Universität zu Köln

Mackey, Jonathan ORCID: 0000-0002-5449-6131, Walch, Stefanie, Seifried, Daniel ORCID: 0000-0002-0368-9160, Glover, Simon C. O., Wuensch, Richard and Aharonian, Felix (2019). Non-equilibrium chemistry and destruction of CO by X-ray flares. Mon. Not. Roy. Astron. Soc., 486 (1). S. 1094 - 1123. OXFORD: OXFORD UNIV PRESS. ISSN 1365-2966

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Abstract

Sources of X-rays such as active galactic nuclei and X-ray binaries are often variable by orders of magnitude in luminosity over time-scales of years. During and after these flares the surrounding gas is out of chemical and thermal equilibrium. We introduce a new implementation of X-ray radiative transfer coupled to a time-dependent chemical network for use in 3D magnetohydrodynamical simulations. A static fractal molecular cloud is irradiated with X-rays of different intensity, and the chemical and thermal evolution of the cloud are studied. For a simulated 10(5) M-circle dot fractal cloud, an X-ray flux <0.01 erg cm(-2) s(-1) allows the cloud to remain molecular, whereas most of the CO and H-2 are destroyed for a flux of >= 1 erg cm(-2) s(-1). The effects of an X-ray flare, which suddenly increases the X-ray flux by 10(5)x, are then studied. A cloud exposed to a bright flare has 99 per cent of its CO destroyed in 10-20 yr, whereas it takes >10(3) yr for 99 per cent of the H-2 to be destroyed. CO is primarily destroyed by locally generated far-UVemission from collisions between non-thermal electrons and H-2; He+ only becomes an important destruction agent when the CO abundance is already very small. After the flare is over, CO re-forms and approaches its equilibrium abundance after 10(3)-10(5) yr. This implies that molecular clouds close to Sgr A(star) in the Galactic Centre may still be out of chemical equilibrium, and we predict the existence of clouds near flaring X-ray sources in which CO has been mostly destroyed but H is fully molecular.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Mackey, Jonathan UNSPECIFIED orcid.org/0000-0002-5449-6131 UNSPECIFIED Walch, Stefanie UNSPECIFIED UNSPECIFIED UNSPECIFIED Seifried, Daniel UNSPECIFIED orcid.org/0000-0002-0368-9160 UNSPECIFIED Glover, Simon C. O. UNSPECIFIED UNSPECIFIED UNSPECIFIED Wuensch, Richard UNSPECIFIED UNSPECIFIED UNSPECIFIED Aharonian, Felix UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-138687
DOI:	10.1093/mnras/stz902
Journal or Publication Title:	Mon. Not. Roy. Astron. Soc.
Volume:	486
Number:	1
Page Range:	S. 1094 - 1123
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 FINE-STRUCTURE TRANSITIONS; EFFECTIVE COLLISION STRENGTHS; FAST INTERSTELLAR SHOCKS; MOLECULAR CLOUDS; STAR-FORMATION; GROUND-STATE; ELECTRON-IMPACT; GALACTIC-CENTER; LINE EMISSION; GAS-PHASE Multiple languages Astronomy & Astrophysics Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/13868