EDP Sciences
Free access
Volume 434, Number 3, May II 2005
Page(s) 849 - 866
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20042157

A&A 434, 849-866 (2005)
DOI: 10.1051/0004-6361:20042157

The optical-to-radio spectral energy distributions of low-metallicity blue compact dwarf galaxies

L. Hunt1, S. Bianchi1 and R. Maiolino2

1  INAF - Istituto di Radioastronomia/Sez. Firenze, Largo Enrico Fermi, 5, 50125 Firenze, Italy
    e-mail: [hunt;sbianchi]@arcetri.astro.it
2  INAF - Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi, 5, 50125, Firenze, Italy
    e-mail: maiolino@arcetri.astro.it

(Received 11 October 2004 / Accepted 3 January 2005 )

We present global spectral energy distributions (SEDs) from 0.3 $\mu$m to 90 cm for a sample of seven low-metallicity blue compact dwarf galaxies (BCDs). In addition to data compiled from the literature, we report new SCUBA data for the galaxies in the sample, including the two most metal-poor star-forming galaxies known, I Zw 18 and SBS 0335-052. The standard starburst templates, M 82 and Arp 220, do not give a good approximation to any of the BCD SEDs in our sample. Several SEDs are instead characterized by: (i) approximately flat radio spectra suggesting dominant thermal processes; (ii) far-infrared (FIR) spectra which peak at or shortward of 60 $\mu$m; (iii) a significant warm dust component and absence of Aromatic Features in Emission (or PAHs) in the mid-infrared (MIR). The SEDs of low-metallicity BCDs do not follow "canonical" scaling relations, and the "standard" star-formation indicators based on radio continuum, FIR, and MIR luminosities can be discrepant by factors of $\ga$10. We present new models of the dust SEDs from 5 $\mu$m to 1 cm, and derive infrared luminosities, dust distributions, temperatures, and masses. The observed SEDs and dust models are interpreted in terms of the active/passive regimes of star formation and trends with metallicity. Finally, we discuss the implications of our results on the $z\ga6$ starburst populations which will be detected by forthcoming submm and radio facilities.

Key words: galaxies: starburst -- galaxies: ISM -- ISM: dust, extinction -- galaxies: star clusters -- galaxies: evolution

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