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Published June 2019 | Submitted
Journal Article Open

The dominant origin of diffuse Lyα halos around Lyα emitters explored by spectral energy distribution fitting and clustering analysis

Abstract

The physical origin of diffuse Lyα halos (LAHs) around star-forming galaxies is still a matter of debate. We present the dependence of LAH luminosity [L(Lyα)_H] on the stellar mass (M⋆), star formation rate, color excess [E(B − V)⋆], and dark matter halo mass (M_h) of the parent galaxy for ∼900 Lyα emitters (LAEs) at z ∼ 2 divided into ten subsamples. We calculate L(Lyα)_H using the stacked observational relation between L(Lyα)H and central Lyα luminosity of Momose et al. (2016, MNRAS, 457, 2318), which we find agrees with the average trend of VLT/MUSE-detected individual LAEs. We find that our LAEs have relatively high L(Lyα)_H despite low M⋆ and M_h, and that L(Lyα)_H remains almost unchanged with M⋆ and perhaps with M_h. These results are incompatible with the cold stream (cooling radiation) scenario and the satellite-galaxy star-formation scenario, because the former predicts fainter L(Lyα)_H and both predict steeper L(Lyα)_H vs. M⋆ slopes. We argue that LAHs are mainly caused by Lyα photons escaping from the main body and then scattering in the circum-galactic medium. This argument is supported by LAH observations of Hα emitters (HAEs). When LAHs are taken into account, the Lyα escape fractions of our LAEs are about ten times higher than those of HAEs with similar M⋆ or E(B − V)⋆, which may partly arise from lower H I gas masses implied from lower M_h at fixed M⋆, or from another Lyα source in the central part.

Additional Information

© The Author(s) 2019. Published by Oxford University Press on behalf of the Astronomical Society of Japan. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model). Received: 28 March 2018; Accepted: 21 February 2019; Published: 16 May 2019. We thank the anonymous referee for constructive comments and suggestions. We are grateful to Kazuyuki Ogura and Masahiro Nagashima for kindly providing ν2GC data and giving helpful comments. We are grateful to Yoshiaki Ono for giving insightful comments and suggestions on SED fitting. We would like to express our gratitude to Jorryt Matthee and Ken-ichi Tadaki for kindly providing their data, plotted in figure 4, and figures 6–8 and 6, respectively. We thank David Sobral for giving insightful comments and suggestions. We acknowledge Ryosuke Goto, Akira Konno, Ryota Kawamata, Taku Okamura, Kazushi Irikura, Ryota Kakuma, and Makoto Ando for constructive discussions at meetings. This work is based on observations taken by the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. Based on data products produced by TERAPIX and the Cambridge Astronomy Survey Unit on behalf of the UltraVISTA consortium. This research made use of IRAF, which is distributed by NOAO, which is operated by AURA under a cooperative agreement with the National Science Foundation, and of Python packages for astronomy: Astropy (Astropy Collaboration 2013), Colossus, CosmoloPy, and PyRAF, which is produced by the Space Telescope Science Institute, which is operated by AURA for NASA. H.K. acknowledges support from the JSPS through the JSPS Research Fellowship for Young Scientists. This work is supported in part by KAKENHI (16K05286) Grant-in-Aid for Scientific Research (C) through the JSPS.

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August 19, 2023
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