The reionization of carbon

Kristian Finlator, Robert Thompson, Shuiyao Huang, Romeel S Dave, E. Zackrisson, B. D. Oppenheimer

Research output: Contribution to journalArticle

27 Scopus citations


Observations suggest that CII was more abundant than CIV 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 ultraviolet background (UVB) at early times. We study how carbon absorption evolves from z = 10 to 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 times of that from Haardt & Madau, 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 densities of 10<sup>12</sup> cm<sup>-2</sup>.We find, consistent with observations, that the CII mass fraction drops to low redshift while CIV 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.

Original languageEnglish (US)
Pages (from-to)2526-2539
Number of pages14
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
Publication statusPublished - 2015
Externally publishedYes



  • Cosmology: theory
  • Galaxies: evolution
  • Galaxies: formation
  • Galaxies: high-redshift
  • Intergalactic medium
  • Quasars: absorption lines

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Finlator, K., Thompson, R., Huang, S., Dave, R. S., Zackrisson, E., & Oppenheimer, B. D. (2015). The reionization of carbon. Monthly Notices of the Royal Astronomical Society, 447(3), 2526-2539.