Issue |
A&A
Volume 388, Number 2, June III 2002
|
|
---|---|---|
Page(s) | 425 - 438 | |
Section | Cosmology (including clusters of galaxies) | |
DOI | https://doi.org/10.1051/0004-6361:20020427 | |
Published online | 31 May 2002 |
Deep Lyα imaging of two
= 2.04 GRB host galaxy fields
*,**
1
European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748, Garching by München, Germany
2
Institute for Physics and Astronomy University of Århus, Ny Munkegade, 8000 Århus C, Denmark
3
Astronomical Observatory, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark
4
Danish Space Research Institute, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark
5
Laboratorio de Astrofísica Espacial y Física Fundamental (LAEFF-INTA), PO Box 50727, 28080 Madrid, Spain
6
Instituto de Astrofísica de Andalucía (IAA-CSIC), PO Box 03004, 18080 Granada, Spain
7
Division of Astronomy, PO Box 3000, 90014 University of Oulu, Finland
8
Nordic Optical Telescope, Apartado Postal 474, 38700 Santa Cruz de La Palma, Canary Islands, Spain
9
Department of Physics, University of Notre Dame, Notre Dame, IN 46556-5670, USA
Corresponding author: J. P. U. Fynbo, jfynbo@eso.org
Received:
4
December
2001
Accepted:
19
March
2002
We report on the results of deep narrow-band Lyα and broad-band U
and I imaging of the fields
of two Gamma-Ray bursts at redshift (GRB 000301C and GRB 000926).
We find that the host galaxy of GRB 000926 is an extended (more
than 2 arcsec), strong Lyα emitter with a rest-frame
equivalent width of 71
Å. The galaxy consists of two
main components and several fainter knots. GRB 000926 occurred in the
western component, whereas most of the Lyα luminosity
(about 65%) originates in the eastern component. Using archival HST
images of the host galaxy we measure the spectral slopes
(
) of the two
components to
(east) and
(west).
This implies that both components contain at most small amounts of
dust, consistent with the observed strong Lyα emission.
The western component has a slightly redder
colour than the
eastern component, suggesting the presence of at least some dust.
We do not detect the host galaxy of GRB 000301C in neither
Lyα emission nor in U and I broad-band images. The strongest
limit comes from combining the narrow and U-band imaging where we infer
a limit of
(2σ limit per arcsec2). The upper
limits on the Lyα flux implies a Lyα equivalent width
upper limit of ~150 Å.
We find
eleven and eight other galaxies with excess emission in the narrow filter
in the fields of GRB 000301C and GRB 000926 respectively. These galaxies
are candidate Lyα emitting galaxies in the environment of
the host galaxies. Based on these detections we conclude that GRB 000926
occurred in one of the strongest centres of star formation within several
Mpc, whereas GRB 000301C occurred in an intrinsically very faint galaxy far
from being the strongest centre of star formation in its galactic
environment. Under the hypothesis that GRBs trace star formation,
the wide range of GRB host galaxy luminosities implies a very steep
faint end slope of the high redshift galaxy luminosity function.
Key words: cosmology: observations / gamma rays: bursts
© ESO, 2002
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