J/A+A/684/A212 Magnetic field in the Flame nebula (Beslic+, 2024)
The magnetic field in the Flame nebula.
Beslic I., Coude S., Lis D.C., Gerin M., Goldsmith P.F., Pety J., Roueff A.,
Demyk K., Dowell C.D., Einig L., Goicoechea J.R., Levrier F., Orkisz J.,
Peretto N., Santa-Maria M.G., Ysard N., Zakardjian A.
<Astron. Astrophys. 684, A212 (2024)>
=2024A&A...684A.212B 2024A&A...684A.212B (SIMBAD/NED BibCode)
ADC_Keywords: Molecular clouds ; Magnetic fields ; Interstellar medium ;
Radio lines
Keywords: galaxies: star formation - ISM: clouds - ISM: magnetic fields -
ISM: molecules
Abstract:
Star formation is essential in galaxy evolution and the cycling of
matter. The support of interstellar clouds against gravitational
collapse by magnetic (B-) fields has been proposed to explain the low
observed star formation efficiency in galaxies and the Milky Way.
Despite the Planck satellite providing a 5-15' all-sky map of the
B-field geometry in the diffuse interstellar medium, higher spatial
resolution observations are required to understand the transition from
diffuse gas to gravitationally unstable filaments. NGC 2024, the Flame
Nebula, in the nearby Orion B molecular cloud, contains a young,
expanding HII region and a dense filament that harbors embedded
protostellar objects. Therefore, NGC 2024 is an excellent opportunity
to study the role of B-fields in the formation, evolution, and
collapse of filaments, as well as the dynamics and effects of young
HII regions on the surrounding molecular gas. We combine new 154 and
216um dust polarization measurements carried out using the HAWC+
instrument aboard SOFIA with molecular line observations of
12CN(1-0) and HCO+(1-0) from the IRAM 30-meter telescope to
determine the B-field geometry and to estimate the plane of the sky
magnetic field strength across the NGC 2024. The HAWC+ observations
show an ordered B-field geometry in NGC 2024 that follows the
morphology of the expanding HII region and the direction of the main
filament. The derived plane of the sky B-field strength is moderate,
ranging from 30 to 80uG. The strongest B-field is found at the
northern- west edge of the HII region, characterized by the highest
gas densities and molecular line widths. In contrast, the weakest
field is found toward the filament in NGC 2024. The B-field has a
non-negligible influence on the gas stability at the edges of the
expanding HII shell (gas impacted by the stellar feedback) and the
filament (site of the current star formation).
Description:
Our work employs the dust polarization measurements acquired using
HAWC+ on SOFIA in September 2021 for program 09_0015 (PI: D. Lis).
Specifically, we observed NGC 2024 at 154um (Band D) and 214 um (Band
E) with HAWC+ in polarization mode on flights F779 (8 September 2021),
F780 (9 September 2021), F782 (11 September 2021), F783 (14 September
2021), and F784 (15 September 2021).
In our work, we make use of information of the 12CN(1-0) and HCO+
(1-0) emission from the ongoing IRAM-30m ORION-B Large Program (PIs:
M. Gerin & J. Pety, see Pety et al., 2017A&A...599A..98P 2017A&A...599A..98P).
We provide two data cubes of CN and HCO+ at 23 and 30 arcsecond
resolution with a channel width of 0.5km/s of NGC 2024. We also
provide SOFIA HAWC+ Band D and E polarization measurements.
Objects:
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RA (2000) DE Designation(s)
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05 41 43.00 -01 50 30.0 NGC 2024 = NGC 2024
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 32 5 Components of the 12CN(1-0),
from Milam et al., 2009ApJ...690..837M 2009ApJ...690..837M
table2.dat 58 4 Results from non-LTE RADEX modeling
table3.dat 51 4 Angle dispersion and magnetic field strengths
table4.dat 47 4 Estimated mass-to-flux ratio, Alfvenic Mach
number and plasma-beta
tabled1.dat 51 4 Results on the magnetic field strength from
histogram analysis
list.dat 128 4 List of fits files
fits/* . 4 Individual fits files
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 7 A7 --- Trans 12CN(1-0) HF transition
9- 18 F10.6 GHz Nurest [113.48/113.53] Rest frequency
20- 25 F6.2 km/s Veloff [-77.8/7.51] Relative offset
27- 32 F6.4 --- RI [0.01/0.34] Relative intensity
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 15 A15 --- Region Region in NGC 2024
17- 23 F7.4 deg RAdeg [85.34/85.48] Right Ascension (J2000)
25- 31 F7.4 deg DEdeg [-1.99/-1.75] Declination (J2000)
33- 37 F5.2 K Tkin [27.18/53.04] Kinetic temperature
39- 42 F4.2 km/s DeltaVCN [0.56/1.24] CN turbulent line width
44- 48 F5.2 10+3cm-3 nCN [2.27/13.37] CN number density
50- 53 F4.2 km/s DeltaVHCO+ [0.96/1.24] HCO+ turbulent line width
55- 58 F4.2 10+3cm-3 nHCO+ [2.31/5.39] HCO+ number density
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Byte-by-byte Description of file: table3.dat tabled1.dat
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Bytes Format Units Label Explanations
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1- 15 A15 --- Region Region in NGC 2024
17- 20 F4.2 deg Theta Mean angle dispersion from
sliding window for table3,
histogram analysis for tabled1
22- 25 F4.2 deg e_Theta Mean angle dispersion error
27- 29 I3 10-6G BdcfCN POS B using DCF and CN
31- 32 I2 10-6G e_BdcfCN POS B using DCF and CN error
34- 36 I3 10-6G BdcfHCO+ POS B using DCF and HCO+
38- 39 I2 10-6G e_BdcfHCO+ POS B using DCF and HCO+ error
41- 42 I2 10-6G BstCN POS B using ST and CN
44- 45 I2 10-6G e_BstCN POS B using ST and CN error
47- 48 I2 10-6G BstHCO+ POS B using ST and HCO+
50- 51 I2 10-6G e_BstHCO+ POS B using ST and HCO+ error
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 15 A15 --- Region Region in NGC 2024
17- 20 F4.2 --- muCN [0.09/2.5] Mass-to-flux ratio from BstCN
22- 25 F4.2 --- muHCO+ [0.09/1.61] Mass-to-flux ratio from BstHCO+
27- 30 F4.2 --- MaCN [1.42/1.91] Alfven Mach number from BstCN
32- 35 F4.2 --- MaHCO+ [1.21/2.03] Alfven Mach number from BstHCO+
37- 41 F5.3 --- betaCN [0.08/1.06] Plasma-beta parameter from BstCN
43- 47 F5.3 --- betaHCO+ [0.07/0.35] Plasma-beta parameter from BstHCO+
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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- 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 for the datacubes
32- 54 A23 "datime" Obs.date Observation date
56- 58 I3 km/s bVRAD ? Lower value of VRAD interval
for the datacubes
60- 63 F4.1 km/s BVRAD ? Upper value of VRAD interval
for the datacubes
65- 67 F3.1 km/s dVRAD ? VRAD resolution for the datacubes
69- 73 I5 Kibyte size Size of FITS file
75- 97 A23 --- FileName Name of FITS file, in subdirectory fits
99-128 A30 --- Title Title of the FITS file
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Acknowledgements:
Ivana Beslic, astro.beslijica(at)gmail.com
(End) Patricia Vannier [CDS] 23-Feb-2024