研究成果・発表論文

What is the Physical Origin of Strong Ly\ensuremathα Emission? I. Demographics of Ly\ensuremathα Emitter Structures

Shibuya, Takatoshi,   Ouchi, Masami,   Nakajima, Kimihiko,   Yuma, Suraphong,   Hashimoto, Takuya,   Shimasaku, Kazuhiro,   Mori, Masao,   & Umemura, Masayuki


要旨
We present the results of structure analyses for a large sample of 426 Ly\ensuremathα emitters (LAEs) at z åisebox-0.5ex~ 2.2 that are observed with the Hubble Space Telescope/Advanced Camera for Surveys and WFC3-IR during deep extra-galactic legacy surveys. We confirm that the merger fraction and the average ellipticity of LAE's stellar component are 10%-30% and 0.4-0.6, respectively, that are comparable with previous study results. We successfully identify that some LAEs have a spatial offset between Ly\ensuremathα and stellar-continuum emission peaks, \ensuremathδ$_Ly\ensuremathα$, by \i̊sebox-0.5ex~2.5-4 kpc beyond our statistical errors. To uncover the physical origin of strong Ly\ensuremathα emission found in LAEs, we investigate the Ly\ensuremathα equivalent width (EW) dependences of three structural parameters: merger fraction, \ensuremathδ$_Ly\ensuremathα$, and ellipticity of stellar distribution in the range of EW(Ly\ensuremathα) = 20-250 \r̊. Contrary to expectations, we find that the merger fraction does not significantly increase with Ly\ensuremathα EW. We reveal an anti-correlation between \ensuremathδ$_Ly\ensuremathα$ and EW(Ly\ensuremathα) using a Kolmogorov-Smirnov (K-S) test. There is a trend that the LAEs with a large Ly\ensuremathα EW have a small ellipticity. This is consistent with the recent theoretical claims that Ly\ensuremathα photons can more easily escape from face-on disks having a small ellipticity, due to less inter- stellar gas along the line of sight, although our K-S test indicates that this trend is not statistically significant. Our results of Ly\ensuremathα-EW dependence generally support the idea that an H I column density is a key quantity determining Ly\ensuremathα emissivity.

Based on data obtained with the Subaru Telescope operated by the National Astronomical Observatory of Japan.




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