AI 中文总结
本研究利用SRG/eROSITA巡天数据，首次对827个低质量星系群下落区的群内介质进行光谱测量，探测到弥散辐射并分析其热力学性质，探讨了热与非热辐射成分的可能性。
AI 中文摘要
星系群位力半径周围的微弱下落区因X射线面亮度低，至今仍未被充分探索。利用SRG/eROSITA巡天观测的强大统计能力，我们首次对大样本低质量星系群（总质量$M_{\rm tot}<1\times10^{14}\text{太阳质量}$）下落区的群内介质（IGrM）进行了光谱测量，探测范围延伸至约$2R_{200m}$（2.2兆秒差距）。通过对eROSITA全天巡天第一期星表中827个邻近星系群进行光谱堆叠，我们探测到了弥散辐射，并测量了此前X射线观测无法触及的气体密度下的热力学性质。堆叠光谱可由高斯微分发射度模型很好地拟合，得到的温度分布平均温度为$0.96_{-0.04}^{+0.05}$千电子伏，宽度为$0.28_{-0.10}^{+0.10}$千电子伏，金属丰度为$0.21_{-0.04}^{+0.06}$太阳金属丰度，符合星系群外围的预期。推导得到的电子密度从$(0.7-2)R_{500c}$处的$(4.8\rp1.3)\times10^{-5}$厘米$^{-3}$降至$(2-4)R_{500c}$处的$(5.5\rp2.0)\times10^{-6}$厘米$^{-3}$，证明了eROSITA探测星系群低密度外围的能力。光谱中的残余辐射表明存在额外的光谱成分：若用二次热成分解释则需要异常高温、贫金属等离子体，而非热的逆康普顿模型同样合理，贡献了约30%的热辐射通量。假设该额外成分由同一群相对论性电子的逆康普顿辐射产生，推导得到的磁场强度处于亚微高斯范围。
英文摘要
The faint infall regions surrounding the virial radius of galaxy groups remain largely unexplored due to their low X-ray surface brightness. Using the large statistical power of SRG/eROSITA survey observations, we present the first spectroscopic measurement of the intragroup medium (IGrM) in the infall regions of a large sample of low-mass galaxy groups ($M_{\rm tot}<1\times10^{14}\,M_{sun}$), extending to $\sim2\,R_{200m}$ (2.2 Mpc). Through spectral stacking of 827 nearby groups from the first eROSITA All-Sky Survey catalog, we detect diffuse emission and measure the thermodynamic properties of gas at densities previously inaccessible to X-ray observations. The stacked spectra are well described by a Gaussian differential emission measure model, yielding a temperature distribution with a mean temperature of $0.96_{-0.04}^{+0.05}$ keV and width of $0.28_{-0.10}^{+0.10}$ keV, and a metal abundance of $0.21_{-0.04}^{+0.06}$ A$_{sun}$, consistent with expectations for group outskirts. The inferred electron densities decrease from $(4.8\pm1.3)\times10^{-5}$cm$^{-3}$ at $(0.7-2)\,R_{500c}$ to $(5.5\pm2.0)\times10^{-6}$ cm$^{-3}$ at $(2-4)\,R_{500c}$, demonstrating eROSITA's ability to probe the low-density outskirts of galaxy groups. Residual emission in the spectra suggests the presence of an additional spectral component. While a secondary thermal interpretation requires an unexpectedly hot, metal-poor plasma, a non-thermal inverse Compton model provides an equally plausible explanation, contributing $\sim30\%$ of the thermal flux. Assuming that the additional component is produced by inverse Compton emission from a common population of relativistic electrons, the inferred magnetic field strength would be in the sub-$μ$G regime.
CommentsSubmitted to A&A, 12 pages, 5 figures, 1 table
