%0 Generic %1 neufeld2017cosmic %A Neufeld, David A. %A Wolfire, Mark G. %D 2017 %K cosmic ionisation ray %T The cosmic ray ionization rate in the Galactic disk, as determined from observations of molecular ions %U http://arxiv.org/abs/1704.03877 %X 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 $R_g 4 - 9$ kpc, observations of ArH$^+$, OH$^+$, and H$_2$O$^+$ imply a mean primary CRIR of $(2.2 0.3) (R_0-R_g)/4.7\,kpc 10^-16 \, s^-1$ 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 $(2.3 0.6) 10^-16\,\,s^-1$ per H atom, corresponding to a total ionization rate per H$_2$ molecule of $(5.3 1.1) 10^-16\,\,s^-1,$ 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 $2.9 10^-16\,\,s^-1$ per H atom. Our results show marginal evidence that the CRIR in diffuse molecular clouds decreases with cloud extinction, $A_V(tot)$, with a best-fit dependence $A_V(tot)^-1$ for $A_V(\rm tot) 0.5$.

@misc{neufeld2017cosmic, 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 $(2.2 \pm 0.3) \exp [(R_0-R_g)/4.7\,\rm{kpc}] \times 10^{-16} \rm \, s^{-1}$ 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 $(2.3 \pm 0.6) \times 10^{-16}\,\,\rm s^{-1}$ per H atom, corresponding to a total ionization rate per H$_2$ molecule of $(5.3 \pm 1.1) \times 10^{-16}\,\,\rm s^{-1},$ 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 $2.9 \times 10^{-16}\,\,\rm s^{-1}$ per H atom. Our results show marginal evidence that the CRIR in diffuse molecular clouds decreases with cloud extinction, $A_{\rm V}({\rm tot})$, with a best-fit dependence $\propto A_{\rm V}({\rm tot})^{-1}$ for $A_{\rm V}({\rm tot}) \ge 0.5$.}, added-at = {2017-04-14T10:09:27.000+0200}, author = {Neufeld, David A. and Wolfire, Mark G.}, biburl = {https://www.bibsonomy.org/bibtex/2c54406ae535aab1937963a8ab2fc84af/miki}, description = {[1704.03877] The cosmic ray ionization rate in the Galactic disk, as determined from observations of molecular ions}, interhash = {b152edb207c2d6163bcbefeda62c2b72}, intrahash = {c54406ae535aab1937963a8ab2fc84af}, keywords = {cosmic ionisation ray}, note = {cite arxiv:1704.03877Comment: 48 pages, including 3 tables (at end) and 13 figures. Accepted for publication in the Astrophysical Journal}, timestamp = {2017-04-14T10:09:27.000+0200}, title = {The cosmic ray ionization rate in the Galactic disk, as determined from observations of molecular ions}, url = {http://arxiv.org/abs/1704.03877}, year = 2017 }