2008A&A...492..675F


C.D.S. - SIMBAD4 rel 1.7 - 2020.07.04CEST22:01:41

2008A&A...492..675F - Astronomy and Astrophysics, volume 492, 675-684 (2008/12-4)

On the chemistry and distribution of HOC+ in M 82. More evidence for extensive PDRs.

FUENTE A., GARCIA-BURILLO S., USERO A., GERIN M., NERI R., FAURE A., LE BOURLOT J., GONZALEZ-GARCIA M., RIZZO J.R., ALONSO-ALBI T. and TENNYSON J.

Abstract (from CDS):

The molecular gas composition in the inner 1kpc disk of the starburst galaxy M 82 resembles that of Galactic Photon Dominated Regions (PDRs). In particular, large abundances of the reactive ions HOC+ and CO+ have been measured in the nucleus of this galaxy. Two explanations have been proposed for such high abundances: the influence of intense UV fields from massive stars, or a significant role of X-Rays. Our aim is to investigate the origin of the high abundances of reactive ions in M 82. We have completed our previous 30m HOC+ J=1->0 observations with the higher excitation HCO+ and HOC+ J=4->3 and 3->2 rotational lines. In addition, we have obtained with the IRAM Plateau de Bure Interferometer (PdBI) a 4'' resolution map of the HOC+ emission in M 82, the first ever obtained in a Galactic or extragalactic source. Our HOC+ interferometric image shows that the emission of the HOC+ 1->0 line is mainly restricted to the nuclear disk, with the maxima towards the E and W molecular peaks. In addition, line excitation calculations imply that the HOC+ emission arises in dense gas (n≥104cm–3). Therefore, the HOC+ emission is arising in the dense PDRs embedded in the M 82 nuclear disk, rather than in the intercloud phase and/or wind. We have improved our previous chemical model of M 82 by (i) using the new version of the Meudon PDR code; (ii) updating the chemical network; and (iii) considering two different types of clouds (with different thickness) irradiated by the intense interstellar UV field (G0=104 in units of the Habing field) prevailing in the nucleus of M 82. Most molecular observations (HCO+, HOC+, CO+, CN, HCN, H3O+) are well explained assuming that ∼87% of the mass of the molecular gas is forming small clouds (Av=5mag) while only ∼13% of the mass is in large molecular clouds (Av=50mag). Such a small number of large molecular clouds suggests that M 82 is an old starburst, where star formation has almost exhausted the molecular gas reservoir.

Abstract Copyright:

Journal keyword(s): galaxies: individual: M 82 - galaxies: nuclei - galaxies: starburst - ISM: molecules - ISM: abundances - radio lines: galaxies

CDS comments: Paragraph 3.2.1 SNR 41.95+57.5 is [MPW94] 41.95+57.5 in Simbad.

Simbad objects: 7

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Number of rows : 7

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 M 77 GiP 02 42 40.771 -00 00 47.84 9.70 9.61 8.87 10.1 9.9 ~ 4089 2
2 NAME LDN 1448-mm Y*O 03 25 38.83 +30 44 06.2           ~ 301 0
3 [SDA2014] West4 Y*O 03 25 38.83 +30 44 06.2           ~ 242 1
4 NAME Mon R2 HII 06 07 46.6 -06 22 59           ~ 650 2
5 CXOU J095550.6+694043 HXB 09 55 50.68 +69 40 43.8           ~ 92 0
6 M 82 IG 09 55 52.430 +69 40 46.93 9.61 9.30 8.41     ~ 5331 6
7 NAME Cyg A Sy2 19 59 28.35645829 +40 44 02.0966496   16.22 15.10     ~ 2112 2

    Equat.    Gal    SGal    Ecl

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2020.07.04-22:01:41

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