J/MNRAS/514/3024 Magnetic field of L1495/B211 (Li+, 2022)
The role of magnetic fields in the stability and fragmentation of filamentary
molecular clouds: two case studies at OMC-3 and OMC-4.
Li P.-S., Lopez-Rodriguez E., Soam A., Klein R.I.
<Mon. Not. R. Astron. Soc. 514, 3024 (2022)>
=2022MNRAS.514.3024L 2022MNRAS.514.3024L (SIMBAD/NED BibCode)
ADC_Keywords: Molecular clouds ; Polarization
Keywords: methods: numerical - techniques: polarimetric - ISM: clouds -
ISM: kinematics and dynamics - ISM: magnetic fields - ISM: structure
Abstract:
We present the stability analysis of two regions, OMC-3 and OMC-4, in
the massive and long molecular cloud complex of Orion A. We obtained
214um HAWC+/SOFIA polarization data, and we make use of archival data
for the column density and C18O (1-0) emission line. We find clear
depolarization in both observed regions and that the polarization
fraction is anti-correlated with the column density and the
polarization-angle dispersion function. We find that the filamentary
cloud and dense clumps in OMC-3 are magnetically supercritical and
strongly subvirial. This region should be in the gravitational
collapse phase and is consistent with many young stellar objects
(YSOs) forming in the region. Our histogram of relative orientations
(HROs) analysis shows that the magnetic field is dynamically
sub-dominant in the dense gas structures of OMC-3. We present the
first polarization map of OMC-4. We find that the observed region is
generally magnetically subcritical except for an elongated dense core,
which could be a result of projection effect of a filamentary
structure aligned close to the line-of-sight. The relative large
velocity dispersion and the unusual positive shape parameters at high
column densities in the HROs analysis suggest that our viewing angle
may be close to axes of filamentary substructures in OMC-4. The
dominating strong magnetic field in OMC-4 is unfavorable for star
formation and is consistent with much fewer YSOs than in OMC-3.
Description:
FITS file of the HAWC+ observations at 214 microns with an angular
resolution of 18.2 arcseconds (beam size) and a pixel scale of 3.7
arcsecond.
Objects:
-----------------------------------------
RA (2000) DE Designation(s)
-----------------------------------------
05 35 20.0 -05 01 00 OMC-3 = OMC 3
05 36 06 -05 35.7 OMC-4 = OMC 4
-----------------------------------------
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
list.dat 105 2 List of fits files
fits/* . 2 Individual fits files
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Byte-by-byte Description of file: list.dat
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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- 50 A23 "datime" Obs.date Observation date
52- 54 I3 Kibyte size Size of FITS file
56- 65 A10 --- FileName Name of FITS file, in subdirectory fits
67-105 A39 --- Title Title of the FITS file
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Description of file:
HDUs Description of file: omc-3.fits and omc-4.fits
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HDUs Ext.Name Type Units Explanations
--------------------------------------------------------------------------------
0 STOKES I img Jy/px Stokes I (total intensity)
1 ERROR I img Jy/px Error in Stokes I
2 STOKES Q img Jy/px Stokes Q
3 ERROR Q img Jy/px Error in Stokes Q
4 STOKES U img Jy/px Stokes U
5 ERROR U img Jy/px Error in Stokes U
6 IMAGE MASK img - Weighted number of input pixels
combined into output pixels
7 PERCENT POL img % Polarization precent
8 DEBIASED PERCENT POL img % Debiased polarization percent
9 ERROR PERCENT POL img % Error in polarization percent
10 POL ANGLE img deg. Polarization angle in sky
coordinates (E-vector)
11 ROTATED POL ANGLE img deg. Polarization angle rotated by
90 deg. (B-field)
12 ERROR POL ANGLE img deg. Error in polarization angle
13 POL FLUX img Jy/px Polarized intensity
14 ERROR POL FLUX img Jy/px Error in polarized intensity
15 DEBIASED POL FLUX img Jy/px Debiased polarized intensity
16 MERGED DATA tab - Detector info from all merged
images in cube
17 POL DATA tab - Polarization data for each
pixel (1)
18 FINAL POL DATA tab - Subset of POL DATA with
quality cuts (2)
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Note (1): POL DATA is a table representation of the degree, polarization,
and debiased polarization maps in extensions 7-12 for every pixel in
both x,y and ra,dec coordinates. (see next table)
Note (2): FINAL POL DATA is a quality cut of POL DATA for all pixels with
I/sigma_I ≥ 200, p/sigma_p ≥ 3, and p < 50%.
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HDU: POL DATA from omc-3.fits and omc-4.fits
--------------------------------------------------------------------------------
Column name Units Explanations
--------------------------------------------------------------------------------
Pixel X pixels pixel coordinates
Pixel Y pixels pixel coordinates
Right Ascension deg Right ascension (J2000.0)
Declination deg Declination (J2000.0)
Debiased Percent Pol % Polarization percent,
extension 7 (PERCENT POL)
Err. Percent Pol % Debiased polarization percent,
extension 8 (DEBIASED PERCENT POL)
Theta deg Polarization angle in sky coordinates,
extension 10 (POL ANGLE)
Rotated Theta deg Polarization angle rotated by 90 deg.,
extension 11 (ROTATED POL ANGLE)
Err. Theta deg Error in theta,
extension 12 (ERROR POL ANGLE)
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Acknowledgements:
Pak Shing Li, psli(at)berkeley.edu
(End) Pak Shing Li [UC Berkeley], Patricia Vannier [CDS] 02-Jun-2022