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

Abstract

Using Voigt-profile-fitting procedures on Keck High Resolution Spectrograph spectra of nine QSOs, we identify 1099 C iv absorber components clumped in 201 systems outside the Lyman forest over 1.6 z 4.4. With associated Si iv, C ii, Si ii and N v where available, we investigate the bulk statistical and ionization properties of the components and systems and find no significant change in redshift for C iv and Si iv while C ii, Si ii and N v change substantially. The C iv components exhibit strong clustering, but no clustering is detected for systems on scales from 150 km s −1 out to 50,000 km s −1. We conclude that 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 that 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 intergalactic medium ionized over the full range 1.9 < z 4.4.

Triple-ionized carbon associated with the low-density neutral hydrogen gas at 1.7 <z< 3.3: the integratedN H I–N C ivrelation

“…Only errors larger than the symbol size are displayed. 2 < z < 3.3 (Bolton et al 2005;Faucher-Giguère et al 2008;Boksenberg & Sargent 2015) and that additional photons from other ionising sources are negligible for aligned C iv components at our NH i, comp range, a higher NC iv, comp/NH i, comp at lower-NH i, comp implies a higher carbon abundance in lower-NH i, comp pairs or a higher gas volume density if a similar carbon abundance, e.g. Schaye et al (2007).…”

“…ally, C iv systems with higher NH i, sys are likely to be associated with more metal species (Simcoe et al 2004;Boksenberg & Sargent 2015). On the other hand, C iv systems without Si iv are likely to be associated with no other ions, and only rarely with N v or O vi (Carswell et al 2002;Schaye et al 2007).…”

“…Most UVES spectra cover from 3050Å (a natural cutoff due to the Earth's atmosphere) to 10000Å (due to the limitation of the optical instrument), with some gaps due to the CCD detector configuration. The 2 HIRES spectra are described by Boksenberg & Sargent (2015). A HST/STIS echelle spectrum is available for J2233-606 1 (Savaglio et al 1999), so it was used here to extend its wavelength coverage down to 2300Å.…”

“…However, the component structure determined by fitting Voigt profiles is not unique and is strongly dependent on the spectral resolution and S/N (Kim et al 2013;Boksenberg & Sargent 2015). So, for all but the simplest line profiles, the component structure is not well-determined.…”

Reionisation and High-Redshift Galaxies: The View from Quasar Absorption Lines

“…At least one of the O i systems lies close to the detection limit of the existing data, however (Becker et al 2011b), so it is possible that the number density of weak low-ionisation systems (N O I 10 13.5 cm −2 , N C II 10 13.0 cm −2 ) may be larger. The observed mass density of O i in systems at z ∼ 6 can be directly computed using Equation (20) (Pettini et al 2003;Danforth & Shull 2008;Becker et al 2009;Ryan-Weber et al 2009;Cooksey et al 2010Cooksey et al , 2013D'Odorico et al 2010D'Odorico et al , 2013Simcoe et al 2011;Tilton et al 2012;Danforth et al 2014;Boksenberg & Sargent 2015, where 'Bok+Sar 14' in the caption refers to Boksenberg & Sargent 2015). Note that some of the variation in these results is due to differences in the column density range over which C IV is integrated.…”