Lyman Break and UV-selected galaxies at z ˜ 1 - II. PACS 100 μm/160 μm FIR detections★

In this work, we report the Photodetector Array Camera and Spectrometer
(PACS) 100 μm/160 μm detections of a sample of 42 GALEX-selected
and far-infrared (FIR)-detected Lyman break galaxies (LBGs) at z ˜
1 located in the Cosmic Evolution Survey (COSMOS) field and analyse
their ultraviolet (UV) to FIR properties. The detection of these LBGs in
the FIR indicates that they have a dust content high enough so that its
emission can be directly detected. According to a spectral energy
distribution (SED) fitting with stellar population templates to their
UV-to-near-IR observed photometry, PACS-detected LBGs tend to be bigger
(R<SUB>eff</SUB> ˜ 4.1 kpc), more massive [log
(M<SUB>*</SUB>/M<SUB>⊙</SUB>) ˜ 10.7], dustier
[E<SUB>s</SUB>(B – V) ˜ 0.40], redder in the UV continuum (β
˜ -0.60) and UV-brighter [log (L<SUB>UV</SUB>/L<SUB>⊙</SUB>)
˜ 10.1] than PACS-undetected LBGs. PACS-detected LBGs at z ˜
1 are mostly disc-like galaxies and are located over the green valley
and red sequence of the colour-magnitude diagram of galaxies at their
redshift. By using their UV and IR emission, we find that PACS-detected
LBGs tend to be less dusty and have slightly higher total star formation
rates (SFRs) than other PACS-detected UV-selected galaxies within the
same redshift range. As a consequence of the selection effect due to the
depth of the FIR observations employed, all our PACS-detected LBGs have
total IR luminosities, L<SUB>IR</SUB>, higher than 10<SUP>11</SUP>
L<SUB>⊙</SUB> and thus are luminous IR galaxies. However, none of
the PACS-detected LBGs are in the ultra-luminous IR galaxy (ULIRG)
regime, L<SUB>IR</SUB> ≥ 10<SUP>12</SUP> L<SUB>⊙</SUB>, where the
FIR observations are complete. The finding of ULIRGs-LBGs at higher
redshifts (z ˜ 3) suggests an evolution of the FIR emission of
LBGs with cosmic time. In an IRX-β diagram, PACS-detected LBGs at z
˜ 1 tend to be located around the relation for local starburst
similarly to other UV-selected PACS-detected galaxies at the same
redshift. Consequently, the dust-correction factors obtained with their
UV continuum slope allow us to determine their total SFR, unlike at
higher redshifts. However, the dust attenuation derived from UV to NIR
SED fitting overestimates the total SFR for most of our PACS-detected
LBGs in an age-dependent way: the overestimation factor is higher in
younger galaxies. This is likely due to the typical degeneracy between
dust attenuation and age in the SED fitting with synthetic templates and
highlights the importance of the FIR measurements in the analysis of
star-forming galaxies at intermediate redshifts.