Chasing highly obscured QSOs in the cosmos field

F. Fiore, S. Puccetti, M. Brusa, M. Salvato, G. Zamorani, T. Aldcroft, H. Aussel, H. Brunner, P. Capak, Nico Cappelluti, F. Civano, A. Comastri, M. Elvis, C. Feruglio, A. Finoguenov, A. Fruscione, R. Gilli, G. Hasinger, A. Koekemoer, J. KartaltepeO. Ilbert, C. Impey, E. Le Floc'H, S. Lilly, V. Mainieri, A. Martinez-Sansigre, H. J. McCracken, N. Menci, A. Merloni, T. Miyaji, D. B. Sanders, M. Sargent, E. Schinnerer, N. Scoville, J. Silverman, V. Smolcic, A. Steffen, P. Santini, Y. Taniguchi, D. Thompson, J. R. Trump, C. Vignali, M. Urry, L. Yan

Research output: Contribution to journalArticle

159 Citations (Scopus)

Abstract

A large population of heavily obscured, Compton-thick active galactic nuclei (AGNs) is predicted by AGN synthesis models for the cosmic X-ray background and by the "relic" supermassive black hole mass function measured from local bulges. However, even the deepest X-ray surveys are inefficient to search for these elusive AGNs. Alternative selection criteria, combining mid-infrared with near-infrared, and optical photometry, have instead been successful in pinpointing a large population of Compton-thick AGNs. We take advantage of the deep Chandra and Spitzer coverage of a large area (more than 10 times the area covered by the Chandra deep fields, CDFs) in the Cosmic Evolution Survey (COSMOS) field to extend the search of highly obscured, Compton-thick active nuclei to higher luminosity. These sources have low surface density, and therefore large samples can be provided only through large area surveys, like the COSMOS survey. We analyze the X-ray properties of COSMOS MIPS sources with 24 μm fluxes higher than 550 μJy. For the MIPS sources not directly detected in the Chandra images, we produce stacked images in soft and hard X-rays bands. To estimate the fraction of Compton-thick AGN in the MIPS source population, we compare the observed stacked count rates and hardness ratios to those predicted by detailed Monte Carlo simulations, including both obscured AGN and star-forming galaxies. The volume density of Compton-thick QSOs (log L(2-10 keV) = 44-45 erg s-1, or logλL λ(5.8 μm) = 44.79-46.18 erg s-1 for a typical infrared to X-ray luminosity ratio) evaluated in this way is (4.8 ± 1.1) × 10-6 Mpc-3 in the redshift bin 1.2-2.2. This density is ∼44% of all X-ray-selected QSOs in the same redshift and luminosity bin, and it is consistent with the expectation of the most up-to-date AGN synthesis models for the cosmic X-ray background (Gilli et al. 2007). The density of lower luminosity Compton-thick AGNs (log L(2-10 keV) = 43.5-44) at z = 0.7-1.2 is (3.7 ± 1.1) × 10-5 Mpc-3, corresponding to ∼67% of X-ray-selected AGNs. The comparison between the fraction of infrared-selected, Compton-thick AGNs to the X-ray selected, unobscured, and moderately obscured AGNs at high and low luminosity suggests that Compton-thick AGNs follow a luminosity dependence similar to that discovered for Compton-thin AGNs, becoming relatively rarer at high luminosities. We estimate that the fraction of AGNs (unobscured, moderately obscured, and Compton thick) to the total MIPS source population is 49 ± 10%, a value significantly higher than that previously estimated at similar 24 μm fluxes. We discuss how our findings can constrain AGN feedback models.

Original languageEnglish (US)
Pages (from-to)447-462
Number of pages16
JournalAstrophysical Journal
Volume693
Issue number1
DOIs
StatePublished - Mar 1 2009
Externally publishedYes

Fingerprint

cosmos
active galactic nuclei
quasars
luminosity
x rays
erg
field survey
hardness
near infrared
synthesis
estimates

Keywords

  • galaxies: active
  • galaxies: high-redshift
  • X-rays: diffuse background

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Fiore, F., Puccetti, S., Brusa, M., Salvato, M., Zamorani, G., Aldcroft, T., ... Yan, L. (2009). Chasing highly obscured QSOs in the cosmos field. Astrophysical Journal, 693(1), 447-462. https://doi.org/10.1088/0004-637X/693/1/447

Chasing highly obscured QSOs in the cosmos field. / Fiore, F.; Puccetti, S.; Brusa, M.; Salvato, M.; Zamorani, G.; Aldcroft, T.; Aussel, H.; Brunner, H.; Capak, P.; Cappelluti, Nico; Civano, F.; Comastri, A.; Elvis, M.; Feruglio, C.; Finoguenov, A.; Fruscione, A.; Gilli, R.; Hasinger, G.; Koekemoer, A.; Kartaltepe, J.; Ilbert, O.; Impey, C.; Le Floc'H, E.; Lilly, S.; Mainieri, V.; Martinez-Sansigre, A.; McCracken, H. J.; Menci, N.; Merloni, A.; Miyaji, T.; Sanders, D. B.; Sargent, M.; Schinnerer, E.; Scoville, N.; Silverman, J.; Smolcic, V.; Steffen, A.; Santini, P.; Taniguchi, Y.; Thompson, D.; Trump, J. R.; Vignali, C.; Urry, M.; Yan, L.

In: Astrophysical Journal, Vol. 693, No. 1, 01.03.2009, p. 447-462.

Research output: Contribution to journalArticle

Fiore, F, Puccetti, S, Brusa, M, Salvato, M, Zamorani, G, Aldcroft, T, Aussel, H, Brunner, H, Capak, P, Cappelluti, N, Civano, F, Comastri, A, Elvis, M, Feruglio, C, Finoguenov, A, Fruscione, A, Gilli, R, Hasinger, G, Koekemoer, A, Kartaltepe, J, Ilbert, O, Impey, C, Le Floc'H, E, Lilly, S, Mainieri, V, Martinez-Sansigre, A, McCracken, HJ, Menci, N, Merloni, A, Miyaji, T, Sanders, DB, Sargent, M, Schinnerer, E, Scoville, N, Silverman, J, Smolcic, V, Steffen, A, Santini, P, Taniguchi, Y, Thompson, D, Trump, JR, Vignali, C, Urry, M & Yan, L 2009, 'Chasing highly obscured QSOs in the cosmos field', Astrophysical Journal, vol. 693, no. 1, pp. 447-462. https://doi.org/10.1088/0004-637X/693/1/447
Fiore F, Puccetti S, Brusa M, Salvato M, Zamorani G, Aldcroft T et al. Chasing highly obscured QSOs in the cosmos field. Astrophysical Journal. 2009 Mar 1;693(1):447-462. https://doi.org/10.1088/0004-637X/693/1/447
Fiore, F. ; Puccetti, S. ; Brusa, M. ; Salvato, M. ; Zamorani, G. ; Aldcroft, T. ; Aussel, H. ; Brunner, H. ; Capak, P. ; Cappelluti, Nico ; Civano, F. ; Comastri, A. ; Elvis, M. ; Feruglio, C. ; Finoguenov, A. ; Fruscione, A. ; Gilli, R. ; Hasinger, G. ; Koekemoer, A. ; Kartaltepe, J. ; Ilbert, O. ; Impey, C. ; Le Floc'H, E. ; Lilly, S. ; Mainieri, V. ; Martinez-Sansigre, A. ; McCracken, H. J. ; Menci, N. ; Merloni, A. ; Miyaji, T. ; Sanders, D. B. ; Sargent, M. ; Schinnerer, E. ; Scoville, N. ; Silverman, J. ; Smolcic, V. ; Steffen, A. ; Santini, P. ; Taniguchi, Y. ; Thompson, D. ; Trump, J. R. ; Vignali, C. ; Urry, M. ; Yan, L. / Chasing highly obscured QSOs in the cosmos field. In: Astrophysical Journal. 2009 ; Vol. 693, No. 1. pp. 447-462.
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abstract = "A large population of heavily obscured, Compton-thick active galactic nuclei (AGNs) is predicted by AGN synthesis models for the cosmic X-ray background and by the {"}relic{"} supermassive black hole mass function measured from local bulges. However, even the deepest X-ray surveys are inefficient to search for these elusive AGNs. Alternative selection criteria, combining mid-infrared with near-infrared, and optical photometry, have instead been successful in pinpointing a large population of Compton-thick AGNs. We take advantage of the deep Chandra and Spitzer coverage of a large area (more than 10 times the area covered by the Chandra deep fields, CDFs) in the Cosmic Evolution Survey (COSMOS) field to extend the search of highly obscured, Compton-thick active nuclei to higher luminosity. These sources have low surface density, and therefore large samples can be provided only through large area surveys, like the COSMOS survey. We analyze the X-ray properties of COSMOS MIPS sources with 24 μm fluxes higher than 550 μJy. For the MIPS sources not directly detected in the Chandra images, we produce stacked images in soft and hard X-rays bands. To estimate the fraction of Compton-thick AGN in the MIPS source population, we compare the observed stacked count rates and hardness ratios to those predicted by detailed Monte Carlo simulations, including both obscured AGN and star-forming galaxies. The volume density of Compton-thick QSOs (log L(2-10 keV) = 44-45 erg s-1, or logλL λ(5.8 μm) = 44.79-46.18 erg s-1 for a typical infrared to X-ray luminosity ratio) evaluated in this way is (4.8 ± 1.1) × 10-6 Mpc-3 in the redshift bin 1.2-2.2. This density is ∼44{\%} of all X-ray-selected QSOs in the same redshift and luminosity bin, and it is consistent with the expectation of the most up-to-date AGN synthesis models for the cosmic X-ray background (Gilli et al. 2007). The density of lower luminosity Compton-thick AGNs (log L(2-10 keV) = 43.5-44) at z = 0.7-1.2 is (3.7 ± 1.1) × 10-5 Mpc-3, corresponding to ∼67{\%} of X-ray-selected AGNs. The comparison between the fraction of infrared-selected, Compton-thick AGNs to the X-ray selected, unobscured, and moderately obscured AGNs at high and low luminosity suggests that Compton-thick AGNs follow a luminosity dependence similar to that discovered for Compton-thin AGNs, becoming relatively rarer at high luminosities. We estimate that the fraction of AGNs (unobscured, moderately obscured, and Compton thick) to the total MIPS source population is 49 ± 10{\%}, a value significantly higher than that previously estimated at similar 24 μm fluxes. We discuss how our findings can constrain AGN feedback models.",
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author = "F. Fiore and S. Puccetti and M. Brusa and M. Salvato and G. Zamorani and T. Aldcroft and H. Aussel and H. Brunner and P. Capak and Nico Cappelluti and F. Civano and A. Comastri and M. Elvis and C. Feruglio and A. Finoguenov and A. Fruscione and R. Gilli and G. Hasinger and A. Koekemoer and J. Kartaltepe and O. Ilbert and C. Impey and {Le Floc'H}, E. and S. Lilly and V. Mainieri and A. Martinez-Sansigre and McCracken, {H. J.} and N. Menci and A. Merloni and T. Miyaji and Sanders, {D. B.} and M. Sargent and E. Schinnerer and N. Scoville and J. Silverman and V. Smolcic and A. Steffen and P. Santini and Y. Taniguchi and D. Thompson and Trump, {J. R.} and C. Vignali and M. Urry and L. Yan",
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T1 - Chasing highly obscured QSOs in the cosmos field

AU - Fiore, F.

AU - Puccetti, S.

AU - Brusa, M.

AU - Salvato, M.

AU - Zamorani, G.

AU - Aldcroft, T.

AU - Aussel, H.

AU - Brunner, H.

AU - Capak, P.

AU - Cappelluti, Nico

AU - Civano, F.

AU - Comastri, A.

AU - Elvis, M.

AU - Feruglio, C.

AU - Finoguenov, A.

AU - Fruscione, A.

AU - Gilli, R.

AU - Hasinger, G.

AU - Koekemoer, A.

AU - Kartaltepe, J.

AU - Ilbert, O.

AU - Impey, C.

AU - Le Floc'H, E.

AU - Lilly, S.

AU - Mainieri, V.

AU - Martinez-Sansigre, A.

AU - McCracken, H. J.

AU - Menci, N.

AU - Merloni, A.

AU - Miyaji, T.

AU - Sanders, D. B.

AU - Sargent, M.

AU - Schinnerer, E.

AU - Scoville, N.

AU - Silverman, J.

AU - Smolcic, V.

AU - Steffen, A.

AU - Santini, P.

AU - Taniguchi, Y.

AU - Thompson, D.

AU - Trump, J. R.

AU - Vignali, C.

AU - Urry, M.

AU - Yan, L.

PY - 2009/3/1

Y1 - 2009/3/1

N2 - A large population of heavily obscured, Compton-thick active galactic nuclei (AGNs) is predicted by AGN synthesis models for the cosmic X-ray background and by the "relic" supermassive black hole mass function measured from local bulges. However, even the deepest X-ray surveys are inefficient to search for these elusive AGNs. Alternative selection criteria, combining mid-infrared with near-infrared, and optical photometry, have instead been successful in pinpointing a large population of Compton-thick AGNs. We take advantage of the deep Chandra and Spitzer coverage of a large area (more than 10 times the area covered by the Chandra deep fields, CDFs) in the Cosmic Evolution Survey (COSMOS) field to extend the search of highly obscured, Compton-thick active nuclei to higher luminosity. These sources have low surface density, and therefore large samples can be provided only through large area surveys, like the COSMOS survey. We analyze the X-ray properties of COSMOS MIPS sources with 24 μm fluxes higher than 550 μJy. For the MIPS sources not directly detected in the Chandra images, we produce stacked images in soft and hard X-rays bands. To estimate the fraction of Compton-thick AGN in the MIPS source population, we compare the observed stacked count rates and hardness ratios to those predicted by detailed Monte Carlo simulations, including both obscured AGN and star-forming galaxies. The volume density of Compton-thick QSOs (log L(2-10 keV) = 44-45 erg s-1, or logλL λ(5.8 μm) = 44.79-46.18 erg s-1 for a typical infrared to X-ray luminosity ratio) evaluated in this way is (4.8 ± 1.1) × 10-6 Mpc-3 in the redshift bin 1.2-2.2. This density is ∼44% of all X-ray-selected QSOs in the same redshift and luminosity bin, and it is consistent with the expectation of the most up-to-date AGN synthesis models for the cosmic X-ray background (Gilli et al. 2007). The density of lower luminosity Compton-thick AGNs (log L(2-10 keV) = 43.5-44) at z = 0.7-1.2 is (3.7 ± 1.1) × 10-5 Mpc-3, corresponding to ∼67% of X-ray-selected AGNs. The comparison between the fraction of infrared-selected, Compton-thick AGNs to the X-ray selected, unobscured, and moderately obscured AGNs at high and low luminosity suggests that Compton-thick AGNs follow a luminosity dependence similar to that discovered for Compton-thin AGNs, becoming relatively rarer at high luminosities. We estimate that the fraction of AGNs (unobscured, moderately obscured, and Compton thick) to the total MIPS source population is 49 ± 10%, a value significantly higher than that previously estimated at similar 24 μm fluxes. We discuss how our findings can constrain AGN feedback models.

AB - A large population of heavily obscured, Compton-thick active galactic nuclei (AGNs) is predicted by AGN synthesis models for the cosmic X-ray background and by the "relic" supermassive black hole mass function measured from local bulges. However, even the deepest X-ray surveys are inefficient to search for these elusive AGNs. Alternative selection criteria, combining mid-infrared with near-infrared, and optical photometry, have instead been successful in pinpointing a large population of Compton-thick AGNs. We take advantage of the deep Chandra and Spitzer coverage of a large area (more than 10 times the area covered by the Chandra deep fields, CDFs) in the Cosmic Evolution Survey (COSMOS) field to extend the search of highly obscured, Compton-thick active nuclei to higher luminosity. These sources have low surface density, and therefore large samples can be provided only through large area surveys, like the COSMOS survey. We analyze the X-ray properties of COSMOS MIPS sources with 24 μm fluxes higher than 550 μJy. For the MIPS sources not directly detected in the Chandra images, we produce stacked images in soft and hard X-rays bands. To estimate the fraction of Compton-thick AGN in the MIPS source population, we compare the observed stacked count rates and hardness ratios to those predicted by detailed Monte Carlo simulations, including both obscured AGN and star-forming galaxies. The volume density of Compton-thick QSOs (log L(2-10 keV) = 44-45 erg s-1, or logλL λ(5.8 μm) = 44.79-46.18 erg s-1 for a typical infrared to X-ray luminosity ratio) evaluated in this way is (4.8 ± 1.1) × 10-6 Mpc-3 in the redshift bin 1.2-2.2. This density is ∼44% of all X-ray-selected QSOs in the same redshift and luminosity bin, and it is consistent with the expectation of the most up-to-date AGN synthesis models for the cosmic X-ray background (Gilli et al. 2007). The density of lower luminosity Compton-thick AGNs (log L(2-10 keV) = 43.5-44) at z = 0.7-1.2 is (3.7 ± 1.1) × 10-5 Mpc-3, corresponding to ∼67% of X-ray-selected AGNs. The comparison between the fraction of infrared-selected, Compton-thick AGNs to the X-ray selected, unobscured, and moderately obscured AGNs at high and low luminosity suggests that Compton-thick AGNs follow a luminosity dependence similar to that discovered for Compton-thin AGNs, becoming relatively rarer at high luminosities. We estimate that the fraction of AGNs (unobscured, moderately obscured, and Compton thick) to the total MIPS source population is 49 ± 10%, a value significantly higher than that previously estimated at similar 24 μm fluxes. We discuss how our findings can constrain AGN feedback models.

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KW - X-rays: diffuse background

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