The UV to FIR spectral energy distribution of star-forming galaxies in the redshift desert

TL;DR

This study analyzes the UV-to-FIR spectral energy distributions of star-forming galaxies at redshifts 1.5 to 2.5, revealing differences in dust properties, star formation rates, and galaxy populations, with implications for galaxy evolution models.

Contribution

It provides a comprehensive comparison of LBGs, sBzK, and UV-selected galaxies at z~2, highlighting their dust attenuation, star formation, and evolution, especially with FIR data from Herschel.

Findings

sBzK galaxies better represent the star-forming population at z~2

PACS detections show SFRs are underestimated by local IRX-beta relations

Dust properties evolve with redshift, but the dust attenuation-stellar mass relation remains stable

Abstract

We analyse the rest-frame UV-to-NIR 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 multi-wavelength coverage of the galaxies located in the GOODS fields with deep FIR data taken from the GOODS-Herschel project. We find that sBzK galaxies represent the general population of SF galaxies at z ~ 2 better than LBGs. For a given stellar mass, LBGs tend to have bluer optical colours than sBzK and UV-selected galaxies. We find clean PACS 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 with their continuum slope and the IRX-beta relations for local starbursts. This has implications, for example, in the definition of the main sequence (MS) at z ~ 2. PACS-detected galaxies are located above the z ~ 2 MS and thus their star formation is probably driven by starburst. 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 SPIRE bands. We speculate that SPIRE-detected LBGs are the bridging population between sub-mm galaxies and LBGs.