S. Basa, J. G. Cuby, S. Savaglio, S. Boissier, B. Clement, H. Flores, D. Le Borgne, A. Mazure
Long duration Gamma-Ray Bursts (GRBs) allow us to explore the distant
Universe, and are potentially the best tracer of the most distant objects. Our
current knowledge of the properties of GRB host galaxies at redshifts > 5 is
very scarce, and more observations of high-redshift hosts are required to
better understand their properties and the implications of using GRBs as probes
of the high-redshift universe. We performed very deep photometric observations
of three high-redshift GRB host galaxies, GRB 080913 at z = 6.7, GRB 060927 at
z = 5.5 and GRB 060522 at z = 5.1. Our FORS2 and HAWK-I observations at the VLT
targeted the rest-frame UV continuum of these galaxies, allowing us to
constrain their star formation rates. In addition, we performed deep
spectroscopic observations of the GRB080913 host galaxy with X-Shooter at the
VLT to search for Ly-{\alpha} emission. For the sake of the discussion, we make
use of published results on another GRB host, GRB 050904 at z = 6.3. The sample
of GRB host galaxies studied in this paper consists of 4 out of the 6
spectroscopically confirmed GRB host galaxies at z > 5. Despite being the
deepest observations ever reported of high-redshift GRB host galaxies, we do
not detect any of the hosts, neither in photometry nor in spectroscopy in the
case of GRB 080913. These observations indicate that the GRB host galaxies seem
to evolve with time and to have lower star formation rates (SFR) at z > 5 than
they have at z < 2. In addition, the host galaxy of GRB 080913 at z = 6.7 does
not show Ly-{\alpha} emission. While the measured properties of the galaxies in
our sample are in agreement with the properties of the general galaxy
population at z > 5, our observations are not sensitive enough to allow us to
infer further conclusions on whether this specific population is representative
of the general one.
View original:
http://arxiv.org/abs/1201.6383
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