Detection of Two Intervening Ne VIII Absorbers Probing Warm Gas at z~0.6

Abstract

We report on the detection of two Ne VIII absorbers, at z = 0.61907 and z = 0.57052 in the HST/COS spectrum of background quasars SDSS J 080908.13+461925.6 and SBS 1122+594 respectively. The Ne VIII 770 line is at $\sim 3\sigma$ significance. In both instances, the NeVIII is found to be tracing gas with $T\gtrsim 10^5$ K, predominantly collisionally ionized, with moderate densities of $n_H\lesssim 10^{-4}$ $c{m}^{-3}$, sub-solar metallicities and total hydrogen column densities of $N(H)\gtrsim 10^{19}$ $c{m}^2$. In the z = 0.61907 absorber, the low, intermediate ions and O VI are consistent with origin in photoionized gas, with the O VI potentially having some contribution from the warm collisional phase traced by Ne VIII. The z = 0.57052 system has H I absorption in at least three kinematically distinct components, with one of them having $b(HI)=49\pm 11$ $km{s}^{-1}$. The intermediate ionization lines, O VI and Ne VIII are coincident in velocity with this component. Their different line widths suggest warm temperatures of $T=(0.5-1.5)\times 10^5$ K. Both absorbers are residing in regions where there are several luminous ($\gtrsim L^{\ast }$) galaxies. The absorber at z = 0.57052 is within the virial radius of a $2.6L^{\ast }$ galaxy, possibly associated with shock heated circumgalactic material.

20 pages, 11 figures, 4 tables. Accepted by MNRAS

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