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 (LFUV), UV continuum slope (βUV), and stellar mass (M*), and then stacked at optical (BVriz bands), near-infrared (YJHKs 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*, βUV, LFUV, LIR, AFUV, 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 LFUV, βUV, and M*. Results. We used the so-called IR-excess (IRX ≡ LIR/LFUV) to investigate the dust attenuation as a function of βUV and M*. Our LBGs, averaged as a function of βUV, follow the well-known IRX–βUV 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* [M⊙]) > 10). However, a large dispersion is shown in the IRX–βUV and IRX–M* planes, in which the βUV and M* are combined to average the sample. Additionally, the SED-fitting 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* [M⊙]) < 10.25), while grayer dust attenuation curves are favored in high stellar mass LBGs (log(M* [M⊙]) > 10.25). We also demonstrate that the slope of the dust attenuation curves is one of the main drivers that shapes the IRX–βUV plane.
Highlights
About 20 years ago, the Hubble Space Telescope (HST) allied to the 10 m class ground-based telescopes opened up a window on the first 2 Gyr of cosmic times (Madau et al 1996)
The results suggest that our procedure well constrain the physical parameters: stellar mass, IR luminosity, FUV dust attenuation, star formation rate (SFR), and change of the slope of the dust attenuation law with respect to Calzetti – δ, with the chosen delay-τ star formation history (SFH)
We reviewed the information in the IRX–βUV and IRX–M∗ planes using the results obtained from the rest-frame FUV-to-FIR spectral energy distributions (SEDs)-fitting analysis on the stacked Lyman-break galaxies (LBGs) SEDs
Summary
About 20 years ago, the Hubble Space Telescope (HST) allied to the 10 m class ground-based telescopes opened up a window on the first 2 Gyr of cosmic times (Madau et al 1996). Stacking analyses of LBG and star-forming galaxies at redshifts of 1.5 < z < 5 have shown different behaviors; some of these results follow the M99 relation (Magdis et al 2010c; Reddy et al 2012; Koprowski et al 2018; McLure et al 2018) and others lie above (Coppin et al 2015; Bourne et al 2017) or below this relation (ÁlvarezMárquez et al 2016; Bouwens et al 2016; Reddy et al 2018) These deviations have been shown to be driven by the stellar masses (Álvarez-Márquez et al 2016; Bourne et al 2017), the shape of the dust attenuation curve (Salmon et al 2016; Lo Faro et al 2017), and the sample selection (Buat et al 2015).
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