Query : 2007A&A...469..173H

2007A&A...469..173H - Astronomy and Astrophysics, volume 469, 173-187 (2007/7-1)

Dissipative structures of diffuse molecular gas. II. The translucent environment of a dense core.


Abstract (from CDS):

This paper belongs to a series of four, dedicated to the analysis of the dynamical, thermal and chemical properties of translucent molecular gas, with the perspective of characterizing the processes driving the dissipation of supersonic turbulence, an anticipated prerequisite of dense core formation. We analyze the small scale morphology and velocity structure of the parsec-scale environment of a low mass dense core (1M). Our work is based on large maps made with the IRAM-30m telescope in the two lowest rotational transitions of 12CO and 13CO with high angular (20'' or 0.015 pc at 115GHz) and spectral (0.055km/s) resolutions. The field is translucent, hence providing strong constraints on the column density and physical conditions in the gas. More than one third of the field mass (6.5M) lies in an elongated tail of dense and cold gas, possibly extending beyond the edge of the map and connected to the core in space and velocity. This core tail is highly turbulent and sub-structured into narrow filaments of aspect ratio up to 20. These are pure velocity structures with velocity shears in the range 2-10km/s/pc. Another third of the mass, according to the weak extinction of the field, lies in more dilute molecular and atomic gas. Its molecular fraction, largely traced by optically thick 12CO lines, is even more turbulent than the dense core tail. The gas emitting in the broad wings of the 12CO lines is organized into a conspicuous network of narrow criss-crossed filaments, whose pattern at the parsec scale is seen for the first time. The gas there is optically thin in the 12CO(1-0) line (τ12<0.2), warmer than 25K and more dilute than 1000cm–3. These optically thin 12CO-filaments, though contributing to about 10% of the mass of the environment, have a CO cooling rate a few times larger than that of the whole field on average. Whether dense or dilute, all the filamentary structures in the field (with transverse sizes 0.015-0.03pc), are preferentially oriented along the direction of the magnetic fields, as measured a few parsecs away. Using the Chandrasekhar-Fermi method, we estimate the intensity of the magnetic fields intensity in the dilute molecular gas to be Bpos=15µG. We infer that the turbulent motions in the dilute gas are in the trans-Alfvenic range. The 1M dense core is surrounded by a translucent and highly turbulent environment whose gas dynamics are not super-Alfvenic. The low mass dense core is not isolated but still connected to a massive reservoir of dense gas. Filaments of optically thin 12CO are found to radiate more efficiently in the CO lines than the whole field on average. These are the structures that we tentatively identify with the locus of intermittent dissipation of turbulence, and for which there is no observational evidence that they are shocks.

Abstract Copyright:

Journal keyword(s): ISM: kinematics and dynamics - ISM: structure - ISM: magnetic fields - line: profiles

VizieR on-line data: <Available at CDS (J/A+A/469/173): fits/*>

CDS comments: Paragr.7.1: Objects BNNNN are BHHMM+DDd objects with an incomplete format.

Simbad objects: 7

goto Full paper

goto View the references in ADS

Number of rows : 7
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
1 NAME Polaris Cirrus Cloud MoC 01 52 29.6 +87 40 31           ~ 76 0
2 4C 67.05 QSO 02 28 50.05148365 +67 21 03.0293322   19.5 19.50 18.1   ~ 247 1
3 4C 50.11 QSO 03 59 29.74727351 +50 57 50.1618607           ~ 431 1
4 NAME Polaris Flare MoC 11 00 14.8 +86 10 52           ~ 186 1
5 QSO B1730-130 QSO 17 33 02.70578907 -13 04 49.5482119   18 19.50 18.78 17.39 ~ 1107 1
6 QSO J2015+371 BLL 20 15 28.72978661 +37 10 59.5147372     21.82 21.4   ~ 281 2
7 3C 454.3 Bla 22 53 57.7480438728 +16 08 53.561508864   16.57 16.10 15.22   ~ 2783 2

To bookmark this query, right click on this link: simbad:objects in 2007A&A...469..173H and select 'bookmark this link' or equivalent in the popup menu


© Université de Strasbourg/CNRS

    • Contact