Seifried, D., Haid, S., Walch, S., Borchert, E. M. A. and Bisbas, T. G. (2020). SILCC-Zoom: H-2 and CO-dark gas in molecular clouds - the impact of feedback and magnetic fields. Mon. Not. Roy. Astron. Soc., 492 (1). S. 1465 - 1484. OXFORD: OXFORD UNIV PRESS. ISSN 1365-2966

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Abstract

We analyse the CO-dark molecular gas content of simulated molecular clouds from the SILCC-Zoom project. The simulations reach a resolution of 0.1 pc and include H-2 and CO formation, radiative stellar feedback and magnetic fields. CO-dark gas is found in regions with local visual extinctions A(V,3D) similar to 0.2-1.5, number densities of 10-10(3) cm(-3) and gas temperatures of few 10-100 K. CO-bright gas is found at number densities above 300 cm(-3) and temperatures below 50 K. The CO-dark gas fractions range from 40 per cent to 95 per cent and scale inversely with the amount of well-shielded gas ( A(V, 3D) greater than or similar to 1.5), which is smaller in magnetized molecular clouds. We show that the density, chemical abundances and A(V, 3D) along a given line-of-sight cannot be properly determined from projected quantities. As an example, pixels with a projected visual extinction of A(V, 2D) similar or equal to 2.5-5 can be both, CO-bright or CO-dark, which can be attributed to the presence or absence of strong density enhancements along the line-ofsight. By producing synthetic CO(1-0) emission maps of the simulations with RADMC-3D, we show that about 15-65 per cent of the H-2 is in regions with intensities below the detection limit. Our clouds have XCO-factors around 1.5 x 10(20) cm(-2) (K km s(-1))(-1) with a spread of up to a factor similar to 4, implying a similar uncertainty in the derived total H-2 masses and even worse for individual pixels. Based on our results, we suggest a new approach to determine the H-2 mass, which relies on the availability of CO(1-0) emission and A(V, 2D) maps. It reduces the uncertainty of the clouds' overall H-2 mass to a factor of less than or similar to 1.8 and for individual pixels, i.e. on sub-pc scales, to a factor of less than or similar to 3.

Item Type: Journal Article
Creators:
CreatorsEmailORCIDORCID Put Code
Seifried, D.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Haid, S.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Walch, S.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Borchert, E. M. A.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Bisbas, T. G.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
URN: urn:nbn:de:hbz:38-347523
DOI: 10.1093/mnras/stz3563
Journal or Publication Title: Mon. Not. Roy. Astron. Soc.
Volume: 492
Number: 1
Page Range: S. 1465 - 1484
Date: 2020
Publisher: OXFORD UNIV PRESS
Place of Publication: OXFORD
ISSN: 1365-2966
Language: English
Faculty: Unspecified
Divisions: Unspecified
Subjects: no entry
Uncontrolled Keywords:
KeywordsLanguage
SUPERNOVA-DRIVEN ISM; STAR-FORMATION; MILKY-WAY; X-FACTOR; NONEQUILIBRIUM CHEMISTRY; IONIZING-RADIATION; CHEMICAL EVOLUTION; INTERSTELLAR GAS; STELLAR WINDS; ATOMIC CARBONMultiple languages
Astronomy & AstrophysicsMultiple languages
URI: http://kups.ub.uni-koeln.de/id/eprint/34752

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