化学富集的暖-热环银河系气体的深度
The Dearth of Chemically Enriched Warm-Hot Circumgalactic Gas
摘要：
围绕星系的环星系介质（CGM）被认为记录了各种形式的星系反馈，并包含了相当一部分的“失踪重子”的个别暗物质晕。然而，热CGM存在的明确观测证据仍然缺乏。我们使用沿12个背景活动星系核的居间星系作为示踪剂，寻找相应的CGM中产生的X射线吸收线。堆叠钱德拉光栅观测相对于星系群和不同的亮度，这些干预星系，我们得到的光谱与信噪比为46-72每20毫安的光谱箱在预期的OVII Ka线。我们没有发现可检测到的吸收线的CVI，NVII，OVII，OVIII，或NeIX。高光谱质量允许我们将上限严格限制到相应的离子柱密度（特别是log[N（OVII）（cm^{-2}）]<=14.2- 14.8）。这些未探测到的现象与活动星系核光谱中常见的z~0处X射线吸收线的局域群假设是不一致的。这些结果表明，在10^{5.5}-10 ^{6.3} K温度范围内的假定CGM可能无法解释丢失的重子，除非金属丰度小于10%太阳。
英文摘要：
The circumgalactic medium (CGM) around galaxies is believed to record various forms of galaxy feedback and contain a significant portion of the "missing baryons" of individual dark matter halos. However, clear observational evidence for the existence of the hot CGM is still absent. We use intervening galaxies along 12 background AGNs as tracers to search for X-ray absorption lines produced in the corresponding CGM. Stacking Chandra grating observations with respect to galaxy groups and different luminosities of these intervening galaxies, we obtain spectra with signal-to-noise ratios of 46-72 per 20-mA spectral bin at the expected OVII Kalpha line. We find no detectable absorption lines of CVI, NVII, OVII, OVIII, or NeIX. The high spectral quality allows us to tightly constrain upper limits to the corresponding ionic column densities (in particular log[N(OVII)(cm^{-2})]<=14.2--14.8). These nondetections are inconsistent with the Local Group hypothesis of the X-ray absorption lines at z~0 commonly observed in the spectra of AGNs. These results indicate that the putative CGM in the temperature range of 10^{5.5}-10^{6.3} K may not be able to account for the missing baryons unless the metallicity is less than 10% solar.
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