Cos observations of metal line and broad lyman alpha absorption in the multi-phase o vi and ne viii system toward he 02226-4110

TL;DR

This study uses high-quality COS observations to analyze a multi-phase O VI and Ne VIII absorption system at z=0.207, revealing broad Lyman alpha features and providing insights into the temperature, metallicity, and baryonic content of the circumgalactic medium.

Contribution

First high-resolution COS data enabled reliable detection of broad Lyman alpha and metal lines, improving understanding of the physical conditions in the circumgalactic medium.

Findings

Detection of broad Lyman alpha with b=72 km/s indicating warm gas.

Collisionally ionized gas has a temperature of log T ~5.7.

Metallicity of the collisionally ionized gas is [O/H] = -0.89.

Abstract

Observations of the QSO HE 0226-4110 (zem = 0.495) with the Cosmic Origins Spectrograph (COS) from 1134 to 1796 {\AA} with a resolution of ~17 km s-1 and signal-to- noise (S/N) per resolution element of 20 to 40 are used to study the multi-phase absorption system at z = 0.20701 containing O VI and Ne VIII. The system was previously studied with lower S/N observations with FUSE and STIS. The COS observations provide more reliable measures of the H I and metal lines present in the system and reveal the clear presence of broad Lyman {\alpha} (BLA) absorption with b = 72(+13, -6) km s-1 and logN(H I) = 13.87\pm0.08. Detecting BLAs associated with warm gas absorbers is crucial for determining the temperature, metallicity and total baryonic content of the absorbers. The BLA is probably recording the trace amount of thermally broadened H I in the collisionally ionized plasma with log T ~5.7 that also produces the O VI and Ne VIII absorption. The total hydrogen column in the collisionally ionized gas, logN(H) ~ 20.1, exceeds that in the cooler photoionized gas in the system by a factor of ~22. The oxygen abundance in the collisionally ionized gas is [O/H] = -0.89\pm0.08\pm0.07. The absorber probably occurs in the circumgalactic environment (halo) of a foreground L = 0.25L* disk galaxy with an impact parameter of 109h70-1 kpc identified by Mulchaey & Chen (2009).