The GRB 030329 host: a blue low metallicity subluminous galaxy with intense star formation

¹ Instituto de Astrofísica de Andalucía (IAA-CSIC), PO Box 03004, 18080 Granada, Spain e-mail: [jgu;ajct;deugarte;gss]@iaa.es
² Universidad de Jaén, Departamento de Física (EPS), Virgen de la Cabeza 2, Jaén 23071, Spain e-mail: dperez@ujaen.es
³ Stockholm Observatory, Department of Astronomy, AlbaNova, 106 91 Stockholm, Sweden e-mail: jesper@astro.su.se
⁴ Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark e-mail: [jfynbo;pallja;jens;kim]@astro.ku.dk; josemari@alumni.nd.edu
⁵ Science Institute, University of Iceland, Dunhaga 3, 107 Reykjavík, Iceland e-mail: [gudlaugu;gulli]@raunvis.hi.is
⁶ Astrophysikalisches Institut, 14482 Potsdam, Germany e-mail: lchristensen@aip.de
⁷ Special Astrophysical Observatory of the Russian Academy of Sciences, Nizhnij Arkhyz, 357 147 Karachai-Cherkessia, Rusia e-mail: [sokolov;timur]@sao.ru
⁸ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei Munchen, Germany

Received: 25 January 2005
Accepted: 20 July 2005

Abstract

We present broad band photometry and spectroscopic observations of the host galaxy of GRB 030329. Analysis of the spectral emission lines shows that the host is likely a low metallicity galaxy (). The spectral energy distribution (SED) constructed with the photometric points has been fitted using synthetic and observational templates. The best SED fit is obtained with a starburst template with an age of ~150 Myr and an extinction . We find that the GRB 030329 host galaxy is a subluminous galaxy () with a stellar mass of ≳. Three independent diagnostics, based on the restframe UV continuum, the [], and the Balmer emission lines, provide a consistent unextinguished star formation rate of  yr^-1, implying a high unextinguished specific star formation rate (~ yr). We estimate that the unextinguished specific star formation rate of the GRB 030329 host is higher than ~93.5% of the galaxies at a similar redshift.