2013A&A...560A..95V


C.D.S. - SIMBAD4 rel 1.7 - 2019.10.16CEST22:50:20

2013A&A...560A..95V - Astronomy and Astrophysics, volume 560A, 95-95 (2013/12-1)

Spatially extended OH+ emission from the Orion Bar and Ridge.

VAN DER TAK F.F.S., NAGY Z., OSSENKOPF V., MAKAI Z., BLACK J.H., FAURE A., GERIN M. and BERGIN E.A.

Abstract (from CDS):

The reactive HnO+ ions (OH+, H2O+ and H3O+) are widespread in the interstellar medium and act as precursors to the H2O molecule. While HnO+ absorption is seen on many Galactic lines of sight, active galactic nuclei often show the lines in emission. This paper shows the first example of a Galactic source of HnO+ line emission: the Orion Bar, a bright nearby photon-dominated region (PDR). We present line profiles and maps of OH+ line emission toward the Orion Bar, and upper limits to H2O+ and H3O+ lines. We analyze these HIFI data with non-local thermodynamic equilibrium radiative transfer and PDR chemical models, using newly calculated inelastic collision data for the e-OH+ system. Line emission is detected over ∼1' (0.12pc), tracing the Bar itself as well as a perpendicular feature identified as the southern tip of the Orion Ridge, which borders the Orion Nebula on its western side. The line width of ≃4km/s suggests an origin of the OH+ emission close to the PDR surface, at a depth of AV∼0.3-0.5 into the cloud where most hydrogen is in atomic form. Steady-state collisional and radiative excitation models for OH+ require unrealistically high column densities to match the observed line intensity, indicating that the formation of OH+ in the Bar is rapid enough to influence its excitation. Our best-fit OH+ column density of ∼1.0x1014cm–2 is similar to that in previous absorption line studies, while our limits on the ratios of OH+/H2O+ (> 40) and OH+/H3O+ (> 15) are somewhat higher than seen before. The column density of OH+ is consistent with estimates from a thermo-chemical model for parameters applicable to the Orion Bar, given the current uncertainties in the local gas pressure and the spectral shape of the ionizing radiation field. The unusually high OH+/H2O+ and OH+/H3O+ ratios are probably due to the high UV radiation field and electron density in this object. In the Bar, photodissociation and electron recombination are more effective destroyers of OH+ than the reaction with H2, which limits the production of H2O+. The appearance of the OH+ lines in emission is the result of the high density of electrons and H atoms in the Orion Bar, since for these species, inelastic collisions with OH+ are faster than reactive ones. In addition, chemical pumping, far-infrared pumping by local dust, and near-UV pumping by Trapezium starlight contribute to the OH+ excitation. Similar conditions may apply to extragalactic nuclei where HnO+ lines are seen in emission.

Abstract Copyright:

Journal keyword(s): ISM: molecules - astrochemistry

Simbad objects: 22

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Number of rows : 22

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2019
#notes
1 NAME W3 IRS 5 Y*O 02 25 40.54 +62 05 51.4           B1 322 0
2 M 77 GiP 02 42 40.771 -00 00 47.84 9.70 9.61 8.87 10.1 9.9 ~ 3981 2
3 M 1 SNR 05 34 31.94 +22 00 52.2           ~ 5486 4
4 NAME Orion S reg 05 35 12.9 -05 24 10           ~ 117 0
5 NAME OMC1 Ridge reg 05 35 13.4 -05 23 07           ~ 120 0
6 NAME Orion-KL SFR 05 35 14.16 -05 22 21.5           ~ 1937 1
7 NAME Trapezium Cluster As* 05 35 16.5 -05 23 14           ~ 1432 1
8 M 42 HII 05 35 17.3 -05 23 28           ~ 3657 0
9 NAME Orion Bright Bar reg 05 35 22.30 -05 24 33.0           ~ 690 0
10 OMC 2 MoC 05 35 27 -05 10.1           ~ 374 1
11 M 82 IG 09 55 52.430 +69 40 46.93 9.61 9.30 8.41     ~ 5210 6
12 NGC 3603 HII 11 15 24 -61 15.0           ~ 919 2
13 NGC 4355 Sy2 12 26 54.628 -00 52 39.51   14.21 13.37     ~ 384 2
14 Mrk 231 Sy1 12 56 14.2340989340 +56 52 25.238555193   14.68 13.84     ~ 1733 3
15 IC 4553 SyG 15 34 57.22396 +23 30 11.6084   14.76 13.88     ~ 2617 4
16 NAME Gal Center reg 17 45 40.04 -29 00 28.1           ~ 10997 0
17 NAME Sgr B2 MoC 17 47 20.4 -28 23 07           ~ 1849 1
18 W 31c HII 18 10 29.1 -19 56 05           ~ 298 0
19 W 49n HII 19 10 13.2 +09 06 12           ~ 403 3
20 W 51 SNR 19 23 50 +14 06.0           ~ 1118 1
21 RAFGL 2591 Y*O 20 29 25.2650 +40 11 26.532   18       ~ 562 5
22 NGC 7293 PN 22 29 38.5453078023 -20 50 13.746093105 11.894 13.158 13.524 13.689 13.898 DAO.5 882 0

    Equat.    Gal    SGal    Ecl

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2019.10.16-22:50:20

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