J/A+A/659/A36 Self-absorption in RCW 120 (Kabanovic+, 2022)
Self-absorption in [C II], 12CO, and H I in RCW 120.
Building up a geometrical and physical model of the region.
Kabanovic S., Schneider N., Ossenkopf-Okada V., Falasca F., Guesten R.,
Stutzki J., Simon R., Buchbender C., Anderson L., Bonne L., Guevara C.,
Higgins R., Koribalski B., Luisi M., Mertens M., Okada Y., Roellig M.,
Seifried D., Tiwari M., Wyrowski F., Zavagno A., Tielens A.G.G.M.
<Astron. Astrophys. 659, A36 (2022)>
=2022A&A...659A..36K 2022A&A...659A..36K (SIMBAD/NED BibCode)
ADC_Keywords: H II regions ; Molecular clouds ; Carbon monoxide
Keywords: ISM: bubbles - ISM: clouds - H II regions - ISM: molecules -
photon-dominated region (PDR) - methods: data analysis
Abstract:
Revealing the 3D dynamics of HII region bubbles and their associated
molecular clouds and HI envelopes is important for developing an
understanding of the longstanding problem as to how stellar feedback
affects the density structure and kinematics of the different phases
of the interstellar medium.
We employed observations of the HII region RCW 120 in the [CII] 158um
line, observed within the Stratospheric Observatory for Infrared
Astronomy (SOFIA) legacy program FEEDBACK, and in the 12CO and
13CO (3-2) lines, obtained with the Atacama Pathfinder Experiment
(APEX) to derive the physical properties of the gas in the
photodissociation region (PDR) and in the molecular cloud. We used
high angular resolution HI data from the Southern Galactic Plane
Survey to quantify the physical properties of the cold atomic gas
through HI self-absorption. The high spectral resolution of the
heterodyne observations turns out to be essential in order to analyze
the physical conditions, geometry, and overall structure of the
sources. Two types of radiative transfer models were used to fit the
observed [CII] and CO spectra. A line profile analysis with the 1D
non-LTE radiative transfer code SimLine proves that the CO emission
cannot stem from a spherically symmetric molecular cloud
configuration. With a two-layer multicomponent model, we then
quantified the amount of warm background and cold foreground gas. To
fully exploit the spectral-spatial information in the CO spectra, a
Gaussian mixture model was introduced that allows for grouping spectra
into clusters with similar properties.
The CO emission arises mostly from a limb-brightened, warm molecular
ring, or more specifically a torus when extrapolated in 3D. There is a
deficit of CO emission along the line-of-sight toward the center of
the HII region which indicates that the HII region is associated with
a flattened molecular cloud. Self-absorption in the CO line may hide
signatures of infalling and expanding molecular gas. The [CII]
emission arises from an expanding [CII] bubble and from the PDRs in
the ring/torus. A significant part of [CII] emission is absorbed in a
cool (∼60-100K), low-density (<500cm-3) atomic foreground layer
with a thickness of a few parsec.
We propose that the RCW 120 HII region formed in a flattened,
filamentary, or sheet-like, molecular cloud and is now bursting out of
its parental cloud. The compressed surrounding molecular layer formed
a torus around the spherically expanding HII bubble. This scenario can
possibly be generalized for other HII bubbles and would explain the
observed "flat" structure of molecular clouds associated with HII
bubbles. We suggest that the [CII] absorption observed in many
star-forming regions is at least partly caused by low-density, cool,
HI-envelopes surrounding the molecular clouds.
Description:
Spectral data cubes of 12CO (3-2) (at 345.796GHz) and 13CO (3-2)
(at 330.588GHz),using the LAsMA array on APEX (Atacama Pathfinder
Experiment) telescope. All spectra are calibrated in main beam
brightness temperatures with a main-beam efficiency of 0.68 at
345.8GHz.
The observed spectra are convolved with a Gaussian function to 20''
resolution on a grid with a pixel size of 5''.
The spectra are resampled to a velocity resolution of 1 km/s.
Objects:
-----------------------------------------
RA (2000) DE Designation(s)
-----------------------------------------
17 12 24.0 -38 28 00 RCW 120 = Sh 2-3
-----------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
list.dat 151 2 List of fits datacubes
fits/* . 2 Individual fits datacubes
--------------------------------------------------------------------------------
See also:
J/A+A/472/835 : JHKs and GLIMPSE photometry of RCW 120 (Zavagno+, 2007)
J/A+A/496/177 : JHKs and GLIMPSE photometry of RCW 120 (Deharveng+, 2009)
J/A+A/616/L10 : RCW120 fragmentation at 0.01pc scale (Figueira+, 2018)
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- 30 I3 --- Nz Number of slices
32- 34 I3 km/s bVRAD [-50] Lower value od VRAD interval
36- 37 I2 km/s BVRAD [50] Upper value od VRAD interval
39 I1 km/s dVRAD [1] VRAD resolution
41- 45 I5 Kibyte size Size of FITS file
47-119 A73 --- FileName Name of FITS file, in subdirectory fits
121-151 A31 --- Title Title of the FITS file
--------------------------------------------------------------------------------
History:
From Slawa Kabanovic, kabanovic(at)ph1.uni-koeln.de
Acknowledgements:
APEX, the Atacama Pathfinder Experiment is a collaboration between
the Max-Planck-Institut fur Radioastronomie, Onsala Space
Observatory (OSO), and the European Southern Observatory (ESO)
(End) Slawa Kabanovic [Universitat zu Koln], Patricia Vannier [CDS] 27-Dec-2021