Query : 2017A&A...605L...5K

2017A&A...605L...5K - Astronomy and Astrophysics, volume 605, L5-5 (2017/9-1)

Molecular Line Emission as a Tool for Galaxy Observations (LEGO). I. HCN as a tracer of moderate gas densities in molecular clouds and galaxies.


Abstract (from CDS):

Trends observed in galaxies, such as the Gao & Solomon relation, suggest a linear relationship between the star formation rate and the mass of dense gas available for star formation. Validation of such trends requires the establishment of reliable methods to trace the dense gas in galaxies. One frequent assumption is that the HCN (J=1-0) transition is unambiguously associated with gas at H2 densities ≫104cm–3. If so, the mass of gas at densities ≫104cm–3 could be inferred from the luminosity of this emission line, L_HCN (1-0)_. Here we use observations of the Orion A molecular cloud to show that the HCN (J=1-0) line traces much lower densities ∼103cm–3 in cold sections of this molecular cloud, corresponding to visual extinctions AV~=6mag. We also find that cold and dense gas in a cloud like Orion produces too little HCN emission to explain L_HCN (1-0)_ in star forming galaxies, suggesting that galaxies might contain a hitherto unknown source of HCN emission. In our sample of molecules observed at frequencies near 100GHz (also including 12CO, 13CO, C18O, CN, and CCH), N2H+ is the only species clearly associated with relatively dense gas.

Abstract Copyright: © ESO, 2017

Journal keyword(s): stars: formation - ISM: clouds - ISM: molecules - galaxies: evolution - galaxies: ISM - galaxies: star formation - galaxies: star formation

Simbad objects: 6

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Number of rows : 6
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2024
1 M 42 HII 05 35 17 -05 23.4           ~ 4041 0
2 NAME Ori A MoC 05 38 -07.1           ~ 2969 0
3 NAME Ori B MoC 05 41 43.0 -01 54 44           ~ 1352 0
4 NAME Ophiuchus Molecular Cloud SFR 16 28 06 -24 32.5           ~ 3569 1
5 NAME Galactic Center reg 17 45 39.60213 -29 00 22.0000           ~ 14074 0
6 NAME Aql Region reg 18 31.1 -02 10           ~ 384 0

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