First Infrared-based implications for the dust attenuation and star formation of typical Ly$\alpha$ emitters

Abstract

By stacking publicly available deep Spitzer/MIPS 24 $\mu$m and Herschel/PACS images for 213 $z\simeq 2.18$ Ly$\alpha$ 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 $3\sigma$ upper limit $L_{\mathrm{TIR}}^{3\sigma }=1.1\times 10^{10}{L}_{\odot }$, determined from the MIPS data providing the lowest limit, gives $IRX\equiv L_{\mathrm{TIR}}/L_{\mathrm{UV}}\le 2.2$. Here we assume that the local calibration between the 8 $\mu$m 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 Ly$\alpha$, $16$--$37$, and UV continuum, $\ge 44$, are higher than the cosmic averages at the same epoch. The SMC attenuation curve is consistent with the IRX and the UV slope $\beta =-1.4_{-0.2}^{+0.2}$ 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 $L_{\mathrm{TIR}}^{3\sigma }$ allowing the Meurer's relation. SED fitting using the Calzetti curve also gives a $\sim 10$ times higher SFR than from the $L_{\mathrm{TIR}}^{3\sigma }$ and $L_{\mathrm{UV}}$. With $M_{\star }=6.3_{-2.0}^{+0.8}\times 10^8{\mathrm{M}}_{\odot }$, our LAEs lie on a lower-mass extrapolation of the star formation main sequence at $z\sim 2$, suggesting that the majority of $z\sim 2$ LAEs are mildly star forming with relatively old ages of $\sim 200$ Myr. The faint $L_{\mathrm{TIR}}^{3\sigma }$ implies that LAEs contribute little to the faint ($\gtrsim 100\mu$Jy) submm number counts by ALMA.

7 pages, 3 figures, accepted to ApJL (added some discussions and then removed the conclusion section)

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Cited by in corpus (5)

• A Hard Ionizing Spectrum in z=3-4 Ly-alpha Emitters with Intense [OIII] Emission: Analogs of Galaxies in the Reionization Era?
• The Stellar Mass, Star Formation Rate and Dark Matter Halo Properties of LAEs at $z\sim 2$
• Lyman-Alpha Emitter Galaxies at z ~ 2.8 in the Extended Chandra Deep Field-South: I. Tracing the Large-Scale Structure via Lyman-Alpha Imaging
• Ly$\alpha$ Emitters with Very Large Ly$\alpha$ Equivalent Widths, EW${}_0$(Ly$\alpha$) $\simeq 200-400$ Å, at $z\sim 2$
• Observations of Ly$\alpha$ Emitters at High Redshift