Issue |
A&A
Volume 566, June 2014
|
|
---|---|---|
Article Number | A19 | |
Number of page(s) | 17 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361/201322704 | |
Published online | 02 June 2014 |
Constraints on the star-formation rate of z ~ 3 LBGs with measured metallicity in the CANDELS GOODS-South field⋆
1
INAF – Osservatorio Astronomico di Roma, via Frascati 33,
00040
Monteporzio,
Italy
e-mail:
marco.castellano@oa-roma.inaf.it
2
Los Alamos National Laboratory, Los Alamos, NM, USA
3
Institute for Astronomy, University of Edinburgh, Royal
Observatory, Edinburgh
EH9 3HJ,
UK
4
Space Telescope Science Institute, 3700 San Martin Drive, Baltimore
MD
21218,
USA
5
UCO/Lick Observatory, Department of Astronomy and Astrophysics,
University of California, Santa
Cruz, CA,
USA
6
Department of Physics, University of California,
Davis, CA
95616,
USA
7
Department of Physics and Astronomy, Johns Hopkins
University, Baltimore
MD
21218,
USA
8
Cavendish Laboratory, University of Cambridge, 19 J.J. Thomson
Avenue, Cambridge
CB3 0HE,
UK
9
Kavli Institute for Cosmology, University of Cambridge, Madingley Road,
Cambridge, CB3 0HA, UK
10
Observatoire de Genève, Université de Genève, 51 Ch. des
Maillettes, 1290
Versoix,
Switzerland
11
CNRS, IRAP, 14
Avenue E. Belin, 31400
Toulouse,
France
12
Astronomisches Institut, Ruhr-Universität Bochum,
Universitätsstraße 150, 44780
Bochum,
Germany
13
INAF – Osservatorio Astronomico di Bologna,
via Ranzani 1, 40127
Bologna,
Italy
Received:
18
September
2013
Accepted:
4
March
2014
Aims. We aim to constrain the assembly history of high-redshift galaxies and the reliability of UV-based estimates of their physical parameters from an accurate analysis of a unique sample of z ~ 3 Lyman-break galaxies (LBGs).
Methods. We analyse 14 LBGs at z ~ 2.8–3.8 constituting the only sample where both a spectroscopic measurement of their metallicity and deep IR observations (CANDELS+HUGS survey) are available. Fixing the metallicity of population synthesis models to the observed values, we determine best-fit physical parameters under different assumptions about the star-formation history (SFH) and also consider the effect of nebular emission. For comparison, we determine the UV slope of the objects, and use it to estimate their SFRUV99 by correcting the UV luminosity.
Results. A comparison between star-formation rate (SFR) obtained through SED-fitting (SFRfit) and the SFRUV99 shows that the latter are underestimated by a factor of 2–10, regardless of the assumed SFH. Other SFR indicators (radio, far-IR, X-ray, recombination lines) coherently indicate SFRs a factor of 2–4 larger than SFRUV99 and in closer agreement with SFRfit. This discrepancy is due to the solar metallicity implied by the usual β − A1600 conversion factor. We propose a refined relation, appropriate for subsolar metallicity LBGs: A1600 = 5.32 + 1.99 ∗ β. This relation reconciles the dust-corrected UV with the SED-fitting and the other SFR indicators. We show that the fact that z ~ 3 galaxies have subsolar metallicity implies an upward revision by a factor of ~1.5–2 of the global SFRD, depending on the assumptions about the age of the stellar populations. We find very young best-fit ages (10–500 Myr) for all our objects. From a careful examination of the uncertainties in the fit and the amplitude of the Balmer break we conclude that there is little evidence of the presence of old stellar population in at least half of the LBGs in our sample, suggesting that these objects are probably caught during a huge star-formation burst, rather than being the result of a smooth evolution.
Key words: galaxies: distances and redshifts / galaxies: evolution / galaxies: high-redshift
Appendices are available in electronic form at http://www.aanda.org
© ESO, 2014
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.