A STIS Survey for OVI Absorption Systems at 0.12 < z < 0.5 II.: Physical Conditions of the Ionised Gas

Abstract

We present a complete catalogue of 27 O VI absorbers at low redshift (0.12 < z < 0.5) from a blind survey of 16 QSO echelle spectra in the HST/STIS data archive. These absorbers are identified based only upon matching line profiles and the expected doublet ratio between the λλ1031, 1037 transitions. Subsequent searches are carried out to identify their associated transitions. Here we present all relevant absorption properties. By considering absorption components of different species which are well-aligned in velocity-space, we derive gas temperatures and non-thermal broadening values, b_{nt}. We show that in all 16 cases considered the observed line width is dominated by non-thermal motion and that gas temperatures are well below those expected for O^5+ in collisional ionization equilibrium. This result reaffirms previous findings from studies of individual lines of sight, but are at odds with expectations for a WHIM origin. At least half of the absorbers can be explained by a simple photoionization model. In addition, in some absorbers we find evidence for large variation in gas density/metallicity across components in individual absorbers. Comparisons of multiple associated metal species further show that under the assumption of the gas being photoionized by the metagalacitic background radiation field, the absorbing clouds have gas densities <n_H> < -2.9 and sizes L > 1\kpc. Finally, we compare our absorber selection with the results of other independent studies.

15 pages + lots of figures and tables. ApJS accepted

References in corpus (8)

• Time-Dependent Ionization in Radiatively Cooling Gas
• A High-Resolution Survey of Low-Redshift QSO Absorption Lines: Statistics and Physical Conditions of O VI Absorbers
• The Low-z Intergalactic Medium. III. HI and Metal Absorbers at z<0.4
• Characterizing the Low-Redshift Intergalactic Medium towards PKS1302-102
• A STIS Survey for OVI Absorption Systems at 0.12 < z < 0.5 I.: The Statistical Properties of Ionized Gas
• Probing the IGM/Galaxy Connection Toward PKS0405-123 III: The Galaxy Survey and Correlations with OVI Absorbers
• Low Redshift Intergalactic Absorption Lines in the Spectrum of HE0226-4110
• Galactic Wind Signatures around High Redshift Galaxies

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• The Cosmic Ultraviolet Baryon Survey (CUBS) I. Overview and the diverse environments of Lyman limit systems at z<1
• Absorption signatures of warm-hot gas at low redshift: OVI
• Thermal Instability in the CGM of $L_{\star }$ Galaxies: Testing "Precipitation" Models with the FIRE Simulations
• HST/COS detection of a Ne VIII absorber towards PG 1407+265: An unambiguous tracer of collisionally ionized hot gas?
• Limits on non-canonical heating and turbulence in the intergalactic medium from the low redshift Lyman-alpha forest
• A hot gaseous galaxy halo candidate with Mg X absorption
• The large-scale distribution of ionized metals in IllustrisTNG