Encoding of the infrared excess in the NUVrK color diagram for star-forming galaxies

S. Arnouts (1) , E. Le Floc’h (2) , J. Chevallard (3) , B. D. Johnson (3) , O. Ilbert , M. Treyer , H. Aussel (2) , P. Capak , D. B. Sanders , N. Scoville , H. J. Mccracken , B. Milliard , L. Pozzetti , M. Salvato

1 CFHT - Canada-France-Hawaii Telescope Corporation
2 AIM (UMR7158 / UMR_E_9005 / UM_112) - Astrophysique Interprétation Modélisation
3 IAP - Institut d'Astrophysique de Paris

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  μm sample in the COSMOS field (~16 400 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 ⟨IRX⟩ = ⟨ LIR/LUV ⟩ can be described by a single vector, NRK , that combines the two colors. The calibration between ⟨IRX⟩ and NRK allows us to recover the IR luminosity, LIR, with an accuracy of σ ~ 0.21 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 (SED) 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 ⟨IRX⟩ stripes in the NUVrK diagram. In conclusion, the NRK method, based only on the rest-frame UV/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.

Mots clés: infrared: galaxies; galaxies: evolution; ultraviolet: galaxies

Domaines: Astrophysique [astro-ph]

S. Arnouts, E. Le Floc’h, J. Chevallard, B. D. Johnson, O. Ilbert, et al.. Encoding of the infrared excess in the NUVrK color diagram for star-forming galaxies. Astronomy and Astrophysics - A&A, 2013, 558, pp.A67. ⟨10.1051/0004-6361/201321768⟩. ⟨cea-01135438⟩