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arXiv · 1309.0008

Encoding the infrared excess (IRX) in the NUVrK color diagram for star-forming galaxies

Stephane Arnouts·Emeric Le Floc'h·Jacopo Chevallard·Benjamin D. Johnson·Olivier Ilbert·Marie Treyer·Herve Aussel·Peter Capak·Dave B. Sanders·Nick Scoville·Henry J. McCracken·Bruno Milliard·Lucia Pozzetti·Mara Salvato
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Abstract

We present an empirical method of assessing the star formation rate (SFR) of star-forming galaxies based on their locations in the rest-frame color-color diagram (NUV-r) vs (r-K). By using the Spitzer 24 micron sample in the COSMOS field (~16400 galaxies with 0.2 < z < 1.3) and a local GALEX-SDSS-SWIRE sample (~700 galaxies with z < 0.2), we show that the mean infrared excess = < L_IR / L_UV > can be described by a single vector, NRK, that combines the two colors. The calibration between and NRK allows us to recover the IR luminosity, L_IR, with an accuracy of ~0.21 dex for the COSMOS sample and ~0.27 dex for the local one. The SFRs derived with this method agree with the ones based on the observed (UV+IR) luminosities and on the spectral energy distribution fitting for the vast majority (~85 %) of the star-forming population. Thanks to a library of model galaxy SEDs with realistic prescriptions for the star formation history, we show that we need to include a two-component dust model (i.e., birth clouds and diffuse ISM) and a full distribution of galaxy inclinations in order to reproduce the behavior of the stripes in the NUVrK diagram. In conclusion, the NRK method, based only on rest-frame UV and optical colors available in most of the extragalactic fields, offers a simple alternative of assessing the SFR of star-forming galaxies in the absence of far-IR or spectral diagnostic observations.

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Stephane Arnouts, Emeric Le Floc'h, Jacopo Chevallard, Benjamin D. Johnson, Olivier Ilbert, Marie Treyer, Herve Aussel, Peter Capak, Dave B. Sanders, Nick Scoville, Henry J. McCracken, Bruno Milliard, Lucia Pozzetti, Mara Salvato. 2013-08-30. Encoding the infrared excess (IRX) in the NUVrK color diagram for star-forming galaxies. https://doi.org/10.1051/0004-6361%2F201321768

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