The cosmological missing baryons at z<1 most likely hide in the hot (T$\gtrsim10^{5.5}$ K) phase of the Warm Hot Intergalactic Medium (WHIM). While the hot WHIM is hard to detect due to its high ionisation level, the warm (T$\lesssim10^{5.5}$ K) phase of the WHIM has been very robustly detected in the FUV band. We adopted the assumption that the hot and warm WHIM phases are co-located and thus used the FUV-detected warm WHIM as a tracer for the cosmologically interesting hot WHIM. We utilised the assumption by performing an X-ray follow-up in the sight line of a blazar PKS 2155-304 at the redshifts where previous FUV measurements of OVI, SiIV and BLA absorption have indicated the existence of the warm WHIM. We looked for the OVII He$α$ and OVIII Ly$α$ absorption lines, the most likely hot WHIM tracers. Despite of the very large exposure time ($\approx$ 1 Ms), the XMM-Newton/RGS1 data yielded no significant detection which corresponds to upper limits of $\log{N({\rm OVII})({\rm cm}^{-2}))} \le 14.5-15.2$ and $\log{N({\rm OVIII})({\rm cm}^{-2}))} \le 14.9-15.2$. An analysis of LETG/HRC data yielded consistent results. However, the LETG/ACIS data yielded a detection of an absorption line - like feature at $λ\approx$ 20 Å at simple one parameter uncertainty - based confidence level of 3.7 $σ$, consistently with several earlier LETG/ACIS reports. Given the high statistical quality of the RGS1 data, the possibility of RGS1 accidentally missing the true line at $λ\sim$ 20 Å is very low, 0.006%. Neglecting this, the LETG/ACIS detection can be interpreted as Ly$α$ transition of OVIII at one of the redshifts (z$\approx$ 0.054) of FUV-detected warm WHIM. Given the very convincing X-ray spectral evidence for and against the existence of the $λ\sim$ 20 Å feature, we cannot conclude whether or not it is a true astrophysical absorption line.
Confirmation of Intervening Filaments of Galaxies at the Redshifts of $Chandra$ WHIM Absorption Features
利用$a~posteriori$方法证实了在耀变体1 ES ~1553+113的视线方向上存在两个大尺度的暗条，这两个暗条对应于温暖-炽热星系际介质（WHIM）在X射线和远紫外波段的吸收特征。我们使用WISE-SuperCOSMOS测光表来绘制耀变体方向的宇宙网，并在红移为$z=0.23\pm0.02$和$z=0.31\pm0.02$的位置发现了重要的细丝，它们与吸收红移大致一致。$z_X=0.133$的第三个X射线吸收特征在光度目录中没有任何对应的结构。
我们提出了XMM RGS和钱德拉LETG观测的耀变体，H 2356 - 309，位于后面的雕塑家墙，一个大规模的星系结构，预计港口高密度的温热星系际介质（WHIM）。我们对RGS和LETG光谱的同时分析产生了对关键的红移O vii K-α线的3-sigma检测，其柱密度（>~10 ^{16} cm ^{-2}）与宇宙学模拟中产生的类似大尺度结构一致。这代表了第一次检测到非本地WHIM从X射线吸收研究，XMM和钱德拉数据进行了分析，同时吸收体红移是已知的，从而提供了强大的证据，预期的存储库的"失踪重子"。
PKS\,1351$-$018 at a redshift of $z=3.71$ is one of the most luminous, steady synchrotron sources with a luminosity $> 10^{47}$\,erg~s$^{-1}$. The synchrotron luminosity does not seem to vary by more than $\sim 25\%$ over 35 years. In order to appreciate this remarkable behavior, if it were at $z=0.5$, it would have a flux density at 15 GHz in a range of $110 - 137$\,Jy over 11 yrs. In spite of this steady behavior, two strong $γ$-ray flares $\lesssim 10^{49}$\,erg~s$^{-1}$ were detected in 2011 and 2016. There is blazar-like behavior coexisting with the steady behavior. This study is aimed at…
The problem of missing baryons in the local universe remains an open question. One propose alternative is that at low redshift missing baryons are in the form of the Warm Hot Intergalactic Medium (WHIM). In order to test this idea, we present a detailed analysis of X-ray high-resolution spectra of six extragalactic sources, Mrk 421, 1ES 1028+511, 1ES 1553+113, H2356-309, PKS 0558-504 and PG 1116+215, obtained with the XMM-Newton Reflection Grating Spectrometer to search for signals of WHIM and/or circumgalactic medium (CGM) X-ray absorbing gas. We fit the X-ray absorption with the IONeq model,…
