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由GRB余辉揭示的高红移恒星爆发矮星系

High-Redshift Starbursting Dwarf Galaxies Revealed by GRB Afterglows

Hsiao-Wen Chen, Daniel A. Perley, Lindsey K. Pollack, J. X. Prochaska, J. S. Bloom, M. Dessauges-Zavadsky, M. Pettini, S. Lopez, A. Dall'Aglio, G. D. Becker

摘要:

本文研究了15个z>2的长持续时间伽马射线暴(GRB)宿主星系。为了比较星际介质(ISM)吸收线特性与宿主星系的恒星特性,我们选择了具有早期余辉光谱的伽玛暴。除了五个以前研究的主机,我们认为新的检测GRB 050820和GRB 060206的主机星系和地方2西格玛上限的亮度剩余的身份不明的主机。研究发现:(1)GRB宿主星系的紫外光度分布与平均光度<L(UV)>= 0.1L * 的紫外光度加权随机星系群的期望值一致;(2)紫外发光度与Si Ⅱ 1526吸收宽度之间存在中等程度的相关性,这与观测到的W(1526)>1.5 Ang的大线宽一起表明宿主星系中存在星系外流驱动的速度场;(3)在z=2-4的恒星形成星系中,ISM金属丰度随星系光度的降低而降低;(4)发现GRB宿主中的星际紫外辐射场比银河系平均值高约35-350倍;(5)在所有已知存在强MgII吸收体的区域中,在距离GRB宿主< 2”处发现了额外的星系,但在没有强MgII吸收体的区域中,在距离GRB宿主< 2”处没有发现额外的昏暗星系。我们的研究证实了伽玛暴宿主星系(具有已知的光学余辉)是z>2时未被遮蔽的恒星形成星系的代表,并表明高空间分辨率图像对于精确识别存在强干涉吸收体的伽玛暴宿主星系是必要的。

英文摘要:

We present a study of 15 long-duration gamma-ray burst (GRB) host galaxies at z>2. The GRBs are selected with available early-time afterglow spectra in order to compare interstellar medium (ISM) absorption-line properties with stellar properties of the host galaxies. In addition to five previously studied hosts, we consider new detections for the host galaxies of GRB050820 and GRB060206 and place 2-sigma upper limits to the luminosities of the remaining unidentified hosts. We examine the nature of the host galaxy population and find that (1) the UV luminosity distribution of GRB host galaxies is consistent with expectations from a UV luminosity weighted random galaxy population with a median luminosity of <L(UV)>=0.1 L*; (2) there exists a moderate correlation between UV luminosity and SiII 1526 absorption width, which together with the observed large line widths of W(1526)>1.5 Ang for a large fraction of the objects suggests a galactic outflow driven velocity field in the host galaxies; (3) there is tentative evidence for a trend of declining ISM metallicity with decreasing galaxy luminosity in the star-forming galaxy population at z=2-4; (4) the interstellar UV radiation field is found ~ 35-350 times higher in GRB hosts than the Galactic mean value; and (5) additional galaxies are found at < 2" from the GRB host in all fields with known presence of strong MgII absorbers, but no additional faint galaxies are found at < 2" in fields without strong MgII absorbers. Our study confirms that the GRB host galaxies (with known optical afterglows) are representative of unobscured star-forming galaxies at z>2, and demonstrates that high spatial resolution images are necessary for an accurate identification of GRB host galaxies in the presence of strong intervening absorbers.

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