Multiwavelength Study of Massive Galaxies at z ~ 2. II. Widespread Compton-thick Active Galactic Nuclei and the Concurrent Growth of Black Holes and Bulges

By E. Daddi, D. Alexander, Mark Dickinson, R. Gilli, A. Renzini, D. Elbaz, A. Cimatti, R. Chary, D. Frayer, F. Bauer and 9 more. 2007

280 citations recorded by the source corpus.

Approximately 20%-30% of 1.4 ≲ z ≲ 2.5 galaxies with KVega < 22 detected with Spitzer MIPS at 24 μm show excess mid-IR emission relative to that expected based on the rates of star formation measured from other multiwavelength data. These galaxies also display some near-IR excess in Spitzer IRAC data, with an SED peaking longward of 1.6 μm in the rest frame, indicating the presence of warm dust emission usually absent in star-forming galaxies. Stacking Chandra data for the mid-IR excess galaxies yields a significant hard X-ray detection at rest-frame energies >6.2 keV. The stacked X-ray spectrum rises steeply at >10 keV, suggesting that these sources host Compton-thick AGNs with column densities NH ≳ 1024 cm-2 and an average, unobscured X-ray luminosity L2-8 keV ≈ (1-4) × 1043 ergs s-1. Their sky density (~3200 deg-2) and space density (~2.6 × 10-4 Mpc-3) are twice those of X-ray-detected AGNs at z ≈ 2, and much larger than those of previously known Compton-thick sources at similar redshifts. The mid-IR excess galaxies are part of the long sought after population of distant heavily obscured AGNs predicted by synthesis models of the X-ray background. The fraction of mid-IR excess objects increases with galaxy mass, reaching ~50%-60% for M ~ 1011 M☉, an effect likely connected with downsizing in galaxy formation. The ratio of the inferred black hole growth rate from these Compton-thick sources to the global star formation rate at z = 2 is similar to the mass ratio of black holes to stars in local spheroids, implying concurrent growth of both within the precursors of today's massive galaxies.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/18664df046effa3c031623c6f4497d1b3d51da4d

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In Astronomy and Astrophysics

1. D. M. Alexander
2. P. Hopkins
3. L. Hernquist
4. P. V. van Dokkum
5. R. Dav'e
6. E. Daddi
7. C. Conroy
8. R. Somerville

In Instrumentation

1. P. V. van Dokkum
2. M. Franx
3. P. Hopkins
4. C. Conroy
5. R. Dav'e
6. L. Hernquist
7. D. M. Alexander
8. A. Dekel

Citations in the corpus

• TOWARD THE STANDARD POPULATION SYNTHESIS MODEL OF THE X-RAY BACKGROUND: EVOLUTION OF X-RAY LUMINOSITY AND ABSORPTION FUNCTIONS OF ACTIVE GALACTIC NUCLEI INCLUDING COMPTON-THICK POPULATIONS (2014, methodology): “In the figure, we also plot the estimate based on X-ray detected heavily obscured AGNs in the CDFS atz= 1.4− 2.6 with log LX >∼ 43 obtained by Alexander et al. (2011) (filled circle), who updated the Daddi et al. (2007) result using deeper X-ray data and new analyses.”
• EMU: Evolutionary Map of the Universe (2011, background): “Intriguingly, embedded AGNs have been found in 20–30% of z, 2 massive star-forming galaxies (Daddi et al. 2007).”
• IDENTIFYING LUMINOUS ACTIVE GALACTIC NUCLEI IN DEEP SURVEYS: REVISED IRAC SELECTION CRITERIA (2012, background): “…al. (2004) was designed to identify star-forming (sBzK) and passive (pBzK) galaxies at 1.4 ∼< z ∼< 2.5, although it also identifies luminous AGN generally removed from BzK-selected samples on the basis of their hard X-ray or MIR power-law emission (see, e.g., Sharp et al. 2002; Daddi et al. 2007a).”
• Unveiling Obscured Accretion in the Chandra Deep Field-South (2007, result): “After submission of this paper to ApJ we became aware of a work by a different group reaching similar conclusions (Daddi et al. 2007).”
• ALMA SPECTROSCOPIC SURVEY IN THE HUBBLE ULTRA DEEP FIELD: THE INFRARED EXCESS OF UV-SELECTED z = 2–10 GALAXIES AS A FUNCTION OF UV-CONTINUUM SLOPE AND STELLAR MASS (2016, methodology): “A series of intermediateredshift studies (Reddy et al. 2006, 2010; Daddi et al. 2007; Pannella et al. 2009) found this relationship to be approximately valid when comparing the observed IR luminosities of galaxies to the predictions from the M99 IRX-β relationship.”
• A Herschel view of the far-infrared properties of submillimetre galaxies (2012, background): “…SMGs belong to a class of galaxies offset from the so-called “main sequence of star-formation” which links the SFRs and stellar masses of normal star-forming galaxies (SFGs) over a broad range of redshifts (Noeske et al. 2007; Daddi et al. 2007b; Elbaz et al. 2007; Rodighiero et al. 2010, 2011).”
• Enhanced star formation rates in AGN hosts with respect to inactive galaxies from PEP-Herschel observations (2012, background): “The first reason is that, given their strong MIR emission (e.g. Daddi et al. 2007a; Fiore et al. 2008), AGN hosts are more represented in the 24µm prior list compared to inactive galaxies (for a given FIR host’s luminosity, they have a larger probability of being detected at 24µm).”
• THE SPACE DENSITY OF COMPTON-THICK ACTIVE GALACTIC NUCLEUS AND THE X-RAY BACKGROUND (2009, methodology): “…of the absorbed energy is re-emitted at mid-IR wavelengths, deep observations with the Spitzer observatory can be used to select CT AGN candidates at high redshift, z∼2 (Daddi et al. 2007; Fiore et al. 2008; Alexander et al. 2008), yielding an upper limit to the number density of these sources.”
• VERY HIGH GAS FRACTIONS AND EXTENDED GAS RESERVOIRS IN z = 1.5 DISK GALAXIES (2009, methodology): “Currently, 89 BzK galaxies of the Daddi et al. (2007) sample in GOODS-N have a spectroscopic redshift, from various observing campaigns and from the literature.”
• Herschel unveils a puzzling uniformity of distant dusty galaxies (2010, methodology): “At z > 1.5, IR SEDs are substantially different from local ones as suggested by previous studies (Daddi et al. 2007; Papovich et al. 2007; Magnelli et al. 2010).”
• ON STAR FORMATION RATES AND STAR FORMATION HISTORIES OF GALAXIES OUT TO z ∼ 3 (2011, methodology): “The relation between the instantaneous star formation rate (SFR) and stellar mass of individual galaxies sheds light on how (in bursts or gradually) and where (in galaxies of what mass) the star-forming activity took place (Noeske et al. 2007; Elbaz et al. 2007; Daddi et al. 2007a).”
• Cosmic X-ray surveys of distant active galaxies (2015, background): “The strong increase in the average SFR for the X-ray AGNs with redshift tracks the increase seen in the overall star-forming galaxy population [≈ (1 + z)4; e.g., Daddi et al 2007b; Noeske et al 2007; Rodighiero et al 2010; Elbaz et al 2011].”
• THE BULK OF THE BLACK HOLE GROWTH SINCE z ∼ 1 OCCURS IN A SECULAR UNIVERSE: NO MAJOR MERGER–AGN CONNECTION (2010, methodology): “The Xray properties of such obscured objects have been successfully studied in the literature by the means of a stacking analysis of X-ray data (e.g., Daddi et al. 2007; Fiore et al. 2009).”
• THE KMOS3D SURVEY: DESIGN, FIRST RESULTS, AND THE EVOLUTION OF GALAXY KINEMATICS FROM 0.7 ⩽ z ⩽ 2.7 (2014, background): “The amplitude of the MS reflects the evolution of the cosmic SFR density from the peak activity at z ∼ 1 − 2.5 to the “winding down” epochs at z < 1 (e.g. Noeske et al. 2007; Daddi et al. 2007a; Elbaz et al. 2007; Rodighiero et al. 2011; Whitaker et al. 2014).”
• FORMING COMPACT MASSIVE GALAXIES (2015, result): “This high AGN fraction is consistent with previous studies of massive star forming galaxies at these redshifts (e.g., Papovich et al. 2006; Daddi et al. 2007; Kriek et al. 2007; Barro et al. 2013; Förster Schreiber et al. 2014).”
• MASS AND ENVIRONMENT AS DRIVERS OF GALAXY EVOLUTION IN SDSS AND zCOSMOS AND THE ORIGIN OF THE SCHECHTER FUNCTION (2010, methodology): “…constancy of sSFR with stellar mass in star-forming galaxies has also been seen at higher redshifts, e.g. Elbaz et al. (2007) at z ~ 1 and Daddi et al. (2007) at z ~ 2, and a similar relation was derived by Pannella et al. (2009) using a completely independent indicator of SFR (radio…”
• PACS Evolutionary Probe (PEP) – a Herschel key program (2011, methodology): “The GOODS-N SDP observation thus reach the star formation ‘main sequence’ for massive galaxies at that redshift (Daddi et al. 2007a).”