Rest-frame far-ultraviolet to far-infrared view of Lyman break galaxies at z=3: templates and dust attenuation

Abstract

Aims. This work explores, from a statistical point of view, the rest-frame far-ultraviolet (FUV) to far-infrared (FIR) emission of a population of Lyman-break galaxies (LBGs) at z ∼ 3 that cannot be individually detected from current FIR observations. Methods. We performed a stacking analysis over a sample of ∼17 000 LBGs at redshift 2.5 < z < 3.5 in the COSMOS field. The sample is binned as a function of UV luminosity (L_(FUV)), UV continuum slope (β_(UV)), and stellar mass (M∗), and then stacked at optical (BVriz bands), near-infrared (Y JHK_(s) bands), IRAC (3.6, 4.5, 5.6, and 8.0 µm), MIPS (24 µm), PACS (100 and 160 µm), SPIRE (250, 350, and 500 µm), and AzTEC (1.1 mm) observations. We obtained 30 rest-frame FUV-to-FIR spectral energy distributions (SEDs) of LBGs at z ∼ 3, and analyzed these with the CIGALE SED-fitting analysis code. We were able to derive fully consistent physical parameters, that is, M∗, β_(UV), L_(FUV), L_(IR), A_(FUV), star formation rate, and the slope of the dust attenuation law; we built a semiempirical library of 30 rest-frame FUV-to-FIR stacked LBG SEDs as functions of L_(FUV), β_(UV), and M∗. Results. We used the so-called IR-excess (IRX ≡ L_(IR)/L_(FUV)) to investigate the dust attenuation as a function of β_(UV) and M∗. Our LBGs, averaged as a function of β_(UV), follow the well-known IRX–β_(UV) calibration of local starburst galaxies. Stacks as a function of M∗ follow the IRX–M∗ relationship presented in the literature at high M∗ (log(M∗ [Mꙩ]) > 10). However, a large dispersion is shown in the IRX–β_(UV) and IRX–M∗ planes, in which the β_(UV) and M∗ are combined to average the sample. Additionally, the SEDfitting analysis results provide a diversity of dust attenuation curve along the LBG sample, and their slopes are well correlated with M∗. Steeper dust attenuation curves than Calzetti’s are favored in low stellar mass LBGs (log(M∗ [Mꙩ]) < 10.25), while grayer dust attenuation curves are favored in high stellar mass LBGs (log(M∗ [Mꙩ]) > 10.25). We also demonstrate that the slope of the dust attenuation curves is one of the main drivers that shapes the IRX–β_(UV) plane.