Universität zu Köln

Mac Low, Mordecai-Mark ORCID: 0000-0003-0064-4060, Burkert, Andreas and Ibanez-Mejia, Juan C. (2017). Fast Molecular Cloud Destruction Requires Fast Cloud Formation. Astrophys. J. Lett., 847 (1). BRISTOL: IOP PUBLISHING LTD. ISSN 2041-8213

Full text not available from this repository.

Abstract

A large fraction of the gas in the Galaxy is cold, dense, and molecular. If all this gas collapsed under the influence of gravity and formed stars in a local free-fall time, the star formation rate in the Galaxy would exceed that observed by more than an order of magnitude. Other star-forming galaxies behave similarly. Yet, observations and simulations both suggest that the molecular gas is indeed gravitationally collapsing, albeit hierarchically. Prompt stellar feedback offers a potential solution to the low observed star formation rate if it quickly disrupts star-forming clouds during gravitational collapse. However, this requires that molecular clouds must be short-lived objects, raising the question of how so much gas can be observed in the molecular phase. This can occur only if molecular clouds form as quickly as they are destroyed, maintaining a global equilibrium fraction of dense gas. We therefore examine cloud formation timescales. We first demonstrate that supernova and superbubble sweeping cannot produce dense gas at the rate required to match the cloud destruction rate. On the other hand, Toomre gravitational instability can reach the required production rate. We thus argue that, although dense, star-forming gas may last only around a single global free-fall time; the dense gas in star-forming galaxies can globally exist in a state of dynamic equilibrium between formation by gravitational instability and disruption by stellar feedback. At redshift z greater than or similar to 2, the Toomre instability timescale decreases, resulting in a prediction of higher molecular gas fractions at early times, in agreement with the observations.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Mac Low, Mordecai-Mark UNSPECIFIED orcid.org/0000-0003-0064-4060 UNSPECIFIED Burkert, Andreas UNSPECIFIED UNSPECIFIED UNSPECIFIED Ibanez-Mejia, Juan C. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-217525
DOI:	10.3847/2041-8213/aa8a61
Journal or Publication Title:	Astrophys. J. Lett.
Volume:	847
Number:	1
Date:	2017
Publisher:	IOP PUBLISHING LTD
Place of Publication:	BRISTOL
ISSN:	2041-8213
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language STAR-FORMING GALAXIES; GRAVITATIONAL-INSTABILITY; MAGNETIC-FIELDS; DISC FORMATION; HIGH-REDSHIFT; UNIVERSE; STARBURSTS; EVOLUTION; RADIATION; MODELS Multiple languages Astronomy & Astrophysics Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/21752