J/A+A/636/A16 M43, Horsehead, MonR2, M17SW [CII]158um spectra (Guevara+, 2020)
[CII] 158 um self-absorption and optical depth effects.
Guevara C., Stutzki J., Ossenkopf-Okada V., Simon R., Perez-Beaupuits J.P.,
Beuther H., Bihr S., Higgins R., Graf U., Guesten R.
<Astron. Astrophys. 636, A16 (2020)>
=2020A&A...636A..16G 2020A&A...636A..16G (SIMBAD/NED BibCode)
ADC_Keywords: Interstellar medium ; Molecular clouds ; Radio lines
Keywords: submillimeter: ISM - photon-dominated region - ISM: atoms -
ISM: clouds - dust, extinction
Abstract:
The [CII] 158um FIR fine-structure line is one of the most important
cooling lines of the star-forming ISM. It is used as a tracer of star
formation efficiency in external galaxies and to study feedback
effects in parental clouds. High spectral resolution observations have
shown complex structures in the line profiles of the [CII] emission.
To determine whether the complex profiles observed in [12CII] are
due to individual velocity components along the line-of-sight or due
to self-absorption, one has to compare the [12CII] and isotopic
[13CII] line profiles.
Deep integrations with the SOFIA/upGREAT 7-pixel array receiver in the
sources M43, Horsehead PDR, Monoceros R2 and M17 SW allow to detect
with high S/N the optically thin [13CII] and simultaneously the
[12CII] emission lines. We first derive the [12CII] optical depth and
the [CII] column density from a single component model. However, the
complex line profiles observed require a double layer model with an
emitting background and an absorbing foreground. A multi-component
velocity fit allows to derive the physical conditions of the [CII]
gas: column density and excitation temperature.
We find moderate to high [12CII] optical depths in all four sources,
and self-absorption of [12CII] in Mon R2 and M17 SW. The high column
density of the warm background emission corresponds to an equivalent
Av of up to 41mag. The foreground absorption requires substantial
column densities of cold and dense [CII] gas, with an equivalent Av
ranging up to about 13mag.
The column density of the warm background material requires multiple
PDR surfaces stacked along the line of sight and in velocity. The
substantial column density of dense and cold foreground [CII] gas
detected in absorption cannot be explained with any known scenario and
we can only speculate about its origin.
Description:
Each fits file contains the collection of single pointing spectra of
[12CII] and [13CII]. The data is located in the hdul[1], each
element of the fit contains a single spectrum with its individual
information explained in TTYPE in the header. The spectrum is always
located in the last position of TTYPE as SPECTRUM in Kelvin. From the
header, MAXIS1 represents the total number of channels, CRPIX1 the
reference channel, VELO-LSR the velocity of the reference channel and
DELTAV the velocity resolution, RESTFREQ the frequency of the
reference channel and CDELT1 the frequency resolution.
Objects:
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RA (2000) DE Designation(s)
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05 35 31. -05 16.2 M43 = NGC 1982
18 20 47. -16 10.3 M17 = NGC 6618
05 40 59.0 -02 27 30 Horsehead = Name Horsehead Nebula
06 07 46.6 -06 22 59 Mon R2 = NAME Monoceros R2
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 172 4 List of fits tables with spectra
fits/* . 4 Individual fits tables with spectra
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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- 24 I5 --- Nx Number of pixels along X-axis
26 I1 --- Ny Number of pointings in the fits table
28- 50 A23 "datime" Obs.date Observation date
52- 59 F8.5 GHz bFreq Lower value of frequency interval
61- 67 F7.5 GHz BFreq Upper value of frequency interval
69- 77 F9.4 GHz RestFreq Rest frequency
79- 85 I7 Hz dFreq Frequency resolution
87- 89 I3 Kibyte size Size of FITS file
91-104 A14 --- FileName Name of FITS file, in subdirectory fits
106-172 A67 --- Title Title of the FITS file
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Acknowledgements:
Cristian Guevara, guevara(at)ph1.uni-koeln.de
(End) Patricia Vannier [CDS] 06-Feb-2020