Query : 2006A&A...445..601G

2006A&A...445..601G - Astronomy and Astrophysics, volume 445, 601-616 (2006/1-2)

Probing turbulence with infrared observations in OMC1.


Abstract (from CDS):

A statistical analysis is presented of the turbulent velocity structure in the Orion Molecular Cloud at scales ranging from 70AU to 3x104AU.
Result. are based on IR Fabry-Perot interferometric observations of shock and photon-excited H2 in the K-band S(1) v=1-0 line at 2.121µm and refer to the dynamical characteristics of warm perturbed gas. Data consist of a spatially resolved image with a measured velocity for each resolution limited region (70AUx70AU) in the image. The effect of removal of apparent large scale velocity gradients is discussed and the conclusion drawn that these apparent gradients represent part of the turbulent cascade and should remain within the data. Using our full data set, observations establish that the Larson size-linewidth relation is obeyed to the smallest scales studied here extending the range of validity of this relationship by nearly 2 orders of magnitude. The velocity probability distribution function (PDF) is constructed showing extended exponential wings, providing evidence of intermittency, further supported by the skewness (third moment) and kurtosis (fourth moment) of the velocity distribution. Variance and kurtosis of the PDF of velocity differences are constructed as a function of lag. The variance shows an approximate power law dependence on lag, with exponent significantly lower than the Kolmogorov value, and with deviations below 2000AU which are attributed to outflows and possibly disk structures associated with low mass star formation within OMC1. The kurtosis shows strong deviation from a Gaussian velocity field, providing evidence of velocity correlations at small lags. Results agree accurately with semi-empirical simulations in Eggers & Wang (1998, Phys. Rev. E, 57, 4281). In addition, 170 individual H2 emitting clumps have been analysed with sizes between 500 and 2200AU. These show considerable diversity with regard to PDFs and variance functions (related to second order structure functions) displaying a variety of shapes of the PDF and different values of the scaling exponent within a restricted spatial region. However, a region associated with an outflow from a deeply embedded O-star shows high values of the scaling exponent of the variance function, representing a strong segregation of high and low exponent clumps. Our analysis constitutes the first characterization of the turbulent velocity field at the scale of star formation and provide a dataset which models of star-forming regions should aim to reproduce.

Abstract Copyright:

Journal keyword(s): ISM: individual objects: OMC1 - ISM: kinematics and dynamics - ISM: molecules - shock waves - turbulence - infrared: ISM

Simbad objects: 9

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Number of rows : 9
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
1 NAME OMC-1 MoC 05 35 14 -05 22.4           ~ 1138 2
2 V* V2254 Ori Or* 05 35 14.11296 -05 22 22.7316           B 311 2
3 COUP 621 Y*O 05 35 14.35371 -05 22 32.8820           ~ 106 0
4 [RLK73] IRc 2 IR 05 35 14.51548 -05 22 30.5943           ~ 626 1
5 V* V1330 Ori BY* 05 35 14.9155657944 -05 22 39.203240880   15.040 13.940   11.632 K4 71 0
6 * tet01 Ori C SB* 05 35 16.4662967280 -05 23 22.921811880 4.20 5.15 5.13 4.91 4.73 O7Vp 1376 1
7 NAME Horsehead Nebula DNe 05 40 59.0 -02 27 30           ~ 498 0
8 NGC 2023 RNe 05 41 37.9 -02 15 52           ~ 616 1
9 LDN 1630 DNe 05 45.5 -00 59           ~ 374 0

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