Universität zu Köln

Dib, Sami, Bontemps, Sylvain, Schneider, Nicola, Elia, Davide, Ossenkopf-Okada, Volker, Shadmehri, Mohsen, Arzoumanian, Doris, Motte, Frederique, Heyer, Mark, Nordlund, Ake and Ladjelate, Bilal (2020). The structure and characteristic scales of molecular clouds. Astron. Astrophys., 642. LES ULIS CEDEX A: EDP SCIENCES S A. ISSN 1432-0746

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Abstract

The structure of molecular clouds holds important clues regarding the physical processes that lead to their formation and subsequent dynamical evolution. While it is well established that turbulence imprints a self-similar structure onto the clouds, other processes, such as gravity and stellar feedback, can break their scale-free nature. The break of self-similarity can manifest itself in the existence of characteristic scales that stand out from the underlying structure generated by turbulent motions. In this work, we investigate the structure of the Cygnus-X North and Polaris Flare molecular clouds, which represent two extremes in terms of their star formation activity. We characterize the structure of the clouds using the delta-variance (Delta -variance) spectrum. In the Polaris Flare, the structure of the cloud is self-similar over more than one order of magnitude in spatial scales. In contrast, the Delta -variance spectrum of Cygnus-X North exhibits an excess and a plateau on physical scales of approximate to 0.5-1.2 pc. In order to explain the observations for Cygnus-X North, we use synthetic maps where we overlay populations of discrete structures on top of a fractal Brownian motion (fBm) image. The properties of these structures, such as their major axis sizes, aspect ratios, and column density contrasts with the fBm image, are randomly drawn from parameterized distribution functions. We are able to show that, under plausible assumptions, it is possible to reproduce a Delta -variance spectrum that resembles that of the Cygnus-X North region. We also use a reverse engineering approach in which we extract the compact structures in the Cygnus-X North cloud and reinject them onto an fBm map. Using this approach, the calculated Delta -variance spectrum deviates from the observations and is an indication that the range of characteristic scales (approximate to 0.5-1.2 pc) observed in Cygnus-X North is not only due to the existence of compact sources, but is a signature of the whole population of structures that exist in the cloud, including more extended and elongated structures.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Dib, Sami UNSPECIFIED UNSPECIFIED UNSPECIFIED Bontemps, Sylvain UNSPECIFIED UNSPECIFIED UNSPECIFIED Schneider, Nicola UNSPECIFIED UNSPECIFIED UNSPECIFIED Elia, Davide UNSPECIFIED UNSPECIFIED UNSPECIFIED Ossenkopf-Okada, Volker UNSPECIFIED UNSPECIFIED UNSPECIFIED Shadmehri, Mohsen UNSPECIFIED UNSPECIFIED UNSPECIFIED Arzoumanian, Doris UNSPECIFIED UNSPECIFIED UNSPECIFIED Motte, Frederique UNSPECIFIED UNSPECIFIED UNSPECIFIED Heyer, Mark UNSPECIFIED UNSPECIFIED UNSPECIFIED Nordlund, Ake UNSPECIFIED UNSPECIFIED UNSPECIFIED Ladjelate, Bilal UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-314643
DOI:	10.1051/0004-6361/202038849
Journal or Publication Title:	Astron. Astrophys.
Volume:	642
Date:	2020
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 STAR-FORMATION RATES; INTERSTELLAR H-I; POWER SPECTRUM; DELTA-VARIANCE; TURBULENCE; HERSCHEL; EMISSION; CLUSTERS; YOUNG; SIMULATIONS Multiple languages Astronomy & Astrophysics Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/31464