The reionization of carbon

Abstract

Observations suggest that C II was more abundant than C IV in the intergalactic medium towards the end of the hydrogen reionization epoch (z ∼ 6). This transition provides a unique opportunity to study the enrichment history of intergalactic gas and the growth of the ionizing background (UVB) at early times. We study how carbon absorption evolves from z = 10-5 using a cosmological hydrodynamic simulation that includes a self-consistent multifrequency UVB as well as a well-constrained model for galactic outflows to disperse metals. Our predicted UVB is within ∼ 2-4× of that from Haardt & Madau (2012), which is fair agreement given the uncertainties. Nonetheless, we use a calibration in post-processing to account for Lyman-α forest measurements while preserving the predicted spectral slope and inhomogeneity. The UVB fluctuates spatially in such a way that it always exceeds the volume average in regions where metals are found. This implies both that a spatially-uniform UVB is a poor approximation and that metal absorption is not sensitive to the epoch when HII regions overlap globally even at column densites of 10 12 cm −2 . We find, consistent with observations, that the C II mass fraction drops to low redshift while C IV rises owing the combined effects of a growing UVB and continued addition of carbon in low-density regions. This is mimicked in absorption statistics, which broadly agree with observations at z = 6-3 while predicting that the absorber column density distributions rise steeply to the lowest observable columns. Our model reproduces the large observed scatter in the number of low-ionization absorbers per sightline, implying that the scatter does not indicate a partially-neutral Universe at z ∼ 6.

Cosmic reionization after Planck

“…Based on a robust statistical analysis on full CMB spectrum and quasar data and using the observations of high-z galaxy LFs, we (Mitra et al 2013) derived that mean value of fesc is moderately increasing from 7% at z = 6 to 18% at z = 8. This increasing behavior of fesc on redshift is somewhat similar to that obtained or assumed in Inoue et al (2006); Razoumov & Sommer-Larsen (2010); Haardt & Madau (2011 ;Ferrara & Loeb (2013);Finlator et al (2015). More recently, using a high-resolution cosmological zoom-in simulation of galaxy formation, Ma et al (2015) found a considerably lower (< 5%; much less than required by reionization models) and a non-evolving escape fraction.…”

The z ∼ 6 Luminosity Function Fainter than −15 mag from the Hubble Frontier Fields: The Impact of Magnification Uncertainties

“…The impact of radiative feedback is less important in the CROC simulations than in CoDa. Finlator et al (2015Finlator et al ( , 2016Finlator et al ( , 2017: the Finlator et al (2015Finlator et al ( , 2016Finlator et al ( , 2017 LF results are based on a cosmological simulation of galaxy formation in a h 7.5 1 3 -( ) Mpc 3 volume of the universe including both gravity and hydrodynamics as implemented in the GADGET-3 code (Springel 2005). To this code, gas cooling is added through collisional excitation of hydrogen and helium as in Katz et al (1996), and metal line cooling is implemented using the collisional ionization equilibrium tables of Sutherland & Dopita (1993).…”

“…Star formation is added using the Kennicutt-Schmidt law, with supernovae feedback included following the "ezw" prescription from Davé et al (2013) and metal enrichment from supernovae as implemented as in Oppenheimer & Davé (2008). Flattening in the Finlator et al (2015Finlator et al ( , 2016Finlator et al ( , 2017 LFs occurs mostly due to less efficient gas cooling at lower halo masses.…”

The First Billion Years project: the escape fraction of ionizing photons in the epoch of reionization

“…This in turn is important for the temperature state of the intergalactic medium (Ciardi et al 2012). Another example is the modelling of carbon absorption systems during reionization, in which a frequency-dependent escape fraction could play an important role for modelling the ratio of C II to C IV (Finlator et al 2014). …”