Takuya Hashimoto, Masami Ouchi, Kazuhiro Shimasaku, Yoshiaki Ono, Kimihiko Nakajima, Michael Rauch, Janice Lee, Sadanori Okamura
We present the results of Magellan/MMIRS and Keck/NIRSPEC spectroscopy for five Lya emitters (LAEs) at z=2.2 for which high-resolution Lya spectra are available. We detect Ha emission for all five objects and [OII], Hb, and/or [OIII] emission for some, from which the systemic velocity is measured. We obtain the offset of Lya line with respect to the systemic velocity, Delta_v_Lya. For a sample of eight z~2-3 LAEs without AGN from our study and the literature, we find the average offset velocity of Delta_v_Lya = 145 ^{+45}_{-23} km s^{-1}, which is significantly smaller than that of Lyman Break Galaxies (LBGs), Delta_v_Lya ~ 400 km s^{-1}. Since any of the LAEs with positive Delta_v_Lya has an asymmetric Lya profile that cannot be explained by static gas cloud models, this average Delta_v_Lya implies that most LAEs have a gas outflow but with a systematically smaller velocity than those of LBGs. Interestingly, we find an anti-correlation between Lya equivalent width (EW) and Delta_v_Lya in the compilation of the LAE and LBG samples that galaxies with stronger Lya emission have smaller Delta_v_Lya. Although its physical origin is unknown, this anti-correlation result would challenge the hypothesis that a strong outflow produces a large Lya EW because of reduced numbers of resonant scattering through the inter-stellar medium. If LAEs at z>6 have similarly small Delta_v_Lya, some reionization models need to revise the amount of Lya photons scattered by the inter-galactic medium.
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http://arxiv.org/abs/1206.2316
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