Star formation rates of distant luminous infrared galaxies derived from Hα and IR luminosities ^*

¹ GEPI, Observatoire de Paris Meudon, 92190 Meudon, France
² CEA Saclay – Service d'Astrophysique, Orme des Merisiers, 91191 Gif-sur-Yvette Cedex, France
³ ESO, Karl-Schwarzschild Straße 2, 85748 Garching bei München, Germany
⁴ Instituto de Astrofísica de Canarias (IAC), via Lactea S/N, 38205 La Laguna, Tenerife, Spain 


Corresponding author: H. Flores, hector.flores@obspm.fr

Received: 14 March 2003
Accepted: 31 October 2003

Abstract

We present a study of the star formation rate (SFR) for a sample of 16 distant galaxies detected by ISOCAM at 15 μm in the CFRS0300+00 and CFRS1400+52 fields. Their high quality and intermediate resolution VLT/FORS spectra have allowed a proper correction of the Balmer emission lines from the underlying absorption. Extinction estimates using the Hβ/Hγ and the Hα/Hβ Balmer decrement are in excellent agreement, providing a robust measurement of the instantaneous SFR based on the extinction-corrected Hα luminosity. Star formation has also been estimated exploiting the correlations between IR luminosity and those at MIR and radio wavelengths. Our study shows that the relationship between the two SFR estimates follow two distinct regimes: (1) for galaxies with SFR_IR below ~100 /yr, the SFR deduced from Hα measurements is a good approximation of the global SFR and (2) for galaxies near ULIRG regime. The corrected Hα SFR understimated the SFR by a factor of 1.5 to 2. Our analyses suggest that heavily extincted regions completely hidden in optical bands (such as those found in Arp 220) contribute less than 20% of the global budget of star formation up to .