Bibcode
Schaerer, D.; Hempel, A.; Egami, E.; Pelló, R.; Richard, J.; Le Borgne, J.-F.; Kneib, J.-P.; Wise, M.; Boone, F.
Bibliographical reference
Astronomy and Astrophysics, Volume 469, Issue 1, July I 2007, pp.47-60
Advertised on:
7
2007
Journal
Citations
5
Refereed citations
4
Description
Context: On the nature, redshift, stellar populations and dust
properties of optically faint or non-detected extremely red objects. Aims: Determining the nature, redshift, stellar populations and dust
properties of optically faint or non-detected, extremely red objects
(ERO) found from our survey of the lensing clusters A1835 and AC114
(Richard et al. 2006, A&A, 456, 861). Comparison with properties of
related galaxies, such as IRAC selected EROs and a z 6.5
post-starburst galaxy candidate from the Hubble Ultra Deep Field. Methods: Using an updated version of Hyperz (Bolzonella et al. 2000,
A&A, 363, 476) and a large number of spectral templates we perform
broad-band SED fitting. The photometric observations, taken from Hempel
et al. (2007, A&A, submitted), include deep optical, ACS/HST,
ISAAC/VLT, IRAC/Spitzer data, and for some objects 24 μm MIPS/Spitzer
and sub-mm data as well. Results: For most of the lensed EROs we
find photometric redshifts showing a strong degeneracy between
“low-z” (z 1-3) and high-z (z 6-7). Although formally
best fits are often found at high-z, their resulting bright absolute
magnitudes, the number density of these objects, and in some cases
Spitzer photometry or longer wavelength observations, suggest strongly
that all of these objects are at “low-z”. The majority of
these objects are best fitted with relatively young (⪉0.5-0.7 Gyr)
and dusty starbursts. Three of our objects show indications for strong
extinction, with AV 2.4-4. The typical stellar masses of
our objects are M_star (0.5-5)×1010 M&sun;
after correction for lensing; for the most extreme ERO in our sample,
the sub-mm galaxy SMMJ14009+0252 most likely at z_fit 3, we estimate
M_star ˜ 6.×1011 M&sun;. For dusty
objects star formation rates (SFR) have been estimated from the
bolometric luminosity determined after fitting of semi-empirical
starburst, ERO, and ULIRG templates.Typically we find SFR (1-18)
M&sun; yr-1. Again, SMMJ14009+0252 stands out as a
LIRG with SFR 1000 M&sun; yr-1. Finally, we
predict the mid-IR to sub-mm SED of the dusty objects for comparison
with future observations with APEX, Herschel, and ALMA. Concerning the
comparison objects, we argue that the massive post-starburst z 6.5
galaxy candidate HUDF-J2 showing observed properties very similar to our
EROs, is more likely a dusty starburst at z 2.3-2.6. This
interpretation also naturally explains the observed 24 μm emission
from this object and we predict its IR to sub-mm SED. Both empirically
and from our SED fits we find that the IRAC selectec EROs from Yan et
al. (2004, ApJ, 616, 63) show very similar properties to our lensed
EROs. Reasonable fits are found for most of them with relatively young
and dusty stellar populations.
Based on observations collected at the Very Large Telescope (Antu/UT1),
European Southern Observatory, Paranal, Chile (ESO Programs 69.A-0508,
70.A-0355, 73.A-0471), the NASA/ESA Hubble Space Telescope obtained at
the Space Telescope Science Institute which is operated by AURA under
NASA contract NAS5-26555, the Spitzer Space Telescope, which is operated
by the Jet Propulsion Laboratory, California Institute of Technology
under NASA contract 1407, and the Chandra satellite.