J/A+A/645/A27 Orion B in 18 molecular tracers maps (Gratier+, 2021)
Quantitative inference of the H2 column densities from 3mm molecular emission:
case study towards Orion B.
Gratier P., Pety J., Bron E., Roueff A., Orkisz J.H., Gerin M.,
de Souza Magalhaes V., Gaudel M., Vono M., Bardeau S., Chanussot J.,
Chainais P., Goicoechea J.R., Guzman V.V., Hughes A., Kainulainen J.,
Languignon D., Le Bourlot J., Le Petit F., Levrier F., Liszt H.,
Peretto N., Roue E., Sievers A.
<Astron. Astrophys. 645, A27 (2021)>
=2021A&A...645A..27G 2021A&A...645A..27G (SIMBAD/NED BibCode)
ADC_Keywords: Molecular clouds ; Interstellar medium ; Radio lines
Keywords: methods: statistical - ISM: clouds - ISM: molecules
Abstract:
Molecular hydrogen being unobservable in cold molecular clouds, the
column density measurements of molecular gas currently rely either on
dust emission observation in the far-IR or on star counting.
(Sub-)millimeter observations of numerous trace molecules are
effective from ground based telescopes, but the relationships between
the emission of one molecular line and the H2 column density (NH2)
is non-linear and sensitive to excitation conditions, optical depths,
abundance variations due to the underlying physico-chemistry. We aim
to use multi-molecule line emission to infer NH2 from radio
observations. We propose a data-driven approach to determine NH2
from radio molecular line observations. We use supervised machine
learning methods (Random Forests) on wide-field hyperspectral IRAM-30m
observations of the Orion B molecular cloud to train a predictor of
NH2, using a limited set of molecular lines as input, and the
Herschel-based dust-derived NH2 as ground truth output. For
conditions similar to the Orion B molecular cloud, we obtain
predictions of NH2 within a typical factor of 1.2 from the
Herschel-based estimates. An analysis of the contributions of the
different lines to the predictions show that the most important lines
are 13CO(1-0), 12CO(1-0), C18O(1-0), and HCO+(1-0). A detailed
analysis distinguishing between diffuse, translucent, filamentary, and
dense core conditions show that the importance of these four lines
depends on the regime, and that it is recommended to add the
N2H+(1-0) and CH3OH(20-10) lines for the prediction of NH2
in dense core conditions. This article opens a promising avenue to
directly infer important physical parameters from the molecular line
emission in the millimeter domain. The next step will be to try to
infer several parameters simultaneously (e.g., NH2 and far-UV
illumination field) to further test the method.
Description:
Fits files used for the machine learning algorithm used in the
article.
These data are mostly derived from observations with the IRAM-30m
telescope in the context of the ORION-B project, cf.,
https://www.iram.fr/~pety/ORION-B/
The original version of this archive is available at
https://www.iram.fr/~pety/ORION-B/data/orionb-2020-gratier.tar.xz
All the maps are gridded in a custom set of coordinates, with the
origin set on the PDR of the Horsehead Nebula (RA-Dec coordinates
provided in the header), and with an axis position angle rotated by 14
degrees with respect to the North-South orientation. The FITS file
headers are WCS compliant, and our custom set of coordinates should be
understood by any standard FITS reader.
fits subdirectory contains the integrated line intensities maps (files
ending in -area-cropped.fits) and the peak temperatures (files ending
in -tpeak-cropped.fits) of the Orion B molecular cloud in 18 molecular
tracers, used as features for the machine learning algorithms used in
the paper. Maps of two physical parameters NH2 and Tdust derived from
Hershel data and used as predictor are also included, you should refer
to Lombardi et al. (2014A&A...566A..45L 2014A&A...566A..45L) for the details of the
Herschel data reduction.
The molecular line is encoded in the string at the begining of the
filenames, see Table 1 for the corresponding frequencies.
Objects:
---------------------------------------------
RA (2000) DE Designation(s)
---------------------------------------------
05 41 43.0 -01 54 44 Ori B = NAME Ori B
---------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 79 18 Spectral properties of the observed lines
list.dat 146 38 List of fits files
fits/* . 38 Individual fits images
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See also:
https://www.iram.fr/~pety/ORION-B : ORION-B project Home Page
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Species Species
12- 18 A7 --- QNA Simplified quantum number
20- 61 A42 --- QN Complete quantum numbers
63- 72 F10.3 MHz Freq Frequency
74 I1 --- s Number of the IRAM-30m tuning setup the line
was observed with (see Sect. 2.1 for details)
76- 79 F4.2 K Noise Typical noise level in channels of 0.5km/s
measured on the cubes that were smoothed at
an angular resolution of 40"
--------------------------------------------------------------------------------
Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 22 I3 --- Nx Number of pixels along X-axis
24- 26 I3 --- Ny Number of pixels along Y-axis
28- 31 I4 Kibyte size Size of FITS file
33- 67 A35 --- FileName Name of FITS file, in subdirectory fits
69-146 A78 --- Title Title of the FITS file
--------------------------------------------------------------------------------
Acknowledgements:
Pierre Gratier, pierre.gratier(at)u-bordeaux.fr
(End) Patricia Vannier [CDS] 16-Dec-2020