EDP Sciences
Free access
Volume 415, Number 3, March I 2004
Page(s) 885 - 888
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20034491

A&A 415, 885-888 (2004)
DOI: 10.1051/0004-6361:20034491

Star formation rates of distant luminous infrared galaxies derived from H $\alpha$ and IR luminosities

H. Flores1, F. Hammer1, D. Elbaz2, C. J. Cesarsky3, Y. C. Liang1, D. Fadda4 and N. Gruel1

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

(Received 14 March 2003 / Accepted 31 October 2003)

We present a study of the star formation rate (SFR) for a sample of 16 distant galaxies detected by ISOCAM at 15  $\mu$m 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 H $\beta$/H $\gamma$ and the H $\alpha$/H $\beta$ Balmer decrement are in excellent agreement, providing a robust measurement of the instantaneous SFR based on the extinction-corrected H $\alpha$ 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$_{\rm IR}$ below ~100  $M_{\odot}$/yr, the SFR deduced from H $\alpha$ measurements is a good approximation of the global SFR and (2) for galaxies near ULIRG regime. The corrected H $\alpha$ 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 z=1.

Key words: galaxies: formation

Offprint request: H. Flores, hector.flores@obspm.fr

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