Star Formation Rates and Extinction Properties of IR-luminous Galaxies in the Spitzer First Look Survey

January 2006 • 2006ApJ...637..227C

Authors • Choi, P. I. • Yan, L. • Im, M. • Helou, G. • Soifer, B. T. • Storrie-Lombardi, L. J. • Chary, R. • Teplitz, H. I. • Fadda, D. • Marleau, F. R. • Lacy, M. • Wilson, G. • Appleton, P. N. • Frayer, D. T. • Surace, J. A.

Abstract • We investigate the instantaneous star formation rates (SFRs) and extinction properties for a large (N=274), near-infrared (NIR: 2.2 μm) + mid-infrared (MIR: 24 μm)-selected sample of normal to ultraluminous infrared galaxies (ULIRGs; 10⁹<L_IR/L_solar<10^12.5) with <z>~0.8 in the Spitzer Extragalactic First Look Survey (FLS). We combine 24 μm observations with high-resolution Keck DEIMOS spectroscopy to derive optical emission-line (Hα, Hβ, and [O II]) and infrared star formation rates (SFR_opt and SFR_IR, respectively). Comparison of SFR diagnostics reveals a wide extinction range (1.0<A_V<4.0 mag) for this sample, even after removing spectroscopic and IRAC color-selected AGN candidates (~12% of the sample). Objects with SFRs of a few M_solar yr^-1 have extinction values consistent with normal spirals (A_V~1.0 mag). By contrast, LIRGs at z>~1, which comprise a fraction of our sample, have SFR~100 M_solar yr^-1 and a mean A_V~2.5 mag. This translates to a 97% mean [O II] λλ3727 attentuation and in extreme cases is as high as 99.7%. We derive an IR-luminosity-dependent A^IR_V function [A^IR_V=0.75log(L_IR/L_solar)-6.35 mag] that we use to extinction correct our line luminosities. The resulting correlation between SFR_IR and SFR_opt has a dispersion of ~0.2 dex (semi-interquartile range). Comparison of the A_V dependence on redshift and L_IR reveals that for a fixed L_IR, there is no significant A_V evolution. Comparison to previous studies reveals a mean attenuation that is intermediate between that of local optical/UV- and radio-selected samples with a marginally stronger L_IR dependence.

Links

• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2006ApJ...637..227C
• PREPRINT http://arxiv.org/abs/astro-ph/0509894
• DATA https://irsa.ipac.caltech.edu/bibdata/2006/C/2006ApJ...637..227C.html
• ELECTR https://doi.org/10.1086%2F498388
• SPIRES http://inspirehep.net/search?p=find+eprint+astro-ph/0509894