2005A&A...433..997F


C.D.S. - SIMBAD4 rel 1.7 - 2021.03.08CET20:30:55

2005A&A...433..997F - Astronomy and Astrophysics, volume 433, 997-1006 (2005/4-3)

Warm gas in the cold diffuse interstellar medium: Spectral signatures in the H2 pure rotational lines.

FALGARONE E., VERSTRAETE L., PINEAU DES FORETS G. and HILY-BLANT P.

Abstract (from CDS):

We present ISO-SWS observations of five pure rotational lines of H2 along a line of sight through the Galaxy which avoids regions of massive star formation. It samples 30 mag of gas, half of it (i.e. 15mag) being diffuse gas running from the solar neighbourhood to the molecular ring, up to the far side of the Galaxy. The intensities of the S(1) and S(2) lines are too large relative to S(0) to be produced by UV excitation in the known radiation field of the Galaxy. The excitation of these transitions has to tap a more powerful source of energy. We investigate the possibility that it takes place in a large number of magneto-hydrodynamic (MHD) shocks or coherent small-scale vortices, two processes responsible for the intermittent dissipation of MHD turbulence. These dissipation bursts locally and temporarily heat the diffuse gas to temperatures (Tk∼103K) well above that of the ambient diffuse gas. We compute the spectroscopic signatures of these processes in the H2 lines. Not only are the computed relative line intensities in good agreement with the observations, but the few percent of warm gas involved is consistent with other independent determinations. We find that the fraction of warm H2 in the diffuse gas (i.e. H2 molecules in Ju≥3 levels) on that line of sight, N(H2*)/Av≃4x1017/cm2/mag, is the same as that found from far UV spectroscopy in the direction of nearby stars. It is also the same as that estimated in the solar neighbourhood to reproduce the large observed abundances of molecules like CH+. These results suggest that the existence, within the cold neutral medium (CNM), of a few percent of warm gas, for which UV photons cannot be the sole heating source, is ubiquitous and presumably traces the intermittent dissipation of MHD turbulence in the cold diffuse gas.

Abstract Copyright:

Journal keyword(s): turbulence - ISM: molecules - ISM: general - infrared: ISM - ISM: evolution - Galaxy: general

Simbad objects: 9

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Number of rows : 9

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 * eps Eri BY* 03 32 55.8449634 -09 27 29.731165 5.19 4.61 3.73 3.00 2.54 K2V 1734 1
2 * bet Pic PM* 05 47 17.0876901 -51 03 59.441135 4.13 4.03 3.86 3.74 3.58 A6V 1696 1
3 HD 98800 RS* 11 22 05.28975 -24 46 39.7571   10.20 9.28 9.26 7.386 K5V(e) 335 0
4 * eta Crv PM* 12 32 04.2265302 -16 11 45.616473   4.658 4.294     F2V 288 0
5 HD 109573 PM* 12 36 01.0317721349 -39 52 10.222698506   5.786 5.774 7.25 5.81 A0V 564 1
6 HD 141569 Y*O 15 49 57.7484743862 -03 55 16.344023102 7.22 7.20 7.12 7.00 7.04 A2VekB9mB9(_lB) 480 0
7 GAL 000.0+00.0 gam 17 45 39.60213 -29 00 22.0000           ~ 12014 0
8 * alf Lyr dS* 18 36 56.33635 +38 47 01.2802 0.03 0.03 0.03 0.07 0.10 A0Va 2538 0
9 * alf PsA ** 22 57 39.04625 -29 37 20.0533 1.31 1.25 1.16 1.11 1.09 A4V 1135 3

    Equat.    Gal    SGal    Ecl

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2021.03.08-20:30:55

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