J/A+A/659/A77 FEEDBACK from the NGC7538 HII region (Beuther+, 2022)
FEEDBACK from the NGC 7538 HII region.
Beuther H., Schneider N., Simon R., Suri S., Ossenkopf-Okada V.,
Kabanovic S., Roellig M., Guevara C., Tielens A.G.G.M., Sandell G.,
Buchbender C., Ricken O., Guesten R.
<Astron. Astrophys. 659, A77 (2022)>
=2022A&A...659A..77B 2022A&A...659A..77B (SIMBAD/NED BibCode)
ADC_Keywords: H II regions ; Infrared sources ; Carbon monoxide
Keywords: stars: formation - ISM: clouds - ISM: kinematics and dynamic -
ISM: bubbles - ISM: individual objects: NGC 7538 - ISM: HII regions
Abstract:
The interaction of expanding HII regions with their environmental
cloud is one of the central questions driving the SOFIA legacy program
FEEDBACK.
We want to understand the interaction of the prototypical NGC7538 HII
region with the neighboring molecular cloud hosting several active
star-forming regions.
Using the Stratospheric Observatory for Infrared Astronomy (SOFIA), we
mapped an area of ∼210'2 (∼125pc2) around NGC7538 in the
velocity-resolved ionized carbon fine-structure line [CII] at 1.9THz
(158um). Complementary observed atomic carbon [CI] at 492GHz and
high-J CO(8-7) data, as well as the archival near- and far-infrared,
cm continuum, CO(3-2), and HI data are folded into the analysis.
The ionized carbon [CII] data reveal rich morphological and kinematic
structures. While the overall morphology follows the general ionized
gas that is also visible in the radio continuum emission, the channel
maps show multiple bubble-like structures with sizes on the order of
∼80-100'' (∼1.0-1.28pc). While at least one of them may be an
individual feedback bubble driven by the main exciting sources of the
NGC7538 HII region (the O3 and O9 stars IRS6 and IRS5), the other
bubble-like morphologies may also be due to the intrinsically porous
structure of the HII region. An analysis of the expansion velocities
around 10km/s indicates that thermal expansion is not sufficient but
that wind-driving from the central O-stars is required. The region
exhibits a general velocity gradient across, but we also identify
several individual velocity components. The most blue-shifted [CII]
component has barely any molecular or atomic counterparts. At the
interface to the molecular cloud, we find a typical photon-dominated
region (PDR) with a bar-shape. Ionized C+, atomic C0 and molecular
carbon CO show a layered structure in this PDR. The carbon in the PDR
is dominated by its ionized C+ form with atomic C0 and molecular CO
masses of ∼0.45±0.1M☉ and ∼1.2±0.1M☉, respectively,
compared to the ionized carbon C+ in the range of 3.6-9.7M☉.
This bar-shaped PDR exhibits a velocity-gradient across, indicating
motions along the line of sight toward the observer.
Even if it is shown to be dominated by two nearby exciting sources
(IRS6 and IRS5), the NGC7538 HII region exhibits a diverse set of
substructures that interact with each other as well as with the
adjacent cloud. Compared to other recent [CII] observations of HII
regions (e.g., Orion Veil, RCW120, RCW49), the bubble-shape
morphologies revealed in [CII] emission that are indicative of
expanding shells are recurring structures of PDRs.
Description:
The region was mapped with the dual-frequency array heterodyne
receiver upGREAT2 in the velocity resolved [CII] fine-structure line
at 158um/1.9THz.
The [OI] 63um line was observed in parallel. Fast Fourier Transform
Spectrometers (FFTS) with 4GHz instantaneous bandwidth (Klein et al.
2012A&A...542L...3K 2012A&A...542L...3K) provided a nominal spectral resolution for the
[CII] line of 0.244MHz or 0.04km/s. The observations were done on
two consecutive days during Cycle 7, on December 12 and 13, 2019, with
an average Tsys single side-band (SSB) of 4486 and 4580K and an
average precipitable water vapor of 6.2 and 3.6um respectively per
day.
The CO(3-2) data were obtained with the James Clark Maxwell
Telescope (JCMT) as part of a large map of the NGC7538 region first
presented in Fallscheer et al. (2013ApJ...773..102F 2013ApJ...773..102F) and later in
Sandell et al. (2020ApJ...904..139S 2020ApJ...904..139S).
Objects:
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RA (2000) DE Designation(s)
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23 13 37 +61 30.0 NGC 7538 = = LBN 542
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
listimg.dat 106 4 List of fits images
img/* . 4 Individual fits images
listsp.dat 160 27 List of fits spectra
sp/* . 36 Individual spectra (fits and CLASS)
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See also:
J/A+A/543/A88 : NGC7538IRS1 and NGC7538S 1.36mm maps (Beuther+, 2012)
J/A+A/606/A52 : NGC7538-IRS1 THz water maser (Herpin+, 2017)
Byte-by-byte Description of file: listimg.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- 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- 63 A31 --- FileName Name of FITS file, in subdirectory img
65-106 A42 --- Title Title of the FITS file
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Byte-by-byte Description of file: listsp.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- 47 A23 "datime" Obs.date Observation date
49- 60 E12.6 Hz bFreq Lower value of frequency interval
62- 72 E11.6 Hz BFreq Upper value of frequency interval
74- 84 E11.6 Hz dFreq Frequency resolution
86- 87 I2 Kibyte size Size of FITS file
89-110 A22 --- FileName Name of FITS file, in subdirectory sp
112-141 A30 --- Title Title of the FITS file
143-160 A18 --- FileName2 Name of the CLASS file, in subdirectory sp
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Acknowledgements:
Henrik Beuther, beuther(at)mpia.de
(End) Patricia Vannier [CDS] 03-Feb-2022