PROBING THE LONG GAMMA-RAY BURST PROGENITOR BY Lyalpha EMISSION OF HOST GALAXIES
- Department of Astronomy, School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502 (Japan)
- Optical and Infrared Astronomy Division, National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan)
Long gamma-ray bursts (GRBs) have been suggested to occur preferentially in low-metallicity environment. We discuss the possibility and theoretical aspects of using Lyalpha emission properties of long GRB host galaxies as a metallicity indicator of high-redshift GRB environments, where direct metallicity measurements are not easy. We propose to use the fraction of Lyalpha emitters (LAEs) in long 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. There are two important effects of metallicity dependence of long GRB rate to change the LAE fraction of host galaxies. One is the enhancement of intrinsic Lyalpha equivalent width (EW) by stronger ionizing UV luminosity of low-metallicity stellar population, and the other is extinction by interstellar dust to change the observable EW. Based on a latest theoretical model of LAEs that reproduce observations, we argue that the latter is likely to work in the opposite direction to the former, i.e., to decrease LAE fraction if GRBs preferentially occur in low-metallicity environments, because of the clumpy interstellar medium effect. The high LAE fraction of GRB host galaxies indicated by observations is quantitatively explained by the LAE model if GRBs occur when Z approx< 0.1 Z{sub sun}, although this result is still indicative because of the limited statistics and theoretical uncertainties. This result demonstrates that the LAE statistics of GRB hosts may give us useful information in the future.
- OSTI ID:
- 21392525
- Journal Information:
- Astrophysical Journal, Vol. 707, Issue 2; Other Information: DOI: 10.1088/0004-637X/707/2/1634; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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