[论文解读] The hot circumgalactic medium in the eROSITA All-Sky Survey I. X-ray surface brightness profiles

Yi Zhang, Johan Comparat+18 more|arXiv (Cornell University)|Jan 30, 2024

Astrophysical Phenomena and Observations被引用 5

一句话总结

本文利用对 eROSITA eRASS:4 数据的叠加，探测并表征到银河系质量及更大中心星系的热围星系际介质（hot circum-galactic medium，CGM），延伸至 virial 半径，同时对 AGN/XRB 污染进行建模与扣除。

ABSTRACT

The circumgalactic medium (CGM) provides the material needed for galaxy formation and influences galaxy evolution. The hot ($T>10^6K$) CGM is poorly detected around galaxies with stellar masses ($M_*$) lower than $3 imes10^{11}M_\odot$ due to the low surface brightness. We used the X-ray data from the first four SRG/eROSITA All-Sky Surveys (eRASS:4). Based on the SDSS spectroscopic survey and halo-based group finder algorithm, we selected central galaxies with spectroscopic redshifts of $z_{ m spec}<0.2$ and stellar masses of $10.0<\log(M_*/M_\odot)<11.5$ (85,222 galaxies) -- or halo masses of $11.5<\log(M_{ m 200m}/M_\odot)<14.0$ (125,512 galaxies). By stacking the X-ray emission around galaxies, masking the detected X-ray point sources and carefully modeling the X-ray emission from the unresolved active galactic nuclei (AGN) and X-ray binaries (XRB), we obtain the X-ray emission from the hot CGM. We detected the X-ray emission around MW-mass and more massive central galaxies extending up to the virial radius ($R_{ m vir}$). We used a $β$ model to describe the X-ray surface brightness profile and found $β=0.43^{+0.10}_{-0.06}\,(0.37^{+0.04}_{-0.02})$ for MW-mass (M31-mass) galaxies.We estimated the baryon budget of the hot CGM and obtained a value that is lower than the prediction of $Λ$CDM cosmology, indicating significant gas depletion in these halos. We extrapolated the hot CGM profile measured within $R_{ m vir}$ to larger radii and found that within $\approx 3 R_{ m vir}$, the baryon budget is close to the $Λ$CDM cosmology prediction. Our results set a firm footing for the presence of the hot CGM around such galaxies. These measurements constitute a new benchmark for galaxy evolution models and possible implementations of feedback processes therein.

研究动机与目标

• 作为主要重子储存库之一的热 CGM 的研究动机及其在星系演化中的作用
• 使用 eROSITA 全天空 survey 数据，测量 MW 质量及更大中心星系周围热 CGM 的 X 射线表面亮度剖面
• 开发并验证一个健壮的叠加与掩蔽框架，以将 CGM 发射与 AGN 和 X 射线星之间的污染分离
• Construct carefully defined central and isolated galaxy samples to minimize satellite contamination in stacking analyses.

提出的方法

• 对前四次 eROSITA 全天空 survey (eRASS:4) 的 0.5–2 keV 带的 X 射线数据进行叠加
• 为每个星系构建物理距离立方体，掩蔽探测到的 X 射线源，并纠正掩蔽面积和吸收
• 对无法分辨的 AGN 与 X 射线双星的残留发射进行建模，以提取热 CGM 发射
• 用 β 模型拟合得到的表面亮度剖面，卷积于 eROSITA 的 PSF，使用 MCMC 估计参数（S_X,0, β, r_c）
• 通过泊松统计和叠加的 Jackknife 重采样来估计不确定性

Figure 1 : Top Panel : An illustration of contamination to the stacking from the satellite boost and sources in the satellites. Bottom Panel : An illustration of the X-ray surface brightness profiles of different components. The X-ray surface brightness profile of central galaxies that we are intere

实验结果

研究问题

• RQ1 MW-质量及更大中心星系在 virial 半径处的热 CGM 的平均 X 射线表面亮度剖面是什么？
• RQ2 未分辨的 AGN/XRB 污染和卫星星系如何偏倚叠加测量，如何加以缓解？
• RQ3 描述热 CGM 的最佳拟合 β 模型参数是什么，它们对其结构有何含义？
• RQ4 MW-质量及更大系统的热 CGM 推断的重子预算是多少，它与 ΛCDM 预测有何对比？

主要发现

• 在 MW 质量及更大中心星系的热 CGM 中，扩展的 X 射线发射在 virial 半径处可显著检测到（R_vir）。
• MW 质量星系：S_X,0 ≈ 3.1×10^35 erg s^-1 kpc^-2，β ≈ 0.42；M31-质量星系：S_X,0 ≈ 1.3×10^36 erg s^-1 kpc^-2，β ≈ 0.37；更高质量区间（log M_* = 11.25–11.50）：S_X,0 ≈ 6.3×10^36 erg s^-1 kpc^-2，β ≈ 0.35。
• 统计显著性水平：MW-质量约 ≈12.3σ，M31-质量约 ≈8.1σ 在 R_vir 内；在 0.5–1 R_vir 内分别约 ≈4.5σ（MW）与 ≈3.1σ（M31）。
• 在 R_vir 处检测到扩展发射，为 MW-质量及更大星系的热 CGM 的存在提供坚定基础。
• 孤立星系在考虑环境因素后，与中心星系的表面亮度剖面没有显著差异。

Figure 2 : An illustration of how the isolated selection works for photometric samples. If after projection, the virial halo of a galaxy has no overlap or is much more massive than overlapped galaxies, they are kept in the isolated galaxy sample (in orange color). Otherwise, they are removed (in col