2016MNRAS.458L.123N

In this Letter, we demonstrate that the two claims of z ≃ 0.03 O vii K α absorption lines from Warm Hot Intergalactic Medium (WHIM) along the lines of sight to the blazars H 2356-309 (Buote et al.; Fang et al.) and Mkn 501 (Ren, Fang & Buote) are likely misidentifications of the z=0 O ii K β line produced by a diffuse Low-Ionization Metal Medium in the Galaxy's interstellar and circum-galactic mediums. We perform detailed modelling of all the available high signal-to-noise Chandra Low Energy Transmission Grating (LETG) and XMM-Newton Reflection Grating Spectrometer (RGS) spectra of H 2356-309 and Mkn 501 and demonstrate that the z ≃ 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 ≃ 0.03 O vii K α 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 x 10⁵ K and the O vii column density is/cm2, twenty times smaller than the O viicolumn density previously reported, and now more consistent with the expectations from cosmological hydrodynamical simulations.