Niino 2009 用宿主星系的Lyman-alpha发射线来探测伽玛暴的前身星性质

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Title:		Probing the Gamma-Ray Burst Progenitor by Lyman-Alpha Emission of Host Galaxies
Authors:		Niino, Yuu; Totani, Tomonori; Kobayashi, Masakazu A. R.
Publication:		eprint arXiv:0905.1525
Publication Date:		05/2009
Origin:		ARXIV
Keywords:		Astrophysics - Cosmology and Extragalactic Astrophysics, Astrophysics - High Energy Astrophysical Phenomena
Comment:		8 pages, 5 figures, submitted to ApJ
Bibliographic Code:		2009arXiv0905.1525N

Abstract

Theoretical and observational studies suggest that long gamma-ray bursts (GRBs) preferentially occur in low metallicity environment. We discuss the possibility and theoretical aspects of using Lyman alpha emission properties of GRB host galaxies as a metallicity indicator of high redshift GRB environments, where direct metallicity measurements are not easy. We consider the fraction of Lyman-alpha emitters (LAEs) in GRB host galaxies as a function of UV luminosity, which can be compared with star-formation-rate weighted LAE fraction of Lyman-break galaxies as the standard in the case of no metallicity dependence. According to recent observational and theoretical studies of LAEs, we argue that there are two important effects of metallicity dependence of GRB rate to change the LAE fraction of host galaxies. One is the enhancement of intrinsic Lyman-alpha EW by stronger ionizing UV luminosity of low metallicity stellar population, and the other is extinction by interstellar dust to change the observable EW. We argue that the latter is likely to work in the opposite direction to the former, i.e., to decrease LAE fraction by the low metallicity preference of GRBs through the clumpy inter-stellar medium effect. The relative importance of the two effects changes by different UV luminosity ranges. The selection effect of GRB host galaxies by extinction of optical afterglows also works to decrease LAE fraction. We find that the observed high LAE fraction of GRB host galaxies can quantitatively be explained if GRBs occur predominantly in low metallicity environments of Z ~ 0.1Z_sun, although statistics is still limited and we need more systematic studies by future data sets.

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