The evolution of the low-density H i intergalactic medium from z = 3.6 to 0: Data, transmitted flux, and H i column density

T. S. Kim, B. P. Wakker, F. Nasir, R. F. Carswell, B. D. Savage, J. S. Bolton, A. J. Fox, M. Viel, M. G. Haehnelt, J. C. Charlton, B. E. Rosenwasser

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12 Scopus citations


We present a new, uniform analysis of the H i transmitted flux (F) and H i column density (N_{\mathrm{H\,{\small I}}}) distribution in the low-density IGM as a function of redshift z for 0 < z < 3.6 using 55 HST/COS FUV (Δz = 7.2 at z < 0.5), five HST/STIS + COS NUV (Δz = 1.3 at z ∼1) and 24 VLT/UVES, and Keck/HIRES (Δz = 11.6 at 1.7 < z < 3.6) AGN spectra. We performed a consistent, uniform Voigt profile analysis to combine spectra taken with different instruments, to reduce systematics and to remove metal-line contamination. We confirm previously known conclusions on firmer quantitative grounds in particular by improving the measurements at z ∼1. Two flux statistics at 0 < F < 1, the mean H i flux and the flux probability distribution function (PDF), show that considerable evolution occurs from z = 3.6 to z = 1.5, after which it slows down to become effectively stable for z < 0.5. However, there are large sightline variations. For the H i column density distribution function (CDDF, f ∝ N_{\rm H\,{\small I}}^{-\beta }) at \log (N_{\mathrm{H\,{\small I}}}/1\, {\mathrm{cm}^{-2}}) [13.5, 16.0], β increases as z decreases from β = 1.60 at z ∼3.4 to β = 1.82 at z ∼0.1. The CDDF shape at lower redshifts can be reproduced by a small amount of clockwise rotation of a higher-z CDDF with a slightly larger CDDF normalization. The absorption line number per z (dn/dz) shows a similar evolutionary break at z ∼1.5 as seen in the flux statistics. High-N_{\mathrm{H\,{\small I}}} absorbers evolve more rapidly than low-N_{\mathrm{H\,{\small I}}} absorbers to decrease in number or cross-section with time. The individual dn/dz shows a large scatter at a given z. The scatter increases towards lower z, possibly caused by a stronger clustering at lower z.

Original languageEnglish (US)
Pages (from-to)5811-5833
Number of pages23
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
StatePublished - Mar 1 2021

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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