Issue |
A&A
Volume 431, Number 3, March I 2005
|
|
---|---|---|
Page(s) | 793 - 812 | |
Section | Cosmology (including clusters of galaxies) | |
DOI | https://doi.org/10.1051/0004-6361:20042038 | |
Published online | 16 February 2005 |
Properties of Lyα emitters around the radio galaxy MRC 0316–257*,**
1
Sterrewacht Leiden, PO Box 9513, 2300 RA, Leiden, The Netherlands e-mail: venemans@strw.leidenuniv.nl
2
INAF, Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, 50125, Firenze, Italy
3
European Southern Observatory, Karl Schwarzschild Straße 2, 85748 Garching, Germany
4
Lawrence Livermore National Laboratory, PO Box 808, Livermore CA, 94550, USA
5
NRAO, PO Box 0, Socorro NM, 87801, USA
6
Dept. of Physics & Astronomy, The Johns Hopkins University, 3400 North Charles Street, Baltimore MD, 21218-2686, USA
7
Dipartimento di Fisica, Università degli studi Roma Tre, via della Vasca Navale 84, Roma, 00146, Italy
8
The Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena CA, 91101, USA
Received:
21
September
2004
Accepted:
21
October
2004
Observations of the radio galaxy MRC 0316–257 at and the surrounding field are presented. Using narrow- and
broad-band imaging obtained with the VLT, 77 candidate
Lyα emitters with a rest-frame equivalent width of >15 Å
were selected in a ∼7´
´ field around
the radio galaxy. Spectroscopy of 40 candidate emitters resulted in
the discovery of 33 emission line galaxies of which 31 are Lyα
emitters with redshifts similar to that of the radio galaxy, while
the remaining two galaxies turned out to be [
]
emitters. The Lyα profiles have widths (FWHM) in the range of
120–800 km s-1, with a median of 260 km s-1. Where the signal-to-noise
was large enough, the Lyα profiles were found to be asymmetric,
with apparent absorption troughs blueward of the profile peaks,
indicative of absorption along the line of sight of an
mass of at least
M
.
Besides that of the radio galaxy and one of the emitters that is a
QSO, the continuum of the emitters is faint, with luminosities
ranging from 1.3 L* to <0.03 L*. The colors of the
confirmed emitters are, on average, very blue. The median UV
continuum slope is
, bluer than the average slope of
LBGs with Lyα emission (
). A large fraction of
the confirmed emitters (∼2/3) have colors consistent with
that of dust-free starburst galaxies. Observations with the
Advanced Camera for Surveys on the Hubble Space Telescope
show that the emitters that were detected in the ACS image have a
range of different morphologies. Four Lyα emitters (∼25%)
were unresolved with upper limits on their half light radii of
kpc, three objects (∼19%) show multiple clumps of
emission, as does the radio galaxy, and the rest (∼56%) are
single, resolved objects with
kpc. A comparison with
the sizes of Lyman break galaxies at
suggests that the
Lyα emitters are on average smaller than LBGs. The average star
formation rate of the Lyα emitters is 2.6 M
as measured by
the Lyα emission line or <3.9 M
as measured by the UV
continuum. The properties of the Lyα galaxies (faint, blue and
small) are consistent with young star forming galaxies which are
still nearly dust free.
The volume density of Lyα emitting galaxies in the field around MRC
0316–257 is a factor of
larger compared with
the density of field Lyα emitters at that redshift. The velocity
distribution of the spectroscopically confirmed emitters has a
dispersion of 640 km s-1, corresponding to a FWHM of 1510 km s-1, which
is substantially smaller than the width of the narrow-band filter
(
km s-1). The peak of the velocity distribution is
located within 200 km s-1 of the redshift of the radio galaxy. We
conclude that the confirmed Lyα emitters are members of a
protocluster of galaxies at
. The size of the
protocluster is unconstrained and is larger than
Mpc2. The mass of this structure is estimated to be >
M
and could be the progenitor of a cluster
of galaxies similar to e.g. the Virgo cluster.
Key words: galaxies: active / galaxies: high-redshift / galaxies: evolution / galaxies: clusters: general / cosmology: observations / cosmology: early Universe
© ESO, 2005
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