What is the Physical Origin of Strong Lyα Emission? II. Gas Kinematics and Distribution of Lyα Emitters

Creators: Shibuya, Takatoshi; Ouchi, Masami; Nakajima, Kimihiko; Hashimoto, Takuya; Ono, Yoshiaki; Rauch, Michael; Gauthier, Jean-René; Shimasaku, Kazuhiro; Goto, Ryosuke; Mori, Masao; Umemura, Masayuki

Abstract

We present a statistical study of velocities of Lyα, interstellar (IS) absorption, and nebular lines and gas covering fraction for Lyα emitters (LAEs) at z ≃ 2. We make a sample of 22 LAEs with a large Lyα equivalent width (EW) of ≳50 Å based on our deep Keck/Low Resolution Imaging Spectrometer (LRIS) observations, in conjunction with spectroscopic data from the Subaru/Fiber Multi Object Spectrograph program and the literature. We estimate the average velocity offset of Lyα from a systemic redshift determined with nebular lines to be Δv_(Lyα) = 234 ± 9 km s^(–1). Using a Kolmogorov-Smirnov test, we confirm the previous claim of Hashimoto et al. that the average Δv Lyα of LAEs is smaller than that of Lyman break galaxies (LBGs). Our LRIS data successfully identify blueshifted multiple IS absorption lines in the UV continua of four LAEs on an individual basis. The average velocity offset of IS absorption lines from a systemic redshift is Δv_(IS) = 204 ± 27 km s^(–1), indicating LAEs' gas outflow with a velocity comparable to typical LBGs. Thus, the ratio R^(Lyα)_(IS) ≡ Δν_(Lyα)/Δν_(IS) of LAEs is around unity, suggestive of low impacts on Lyα transmission by resonant scattering of neutral hydrogen in the IS medium. We find an anti-correlation between Lyα EW and the covering fraction, f_c, estimated from the depth of absorption lines, where f_c is an indicator of average neutral hydrogen column density, N_(H I) . The results of our study support the idea that N_(H I) is a key quantity determining Lyα emissivity.

Additional Information

© 2014 The American Astronomical Society. Received 2014 February 2; accepted 2014 April 28; published 2014 May 22. Based on data obtained with the Subaru Telescope operated by the National Astronomical Observatory of Japan. We thank Anne Verhamme, Zheng Zheng, Lennox L. Cowie, Esther M. Hu, and James E. Rhoads for useful discussions, and an anonymous referee, Mark Dijkstra, and Lucia Guaita for constructive comments. This paper is based on data collected with the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. Some of the data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. The reduction pipeline used to reduce the LRIS data was developed at UC Berkeley with support from NSF grant AST-0071048. This work is based on observations taken by the CANDELS Multi-Cycle Treasury Program with the NASA/ESA HST, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. The NB387 data used in this work were collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech. This work was supported by World Premier International Research Center Initiative (WPI Initiative), MEXT, Japan. This work was supported by KAKENHI (23244025) and (21244013) Grant-in-Aid for Scientific Research (A) through Japan Society for the Promotion of Science (JSPS). M.R. was supported by NSF grant AST-1108815. Facilities: Subaru (Suprime-Cam, FMOS), Keck:I (LRIS), Magellan:Baade (IMACS).

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