The ultraviolet to far-infrared spectral energy distribution of star-forming galaxies in the redshift desert
We analyse the rest-frame ultraviolet (UV) to near-infrared (near-IR)
spectral energy distribution (SED) of Lyman-break galaxies (LBGs),
star-forming (SF) BzK (sBzK) and UV-selected galaxies at 1.5 ≲ z
≲ 2.5 in the COSMOS, GOODS-N and GOODS-S fields. Additionally, we
complement the multiwavelength coverage of the galaxies located in the
GOODS fields with deep far-infrared (FIR) data taken from the
GOODS-Herschel project. According to their best-fitting SED-derived
properties we find that, because of their selection criterion involving
UV measurements, LBGs tend to be UV-brighter and bluer and have a less
prominent Balmer break (i.e. are younger) and higher dust-corrected
total star-formation rate (SFR) than sBzK galaxies. In this way, sBzK
galaxies represent the general population of SF galaxies at z ˜ 2
better than LBGs. In a colour-mass diagram, LBGs at z ˜ 2 are
mostly located over the blue cloud, although galaxies with higher age,
higher dust attenuation and redder UV continuum slope deviate to the
green valley and red sequence. Furthermore, for a given stellar mass,
LBGs tend to have bluer optical colours than sBzK and UV-selected
galaxies. We find clean Photodetector Array Camera and Spectrometer
(PACS: 100- or 160-μm) individual detections for a subsample of 48
LBGs, 89 sBzK and 91 UV-selected galaxies that measure their dust
emission directly. Their SFR_{total = SFR_{UV} + SFR_IR} cannot be
recovered with the dust-correction factors derived from their continuum
slope and the infrared excess (IRX)-β relations for local
starbursts, similar to what happens at higher redshifts. This might have
implications, for example, in the definition of the main sequence (MS)
at z ˜ 2, which is sensitive to the dust-correction factors
adopted. In an SFR-mass diagram, PACS-detected galaxies are located
above the Daddi et al. MS and thus their star formation is probably
driven by starbursts. This is in agreement with the shape of their IR
SEDs. PACS-detected galaxies with redder UV continuum slope and higher
stellar mass are more attenuated. We find that, for a given UV continuum
slope, the dustiest galaxies at higher redshifts are more attenuated and
that for a given stellar mass the dustiest galaxies at higher redshifts
have stronger FIR emission. This suggests an evolution of their dust
properties. However, we do not find significant evolution in the
relation between dust attenuation and stellar mass with redshift, at
least at z ≤ 2.5. There is a subpopulation of 17, 26 and 27 LBGs,
sBzK and UV-selected galaxies, respectively, that are detected in any of
the Spectral and Photometric Imaging REceiver (SPIRE: 250-, 350- and
500-μm) bands. We speculate that this sample of SPIRE-detected LBGs
is the bridging population between submillimetre galaxies and LBGs.