The Temperature-Density Relation in the Intergalactic Medium at Redshift <z> = 2.4
Abstract
We present new measurements of the temperature-density (T-ρ) relation for neutral hydrogen in the 2.0 < z < 2.8 intergalactic medium (IGM) using a sample of ~6000 individual H I absorbers fitted with Voigt profiles constrained in all cases by multiple Lyman series transitions. We find model-independent evidence for a positive correlation between the column density of H I (N_(HI)) and the minimum observed velocity width of absorbers (b_(min)). With minimal interpretation, this implies that the T-ρ relation in the IGM is not "inverted," contrary to many recent studies. Fitting b_(min) as a function of N_(HI) results in line-width-column-density dependence of the form b_(min) = b_0(N_(HI)/N_(HI,0))^(Γ–1) with a minimum line width at mean density (ρ/ρ = 1, N_(HI,0) = 10^(13.6) cm^(–2)) of b_0 = 17.9 ± 0.2 km s^(–1) and a power-law index of (Γ – 1) = 0.15 ± 0.02. Using analytic arguments, these measurements imply an "equation of state" for the IGM at (z) = 2.4 of the form T=T_0 (ρ/ρ)^(y-1) with a temperature at mean density of T_0 = [1.94 ± 0.05] × 10^4 K and a power-law index (γ – 1) = 0.46 ± 0.05.
Additional Information
© 2012 American Astronomical Society. Received 2012 July 20; accepted 2012 August 30; published 2012 September 17. We thank George Becker for his early interest in the T –ρ relation results from the KBSS sample, Joop Schaye who provided helpful advice and insightful comments, and Allison Strom and Ryan Trainor for their careful reading of early drafts. Thanks also to Olivera Rakic for her contributions to the reduction of the QSO data set and for her pertinent advice. The authors wish to acknowledge Ryan Cooke who contributed the fits to the damped profiles in our QSO spectra. We wish to acknowledge the staff of the W.M. Keck Observatory whose efforts insure the telescopes and instruments perform reliably. We thank those of Hawaiian ancestry on whose sacred mountain we are privileged to be guests. This work has been supported by the US National Science Foundation through grants AST-0606912 and AST-0908805. C.C.S. acknowledges additional support from the John D. and Catherine T. MacArthur Foundation and the Peter and Patricia Gruber Foundation. This research has made use of the Keck Observatory Archive (KOA). Facilities: Keck:I (HIRES)Attached Files
Published - 2041-8205_757_2_L30.pdf
Submitted - 1209.0005v1.pdf
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Additional details
- Eprint ID
- 34187
- Resolver ID
- CaltechAUTHORS:20120918-142739382
- AST-0606912
- NSF
- AST-0908805
- NSF
- John D. and Catherine T. MacArthur Foundation
- Peter and Patricia Gruber Foundation
- Created
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2012-09-18Created from EPrint's datestamp field
- Updated
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2021-11-09Created from EPrint's last_modified field