Universität zu Köln

Bisbas, Thomas G., Schruba, Andreas and van Dishoeck, Ewine F. (2019). Simulating the atomic and molecular content of molecular clouds using probability distributions of physical parameters. Mon. Not. Roy. Astron. Soc., 485 (3). S. 3097 - 3112. OXFORD: OXFORD UNIV PRESS. ISSN 1365-2966

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Abstract

Modern observations of the interstellarmedium (ISM) in galaxies detect a variety of atomic and molecular species. The goal is to connect these observations to the astrochemical properties of the ISM. 3D hydro-chemical simulations attempt this but due to extreme computational cost, they have to rely on simplified chemical networks and are bound to individual case studies. We present an alternative approach which models the ISM at larger scales by an ensemble of pre-calculated 1D thermo-chemical photodissociation region (PDR) calculations that determine the abundance and excitation of atomic and molecular species. We adopt lognormal distributions of column density (AV-PDFs) for which each column density is linked to a volume density as derived by hydrodynamical simulations. We consider two lognormal AV-PDFs: a diffuse, low-density medium with average visual extinction of (A(V)) over bar = 0.75 mag and dispersion of s = 0.5 and a denser giant molecular cloud with (A(V)) over bar = 4mag and sigma = 0.8. We treat the UV radiation field, cosmic ray ionization rate, and metallicity as free parameters. We find that the low-density medium remains fully HI- and C II-dominated under all explored conditions. The denser cloud remains almost always molecular (i. e. H-2-dominated) while its carbon phase (CO, C I, and CII) is sensitive to the above free parameters, implying that existing methods of tracing H-2-rich gas may require adjustments depending on environment. Our numerical framework can be used to estimate the PDR properties of large ISM regions and quantify trends with different environmental parameters as it is fast, covers wide parameter space, and is flexible for extensions.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Bisbas, Thomas G. UNSPECIFIED UNSPECIFIED UNSPECIFIED Schruba, Andreas UNSPECIFIED UNSPECIFIED UNSPECIFIED van Dishoeck, Ewine F. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-148832
DOI:	10.1093/mnras/stz405
Journal or Publication Title:	Mon. Not. Roy. Astron. Soc.
Volume:	485
Number:	3
Page Range:	S. 3097 - 3112
Date:	2019
Publisher:	OXFORD UNIV PRESS
Place of Publication:	OXFORD
ISSN:	1365-2966
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language INTERSTELLAR-MEDIUM; COLUMN-DENSITY; CHEMICAL EVOLUTION; DWARF GALAXIES; STAR-FORMATION; COSMIC-RAYS; MILKY-WAY; GAS; CO; PHOTODISSOCIATION Multiple languages Astronomy & Astrophysics Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/14883