We explore the evolution of the ∼107 K hot gas in normal galaxies out to redshift = 0.5 (lookback time = 5 Gyr), using X-ray luminosity functions (XLFs) built from a sample of 575 normal galaxies with z < 0.6 detected in five high-galactic-latitude Chandra wide-field surveys. After estimating the emission due to the hot gas component (reducing the sample to ∼400 galaxies), we compared the XLF in three redshift bins (z = 0.1, 0.3, and 0.5), finding increases in the number of galaxies per unit comoving volume from z = 0.1 to 0.3 and then from z = 0.3 to 0.5. These XLF changes suggest a significant (∼5σ) X-ray luminosity evolution of the hot gas, with LX,GAS decreasing by a factor of 6–10 in the last 5 Gyr (from z = 0.5 to 0.1). The relative abundance of LX,GAS ∼ 1041 erg s−1 galaxies at higher z suggests that high-z, moderate-LX,GAS galaxies may be the optimal target to solve the missing baryon problem. In early-type galaxies, this observational trend is qualitatively consistent with (but larger than) the expected time-dependent mass-loss rate in cooling flow models without active galactic nucleus feedback. In late-type galaxies, the observational trend is also qualitatively consistent with (but larger than) the effect of the z-dependent star formation rate.

中文翻译：

---

光度 正常星系中热气体从近宇宙到 z = 0.5 的演化


我们使用 X 射线光度函数 （XLF） 探索了正常星系中 ∼107 K 热气体向红移 = 0.5（回溯时间 = 5 Gyr）的演变，该函数是从 575 个正常星系的样本构建的，其中 z < 为 0.6，在五次高银河系-钱德拉宽视场巡天中检测到。在估计了热气体成分（将样品减少到 ∼400 个星系）引起的发射后，我们比较了三个红移区间（z = 0.1、0.3 和 0.5）中的 XLF，发现每单位共移动体积的星系数量从 z = 0.1 增加到 0.3，然后从 z = 0.3 增加到 0.5。这些 XLF 变化表明热气体的 X 射线光度发生了显著的 （∼5σ） 演变，LX，GAS 在最后 5 Gyr 中下降了 6-10 倍（从 z = 0.5 到 0.1）。LX，GAS ∼ 1041 erg s−1 星系在较高 z 下的相对丰度表明，高 z、中 LX，GAS 星系可能是解决缺失重子问题的最佳目标。在早期星系中，这种观测趋势与没有活跃星系核反馈的冷却流模型中预期的时间相关质量损失率在质量上是一致的（但更大）。在晚期星系中，观测趋势在质量上也与依赖于 z 的恒星形成速率的影响一致（但更大）。