to explain the still unresolved XRB emission at energy above 20 keV. In this work, we investigated the properties of 94 type 2 AGN in COSMOS at $z=0.6-1.2$, performing optical-to-far-infrared (FIR) spectral energy distribution (SED) fitting of COSMOS2020 photometric data to estimate the AGN bolometric luminosity and stellar mass, star formation rate, age of the oldest stars, and molecular gas mass for their host-galaxy. In addition, we performed an X-ray spectral analysis of the 36 X-ray-detected sources to obtain reliable values of the AGN obscuration and intrinsic luminosity, as well as to constrain the AGN properties of the X-ray-undetected sources. We found that more than two-thirds of our sample is composed of very obscured sources ($ N H $ cm$^ $), with about 20<!PCT!> of the sources being candidate CT-AGN and half being AGNs in a strong phase of accretion ($ Edd > 0.1$). We built a mass- and redshift-matched control sample and its comparison with the sample indicates that the latter has a higher fraction of sources within the main sequence of star-forming galaxies and shows little evidence for AGNs quenching the SF. As the two samples have similar amounts of cold gas available to fuel the SF, this difference points towards a higher efficiency in forming stars in the sample. The comparison with the prediction from the in situ co-evolution model suggests that is an effective tool for selecting galaxies in the obscured growth phase of the BH-galaxy co-evolution paradigm. We find that the "quenching phase" is still to come for most of the sample and only few galaxies show evidence of quenched SF activity.

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Obscured accretion from AGN surveys

Cited by 3 publications

References 100 publications

The space density of Compton-thick AGN atz≈ 0.8 in the zCOSMOS-Bright Survey

The space density of Compton-thick AGN atz≈ 0.8 in the zCOSMOS-Bright Survey

Characterizing the WISE-selected heavily obscured quasar population with optical spectroscopy from the Southern African Large Telescope

COSMOS2020: Investigating the AGN-obscured accretion phase at z ∼ 1 via [Ne V] selection

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Obscured accretion from AGN surveys

Cited by 3 publications

References 100 publications

The space density of Compton-thick AGN atz≈ 0.8 in the zCOSMOS-Bright Survey

The space density of Compton-thick AGN atz≈ 0.8 in the zCOSMOS-Bright Survey

Characterizing the WISE-selected heavily obscured quasar population with optical spectroscopy from the Southern African Large Telescope

COSMOS2020: Investigating the AGN-obscured accretion phase at z ∼ 1 via [Ne V] selection

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COSMOS2020: Investigating the AGN-obscured accretion phase at z ∼ 1 via [Ne V] selection