Diffuse low ionization gas in the galactic halo casts doubts on z 0.03 WHIM detections
In this Letter we demonstrate that the two claims of $z\simeq 0.03$ OVII K$\alpha$ absorption lines from Warm Hot Intergalactic Medium (WHIM) along the lines of sight to the blazars H~2356 309 (Buote et al. 2009; Fang et al. 2010) and Mkn~501 (Ren, Fang Buote, 2014) are likely misidentifications of the $z=0$ OII K$\beta$ line produced by a diffuse Low Ionization Metal Medium in the Galaxy's Interstellar and Circum Galactic mediums. We perform detailed modeling of all the available high signal to noise Chandra LETG and XMM Newton RGS spectra of H 2356 309 and Mkn 501 and demonstrate that the $z\simeq 0.03$ WHIM absorption along these two sightlines is statistically not required. Our results, however, do not rule out a small contribution from the $z\simeq 0.03$ OVII K$\alpha$ absorber along the line of sight to H~2356 309. In our model the temperature of the putative $z 0.031$ WHIM filament is T$ 3\times 10^5$ K and the OVII column density is N$_{OV II} \le 4\times 10^{15} cm$ 2} twenty times smaller than the OVII column density previously reported, and now more consistent with the expectations from cosmological hydrodynamical simulations.