Properties of QSO Metal Line Absorption Systems at High Redshifts: Nature and Evolution of the Absorbers and New Evidence on Escape of Ionizing Radiation from Galaxies

TL;DR

This study analyzes high-redshift QSO metal absorption systems to understand their properties, clustering, and the escape of ionizing radiation from galaxies, proposing a new model involving runaway stars to explain ionization and galaxy evolution.

Contribution

It introduces a novel scenario involving runaway stars to explain ionizing radiation escape and links absorber properties to galaxy morphological evolution.

Findings

CIV and SiIV show no significant redshift evolution.

Clustering is due to gas velocities in galaxy halos.

Runaway stars enable spectral escape of ionizing radiation.

Abstract

Using Voigt-profile-fitting procedures on Keck HIRES spectra of nine QSOs we identify 1099 CIV absorber components clumped in 201 systems outside the Lyman forest over 1.6 < z < 4.4. With associated SiIV, CII, SiII and NV where available we investigate bulk statistical and ionization properties of the components and systems and find no significant change in redshift for CIV and SiIV while CII, SiII and NV change substantially. The CIV components exhibit strong clustering but no clustering is detected for systems on scales from 150 km/s out to 50000 km/s. We conclude the clustering is due entirely to the peculiar velocities of gas present in the circumgalactic media of galaxies. Using specific combinations of ionic ratios we compare our observations with model ionization predictions for absorbers exposed to the metagalactic ionizing radiation background augmented by proximity radiation from their associated galaxies and find the generally accepted means of radiative escape by transparent channels from the internal star-forming sites is spectrally not viable for our stronger absorbers. We develop an active scenario based on runaway stars with resulting changes in the efflux of radiation that naturally enable the needed spectral convergence and in turn provide empirical indicators of morphological evolution in the associated galaxies. Together with a coexisting population of relatively compact galaxies indicated by the weaker absorbers in our sample the collective escape of radiation is sufficient to maintain the IGM ionized over the full range 1.9 < z < 4.4.