2018A&A...617A..54L


C.D.S. - SIMBAD4 rel 1.7 - 2021.05.16CEST21:36:33

2018A&A...617A..54L - Astronomy and Astrophysics, volume 617A, 54-54 (2018/9-1)

Molecular gas and dark neutral medium in the outskirts of Chamaeleon.

LISZT H., GERIN M. and GRENIER I.

Abstract (from CDS):


Context. More gas is inferred to be present in molecular cloud complexes than can be accounted for by HI and CO emission, a phenomenon known as dark neutral medium (DNM) or CO-dark gas for the molecular part.
Aims. We aim to investigate whether molecular gas can be detected in Chamaeleon where gas column densities in the DNM were inferred and CO emission was not detected.
Methods. We took λ3 mm absorption profiles of HCO+ and other molecules toward 13 background quasars across the Chamaeleon complex, only one of which had detectable CO emission. We derived the H2 column density assuming N(HCO+)/N(H2)=3x10–9 as before.
Results. With the possible exception of one weak continuum target, HCO+ absorption was detected in all directions, C2H in eight directions and HCN in four directions. The sightlines divide into two groups according to their DNM content, with one group of eight directions having N(DNM)≥2x1020cm–2 and another group of five directions having N(DNM)<0.5x1020cm–2. The groups have comparable mean N(HI) associated with Chamaeleon 6-7x1020cm–2 and total hydrogen column density per unit reddening 6-7x1021cm–2mag–1. They differ, however, in having quite different mean reddening 0.33 vs. 0.18mag, mean N(DNM) 3.3 vs. 0.14x1020cm–2 and mean molecular column density 2N(H2)=5.6 vs. 0.8x1020cm–2. The gas at more positive velocities is enriched in molecules and DNM.
Conclusions. Overall the quantity of H2 inferred from HCO+ can fully account for the previously inferred DNM along the sightlines studied here. H2 is concentrated in the high-DNM group, where the molecular fraction is 46% vs. 13% otherwise and 38% overall. Thus, neutral gas in the outskirts of the complex is mostly atomic but the DNM is mostly molecular. Saturation of the HI emission line profile may occur along three of the four sightlines having the largest DNM column densities, but there is no substantial reservoir of "dark" atomic or molecular gas that remains undetected as part of the inventory of dark neutral medium.

Abstract Copyright: © ESO 2018

Journal keyword(s): ISM: clouds - ISM: molecules - ISM: structure - ISM: atoms

Simbad objects: 15

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Number of rows : 15

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 PMN J0942-7731 Rad 09 42 42.7501822512 -77 31 11.845480859           ~ 6 0
2 QSO B1057-797 BLL 10 58 43.30977041 -80 03 54.1597166   19.08   17.31   ~ 162 0
3 NAME Cha 1 MoC 11 06 48 -77 18.0           ~ 1014 1
4 QSO B1133-681 Bla 11 36 02.0988122204 -68 27 05.860230839   22.0       ~ 34 1
5 ICRF J114553.6-695401 Sy1 11 45 53.6240281213 -69 54 01.798127146   16.90       ~ 47 1
6 PMN J1147-6753 Rad 11 47 33.41 -67 53 41.5           ~ 2 0
7 AT20G J115253.6-834410 Bz? 11 52 53.2232 -83 44 09.436           ~ 13 1
8 NAME Chamaeleon Region SFR 11 55 -78.0           ~ 712 0
9 QSO B1221-829 Bla 12 24 54.38185745 -83 13 10.1013254   22.5   19.7   ~ 66 2
10 NAME Cha II MoC 12 54 -77.2           ~ 306 0
11 PKS 1308-771 Rad 13 12 38.7525871223 -77 24 13.307819050           ~ 6 0
12 PKS 1541-82 rG 15 50 59.1822110092 -82 58 06.800163243   20.00       ~ 30 1
13 QSO B1610-771 QSO 16 17 49.2776951842 -77 17 18.469164198   19.19 19.0 17.32   ~ 143 1
14 PMN J1723-7713 Rad 17 23 50.83 -77 13 50.9           ~ 3 0
15 ICRF J173340.7-793555 QSO 17 33 40.70027819 -79 35 55.7166934   18.67   18.18   ~ 43 1

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