J/A+A/635/A4 HCN-to-HNC intensity ratio (Hacar+, 2020)
HCN-to-HNC intensity ratio: a new chemical thermometer for the molecular ISM.
Hacar A., Bosman A., van Dishoeck E.F.
<Astron. Astrophys. 635, A4 (2020)>
=2020A&A...635A...4H 2020A&A...635A...4H (SIMBAD/NED BibCode)
ADC_Keywords: Interstellar medium; Spectra, millimetric/submm; Abundances
Keywords: ISM: clouds - ISM: molecules - ISM: structure - stars: formation -
submillimeter: ISM
Abstract:
The gas kinetic temperature (TK) determines the physical and chemical
evolution of the interstellar medium (ISM). However, obtaining
reliable TK estimates usually requires expensive observations
including the combination of multi-line analysis and dedicated
radiative transfer calculations.
This work explores the use of HCN and HNC observations, and
particularly the I(HCN)-to-I(HNC) intensity ratio (I(HCN)/I(HNC)) of
their J=1-0 lines, as direct probe of the gas kinetic temperature in
the molecular ISM.
We obtained a new set of large-scale observations of the HCN and HNC
(1-0) lines throughout the Integral Shape Filament (ISF) in Orion. In
combination with ancillary gas and dust temperature measurements, we
find a systematic temperature dependence of the observed
I(HCN)-to-I(HNC) intensity ratio throughout our maps. Additional
comparisons with chemical models demonstrate that these observed
I(HCN)/I(HNC) variations are driven by the effective destruction and
isomerization mechanisms of HNC under low-energy barriers.
The observed variations of I(HCN)/I(HNC) with TK can be described with
a two-part linear function. This empirical calibration is then used to
create a temperature map of the entire ISF. Comparisons with similar
dust temperature measurements in this cloud, as well as in other
regions and galactic surveys, validate this simple technique for
obtaining direct estimates of the gas kinetic temperature in a wide
range of physical conditions and scales with an optimal working range
between 15K<TK≤40K.
Both observations and models demonstrate the strong sensitivity of the
I(HCN)/I(HNC) ratio to the gas kinetic temperature. Since these lines
are easily obtained in observations of local and extragalactic
sources, our results highlight the potential use of this observable as
new chemical thermometer for the ISM.
Description:
Integrated intensity (moment 0) maps of the HCN(1-0), HNC(1-0) and
H41alpha emission lines, as well as the HCN/HNC temperature map along
the Orion Integral Shape Filament.
Objects:
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RA (2000) DE Designation(s)
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05 35.0 -05 29 Orion = NAME Orion Nebula Cluster
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 112 4 List of fits maps
fits/* . 4 Individual fits maps
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 21 I2 --- Nx Number of pixels along X-axis
23- 25 I3 --- Ny Number of pixels along Y-axis
27- 29 I3 Kibyte size Size of FITS file
31- 55 A25 --- FileName Name of FITS file, in subdirectory fits
57-112 A56 --- Title Title of the FITS file
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Acknowledgements:
Alvaro Hacar, hacar(at)strw.leidenuniv.nl
This work is part of the ORION-4D project (PI: A. Hacar).
See more information in https://sites.google.com/site/orion4dproject
(End) Patricia Vannier [CDS] 21-Feb-2020