Universität zu Köln

Gaches, Brandt A. L., Bisbas, Thomas G. and Bialy, Shmuel (2022). The impact of cosmic-ray attenuation on the carbon cycle emission in molecular clouds. Astron. Astrophys., 658. LES ULIS CEDEX A: EDP SCIENCES S A. ISSN 1432-0746

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Abstract

Context. Observations of the emission of the carbon cycle species (C, C+, CO) are commonly used to diagnose gas properties in the interstellar medium, but they are significantly sensitive to the cosmic-ray ionization rate. The carbon-cycle chemistry is known to be quite sensitive to the cosmic-ray ionization rate, zeta, controlled by the flux of low-energy cosmic rays which get attenuated through molecular clouds. However, astrochemical models commonly assume a constant cosmic-ray ionization rate in the clouds. Aims. We investigate the effect of cosmic-ray attenuation on the emission of carbon cycle species from molecular clouds, in particular the [CII] 158 mu m, [CI] 609 mu m, and CO (J = 1-0) 115.27 GHz lines. Methods. We used a post-processed chemical model of diffuse and dense simulated molecular clouds and quantified the variation in both column densities and velocity-integrated line emission of the carbon cycle with different cosmic-ray ionization rate models. Results. We find that the abundances and column densities of carbon cycle species are significantly impacted by the chosen cosmic-ray ionization rate model: no single constant ionization rate can reproduce the abundances modeled with an attenuated cosmic-ray model. Further, we show that constant ionization rate models fail to simultaneously reproduce the integrated emission of the lines we consider, and their deviations from a physically derived cosmic-ray attenuation model is too complex to be simply corrected. We demonstrate that the two clouds we modeled exhibit a similar average A(V,eff) - n(H) relationship, resulting in an average relation between the cosmic-ray ionization rate and density zeta(n(H)). Conclusions. We conclude by providing a number of implementation recommendations for cosmic rays in astrochemical models, but emphasize the necessity for column-dependent cosmic-ray ionization rate prescriptions.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Gaches, Brandt A. L. UNSPECIFIED UNSPECIFIED UNSPECIFIED Bisbas, Thomas G. UNSPECIFIED UNSPECIFIED UNSPECIFIED Bialy, Shmuel UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-677584
DOI:	10.1051/0004-6361/202142411
Journal or Publication Title:	Astron. Astrophys.
Volume:	658
Date:	2022
Publisher:	EDP SCIENCES S A
Place of Publication:	LES ULIS CEDEX A
ISSN:	1432-0746
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language C-I; ASTROCHEMICAL IMPACT; ATOMIC CARBON; PHOTODISSOCIATION; IONIZATION; GAS; DISTRIBUTIONS; PENETRATION; CHEMISTRY; HYDROGEN Multiple languages Astronomy & Astrophysics Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/67758