Evolution of the Most Luminous Dusty Galaxies

• Published in: The Astrophysical journal 2009-06, Vol.698 (2), p.1682-1697, Article 1682
• Main Authors: Weedman, Daniel W, Houck, James R
• Format: Article
• Language: English
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1088/0004-637X/698/2/1682

A summary of mid-infrared continuum luminosities arising from dust is given for very luminous galaxies, L IR > 1012 L , with 0.005 0.7 in the 9.7 is a subset of m silicate absorption feature (i.e., half of the continuum is absorbed) and having equivalent width of the 6.2 is a subset of m polycyclic aromatic hydrocarbon feature < 0.1 is a subset of m (to avoid sources with a significant starburst component). Unobscured AGNs are defined as those that show silicate in emission. Luminosity Delta L Delta (8 is a subset of m) for the most luminous obscured AGNs is found to scale as (1+z)2.6 to z = 2.8. For unobscured AGNs, the scaling with redshift is similar, but luminosities Delta L Delta (8 is a subset of m) are approximately three times greater for the most luminous sources. Using both obscured and unobscured AGNs having total infrared fluxes from the Infrared Astronomical Satellite, empirical relations are found between Delta L Delta (8 is a subset of m) and L IR. Combining these relations with the redshift scaling of luminosity, we conclude that the total infrared luminosities for the most luminous obscured AGNs, L IR(AGNobscured) in L , scale as log L IR(AGNobscured) = 12.3 - 0.25 + 2.6(-0.3)log(1+z), and for the most luminous unobscured AGNs, scale as log L IR(AGN1) = 12.6(-0.15) + 2.6(-0.3)log(1+z). We previously determined that the most luminous starbursts scale as log L IR(SB) = 11.8 - 0.3 + 2.5(-0.3)log(1+z), indicating that the most luminous AGNs are about 10 times more luminous than the most luminous starbursts. Results are consistent with obscured and unobscured AGNs having the same total luminosities with differences arising only from orientation, such that the obscured AGNs are observed through very dusty clouds which extinct about 50% of the intrinsic luminosity at 8 is a subset of m. Extrapolations of observable f Delta (24 is a subset of m) to z = 6 are made using evolution results for these luminous sources. Both obscured and unobscured AGNs should be detected to z ~ 6 by Spitzer surveys with f Delta (24 is a subset of m) > 0.3 mJy, even without luminosity evolution for z > 2.5. By contrast, the most luminous starbursts cannot be detected for z > 3, even if luminosity evolution continues beyond z = 2.5.