Study of X-ray emission from nearby normal galaxies using eROSITA All-Sky Survey data

对星系的x射线观测使我们能够研究恒星生命结束时形成的致密天体的数量，以及主要由恒星风和超新星电离和加热的弥漫星际气体。由于大多数恒星是在多个系统中形成的，紧凑的物体通常有一颗伴星，紧凑的物体从伴星中吸积物质。吸积中子星和黑洞是正常星系中最亮的恒星x射线源，被称为x射线双星（XRBs）。由于双星的演化和致密天体的形成依赖于潜在的恒星种群，XRBs是星系中恒星种群和恒星形成历史的理想示踪剂。大质量恒星和超新星的强烈恒星风在星际介质（ISM）和被驱逐的恒星物质中引起强烈的冲击波，这些物质将在ISM中形成弥漫性热电离阶段。由于热的低密度等离子体的冷却效率非常低，它将持续很长时间，并且可以在整个星系中观察到漫射x射线。过去几十年的x射线观测使我们能够限制正常星系的发射成分。在邻近的星系中，我们详细地研究了源族和热气体，而对更远星系的综合发射的研究表明，x射线的综合光度L_X与恒星形成速率（SFR）之间存在着关系，XRBs和漫射热气体也分别与之相关。此外，L_X/SFR关系还取决于金属丰度，因此也取决于星系的年龄或距离。因此，对更高距离星系的x射线研究将有助于我们提高对宇宙中星系演化的理解。由于望远镜在较低x射线能量下的相对低灵敏度，到目前为止，漫射热气体的研究只能在最近的星系中进行。由于eROSITA在低能量波段的高灵敏度和它的全天覆盖，我们现在有了理想的x射线望远镜来研究正常星系的完整样本的漫射x射线发射。在我们对非常近星系（D < 10 Mpc）漫射x射线辐射研究的基础上，我们将利用eROSITA全天巡天数据研究星系中漫射热气体的x射线辐射。首先，我们将研究D ~ 20mpc的星系中热漫射气体的发射，我们可以解决星系中的发射问题。我们将根据xmm -牛顿或钱德拉对邻近星系的研究结果，利用发射模型分析光谱。第二步，我们将利用模型研究更远星系在不同间隔（高达~ 200mpc）的叠加光谱，以及x射线光度与SFR、距离或金属丰度之间的关系。在最后一步，我们还将对未来的x射线任务进行模拟，以估计类似研究的预期样本量和深度。

X-ray observations of galaxies allow us to study the population of compact objects formed at the end of the stellar life and the diffuse interstellar gas, which has been ionised and heated mainly by stellar winds and supernovae. As most of the stars are formed in multiple systems, compact objects often have a companion star, from which the compact object accretes matter. Accreting neutron stars and black holes are the brightest stellar X-ray sources in normal galaxies and are called X-ray binaries (XRBs). Since binary evolution and formation of compact objects depend on the underlying stellar population, XRBs are ideal tracers of stellar population and star formation histories in galaxies. Strong stellar winds of massive stars and supernovae cause strong shock waves in the interstellar medium (ISM) and the expelled stellar material, which will form the diffuse hot ionised phase in the ISM. Since the cooling of the hot low-density plasma is very inefficient, it will persist for a long time, and diffuse X-rays can be observed over the entire galaxy. X-ray observations in the last decades have allowed us to constrain the emission components in normal galaxies. In nearby galaxies, the source populations and the hot gas have been studied in detail, while studies of the integrated emission from further distant galaxies have shown that there is a relation between the integrated X-ray luminosity L_X and the star-formation rate (SFR), also separately for the XRBs and the diffuse hot gas. Moreover, the L_X/SFR relations also depend on the metallicity, and hence also on the age or on the distance of galaxies. Therefore, X-ray study of galaxies at higher distances will help us to improve our understanding of the evolution of galaxies in the Universe. The study of the diffuse hot gas has so far only been possible in the closest galaxies due to the relativity low sensitivity of the telescopes at lower X-ray energies. Thanks to eROSITA's high sensitivity in the lower-energy band and its all-sky coverage, we now have the ideal X-ray telescope to study the diffuse X-ray emission from a complete sample of normal galaxies. Based on our studies of the diffuse X-ray emission in very nearby galaxies (D < 10 Mpc), we will study the X-ray emission of the diffuse hot gas in galaxies using eROSITA All-Sky Survey data. First, we will study the emission of the hot diffuse gas in galaxies up to D ~ 20 Mpc, in which we can resolve the emission in the galaxies. We will analyse the spectrum using emission models based on the results of our XMM-Newton or Chandra study of the very nearby galaxies. In the second step, we will use the models to study the stacked spectra of further distant galaxies in different intervals (up to ~200 Mpc) and the relation between the X-ray luminosity and SFR, distance, or metallicity. In the last step, we will also perform simulations for future X-ray missions to estimate the expected sample size and depth of similar studies.