J/A+A/688/A171 Cloud matching in M33. I. (Keilmann+, 2024)
Molecular cloud matching in CO and dust in M33.
I. High-resolution hydrogen column density maps from Herschel.
Keilmann E., Buchbender C., Ossenkopf-Okada V., Schneider N., Kabanovic S.,
Stutzki J., Simon R., Riechers D., Tabatabaei F., Bigiel F.
<Astron. Astrophys. 688, A171 (2024)>
=2024A&A...688A.171K 2024A&A...688A.171K (SIMBAD/NED BibCode)
ADC_Keywords: Carbon monoxide ; Galaxies, IR ; Interstellar medium ;
Molecular clouds
Keywords: methods: analytical - dust, extinction - ISM: general -
ISM: structure - galaxies: ISM - Local Group
Abstract:
This study is aimed to contribute to a more comprehensive under-
standing of the molecular hydrogen distribution in the galaxy M33 by
introducing novel methods for generating high angular resolution
(18.2", equivalent to 75pc for a distance of 847kpc) column density
maps of molecular hydrogen (N(H2)). M33 is a local group galaxy that
has been observed with Herschel in the far-infrared (FIR) wavelength
range from 70 to 500 micron. Previous studies have presented total
hydrogen column density maps (N_H), using these FIR data (partly
combined with mid-IR maps), employing various methods. We first
performed a spectral energy distribution (SED) fit to the 160, 250,
350, and 500 micron continuum data obtain NH, using a technique
similar to one previously reported in the literature. We also use a
second method which involves translating only the 250 micron map into
a NH map at the same angular resolution of 18.2. An N(H2) map via
each method is then obtained by subtracting the HI component.
Distinguishing our study from previous ones, we adopt a more versatile
approach by considering a variable emissivity index, beta, and dust
absorption coefficient, kappa0. This choice enables us to construct
a kappa0 map, thereby enhancing the depth and accuracy of our
investigation of the hydrogen column density. We address the inherent
biases and challenges within both methods (which give similar results)
and compare them with existing maps available in the literature.
Moreover, we calculate a map of the carbon monoxide
CO(1-0)-to-molecular hydrogen (H2) conversion factor (Xco factor),
which shows a strong dispersion around an average value of
1.8*10201/(cm2.K.km/s) throughout the disk. We obtain column
density probability distribution functions (N-PDFs) from the NH,
N(H2), and N(HI) maps and discuss their shape, consisting of
several log-normal and power-law tail components.
Description:
The total hydrogen column density map was derived using Herschel flux
maps in the wavelength range from 160 to 500 micron and has a spatial
resolution of 18.2 arcsec.
The molecular hydrogen column density map has been produced
subtracting the HI component.
The kappa0 map is the dust absorption coefficient of the dust
opacity model derived using HI data and the Herschel 250 micron map
(SPIRE). The Xco conversion factor map has been derived using the
molecular hydrogen column density map and the IRAM 30m CO map.
Objects:
-----------------------------------------
RA (2000) DE Designation(s)
-----------------------------------------
01 33 50.89 +30 39 36.6 M33 = NGC 598
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 137 4 List of fits maps
fits/* . 4 Individual fits maps
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See also:
J/A+A/639/A61 : IR continuum, [CII] and [OI] maps of M33 (Kramer+, 2020)
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- 23 I4 --- Nx Number of pixels along X-axis
25- 28 I4 --- Ny Number of pixels along Y-axis
30- 34 I5 Kibyte size Size of FITS file
36- 67 A32 --- FileName Name of FITS file, in subdirectory fits
69-137 A69 --- Title Title of the FITS file
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Acknowledgements:
Eduard Keilmann, keilmann(at)ph1.uni-koeln.de
(End) Patricia Vannier [CDS] 15-May-2024