Issue |
A&A
Volume 499, Number 1, May III 2009
|
|
---|---|---|
Page(s) | 69 - 85 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361/200811526 | |
Published online | 25 March 2009 |
GMASS ultradeep spectroscopy of galaxies at z ~ 2
IV. The variety of dust populations
1
Observatoire Astronomique de Marseille-Provence, 38 rue Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France e-mail: stefan.noll@oamp.fr
2
Max-Planck-Institut für extraterrestrische Physik, Giessenbachstr., 85748 Garching, Germany
3
Dipartimento di Astronomia, Università di Bologna, via Ranzani 1, 40127 Bologna, Italy
4
CEA-Saclay, DSM/DAPNIA/Service d'Astrophysique, 91191 Gif-sur-Yvette Cedex, AIM-Unité Mixte de Recherche CEA-CNRS (#7158)-Université Paris VII, France
5
Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
6
INAF – Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
7
Department of Astronomy, University of Massachusetts, LGRT-B 619E, 710 North Pleasant Street, Amherst, MA 01003-9305, USA
8
INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
9
INAF – Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122 Padova, Italy
10
NOAO-Tucson, 950 North Cherry Avenue, Tucson, AZ 85719, USA
11
Università di Padova, Dipartimento di Astronomia, Vicolo dell'Osservatorio 2, 35122 Padova, Italy
12
European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
Received:
15
December
2008
Accepted:
4
March
2009
Aims. The properties of dust attenuation at rest-frame UV wavelengths are inferred
from very high-quality FORS 2 spectra of 78 galaxies from the GMASS survey
at redshift . These objects complement a previously investigated
sample of 108 UV-luminous, intermediate-mass (i.e., with stellar masses
~
) galaxies at similar redshifts,
selected from the FDF spectroscopic survey, the K20 survey, and the GDDS.
Detection of the broad absorption feature centred on about 2175 Å
(“UV bump”) implies that the average UV extinction curve of a galaxy more
closely resembles that of the Milky Way (MW) or the Large Magellanic Cloud
(LMC), and differs from that of the Small Magellanic Cloud (SMC).
Methods. The shape of the UV extinction curve is constrained by a parametric description of the rest-frame UV continuum with the support of a suite of models combining radiative transfer and stellar population synthesis. The UV bump is further characterised by fitting Lorentzian-like profiles.
Results. Spectra exhibit a significant 2175 Å feature in at least 30% of the
cases, especially those suffering from substantial reddening. If attenuation
is dominated by dust ejected from the galaxy main body via galactic winds or
more localised superwinds, UV extinction curves in-between those of the SMC
and LMC characterise UV-luminous, intermediate-mass galaxies at
. The fraction of galaxies with extinction curves differing from
the SMC one increases, if more dust resides in the galactic plane or dust
attenuation depends on stellar age. On average, the width of the manifested
UV bumps is about 60% of the values typically measured along sightlines in
the LMC and MW. This suggests the presence of dust similar to that found in
the “supergiant” shell of ionised filaments LMC 2, close to 30 Dor. The
presence of the carriers of the UV bump (probably organic carbon and
amorphous silicates) at
argues for outflows from asymptotic
giant branch (AGB) stars being copious then. Consistent with their higher
star-formation rates, the GMASS galaxies with a manifested UV bump are more
luminous at rest-frame 8 μm, where the emission is dominated by
polycyclic aromatic hydrocarbons (also products of AGB stars). In addition,
they exhibit larger equivalent widths for prominent UV (metal) absorption
features, mostly of interstellar origin, which indicates overall more evolved
stellar populations.
Conclusions. We conclude that diversification of the small-size dust component
(responsible for the differential extinction at UV wavelengths and the
emission at mid-IR wavelengths) has already started in the most evolved
star-forming systems at .
Key words: galaxies: high-redshift / galaxies: starburst / galaxies: ISM / ISM: dust, extinction / ultraviolet: galaxies
© ESO, 2009
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