Universität zu Köln

Beattie, James R., Federrath, Christoph ORCID: 0000-0002-0706-2306, Klessen, Ralf S. and Schneider, Nicola ORCID: 0000-0003-3485-6678 (2019). The relation between the turbulent Mach number and observed fractal dimensions of turbulent clouds. Mon. Not. Roy. Astron. Soc., 488 (2). S. 2493 - 2503. OXFORD: OXFORD UNIV PRESS. ISSN 1365-2966

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Abstract

Supersonic turbulence is a key player in controlling the structure and star formation potential of molecular clouds (MCs). The three-dimensional (3D) turbulent Mach number, M, allows us to predict the rate of star formation. However, determining Mach numbers in observations is challenging because it requires accurate measurements of the velocity dispersion. Moreover, observations are limited to two-dimensional (2D) projections of the MCs and velocity information can usually only be obtained for the line-of-sight component. Here we present a new method that allows us to estimate M from the 2D column density, Sigma, by analysing the fractal dimension, D. We do this by computing D for six simulations, ranging between 1 and 100 in M . From this data we are able to construct an empirical relation, log M(D) = xi(1)(erfc(-1)[(D-D-min)/Omega] +xi(2)), where erfc(-1) is the inverse complimentary error function, D-min = 1.55 +/- 0.13 is the minimum fractal dimension of Sigma, Omega = 0.22 +/- 0.07, xi(1) = 0.9 +/- 0.1, and xi(2) = 0.2 +/- 0.2. We test the accuracy of this newrelation on column density maps from Herschel observations of two quiescent subregions in the Polaris Flare MC, 'saxophone' and 'quiet'. We measure M similar to 10 and M similar to 2 for the subregions, respectively, which are similar to previous estimates based on measuring the velocity dispersion from molecular line data. These results show that this new empirical relation can provide useful estimates of the cloud kinematics, solely based upon the geometry from the column density of the cloud.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Beattie, James R. UNSPECIFIED UNSPECIFIED UNSPECIFIED Federrath, Christoph UNSPECIFIED orcid.org/0000-0002-0706-2306 UNSPECIFIED Klessen, Ralf S. UNSPECIFIED UNSPECIFIED UNSPECIFIED Schneider, Nicola UNSPECIFIED orcid.org/0000-0003-3485-6678 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-143438
DOI:	10.1093/mnras/stz1853
Journal or Publication Title:	Mon. Not. Roy. Astron. Soc.
Volume:	488
Number:	2
Page Range:	S. 2493 - 2503
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 DENSITY PROBABILITY-DISTRIBUTION; STAR-FORMATION; MOLECULAR CLOUDS; SUPERSONIC TURBULENCE; GRAVITATIONAL COLLAPSE; INTERSTELLAR FILAMENTS; VELOCITY STRUCTURE; UNIVERSALITY; MASS; SIMULATIONS Multiple languages Astronomy & Astrophysics Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/14343