2013A&A...550A..25G


C.D.S. - SIMBAD4 rel 1.7 - 2020.07.04CEST14:41:13

2013A&A...550A..25G - Astronomy and Astrophysics, volume 550A, 25-25 (2013/2-1)

Excited OH+, H2O+, and H3O+ in NGC 4418 and Arp 220.

GONZALEZ-ALFONSO E., FISCHER J., BRUDERER S., MUELLER H.S.P., GRACIA-CARPIO J., STURM E., LUTZ D., POGLITSCH A., FEUCHTGRUBER H., VEILLEUX S., CONTURSI A., STERNBERG A., HAILEY-DUNSHEATH S., VERMA A., CHRISTOPHER N., DAVIES R., GENZEL R. and TACCONI L.

Abstract (from CDS):

We report on Herschel/PACS observations of absorption lines of OH+, H2O+ and H3O+ in NGC 4418 and Arp 220. Excited lines of OH+ and H2O+ with Elower of at least 285 and ∼200K, respectively, are detected in both sources, indicating radiative pumping and location in the high radiation density environment of the nuclear regions. Abundance ratios OH+/H2O+ of 1-2.5 are estimated in the nuclei of both sources. The inferred OH+ column and abundance relative to H nuclei are (0.5-1)x1016cm–2 and ∼2x10–8, respectively. Additionally, in Arp 220, an extended low excitation component around the nuclear region is found to have OH+/H2O+∼5-10. H3O+ is detected in both sources with N(H3O+) ~(0.5-2)x1016cm–2, and in Arp 220 the pure inversion, metastable lines indicate a high rotational temperature of ∼500K, indicative of formation pumping and/or hot gas. Simple chemical models favor an ionization sequence dominated by H+ ->O+->OH+->H2O+->H3O+, and we also argue that the H+ production is most likely dominated by X-ray/cosmic ray ionization. The full set of observations and models leads us to propose that the molecular ions arise in a relatively low density (>104cm–3) interclump medium, in which case the ionization rate per H nucleus (including secondary ionizations) is ζ>10–13/s, a lower limit that is several x102 times the highest current rate estimates for Galactic regions. In Arp 220, our lower limit for ζ is compatible with estimates for the cosmic ray energy density inferred previously from the supernova rate and synchrotron radio emission, and also with the expected ionization rate produced by X-rays. In NGC 4418, we argue that X-ray ionization due to an active galactic nucleus is responsible for the molecular ion production.

Abstract Copyright:

Journal keyword(s): line: formation - line: identification - ISM: abundances - galaxies: ISM - infrared: galaxies - molecular processes

Simbad objects: 11

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Number of rows : 11

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
#notes
1 NGC 253 SyG 00 47 33.134 -25 17 19.68   8.03   6.94 8.1 ~ 2929 2
2 NAME Orion-KL SFR 05 35 14.16 -05 22 21.5           ~ 2001 1
3 NAME Orion Bright Bar reg 05 35 22.30 -05 24 33.0           ~ 716 0
4 NGC 4355 Sy2 12 26 54.628 -00 52 39.51   14.21 13.37     ~ 404 2
5 Mrk 231 Sy1 12 56 14.2340989340 +56 52 25.238555193   14.68 13.84     ~ 1777 3
6 IC 4553 SyG 15 34 57.22396 +23 30 11.6084   14.76 13.88     ~ 2679 4
7 NAME Gal Center reg 17 45 40.04 -29 00 28.1           ~ 11533 0
8 NAME Sgr B2 MoC 17 47 20.4 -28 23 07           ~ 1909 1
9 NAME Sgr B2 Main Rad 17 47 20.5 -28 23 06           ~ 331 1
10 W 51 SNR 19 23 50 +14 06.0           ~ 1143 1
11 RAFGL 2591 Y*O 20 29 25.03656 +40 11 20.3316           ~ 570 0

    Equat.    Gal    SGal    Ecl

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2020.07.04-14:41:13

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