ISM studies of GRB 030329 with high resolution spectroscopy

Abstract

We present a series of early UVES/VLT high resolution spectra of the afterglow of GRB 030329 at redshift z=0.16867+-0.00001. In contrast to other spectra from this burst, both emission and absorption lines were detected. None of them showed any temporal evolution. From the emission lines, we determine the properties of the host galaxy which has a star formation rate (SFR) of 0.198 M_solar yr^-1 and a low metallicity of 1/7 Z_solar. Given the low total stellar host mass M_star=10^7.75+-0.15 M_solar and an absolute luminosity m_V=-16.37, we derive specific SFRs (SSFR) of log SFR/M = -8.5 yr^-1 and SFR/L = 14.1 M_solar yr^-1 L_*^-1. This fits well into the picture of GRB hosts as being low mass, low metallicity, actively star forming galaxies. The MgII and MgI absorption lines from the host show multiple narrow (Doppler width b=5-10 km/s) components spanning a range of v about 260 km/s, mainly blueshifted compared to the redshift from the emission lines. These components are likely probing outflowing material of the host galaxy, which could arise from former galactic superwinds, driven by supernovae from star forming regions. Similar features have been observed in QSO spectra. The outflowing material is mainly neutral with high column densities of log N(MgII)=14.0+-0.1 cm^-2 and log N(MgI)=12.3+-0.1 cm^-2.