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Issue A&A
Volume 383, Number 3, March I 2002
Page(s) 801 - 812
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20011832



A&A 383, 801-812 (2002)
DOI: 10.1051/0004-6361:20011832

Star formation and dust extinction in nearby star-forming and starburst galaxies

V. Buat1, A. Boselli1, G. Gavazzi2 and C. Bonfanti2

1  Laboratoire d'Astrophysique de Marseille, BP 8, 13376 Marseille Cedex 12, France
    e-mail: alessandro.boselli@astrsp-mrs.fr
2  Universita degli studi di Milano-Bicocca, Dipatimento di Fisica, Piazza dell'Ateneo Nuovo 1, 20126 Milano, Italy
    e-mail: giuseppe.gavazzi@mib.infn.it; cristian.bonfanti@mib.infn.it

(Received 28 August 2001 / Accepted 18 December 2001 )

Abstract
We study the star formation rate and dust extinction properties of a sample of nearby star-forming galaxies as derived from H $\alpha$ and UV (~2000 Å) observations and we compare them to those of a sample of starburst galaxies. The dust extinction in H $\alpha$ is estimated from the Balmer decrement and the extinction in UV using the FIR to UV flux ratio or the attenuation law for starburst galaxies of Calzetti et al. (2000). The H $\alpha$ and UV emissions are strongly correlated with a very low scatter for the star-forming objects and with a much higher scatter for the starburst galaxies. The H $\alpha$ to UV flux ratio is found to be larger by a factor ~2 for the starburst galaxies. We compare both samples with a purely UV selected sample of galaxies and we conclude that the mean H $\alpha$ and UV properties of nearby star-forming galaxies are more representative of UV-selected galaxies than starburst galaxies. We emphasize that the H $\alpha$ to UV flux ratio is strongly dependent on the dust extinction: the positive correlation found between $F_{\rm H\alpha}/F_{\rm UV}$ and $F_{\rm FIR}/F_{\rm UV}$ vanishes when the H $\alpha$ and UV flux are corrected for dust extinction. The H $\alpha$ to UV flux ratios converted into star formation rate and combined with the Balmer decrement measurements are tentatively used to estimate the dust extinction in UV.


Key words: galaxies: starburst -- ISM: dust extinction -- galaxies: stellar content

Offprint request: V. Buat, veronique.buat@astrsp-mrs.fr,

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