First infrared-based implications for the dust attenuation and star formation of typical Lyα emitters.
KUSAKABE H., SHIMASAKU K., NAKAJIMA K. and OUCHI M.
Abstract (from CDS):
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 3 σ upper limit LTIR^3σ = 1.1 x 1010L☉, determined from the MIPS data providing the lowest limit, gives IRX ≡ LTIR/ LUV ≤ 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, ≥ 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 LTIR^3σ allowing the Meurer's relation. SED fitting using the Calzetti curve also gives a "10 times higher SFR than from the LTIR^3σ and LUV. With M* = 6.3–2.0+0.8, 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 LTIR^3σ implies that LAEs contribute little to the faint (≳ 100µJy) submillimeter number counts by ALMA.