Theoretical models of structure formation predict the presence of a hot gaseous atmosphere around galaxies. While this hot circum-galactic medium (CGM) has been observationally confirmed through UV absorption lines, the detection of its direct X-ray emission remains scarce. We investigate theoretical predictions of the intrinsic CGM X-ray surface brightness (SB) using simulated galaxies and connect them to their global properties such as gas temperature, hot gas fraction and stellar mass. We select a sample of galaxies from the ultra-high resolution ($48\ \rm{cMpc\, h^{-1}}$) cosmological volume of the Magneticum Pathfinder set of hydrodynamical cosmological simulations. We classify them as star-forming (SF) or quiescent (QU) based on their specific star-formation rate. For each galaxy we generate X-ray mock data using the X-ray photon simulator PHOX, from which we obtain SB profiles out to the virial radius for different X-ray emitting components, namely gas, active galactic nuclei and X-ray binaries (XRBs). We fit a $β$-profile to each galaxy and observe trends between its slope and global quantities of the simulated galaxy. We find marginal differences between the average total SB profile of the CGM in SF and QU galaxies, with the contribution from hot gas being the largest ($>50\%$) at radii $r>0.05\,R_{\rm{vir}}$. The contribution from X-ray binaries (XRBs) equals the gas contribution for small radii and is non-zero for large radii. The galaxy population shows positive correlations between global properties and normalization of the SB profile. The slope of fitted $β$-profiles correlates strongly with the total gas luminosity, which in turn shows strong connections to the current accretion rate of the central super-massive black hole (SMBH).
Exploring X-ray Binary Populations in Compact Group Galaxies with $Chandra$
我们获得总星系X射线光度，$L_X$，起源于单独检测点源的样本中的47个星系在15个紧凑的星系群（CG）。对于我们的大多数星系，我们发现，检测到的点源最有可能是本地的相关星系，因此河外X射线双星（XRB）或核活动星系核（AGN）。对于螺旋星系和不规则星系，我们发现，在考虑活动星系核和核源后，大多数CG星系要么在Mineo et al.（2012）$L_X$ -恒星形成率（SFR）相关性的$\pm1σ$散射范围内，要么具有比其SFR相关性更高的$L_X$。我们讨论如何这些“过剩”可能是由于低金属和高的相互作用水平。对于椭圆星系和S 0星系，在考虑活动星系核和核源后，大多数CG星系与Boroson et al.（2011）$L_X$ -低质量XRB的恒星质量相关性一致，具有较大的散射，可能是由于活动星系核活动或热气体等残余效应。假设非核源是低质量或高质量的XRB，我们使用适当的XRB光度函数来估计随机效应可能导致这种极端的$L_X$值的概率。我们发现，虽然随机效应一般似乎并不重要，对于一些星系有一个显着的概率，高$L_X$值可以观察到由于强大的XRB的变化。
Spectroscopic follow-up of hot subdwarf variables found in ZTF -- Atmospheric and fundamental properties of radial-mode sdB pulsators
Hamburger Sternwarte, University of Hamburg（汉堡天文台，汉堡大学）；Department of Physics and Astronomy, Texas Tech University（德克萨斯理工大学物理与天文学系）；Department of Physics and Astronomy, University of North Carolina at Chapel Hill（北卡罗来纳大学教堂山分校物理与天文学系）；Institut für Physik und Astronomie, Universität Potsdam（波茨坦大学物理与天文学研究所）
