cosmic ray background 2017 (trac #387)

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about 50% larger than our default

Title:	
The cosmic ray ionization rate in the Galactic disk, as determined from observations of molecular ions
Authors:	
Neufeld, David A.; Wolfire, Mark G.
Publication:	
eprint arXiv:1704.03877
Publication Date:	
04/2017
Origin:	
ARXIV
Keywords:	
Astrophysics - Astrophysics of Galaxies
Comment:	
48 pages, including 3 tables (at end) and 13 figures. Accepted for publication in the Astrophysical Journal
Bibliographic Code:	
2017arXiv170403877N
Abstract

We have obtained estimates for the cosmic-ray ionization rate (CRIR) in the 
Galactic disk, using a detailed model for the physics and chemistry of diffuse 
interstellar gas clouds to interpret previously-published measurements of the 
abundance of four molecular ions: ArH$^+$, OH$^+$, H$_2$O$^+$ and 
H$_3^+$. For diffuse $atomic$ clouds at Galactocentric distances in the range 
$R_g \sim 4 - 9$ kpc, observations of ArH$^+$, OH$^+$, and H$_2$O$^+$ 
imply a mean primary CRIR of $(2.2 \pm 0.3) \exp [(R_0-R_g)/4.7\,\
m{kpc}] 
\times 10^{-16} \
m \, s^{-1}$ per hydrogen atom, where $R_0=8.5$ kpc. 
Within diffuse $molecular$ clouds observed toward stars in the solar 
neighborhood, measurements of H$_3^+$ and H$_2$ imply a primary CRIR of 
$(2.3 \pm 0.6) \times 10^{-16}\,\,\
m s^{-1}$ per H atom, corresponding to a 
total ionization rate per H$_2$ molecule of $(5.3 \pm 1.1) \times 
10^{-16}\,\,\
m s^{-1},$ in good accord with previous estimates. These 
estimates are also in good agreement with a rederivation, presented here, of 
the CRIR implied by recent observations of carbon and hydrogen radio 
recombination lines along the sight-line to Cas A. Here, our best-fit estimate 
for the primary CRIR is $2.9 \times 10^{-16}\,\,\
m s^{-1}$ per H atom. Our 
results show marginal evidence that the CRIR in diffuse molecular clouds 
decreases with cloud extinction, $A_{\
m V}({\
m tot})$, with a best-fit 
dependence $\propto A_{\
m V}({\
m tot})^{-1}$ for $A_{\
m V}({\
m tot}) \ge 
0.5$.

Migrated from https://www.nublado.org/ticket/387

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    "status": "new",
    "changetime": "2019-02-04T12:10:21Z",
    "_ts": "1549282221449479",
    "description": "about 50% larger than our default\n{{{\nTitle:\t\nThe cosmic ray ionization rate in the Galactic disk, as determined from observations of molecular ions\nAuthors:\t\nNeufeld, David A.; Wolfire, Mark G.\nPublication:\t\neprint arXiv:1704.03877\nPublication Date:\t\n04/2017\nOrigin:\t\nARXIV\nKeywords:\t\nAstrophysics - Astrophysics of Galaxies\nComment:\t\n48 pages, including 3 tables (at end) and 13 figures. Accepted for publication in the Astrophysical Journal\nBibliographic Code:\t\n2017arXiv170403877N\nAbstract\n\nWe have obtained estimates for the cosmic-ray ionization rate (CRIR) in the \nGalactic disk, using a detailed model for the physics and chemistry of diffuse \ninterstellar gas clouds to interpret previously-published measurements of the \nabundance of four molecular ions: ArH$^+$, OH$^+$, H$_2$O$^+$ and \nH$_3^+$. For diffuse $atomic$ clouds at Galactocentric distances in the range \n$R_g \\sim 4 - 9$ kpc, observations of ArH$^+$, OH$^+$, and H$_2$O$^+$ \nimply a mean primary CRIR of $(2.2 \\pm 0.3) \\exp [(R_0-R_g)/4.7\\,\\\nm{kpc}] \n\\times 10^{-16} \\\nm \\, s^{-1}$ per hydrogen atom, where $R_0=8.5$ kpc. \nWithin diffuse $molecular$ clouds observed toward stars in the solar \nneighborhood, measurements of H$_3^+$ and H$_2$ imply a primary CRIR of \n$(2.3 \\pm 0.6) \\times 10^{-16}\\,\\,\\\nm s^{-1}$ per H atom, corresponding to a \ntotal ionization rate per H$_2$ molecule of $(5.3 \\pm 1.1) \\times \n10^{-16}\\,\\,\\\nm s^{-1},$ in good accord with previous estimates. These \nestimates are also in good agreement with a rederivation, presented here, of \nthe CRIR implied by recent observations of carbon and hydrogen radio \nrecombination lines along the sight-line to Cas A. Here, our best-fit estimate \nfor the primary CRIR is $2.9 \\times 10^{-16}\\,\\,\\\nm s^{-1}$ per H atom. Our \nresults show marginal evidence that the CRIR in diffuse molecular clouds \ndecreases with cloud extinction, $A_{\\\nm V}({\\\nm tot})$, with a best-fit \ndependence $\\propto A_{\\\nm V}({\\\nm tot})^{-1}$ for $A_{\\\nm V}({\\\nm tot}) \\ge \n0.5$.\n}}}",
    "reporter": "gary",
    "cc": "",
    "resolution": "",
    "time": "2017-04-19T15:02:08Z",
    "component": "chemical network",
    "summary": "cosmic ray background 2017",
    "priority": "good to do",
    "keywords": "",
    "version": "trunk",
    "milestone": "c19 branch",
    "owner": "nobody",
    "type": "enhancement"
}

[cloudy-bot]

• @peter-van-hoof-noaccount commented:

Milestone renamed

• @peter-van-hoof-noaccount changed milestone from "C19_branch" to "c19 branch"