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arXiv 0907.0231astro-ph.CO
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星系探测星系:来自z = 0.47星暴后星系的冷晕气体

Galaxies probing galaxies: cool halo gas from a z = 0.47 post-starburst galaxy

Kate H. R. Rubin, J. Xavier Prochaska, David C. Koo, Andrew C. Phillips, Benjamin J. Weiner

摘要:

利用Keck/LRIS光谱技术研究了z = 0.4729星系周围的冷气体,背景星系的亮度为B = 21.7,z = 0.6942,横向距离为16.5/h_70 kpc。背景星系的光谱在前景星系的红移处显示出强烈的Fe II、Mg II、Mg I和Ca II吸收,Mg II 2796的静止等效宽度为3.93 +/- 0.08埃,表明速度宽度超过400 km/s。由于背景星系很大(> 4/h_70 kpc),吸收气体的高覆盖率表明它出现在一个空间扩展的复杂的冷云中,具有很大的速度色散。大质量(log M_*/M_sun = 11.15 +/-0.08)主星系的光谱表明,它在大约1 Gyr前经历了一次恒星形成爆发,并拥有一个弱的活动星系核。我们讨论了冷气体在其晕中的可能来源,包括热晕气体的多相冷却,冷流入,潮汐相互作用和星系风。我们的结论是,吸收气体很可能是在过去的星暴事件中从宿主星系或其祖先星系的星际介质中喷出或潮汐剥离。采用后一种解释,这些结果对从遥远宇宙中的星系驱动或剥离的冷气体的径向范围施加了为数不多的限制。未来的研究与空间扩展的背景星系的积分场单位光谱将提供多个视线通过前景吸收器和允许分析的形态和运动学的气体周围的星系与一组不同的属性和环境。

英文摘要:

We study the cool gas around a galaxy at z = 0.4729 using Keck/LRIS spectroscopy of a bright (B = 21.7) background galaxy at z = 0.6942 at a transverse distance of 16.5/h_70 kpc. The background galaxy spectrum reveals strong FeII, MgII, MgI, and CaII absorption at the redshift of the foreground galaxy, with a MgII 2796 rest equivalent width of 3.93 +/- 0.08 Angstroms, indicative of a velocity width exceeding 400 km/s. Because the background galaxy is large (> 4/h_70 kpc), the high covering fraction of the absorbing gas suggests that it arises in a spatially extended complex of cool clouds with large velocity dispersion. Spectroscopy of the massive (log M_*/M_sun = 11.15 +/- 0.08) host galaxy reveals that it experienced a burst of star formation about 1 Gyr ago and that it harbors a weak AGN. We discuss the possible origins of the cool gas in its halo, including multiphase cooling of hot halo gas, cold inflow, tidal interactions, and galactic winds. We conclude the absorbing gas was most likely ejected or tidally stripped from the interstellar medium of the host galaxy or its progenitors during the past starburst event. Adopting the latter interpretation, these results place one of only a few constraints on the radial extent of cool gas driven or stripped from a galaxy in the distant Universe. Future studies with integral field unit spectroscopy of spatially extended background galaxies will provide multiple sightlines through foreground absorbers and permit analysis of the morphology and kinematics of the gas surrounding galaxies with a diverse set of properties and environments.

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