WHAT DETERMINES THE DENSITY STRUCTURE OF MOLECULAR CLOUDS? A CASE STUDY OF ORION B WITH HERSCHEL

Journal Article · Mon Apr 01 00:00:00 EDT 2013 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/766/2/L17· OSTI ID:22130788

Schneider, N.; Andre, Ph.; Koenyves, V.; Motte, F.; Arzoumanian, D.; Didelon, P.; Hennemann, M.; Hill, T.; Palmeirim, P.; Peretto, N.; Roy, A. ^[1]; Bontemps, S. ^[2]; Federrath, C. ^[3]; Ward-Thompson, D. ^[4]; Benedettini, M.; Pezzuto, S.; Rygl, K. L. J. ^[5]; Bressert, E. ^[6]; Di Francesco, J. ^[7]; Griffin, M. ^[8] ; others, and

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1. IRFU/SAp CEA/DSM, Laboratoire AIM CNRS, Universite Paris Diderot, F-91191 Gif-sur-Yvette (France)
2. OASU/LAB-UMR5804, CNRS, Universite Bordeaux 1, F-33270 Floirac (France)
3. MoCA, School of Mathematical Sciences, Monash University, VIC 3800 (Australia)
4. Jeremiah Horrocks Institute, UCLAN, Preston, Lancashire PR1 2HE (United Kingdom)
5. IAPS-INAF, Fosso del Cavaliere 100, I-00133 Roma (Italy)
6. CSIRO Astronomy and Space Science, Epping (Australia)
7. NRCC, Herzberg Institute of Astrophysics, University of Victoria (Canada)
8. University School of Physics and Astronomy, Cardiff (United Kingdom)

A key parameter to the description of all star formation processes is the density structure of the gas. In this Letter, we make use of probability distribution functions (PDFs) of Herschel column density maps of Orion B, Aquila, and Polaris, obtained with the Herschel Gould Belt survey (HGBS). We aim to understand which physical processes influence the PDF shape, and with which signatures. The PDFs of Orion B (Aquila) show a lognormal distribution for low column densities until A{sub V} {approx} 3 (6), and a power-law tail for high column densities, consistent with a {rho}{proportional_to}r {sup -2} profile for the equivalent spherical density distribution. The PDF of Orion B is broadened by external compression due to the nearby OB stellar aggregates. The PDF of a quiescent subregion of the non-star-forming Polaris cloud is nearly lognormal, indicating that supersonic turbulence governs the density distribution. But we also observe a deviation from the lognormal shape at A{sub V} > 1 for a subregion in Polaris that includes a prominent filament. We conclude that (1) the point where the PDF deviates from the lognormal form does not trace a universal A{sub V} -threshold for star formation, (2) statistical density fluctuations, intermittency, and magnetic fields can cause excess from the lognormal PDF at an early cloud formation stage, (3) core formation and/or global collapse of filaments and a non-isothermal gas distribution lead to a power-law tail, and (4) external compression broadens the column density PDF, consistent with numerical simulations.

• OSTI ID: 22130788
• Journal Information: Astrophysical Journal Letters, Vol. 766, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
COMPRESSION
COMPUTERIZED SIMULATION
DENSITY
DISTRIBUTION
DISTRIBUTION FUNCTIONS
DUSTS
FLUCTUATIONS
MAGNETIC FIELDS
STARS
TURBULENCE