Universität zu Köln

Schneider, N., Csengeri, T., Klessen, R. S., Tremblin, P., Ossenkopf, V., Peretto, N., Simon, R., Bontemps, S. and Federrath, C. (2015). Understanding star formation in molecular clouds II. Signatures of gravitational collapse of IRDCs. Astron. Astrophys., 578. LES ULIS CEDEX A: EDP SCIENCES S A. ISSN 1432-0746

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Abstract

We analyse column density and temperature maps derived from Herschel dust continuum observations of a sample of prominent, massive infrared dark clouds (IRDCs) i.e. G11.11-0.12, G18.82-0.28, G28.37+0.07, and G28.53-0.25. We disentangle the velocity structure of the clouds using (CO)-C-13 1 -> 0 and (CO)-C-12 3 -> 2 data, showing that these IRDCs are the densest regions in massive giant molecular clouds (GMCs) and not isolated features. The probability distribution function (PDF) of column densities for all clouds have a power-law distribution over all (high) column densities, regardless of the evolutionary stage of the cloud: G11.11-0.12, G18.82-0.28, and G28.37 + 0.07 contain (proto)-stars, while G28.53-0.25 shows no signs of star formation. This is in contrast to the purely log-normal PDFs reported for near and/or mid-IR extinction maps. We only find a log-normal distribution for lower column densities, if we perform PDFs of the column density maps of the whole GMC in which the IRDCs are embedded. By comparing the PDF slope and the radial column density profile of three of our clouds, we attribute the power law to the effect of large-scale gravitational collapse and to local free-fall collapse of pre- and protostellar cores for the highest column densities. A significant impact on the cloud properties from radiative feedback is unlikely because the clouds are mostly devoid of star formation. Independent from the PDF analysis, we find infall signatures in the spectral profiles of (CO)-C-12 for G28.37 + 0.07 and G11.11-0.12, supporting the scenario of gravitational collapse. Our results are in line with earlier interpretations that see massive IRDCs as the densest regions within GMCs, which may be the progenitors of massive stars or clusters. At least some of the IRDCs are probably the same features as ridges (high column density regions with N > 10(23) cm(-2) over small areas), which were defined for nearby IR-bright GMCs. Because IRDCs are only confined to the densest (gravity dominated) cloud regions, the PDF constructed from this kind of a clipped image does not represent the (turbulence dominated) low column density regime of the cloud.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Schneider, N. UNSPECIFIED UNSPECIFIED UNSPECIFIED Csengeri, T. UNSPECIFIED UNSPECIFIED UNSPECIFIED Klessen, R. S. UNSPECIFIED UNSPECIFIED UNSPECIFIED Tremblin, P. UNSPECIFIED UNSPECIFIED UNSPECIFIED Ossenkopf, V. UNSPECIFIED UNSPECIFIED UNSPECIFIED Peretto, N. UNSPECIFIED UNSPECIFIED UNSPECIFIED Simon, R. UNSPECIFIED UNSPECIFIED UNSPECIFIED Bontemps, S. UNSPECIFIED UNSPECIFIED UNSPECIFIED Federrath, C. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-402291
DOI:	10.1051/0004-6361/201424375
Journal or Publication Title:	Astron. Astrophys.
Volume:	578
Date:	2015
Publisher:	EDP SCIENCES S A
Place of Publication:	LES ULIS CEDEX A
ISSN:	1432-0746
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language INFRARED-DARK CLOUDS; PROBABILITY-DISTRIBUTION FUNCTIONS; GALACTIC RING SURVEY; DENSITY STRUCTURE; COLUMN DENSITY; LINE-PROFILES; MILKY-WAY; ISOTHERMAL TURBULENCE; HERSCHEL VIEW; EXTINCTION Multiple languages Astronomy & Astrophysics Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/40229