Analytic H i-to-H2 Photodissociation Transition Profiles (trac #362)

[cloudy-bot]

reported by: @CloudyLex

Title:  
Analytic H i-to-H2 Photodissociation Transition Profiles
Authors:    
Bialy, Shmuel; Sternberg, Amiel
Affiliation:    
AA(Raymond and Beverly Sackler School of Physics & Astronomy, Tel Aviv University, Ramat Aviv 69978, Israel 0000-0002-0404-003X), AB(Raymond and Beverly Sackler School of Physics & Astronomy, Tel Aviv University, Ramat Aviv 69978, Israel)
Publication:    
The Astrophysical Journal, Volume 822, Issue 2, article id. 83, pp. (2016). (ApJ Homepage)
Publication Date:   
05/2016
Origin: 
IOP
Astronomy Keywords: 
galaxies: star formation, ISM: clouds, methods: analytical, photon-dominated region: PDR, radiative transfer
DOI:    
10.3847/0004-637X/822/2/83
Bibliographic Code: 
2016ApJ...822...83B
Abstract

We present a simple analytic procedure for generating atomic (H i) to molecular 
(
```H```2) density profiles for optically thick hydrogen gas clouds illuminated by 
far-ultraviolet radiation fields. Our procedure is based on the analytic theory for 
the structure of one-dimensional H i/```H```2 photon-dominated regions, 
presented by Sternberg et al. Depth-dependent atomic and molecular density 
fractions may be computed for arbitrary gas density, far-ultraviolet field intensity, 
and the metallicity-dependent H2 formation rate coefficient, and dust absorption 
cross section in the Lyman–Werner photodissociation band. We use our 
procedure to generate a set of {{H}} {{I}}{-}{to}{-}```H```2 transition profiles for a 
wide range of conditions, from the weak- to strong-field limits, and from super-
solar down to low metallicities. We show that if presented as functions of dust 
optical depth, the {{H}} {{I}} and ```H```2 density profiles depend primarily on the 
Sternberg “? G parameter” (dimensionless) that determines the dust optical 
depth associated with the total photodissociated {{H}} {{I}} column. We derive a 
universal analytic formula for the {{H}} {{I}}{-}{to}{-}```H```2 transition points as a 
function of just ? G. Our formula will be useful for interpreting emission-line 
observations of H i/```H```2 interfaces, for estimating star formation thresholds, 
and for sub-grid components in hydrodynamics simulations.

Migrated from https://www.nublado.org/ticket/362

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    "status": "new",
    "changetime": "2019-02-04T13:02:49Z",
    "_ts": "1549285369825011",
    "description": "{{{\nTitle:\t\nAnalytic H i-to-H2 Photodissociation Transition Profiles\nAuthors:\t\nBialy, Shmuel; Sternberg, Amiel\nAffiliation:\t\nAA(Raymond and Beverly Sackler School of Physics & Astronomy, Tel Aviv University, Ramat Aviv 69978, Israel 0000-0002-0404-003X), AB(Raymond and Beverly Sackler School of Physics & Astronomy, Tel Aviv University, Ramat Aviv 69978, Israel)\nPublication:\t\nThe Astrophysical Journal, Volume 822, Issue 2, article id. 83, pp. (2016). (ApJ Homepage)\nPublication Date:\t\n05/2016\nOrigin:\t\nIOP\nAstronomy Keywords:\t\ngalaxies: star formation, ISM: clouds, methods: analytical, photon-dominated region: PDR, radiative transfer\nDOI:\t\n10.3847/0004-637X/822/2/83\nBibliographic Code:\t\n2016ApJ...822...83B\nAbstract\n\nWe present a simple analytic procedure for generating atomic (H i) to molecular \n({{{H}}}2) density profiles for optically thick hydrogen gas clouds illuminated by \nfar-ultraviolet radiation fields. Our procedure is based on the analytic theory for \nthe structure of one-dimensional H i/{{{H}}}2 photon-dominated regions, \npresented by Sternberg et al. Depth-dependent atomic and molecular density \nfractions may be computed for arbitrary gas density, far-ultraviolet field intensity, \nand the metallicity-dependent H2 formation rate coefficient, and dust absorption \ncross section in the Lyman\u2013Werner photodissociation band. We use our \nprocedure to generate a set of {{H}} {{I}}{-}{to}{-}{{{H}}}2 transition profiles for a \nwide range of conditions, from the weak- to strong-field limits, and from super-\nsolar down to low metallicities. We show that if presented as functions of dust \noptical depth, the {{H}} {{I}} and {{{H}}}2 density profiles depend primarily on the \nSternberg \u201c? G parameter\u201d (dimensionless) that determines the dust optical \ndepth associated with the total photodissociated {{H}} {{I}} column. We derive a \nuniversal analytic formula for the {{H}} {{I}}{-}{to}{-}{{{H}}}2 transition points as a \nfunction of just ? G. Our formula will be useful for interpreting emission-line \nobservations of H i/{{{H}}}2 interfaces, for estimating star formation thresholds, \nand for sub-grid components in hydrodynamics simulations.\n}}}",
    "reporter": "gary",
    "cc": "",
    "resolution": "",
    "time": "2016-07-31T19:35:55Z",
    "component": "atomic/molecular data base",
    "summary": "Analytic H i-to-H2 Photodissociation Transition Profiles",
    "priority": "good to do",
    "keywords": "",
    "version": "trunk",
    "milestone": "no milestone",
    "owner": "nobody",
    "type": "enhancement"
}

[cloudy-bot]

@CloudyLex commented:

this theory does not have an explicit density dependence - our testing shows a very powerful density dependence due to changes in populations within X, and resulting electronic line shielding.

[cloudy-bot]

@peter-van-hoof-noaccount changed milestone from "" to "no milestone"