AAS 205th Meeting, 9-13 January 2005
Session 128 The Buildup of Galaxy Disks - Star Formation History
Oral, Wednesday, January 12, 2005, 2:00-3:30pm, California

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[128.02] A Comparison of Optical vs. IR SFR Diagnostics of Starforming Galaxies in the SPITZER Extragalactic First Look Survey

P.I. Choi (Spitzer Science Center), Spitzer Extragalactic First Look Survey Team

We investigate the instantaneous star formation rates (SFR) and extinction properties for a large (N\approx200), NIR (2.2\micron) + MIR (24\micron) selected sample of normal to luminous infrared galaxies (LIRGs) with ~.8 in the First Look Survey (FLS). We combine SPITZER MIPS 24\micron\, observations with high resolution optical Keck Deimos spectroscopy to compare infrared luminosity and optical emission-line derived star formation rates (SFRIR & SFROpt, respectively). The discrepancy between the optical vs. infrared derived SFRs suggest that our sample exhibits a wide range of optical extinctions (1.0v<2.5). Objects with SFRs of a few solar masses per year have Av values consistent with those of normal spirals (Av~.0). In contrast, LIRGs at z\gtrsim1, which make up a large fraction of our sample, have SFR\approx100 M\odot yr-1 and a mean optical extinction of Av\approx2.5. For SFRs derived from [OII] \lambda3727, this translates to as much as 95-98% attenuation of the [OII] line flux due to dust absorption. Measuring Av based on a SFRIR/SFROpt diagnostic, we find that Av is well correlated to the star formation rate. We derive an IR-luminosity-dependent Av function that we use to extinction correct our emission line luminosities. Application of this correction results in a correlation between SFRIR and SFROpt that has a mean scatter of 0.3~dex.

The author(s) of this abstract have provided an email address for comments about the abstract: pchoi@ipac.caltech.edu

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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.