E. Daddi et al. 2007 ApJ 670 173 doi:10.1086/521820
Multiwavelength Study of Massive Galaxies at z ~ 2. II. Widespread Compton-thick Active Galactic Nuclei and the Concurrent Growth of Black Holes and Bulges
FREE ISSUEE. Daddi1, D. M. Alexander2, M. Dickinson3, R. Gilli4, A. Renzini5, D. Elbaz1, A. Cimatti6, R. Chary7, D. Frayer7, F. E. Bauer8, W. N. Brandt9, M. Giavalisco10, N. A. Grogin11, M. Huynh7, J. Kurk12, M. Mignoli4, G. Morrison13,14, A. Pope15 and S. Ravindranath16
Show affiliationsApproximately 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.
- Subject headings
galaxies: active; galaxies: evolution; galaxies: formation; X-rays: galaxies
- Dates
-
Issue 1 (2007 November 20)
Received 2007 May 19, accepted for publication 2007 July 22
-
Multiwavelength Study of Massive Galaxies at z ~ 2. II. Widespread Compton-thick Active Galactic Nuclei and the Concurrent Growth of Black Holes and Bulges
E. Daddi et al. 2007 ApJ 670 173
-
Supergravity and IOSp(3, 1|4) gauge theory
T G Philbin 2003 Class. Quantum Grav. 20 4739
-
On the regularization procedure in classical electrodynamics
Yu Yaremko 2003 J. Phys. A: Math. Gen. 36 5149
-
Application of the non-adiabatic phase matrix method to vibrational excitation near a short-lived resonance: the case of
scattering
S Mazevet et al 1998 J. Phys. B: At. Mol. Opt. Phys. 31 4437
-
A rebinned backprojection-filtration algorithm for image reconstruction in helical cone-beam CT
Lifeng Yu et al 2007 Phys. Med. Biol. 52 5497
-
Time evolution of a catalytic surface reaction: oxidation of carbon monoxide
K Yaldram and A Sadiq 1989 J. Phys. A: Math. Gen. 22 L925
-
Studies of gel viscoelasticity by a wave interference technique
P R Williams and S R Ren 1996 J. Phys. D: Appl. Phys. 29 2718
-
Hybrid organic–inorganic spin-on-glass CuCl films for optoelectronic applications
M M Alam et al 2009 J. Phys. D: Appl. Phys. 42 225307
-
Supersymmetric extension of the scalar Born–Infeld equation
A J Hariton 2006 J. Phys. A: Math. Gen. 39 7105
-
Variability in atomic collision cascade distributions
M Hou et al 2001 J. Phys.: Condens. Matter 13 5365
Users also read
What's this?- Seven-year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Interpretation
- Fermi Large Area Telescope First Source Catalog
- Using 21 cm Absorption in Small Impact Parameter Galaxy-Quasar Pairs to Probe Low-redshift Damped and Sub-damped Lyα Systems