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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:	Creators Email ORCID ORCID Put Code Seifried, D. UNSPECIFIED UNSPECIFIED UNSPECIFIED Haid, S. UNSPECIFIED UNSPECIFIED UNSPECIFIED Walch, S. UNSPECIFIED UNSPECIFIED UNSPECIFIED Borchert, E. M. A. UNSPECIFIED UNSPECIFIED UNSPECIFIED Bisbas, T. G. UNSPECIFIED UNSPECIFIED UNSPECIFIED
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:	Keywords Language SUPERNOVA-DRIVEN ISM; STAR-FORMATION; MILKY-WAY; X-FACTOR; NONEQUILIBRIUM CHEMISTRY; IONIZING-RADIATION; CHEMICAL EVOLUTION; INTERSTELLAR GAS; STELLAR WINDS; ATOMIC CARBON Multiple languages Astronomy & Astrophysics Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/34752