Issue |
A&A
Volume 397, Number 3, January III 2003
|
|
---|---|---|
Page(s) | 839 - 849 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20021564 | |
Published online | 21 January 2003 |
Physical properties of two low-luminosity
galaxies behind
the lensing cluster AC 114*
1
Laboratoire d'Astrophysique de l'Observatoire Midi-Pyrénées – UMR 5572, 14 avenue E. Belin, 31400 Toulouse, France
2
California Institute of Technology – Pasadena, CA 91125, USA
3
European Southern Observatory – Alonso de Cordova 3107, Vitacura, Chile
Corresponding author: T. Contini, contini@ast.obs-mip.fr
Received:
4
September
2002
Accepted:
22
October
2002
We present VLT/ISAAC near-infrared spectroscopy of two
gravitationally-lensed galaxies, A2 and S2, located behind
the cluster AC 114. Thanks to large magnification factors, we have
been successful in detecting rest-frame optical emission lines (from
[O ii]λ3727 to
+[N ii]λ6584) in
star-forming galaxies 1 to 2 mag fainter than in previous
studies of Lyman break galaxies (LBGs) at
. From the
luminosity, we estimate star formation rates (SFRs) of 30 and
15
yr-1for S2 and A2 respectively. These values are 7 to 15 times
higher than those inferred from the UV continuum flux at 1500 Å
without dust extinction correction. In setting
, one derives extinction coefficients
for S2 and
for A2.
The behavior of S2 and A2 in terms of O/H and N/O abundance ratios
are very different, and they are also
different from typical LBGs at
. S2 is a low-metallicity
object (
) with a low N/O ratio, similar to those
derived in the most metal-poor nearby Hiigalaxies. In contrast, A2
is a high-metallicity galaxy (
) with a high N/O abundance
ratio, similar to those derived in the most metal-rich starburst nucleus
galaxies. The line-of-sight velocity dispersions, derived from emission
line widths, are 55 and 105 km s-1, yielding a virial mass of 0.5 and
, for S2 and A2 respectively.
Thanks to the gravitational amplification, the line profiles of S2 are
spatially resolved, leading to a velocity gradient of
km s-1,
which yields a dynamical mass of
within
the inner 1 kpc radius.
Combining these new data with the sample of LBGs at
, including
the lensed galaxy MS 1512-cB58, which is the only LBG for which physical
properties have been determined with similar accuracy, we conclude that
these three galaxies exhibit different physical properties in terms of
abundance ratios, SFRs,
and reddening. High-redshift
galaxies of different luminosities could thus have quite different
star formation histories.
Key words: galaxies: evolution / galaxies: starburst / galaxies: abundances / galaxies: kinematics and dynamics / infrared: galaxies
© ESO, 2003
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