2019A&A...631A.117K


Query : 2019A&A...631A.117K

2019A&A...631A.117K - Astronomy and Astrophysics, volume 631A, 117-117 (2019/11-1)

Origin of hydrogen fluoride emission in the Orion Bar. An excellent tracer for CO-dark H2 gas clouds.

KAVAK U., VAN DER TAK F.F.S., TIELENS A.G.G.M. and SHIPMAN R.F.

Abstract (from CDS):


Context. The hydrogen fluoride (HF) molecule is seen in absorption in the interstellar medium (ISM) along many lines of sight. Surprisingly, it is observed in emission toward the Orion Bar, which is an interface between the ionized region around the Orion Trapezium stars and the Orion molecular cloud.
Aims. We aim to understand the origin of HF emission in the Orion Bar by comparing its spatial distribution with other tracers. We examine three mechanisms to explain the HF emission: thermal excitation, radiative dust pumping, and chemical pumping.
Methods. We used a Herschel/HIFI strip map of the HF J=1-0 line, covering 0.5' by 1.5' that is oriented perpendicular to the Orion Bar. We used the RADEX non-local thermodynamic equilibrium (non-LTE) code to construct the HF column density map. We use the Meudon PDR code to explain the morphology of HF.
Results. The bulk of the HF emission at 10km/s emerges from the CO-dark molecular gas that separates the ionization front from the molecular gas that is deeper in the Orion Bar. The excitation of HF is caused mainly by collisions with H2 at a density of 105 cm–3 together with a small contribution of electrons in the interclump gas of the Orion Bar. Infrared pumping and chemical pumping are not important.
Conclusions. We conclude that the HF J=1-0 line traces CO-dark molecular gas. Similarly, bright photodissociation regions associated with massive star formation may be responsible for the HF emission observed toward active galactic nuclei.

Abstract Copyright: © ESO 2019

Journal keyword(s): astrochemistry - photon-dominated region - ISM: molecules - ISM: individual objects: Orion Bar

VizieR on-line data: <Available at CDS (J/A+A/631/A117): list.dat fits/*>

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 - 2022
#notes
1 * tet01 Ori C SB* 05 35 16.4662967280 -05 23 22.921811880 4.20 5.15 5.13 4.91 4.73 O7Vp 1342 1
2 M 42 HII 05 35 17.3 -05 23 28           ~ 3902 0
3 [QXZ2018] SMA8 cor 05 35 21.97 -05 25 14.9           ~ 2 0
4 NAME Orion Bright Bar reg 05 35 22.30 -05 24 33.0           ~ 797 0
5 NAME ORI MOL CLOUD MoC 05 56 -01.8           ~ 955 1
6 IRC +10216 C* 09 47 57.40632 +13 16 43.5648     10.96     C9,5e 2240 0
7 Mrk 231 Sy1 12 56 14.2341182928 +56 52 25.238373852   14.68 13.84     ~ 1894 3
8 QSO J1415+1129 QSO 14 15 46.25 +11 29 43.4   17.63 17.23     ~ 618 0
9 IC 4553 SyG 15 34 57.22396 +23 30 11.6084   14.76 13.88     ~ 2823 4

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2022.05.28-11:00:51

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