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Astron. Astrophys. 334, 772-782 (1998)


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The observation of the nearby universe in UV and in FIR: an evidence for a moderate extinction in present day star forming galaxies

V. Buat 1, 2 and D. Burgarella 1

1 Laboratoire d'Astronomie Spatiale du CNRS, BP 8, F-13376 Marseille Cedex 12, France
2 Laboratoire des intéractions photons-matière, Faculté des Sciences de Saint Jérôme, F-13397 Marseille Cedex 13, France

Received 22 August 1997 / Accepted 4 March 1998

Abstract

We study the FIR and UV-visible properties of star forming galaxies in the nearby Universe. This comparison is performed using the local luminosity functions at UV and FIR wavelengths and on individual starburst galaxies for which photometric data from UV to NIR and FIR are available.

The FIR and UV luminosity functions have quite different shapes : the UV function exhibits a strong increase for low luminosity galaxies whereas the FIR tail towards ultra luminous galaxies ([FORMULA]) is not detected in UV. The comparison of the FIR and UV local luminosity densities argues for a rather moderate extinction in nearby disk galaxies. The galaxies selected to be detected in FIR and UV are found to be located in the medium range of both luminosity functions.

An emphasis is made on starburst galaxies. For a sample of 22 of these objects, it is found that the UV (912-3650 [FORMULA]), the visible (3600-12500 [FORMULA]) and the NIR (12500-22000 [FORMULA]) wavelength range contribute [FORMULA], [FORMULA] and [FORMULA] respectively to the total emerging stellar emission (for a subsample of 12 galaxies for the NIR and visible light). The mean ratio of the dust to bolometric luminosity of these galaxies is 0.37 [FORMULA] 0.22 similar to the ratio found for normal spiral galaxies. Only 4 out of the 22 galaxies exhibit a very large extinction with more than 60 [FORMULA] of their energy emitted in the FIR-submm range. The mean extinction at 2000 [FORMULA] is found to be [FORMULA] mag although with a large dispersion. The UV, visible and NIR emissions of our sample galaxies are consistent with a burst lasting over [FORMULA] Gyr. The conversion factor of the stellar emission into dust emission is found to correlate with the luminosity of the galaxies, brighter galaxies having a higher conversion factor. Since our sample appears to be representative of the mean properties of the galaxy population in FIR and UV, a very large conversion of the stellar light into dust emission can no longer be assumed as a general property of starburst galaxies at least in the local Universe. Instead a larger amount of energy emerging from the present starburst galaxies seems to come from the stars rather than from the dust.

We compare the UV properties of our local starburst galaxies to those of recently detected high redshift galaxies. The larger extinction found in the distant galaxies is consistent with the trend we find for the nearby starburst galaxies namely the brighter the galaxies the lower the escape fraction of stellar light.

Key words: galaxies: starburst – galaxies: stellar content – galaxies: ISM – infrared: galaxies – ultraviolet: galaxies – dust, extinction

Send offprint requests to: V. Buat

© European Southern Observatory (ESO) 1998

Online publication: June 2, 1998

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