2013ApJ...768..103C -
Astrophys. J., 768, 103 (2013/May-2)
A generalized power-law diagnostic for infrared galaxies at z > 1: active galactic nuclei and hot interstellar dust.
CAPUTI K.I.
Abstract (from CDS):
I present a generalized power-law (PL) diagnostic which allows one to identify the presence of active galactic nuclei (AGNs) in infrared (IR) galaxies at z > 1, down to flux densities at which the extragalactic IR background is mostly resolved. I derive this diagnostic from the analysis of 174 galaxies with Sν(24 µm)>80 µJy and spectroscopic redshifts zspec> 1 in the Chandra Deep Field South, for which I study the rest-frame UV/optical/near-IR spectral energy distributions (SEDs), after subtracting a hot-dust, PL component with three possible spectral indices α = 1.3, 2.0, and 3.0. I obtain that 35% of these 24 µm sources are power-law composite galaxies (PLCGs), which I define as those galaxies for which the SED fitting with stellar templates, without any previous PL subtraction, can be rejected with >2σ confidence. Subtracting the PL component from the PLCG SEDs produces stellar mass correction factors <1.5 in >80% of cases. The PLCG incidence is especially high (47%) at 1.0 < z < 1.5. To unveil which PLCGs host AGNs, I conduct a combined analysis of 4 Ms X-ray data, galaxy morphologies, and a graybody modeling of the hot dust. I find that (1) 77% of all the X-ray AGNs in my 24 µm sample at 1.0 < z < 1.5 are recognized by the PLCG criterion; (2) PLCGs with α = 1.3 or 2.0 have regular morphologies and Tdust ≳ 1000 K, indicating nuclear activity. Instead, PLCGs with α = 3.0 are characterized by disturbed galaxy dynamics, and a hot interstellar medium can explain their dust temperatures Tdust∼ 700-800 K. Overall, my results indicate that the fraction of AGNs among 24 µm sources is between ∼30% and 52% at 1.0 < z < 1.5.
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Journal keyword(s):
infrared: galaxies - galaxies: evolution - galaxies: high-redshift
Simbad objects:
2
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