First Infrared-Based Implications for the Dust Attenuation and Star Formation of Typical Lyα Emitters

Abstract

By stacking publicly available deep Spitzer/MIPS 24 μm and Herschel/PACS images for 213 z≃ 2.18 Lyα Emitters (LAEs) in GOODS-South, we obtain a strong upper limit to the IR luminosity of typical LAEs and discuss their attenuation curve for the first time. The 3σ upper limit L_TIR^3σ = 1.1× {{10}¹⁰} {{L}_⊙ }, determined from the MIPS data providing the lowest limit, gives IRX\equiv {{L}_TIR}/{{L}_UV}≤slant 2.2. Here we assume that the local calibration between the 8 μm emission and the dust SED shape and metallicity applies at high redshifts and that our LAEs have low metallicities as suggested by previous studies. The inferred escape fractions of Lyα , 16-37%, and UV continuum, ≥slant 44%, are higher than the cosmic averages at the same epoch. The SMC attenuation curve is consistent with the IRX and the UV slope β =-1.4_-0.2^+0.2 of our stacked LAE, while the Meurer’s relation (Calzetti curve) predicts a 3.8 times higher IRX; we also discuss the validity of PACS-based L_TIR^3σ allowing the Meurer’s relation. SED fitting using the Calzetti curve also gives a ∼10 times higher SFR than from the L_TIR^3σ and {{L}_UV}. With {{M}_\star }=6.3_-2.0^+0.8× {{10}⁸} {{M}_⊙ }, our LAEs lie on a lower-mass extrapolation of the star formation main sequence at z∼ 2, suggesting that the majority of z∼ 2 LAEs are mildly star forming with relatively old ages of ∼200 Myr. The faint L_TIR^3σ implies that LAEs contribute little to the faint (≳ 100 μ Jy) submillimeter number counts by ALMA.

Based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.