2016A&A...587A..74S


C.D.S. - SIMBAD4 rel 1.7 - 2021.03.01CET20:08:26

2016A&A...587A..74S - Astronomy and Astrophysics, volume 587A, 74-74 (2016/3-1)

Understanding star formation in molecular clouds. III. Probability distribution functions of molecular lines in Cygnus X.

SCHNEIDER N., BONTEMPS S., MOTTE F., OSSENKOPF V., KLESSEN R.S., SIMON R., FECHTENBAUM S., HERPIN F., TREMBLIN P., CSENGERI T., MYERS P.C., HILL T., CUNNINGHAM M. and FEDERRATH C.

Abstract (from CDS):

The probability distribution function of column density (N-PDF) serves as a powerful tool to characterise the various physical processes that influence the structure of molecular clouds. Studies that use extinction maps or H2 column-density maps (N) that are derived from dust show that star-forming clouds can best be characterised by lognormal PDFs for the lower N range and a power-law tail for higher N, which is commonly attributed to turbulence and self-gravity and/or pressure, respectively. While PDFs from dust cover a large dynamic range (typically N∼1020–24cm–2 or Av∼0.1-1000), PDFs obtained from molecular lines - converted into H2 column density - potentially trace more selectively different regimes of (column) densities and temperatures. They also enable us to distinguish different clouds along the line of sight through using the velocity information. We report here on PDFs that were obtained from observations of 12CO, 13CO, C18O, CS, and N2H+ in the Cygnus X North region, and make a comparison to a PDF that was derived from dust observations with the Herschel satellite. The PDF of 12CO is lognormal for Av∼1-30, but is cut for higher Av because of optical depth effects. The PDFs of C18O and 13CO are mostly lognormal up to Av∼1-15, followed by excess up to Av∼40. Above that value, all CO PDFs drop, which is most likely due to depletion. The high density tracers CS and N2H+ exhibit only a power law distribution between Av∼15 and 400, respectively. The PDF from dust is lognormal for Av∼3-15 and has a power-law tail up to Av∼500. Absolute values for the molecular line column densities are, however, rather uncertain because of abundance and excitation temperature variations. If we take the dust PDF at face value, we ``calibrate'' the molecular line PDF of CS to that of the dust and determine an abundance [CS]/[H2] of 10–9. The slopes of the power-law tails of the CS, N2H+, and dust PDFs are -1.6, -1.4, and -2.3, respectively, and are thus consistent with free-fall collapse of filaments and clumps. A quasi static configuration of filaments and clumps can also possibly account for the observed N-PDFs, providing they have a sufficiently condensed density structure and external ram pressure by gas accretion is provided. The somehow flatter slopes of N2H+ and CS can reflect an abundance change and/or subthermal excitation at low column densities.

Abstract Copyright:

Journal keyword(s): ISM: abundances - ISM: clouds - dust, extinction - ISM: molecules - ISM: structure

Simbad objects: 14

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Number of rows : 14

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2021
#notes
1 NAME Per Arm PoG 03 30 +45.0           ~ 1290 0
2 NAME Ori A MoC 05 38 -07.1           ~ 2737 0
3 SNR G030.8-00.0 SNR 18 47 32 -01 56.5           ~ 457 0
4 NAME Northern Coalsack DNe 20 21 +37.0           ~ 106 0
5 NAME Cyg X Cld 20 28 41 +41 10.2           ~ 643 1
6 NAME Cyg Complex reg 20 32 +45.0           ~ 532 0
7 Ass Cyg OB 2 As* 20 33.2 +41 19           ~ 819 0
8 DR 17 HII 20 35.2 +42 25           ~ 34 0
9 NAME Cyg X FIR 33 Y*O 20 38 35.9 +42 37 22           B1.5 364 1
10 GRS G081.70 +00.50 SFR 20 39 01.6 +42 19 38           O4.5 962 0
11 NAME Cyg X FIR 36 Rad 20 39 01.6 +42 22 47           ~ 107 1
12 DR 22 HII 20 39 16.67 +41 18 44.7           ~ 43 1
13 [MBS2007c] CygX-N63 mm 20 40 05.2 +41 32 13           ~ 14 0
14 DR 23 Rad 20 40.8 +41 54           ~ 35 0

    Equat.    Gal    SGal    Ecl

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