J/ApJ/897/90 Polarization measurements of S201 with JCMT (Eswaraiah+, 2020)
Unveiling the Importance of Magnetic Fields in the Evolution of Dense Clumps
Formed at the Waist of Bipolar H.
Eswaraiah C., Li Di, Samal M.R., Wang J.-W., Ma Y., Lai S.-P., Zavagno A.,
Ching T.-C., Liu T., Pattle K., Ward-Thompson D., Pandey A.K., Ojha D.K.
<Astrophys. J., 897, 90 (2020)>
=2020ApJ...897...90E 2020ApJ...897...90E
ADC_Keywords: Interstellar medium; H II regions; Magnetic fields; Polarization;
Optical
Keywords: Interstellar magnetic fields ; Magnetic fields ; H II regions ;
Submillimeter astronomy ; Star formation ; Dust continuum emission ;
Stellar feedback
Abstract:
We present the properties of magnetic fields (B fields) in two clumps
(clump 1 and clump 2), located at the waist of the bipolar HII region
Sh2-201, based on James Clerk Maxwell Telescope SCUBA-2/POL-2
observations of 850µm polarized dust emission. We find that B
fields in the direction of the clumps are bent and compressed, showing
bow-like morphologies, which we attribute to the feedback effect of
the HII region on the surface of the clumps. Using the modified
Davis-Chandrasekhar-Fermi method, we estimate B-field strengths of 266
and 65µG for clump 1 and clump 2, respectively. From virial
analyses and critical mass ratio estimates, we argue that clump 1 is
gravitationally bound and could be undergoing collapse, whereas clump
2 is unbound and stable. We hypothesize that the interplay of the
thermal pressure imparted by the HII region, the B-field morphologies,
and the various internal pressures of the clumps (such as magnetic,
turbulent, and gas thermal pressures) has the following consequences:
(a) formation of clumps at the waist of the HII region; (b)
progressive compression and enhancement of the B fields in the clumps;
(c) stronger B fields that will shield the clumps from erosion by the
HII region and cause pressure equilibrium between the clumps and the
HII region, thereby allowing expanding ionization fronts to blow away
from the filament ridge, forming bipolar HII regions; and (d) stronger
B fields and turbulence that will be able to stabilize the clumps. A
study of a larger sample of bipolar HII regions would help to
determine whether our hypotheses are widely applicable.
Description:
Dust continuum polarization observations have been conducted using the
POL-2 polarimeter installed on the SCUBA-2 camera (hereafter
SCUBAPOL2) at the James Clerk Maxwell Telescope (JCMT), a 15m
single-dish submillimeter observatory located on the summit of
Maunakea in Hawaii, USA. POL-2 observations of the S201 region
(project code: M17BP041; PI: Eswaraiah Chakali) were carried out on
2017 November 18 using the POL-2 DAISY mapping mode. Three sets of
observations were acquired under JCMT Band 1 weather conditions,
during which the atmospheric optical depth at 225GHz, τ225, was
0.03. Each set was observed for 30 minutes, resulting in a total
integration time of ∼1.5hr.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 76 62 Polarization measurements of S201 based on JCMT
SCUBAPOL2 observations at 850microns, along with
the celestial coordinates of the pixels
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See also:
VIII/58 : A Survey of Radio H II Regions in the Northern Sky (Lockman+, 1989)
J/ApJ/688/1142 : Star formation in W5: Spitzer observations (Koenig+, 2008)
J/ApJS/181/321 : Properties of Spitzer c2d dark clouds (Evans+, 2009)
J/ApJ/716/893 : Polarisation at 850mu{m} in OMC-2 and OMC-3 (Poidevin+, 2010)
J/ApJ/738/27 : Galactic HII regions RRL and continuum data (Balser+, 2011)
J/ApJ/741/21 : Polarization of stars in Taurus (Chapman+, 2011)
J/ApJS/213/13 : 1.3mm polarization maps star-forming cores & SFRs (Hull+, 2014)
J/ApJ/783/1 : VRI and H polarization toward Sh 2-29 (Santos+, 2014)
J/ApJ/838/80 : JHK polarimetry of stars behind bubble N4 (Chen+, 2017)
J/ApJ/850/195 : RCW 57A NIR polarimetry and photometry (Eswaraiah+, 2017)
J/ApJ/849/157 : Polarimetry obs. toward IC5146 background stars (Wang+, 2017)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 9 F9.6 deg RAdeg [45.74/45.96] Right Ascension (J2000)
11- 19 F9.6 deg DEdeg [60.44/60.54] Declination (J2000)
21- 24 F4.1 % Pol [1.9/25.2] Debiased degree of polarization
26- 28 F3.1 % e_Pol [0.1/5.6] Uncertainty in Pol
30- 32 I3 deg PA [4/177] Polarization angle (θ)
34- 35 I2 deg e_PA [1/20] Uncertainty in PA
37- 42 F6.1 mJy/beam I [16.2/1300.7] Intensity
44- 47 F4.1 mJy/beam e_I [0.4/13.4] Uncertainty in I
49- 53 F5.1 % Q [-21.4/17.5] Final Stokes Q parameter
55- 57 F3.1 % e_Q [0.3/7.0] Uncertainty in Q
59- 63 F5.1 % U [-13.7/28.2] Final Stokes U parameter
65- 67 F3.1 % e_U [0.1/4.2] Uncertainty in U
69- 72 F4.1 mJy/beam PI [2.0/30.8] Polarized intensity
74- 76 F3.1 mJy/beam e_PI [0.7/5.1] Uncertainty in PI
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History:
From electronic version of the journal
(End) Prepared by [AAS], Coralie Fix [CDS], 28-Sep-2021