The Role of Star Formation and an AGN in Dust Heating of z = 0.3-2.8 Galaxies. I. Evolution with Redshift and Luminosity

November 2015 • 2015ApJ...814....9K

Authors • Kirkpatrick, Allison • Pope, Alexandra • Sajina, Anna • Roebuck, Eric • Yan, Lin • Armus, Lee • Díaz-Santos, Tanio • Stierwalt, Sabrina

Abstract • We characterize infrared spectral energy distributions of 343 (ultra)luminous infrared galaxies from z = 0.3-2.8. We diagnose the presence of an active galactic nucleus (AGN) by decomposing individual Spitzer mid-IR spectroscopy into emission from star formation and an AGN-powered continuum; we classify sources as star-forming galaxies (SFGs), AGNs, or composites. Composites comprise 30% of our sample and are prevalent at faint and bright S₂₄, making them an important source of IR AGN emission. We combine spectroscopy with multiwavelength photometry, including Herschel imaging, to create three libraries of publicly available templates (2-1000 μm). We fit the far-IR emission using a two-temperature modified blackbody to measure cold and warm dust temperatures (T_c and T_w). We find that T_c does not depend on mid-IR classification, while T_w shows a notable increase as the AGN grows more luminous. We measure a quadratic relationship between mid-IR AGN emission and total AGN contribution to L_IR. AGNs, composites, and SFGs separate in S₈/S_3.6 and S₂₅₀/S₂₄, providing a useful diagnostic for estimating relative amounts of these sources. We estimate that >40% of IR-selected samples host an AGN, even at faint selection thresholds (S₂₄ > 100 μJy). Our decomposition technique and color diagnostics are relevant given upcoming observations with the James Webb Space Telescope.

Links

• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2015ApJ...814....9K
• PDF https://iopscience.iop.org/article/10.1088/0004-637X/814/1/9/pdf
• PDF https://stacks.iop.org/0004-637X/814/9/pdf
• PREPRINT http://arxiv.org/abs/1510.02806
• DATA http://archives.esac.esa.int/hsa/whsa/?ACTION=PUBLICATION&ID=2015ApJ...814....9K
• DATA https://irsa.ipac.caltech.edu/bibdata/2015/K/2015ApJ...814....9K.html
• ELECTR https://doi.org/10.1088%2F0004-637X%2F814%2F1%2F9