摘要：Aims. Long gamma-ray bursts (LGRBs) are associated with the deaths of
massive stars and might therefore be a potentially powerful tool for tracing cosmic star
formation. However, especially at low redshifts (z< 1.5) LGRBs seem to
prefer particular types of environment. Our aim is to study the host galaxies of a
complete sample of bright LGRBs to investigate the effect of the environment on GRB
formation.
Methods. We studied host galaxy spectra of the
Swift/BAT6 complete sample of 14 z< 1 bright LGRBs. We
used the detected nebular emission lines to measure the dust extinction, star formation
rate (SFR), and nebular metallicity (Z) of the hosts and supplemented the data set with
previously measured stellar masses M⋆. The distributions
of the obtained properties and their interrelations (e.g. mass-metallicity and
SFR-M⋆ relations) are
compared to samples of field star-forming galaxies.
Results. We find that LGRB hosts at z< 1 have on average
lower SFRs than if they were direct star formation tracers. By directly comparing
metallicity distributions of LGRB hosts and star-forming galaxies, we find a good match
between the two populations up to 12
+log \hbox{$\left( \frac{\rm O}{\rm H}\right)$}~8.4−8.5, after which the paucity of metal-rich LGRB hosts
becomes apparent. The LGRB host galaxies of our complete sample are consistent with the
mass-metallicity relation at similar mean redshift and stellar masses. The cutoff against
high metallicities (and high masses) can explain the low SFR values of LGRB hosts. We find
a hint of an increased incidence of starburst galaxies in the Swift/BAT6
z< 1
sample with respect to that of a field star-forming population. Given that the SFRs are
low on average, the latter is ascribed to low stellar masses. Nevertheless, the limits on
the completeness and metallicity availability of current surveys, coupled with the limited
number of LGRB host galaxies, prevents us from investigating more quantitatively whether
the starburst incidence is such as expected after taking into account the high-metallicity
aversion of LGRB host galaxies.
关键词：gamma-ray burst: general;galaxies: star formation
