Query : 2010A&A...521L..18V

2010A&A...521L..18V - Astronomy and Astrophysics, volume 521, L18-18 (2010/10-1)

[CII] observations of H2 molecular layers in transition clouds.


Abstract (from CDS):

We present the first results on the diffuse transition clouds observed in [CII] line emission at 158µm (1.9THz) towards Galactic longitudes near 340° (5 LOSs) & 20° (11 LOSs) as part of the HIFI tests and GOT C+ survey. Out of the total 146 [CII] velocity components detected by profile fitting we identify 53 as diffuse molecular clouds with associated 12CO emission but without 13CO emission and characterized by AV<5mag. We estimate the fraction of the [CII] emission in the diffuse HI layer in each cloud and then determine the [CII] emitted from the molecular layers in the cloud. We show that the excess [CII] intensities detected in a few clouds is indicative of a thick H2layer around the CO core. The wide range of clouds in our sample with thin to thick H2layers suggests that these are at various evolutionary states characterized by the formation of H2and CO layers from HI and C+, respectively. In about 30% of the clouds the H2column densities (``dark gas'') traced by the [CII] is 50% or more than that traced by 12CO emission. On the average ∼25% of the total H2in these clouds is in an H2layer which is not traced by CO. We use the HI, [CII], and 12CO intensities in each cloud along with simple chemical models to obtain constraints on the FUV fields and cosmic ray ionization rates.

Abstract Copyright:

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

Simbad objects: 3

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Number of rows : 3
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2024
1 NAME Taurus Complex SFR 04 41.0 +25 52           ~ 4316 0
2 SNR G337.8-00.1 SNR 16 39.0 -46 59           ~ 75 0
3 GAL 345.65+00.01 HII 17 06 16.488 -40 49 46.92           ~ 7 1

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