标题： 发光红星系周围的冷气体大尺度分布 显示英文标题

标题： The Large-scale Distribution of Cool Gas around Luminous Red Galaxies

摘要： 我们测量了亮红星系与由Mg II吸收线\lambda \lambda 2796, 2803所追踪的冷气体之间的关联函数，尺度范围从约30千秒差距到20兆秒差距。 该测量基于大约一百万个红移z~0.5的亮红星系位置与来自斯隆数字巡天的约10^5个背景类星体光谱中诱导的流量减少值之间的交叉相关。 我们发现：(i) 这种星系-气体关联显示出约1百万秒差距尺度上的斜率变化，这与预期的从暗物质晕主导环境向晕间关联主导环境的转变一致。 假设平均而言，Mg II气体分布遵循暗物质分布直到气质量比，我们发现在三个数量级的尺度上标准晕模型能准确描述气体分布。 在此框架内，我们估计亮红星系的平均宿主晕质量约为10^{13.5}太阳质量，与其他方法一致。 我们还发现亮红星系周围的Mg II气质量比与在百万秒差距尺度上估算的宇宙值一致。 结合我们的星系-气体关联和星系-星系透镜分析中的星系-质量关联函数，我们可以直接测量不同尺度上的Mg II气质量比，并得出相同结论。 (ii) 根据线宽估计，我们显示气体云的速度弥散也表现出预期的1-晕和2-晕行为。 在大尺度上，气体分布遵循哈勃流，而在小尺度上，我们观察到Mg II气体云的速度弥散低于它们宿主晕内的无碰撞暗物质粒子的速度弥散。 这与冷气体云受到暴风云压力的事实一致。 显示英文摘要

摘要： We present a measurement of the correlation function between luminous red galaxies and cool gas traced by Mg II \lambda \lambda 2796, 2803 absorption, on scales ranging from about 30 kpc to 20 Mpc. The measurement is based on cross-correlating the positions of about one million red galaxies at z~0.5 and the flux decrements induced in the spectra of about 10^5 background quasars from the Sloan Digital Sky Survey. We find that: (i) This galaxy-gas correlation reveals a change of slope on scales of about 1 Mpc, consistent with the expected transition from a dark matter halo dominated environment to a regime where clustering is dominated by halo-halo correlations. Assuming that, on average, the distribution of Mg II gas follows that of dark matter up to a gas-to-mass ratio, we find the standard halo model to provide an accurate description of the gas distribution over three orders of magnitude in scale. Within this framework we estimate the average host halo mass of luminous red galaxies to be about 10^{13.5} M_solar, in agreement with other methods. We also find the Mg II gas-to-mass ratio around LRGs to be consistent with the cosmic value estimated on Mpc scales. Combining our galaxy-gas correlation and the galaxy-mass correlation function from galaxy-galaxy lensing analyses we can directly measure the Mg II gas-to-mass ratio as a function of scale and reach the same conclusion. (ii) From line-width estimates, we show that the velocity dispersion of the gas clouds also shows the expected 1- and 2-halo behaviors. On large scales the gas distribution follows the Hubble flow, whereas on small scales we observe the velocity dispersion of the Mg II gas clouds to be lower than that of collisionless dark matter particles within their host halo. This is in line with the fact that cool clouds are subject to the pressure of the virialized hot gas.