Detection of Ne VIII in an Intervening Multi-Phase Absorption System Towards 3C 263

TL;DR

This paper reports the detection of Ne VIII in an intervening multi-phase absorption system at z=0.326, revealing a warm collisionally ionized medium and expanding understanding of intergalactic gas phases.

Contribution

First detection of Ne VIII in an intervening system at this redshift, demonstrating a multi-phase structure with collisionally ionized Ne VIII.

Findings

Ne VIII detected with 3.9 sigma significance

Absorber has multi-phase structure with collisionally ionized Ne VIII

Properties similar to previous Ne VIII absorber

Abstract

We report on the detection of Ne VIII in an intervening multiphase absorption line system at z=0.32566 in the FUSE spectrum of the quasar 3C 263. The Ne VIII 770 A line detection has a 3.9 sigma significance. At the same velocity we also find absorption lines from C IV, O III, O IV and N IV. The line parameter measurements yield log [N(Ne VIII), cm^-2] =13.98 (+0.10,-0.13) and b = 49.8 +/- 5.5 km/s. We find that the ionization mechanism in the gas phase giving rise to the Ne VIII absorption is inconsistent with photoionization. The absorber has a multi-phase structure, with the intermediate ions produced in cool photoionized gas and the Ne VIII most likely in a warm collisionally ionized medium in the temperature range (0.5 - 1.0) x 10^6 K. This is the second ever detection of an intervening Ne VIII absorption system. Its properties resemble the previous Ne VIII absorber reported by Savage et al. (2005). Direct observations of H I and O VI are needed to better constrain the physical conditions in the collisionally ionized gas phase of this absorber.