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Title: H I-to-H{sub 2} transitions and H I column densities in galaxy star-forming regions

Abstract

We present new analytic theory and radiative transfer computations for the atomic-to-molecular (H I-to-H{sub 2}) transitions and the buildup of atomic hydrogen (H I) gas columns in optically thick interstellar clouds irradiated by far-UV (FUV) photodissociating radiation fields. We derive analytic expressions for the total H I column densities for (one-dimensional (1D)) planar slabs, for beamed or isotropic radiation fields, from the weak- to strong-field limits, for gradual or sharp atomic-to-molecular transitions, and for arbitrary metallicity. Our expressions may be used to evaluate the H I column densities as functions of the radiation field intensity and the H{sub 2}-dust-limited dissociation flux, the hydrogen gas density, and the metallicity-dependent H{sub 2} formation rate coefficient and FUV dust grain absorption cross section. We make the distinction between 'H I-dust' and 'H{sub 2}-dust' opacity, and we present computations for the 'universal H{sub 2}-dust-limited effective dissociation bandwidth'. We validate our analytic formulae with Meudon PDR code computations for the H I-to-H{sub 2} density profiles and total H I column densities. We show that our general 1D formulae predict H I columns and H{sub 2} mass fractions that are essentially identical to those found in more complicated (and approximate) spherical (shell-core) models. We apply ourmore » theory to compute H{sub 2} mass fractions and star-formation thresholds for individual clouds in self-regulated galaxy disks, for a wide range of metallicities. Our formulae for the H I columns and H{sub 2} mass fractions may be incorporated into hydrodynamics simulations for galaxy evolution.« less

Authors:
 [1]; ; ;  [2]
  1. Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Ramat Aviv 69978 (Israel)
  2. LERMA, Observatoire de Paris, CNRS, 5 place Jules Janssen, F-92190 Meudon (France)
Publication Date:
OSTI Identifier:
22365614
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 790; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION; APPROXIMATIONS; BEAMS; CROSS SECTIONS; DENSITY; DISSOCIATION; DUSTS; EVOLUTION; FAR ULTRAVIOLET RADIATION; GALAXIES; HYDRODYNAMICS; HYDROGEN; IRRADIATION; MASS; METALLICITY; RADIANT HEAT TRANSFER; SIMULATION; STARS

Citation Formats

Sternberg, Amiel, Le Petit, Franck, Roueff, Evelyne, and Le Bourlot, Jacques. H I-to-H{sub 2} transitions and H I column densities in galaxy star-forming regions. United States: N. p., 2014. Web. doi:10.1088/0004-637X/790/1/10.
Sternberg, Amiel, Le Petit, Franck, Roueff, Evelyne, & Le Bourlot, Jacques. H I-to-H{sub 2} transitions and H I column densities in galaxy star-forming regions. United States. doi:10.1088/0004-637X/790/1/10.
Sternberg, Amiel, Le Petit, Franck, Roueff, Evelyne, and Le Bourlot, Jacques. Sun . "H I-to-H{sub 2} transitions and H I column densities in galaxy star-forming regions". United States. doi:10.1088/0004-637X/790/1/10.
@article{osti_22365614,
title = {H I-to-H{sub 2} transitions and H I column densities in galaxy star-forming regions},
author = {Sternberg, Amiel and Le Petit, Franck and Roueff, Evelyne and Le Bourlot, Jacques},
abstractNote = {We present new analytic theory and radiative transfer computations for the atomic-to-molecular (H I-to-H{sub 2}) transitions and the buildup of atomic hydrogen (H I) gas columns in optically thick interstellar clouds irradiated by far-UV (FUV) photodissociating radiation fields. We derive analytic expressions for the total H I column densities for (one-dimensional (1D)) planar slabs, for beamed or isotropic radiation fields, from the weak- to strong-field limits, for gradual or sharp atomic-to-molecular transitions, and for arbitrary metallicity. Our expressions may be used to evaluate the H I column densities as functions of the radiation field intensity and the H{sub 2}-dust-limited dissociation flux, the hydrogen gas density, and the metallicity-dependent H{sub 2} formation rate coefficient and FUV dust grain absorption cross section. We make the distinction between 'H I-dust' and 'H{sub 2}-dust' opacity, and we present computations for the 'universal H{sub 2}-dust-limited effective dissociation bandwidth'. We validate our analytic formulae with Meudon PDR code computations for the H I-to-H{sub 2} density profiles and total H I column densities. We show that our general 1D formulae predict H I columns and H{sub 2} mass fractions that are essentially identical to those found in more complicated (and approximate) spherical (shell-core) models. We apply our theory to compute H{sub 2} mass fractions and star-formation thresholds for individual clouds in self-regulated galaxy disks, for a wide range of metallicities. Our formulae for the H I columns and H{sub 2} mass fractions may be incorporated into hydrodynamics simulations for galaxy evolution.},
doi = {10.1088/0004-637X/790/1/10},
journal = {Astrophysical Journal},
number = 1,
volume = 790,
place = {United States},
year = {Sun Jul 20 00:00:00 EDT 2014},
month = {Sun Jul 20 00:00:00 EDT 2014}
}