J/ApJ/850/195 RCW 57A NIR polarimetry and photometry (Eswaraiah+, 2017)
Understanding the links among the magnetic fields, filament, bipolar bubble, and
star formation in RCW 57A using NIR polarimetry.
Eswaraiah C., Lai S.-P., Chen W.-P., Pandey A.K., Tamura M., Maheswar G.,
Sharma S., Wang J.-W., Nishiyama S., Nakajima Y., Kwon J., Purcell R.,
Magalhaes A.M.
<Astrophys. J., 850, 195 (2017)>
=2017ApJ...850..195E 2017ApJ...850..195E
ADC_Keywords: H II regions; Polarization; Photometry, infrared
Keywords: dust, extinction ; ISM: magnetic fields ;
open clusters and associations: individual (RCW 57A) ; polarization
Abstract:
The influence of magnetic fields (B-fields) on the formation and
evolution of bipolar bubbles, due to the expanding ionization fronts
(I-fronts) driven by the HII regions that are formed and embedded in
filamentary molecular clouds, has not been well-studied yet. In
addition to the anisotropic expansion of I-fronts into a filament,
B-fields are expected to introduce an additional anisotropic pressure,
which might favor the expansion and propagation of I-fronts forming a
bipolar bubble. We present results based on near-infrared polarimetric
observations toward the central ∼8'x8' area of the star-forming region
RCW 57A, which hosts an HII region, a filament, and a bipolar bubble.
Polarization measurements of 178 reddened background stars, out of the
919 detected sources in the JHKs bands, reveal B-fields that thread
perpendicularly to the filament long axis. The B-fields exhibit an
hourglass morphology that closely follows the structure of the bipolar
bubble. The mean B-field strength, estimated using the
Chandrasekhar-Fermi method (CF method), is 91±8µG. B-field
pressure dominates over turbulent and thermal pressures. Thermal
pressure might act in the same orientation as the B-fields to
accelerate the expansion of those I-fronts. The observed morphological
correspondence among the B-fields, filament, and bipolar bubble
demonstrate that the B-fields are important to the cloud contraction
that formed the filament, to the gravitational collapse and star
formation in it, and in feedback processes. The last one includes the
formation and evolution of mid- infrared bubbles by means of B-field
supported propagation and expansion of I-fronts. These may shed light
on preexisting conditions favoring the formation of the massive
stellar cluster in RCW 57A.
Description:
Simultaneous observations in the J (1.25um), H (1.63um), and Ks
(2.14um) bands toward the central star-forming region of RCW 57A
(α=11:11:54.8, δ=-61:18:26 (J2000)) were carried out on
2007 May 6 using the imaging polarimeter SIRPOL mounted on the IR
Survey Facility (IRSF) 1.4m telescope at the South Africa Astronomical
Observatory (SAAO).
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
----------------------------------------------------------
11 11 54.8 -61 18 26 RCW 57A = NGC 3576
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 157 1074 The JHKs-band polarimetric and photometric
measurements of 1074 stars
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See also:
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
VII/233 : The 2MASS Extended sources (IPAC/UMass, 2003-2006)
J/ApJ/603/584 : Polarimetry toward Musca dark cloud (Pereyra+, 2004)
J/MNRAS/363/405 : SIMBA observations of cold cores (Hill+, 2005)
J/ApJ/649/759 : Bubbles in the galactic disk (Churchwell+, 2006)
J/A+A/450/253 : JHKL photometry of RCW57/NGC3576 (Maercker+, 2006)
J/ApJ/670/428 : Bubbles in the galactic disk. II. (Churchwell+, 2007)
J/ApJ/667/308 : Weak-line T Tauri in Spitzer c2d Survey. II. (Cieza+, 2007)
J/ApJ/657/884 : Spectroscopy of TTau & Herbig Ae/Be candidates (Lee+, 2007)
J/A+A/487/993 : MAMBO Mapping of c2d Clouds and Cores (Kauffmann+, 2008)
J/ApJS/184/18 : Spitzer survey of young stellar clusters (Gutermuth+, 2009)
J/ApJ/708/758 : Polarimetry of HH1-2 region (Kwon+, 2010)
J/MNRAS/403/1577 : Polarization towards open cluster NGC 6823 (Medhi+, 2010)
J/ApJ/741/21 : Polarization of stars in Taurus (Chapman+, 2011)
J/MNRAS/415/1202 : BVI photometry in W5E HII region (Chauhan+, 2011)
J/ApJ/741/35 : NIR photometry and polarization in NGC 2264 (Kwon+, 2011)
J/ApJ/751/138 : VRIJHK photometry of IRAS 09149-4743 region (Santos+, 2012)
J/MNRAS/424/2442 : Catalog of bubbles from Milky Way Project (Simpson+, 2012)
J/ApJ/783/1 : VRI and H polarization toward Sh 2-29 (Santos+, 2014)
J/ApJS/213/1 : The MSFRs Omnibus X-ray Catalog (MOXC) (Townsley+, 2014)
J/ApJS/220/17 : Wide-field NIR polarimetry of ρ Oph cloud (Kwon+, 2015)
J/MNRAS/462/2266 : RCW121 stars polarimetric study (Seron Navarrete+, 2016)
J/A+A/585/A117 : N131 bubble CO integrated intensity maps (Zhang+, 2016)
J/ApJ/836/199 : IRDC G028.23-00.19 NIR polarimetry analysis (Hoq+, 2017)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- Seq [1/1074] Internal star identifier
6 A1 --- f_Seq [*] *: missing IRSF/SIRPOL JHKs photometry;
data taken from 2MASS
8- 16 F9.5 deg RAdeg [167.8/168.2] Right Ascension (J2000)
18- 26 F9.5 deg DEdeg [-61.4/-61.2] Declination (J2000)
28- 32 F5.2 % PJ [0.2/23.1]? De-biased polarization in J band
34- 37 F4.2 % e_PJ [0.02/4.7]? Uncertainty in PJ
39- 43 F5.2 % PH [0.2/83.2]? De-biased polarization in H band
45- 49 F5.2 % e_PH [0.02/15.5]? Uncertainty in PH
51- 55 F5.2 % PKs [0.1/29.8]? De-biased polarization in Ks band
57- 60 F4.2 % e_PKs [0.02/7.5]? Uncertainty in PKs
62- 66 F5.1 deg thetaJ [0.8/180]? Polarization angle in J band
68- 71 F4.1 deg e_thetaJ [0.2/28.6]? Uncertainty in thetaJ (1)
73- 77 F5.1 deg thetaH [0.1/179.3]? Polarization angle in H band
79- 82 F4.1 deg e_thetaH [0.1/28.4]? Uncertainty in thetaH (1)
84- 88 F5.1 deg thetaKs [0.1/180]? Polarization angle in Ks band
90- 93 F4.1 deg e_thetaKs [0.1/28.4]? Uncertainty in thetaKs (1)
95-100 F6.3 mag Jmag [7.9/18.2]? The J band magnitude
102-106 F5.3 mag e_Jmag [0.004/0.4]? Uncertainty in Jmag
108-113 F6.3 mag Hmag [7.4/17]? The H band magnitude
115-119 F5.3 mag e_Hmag [0.003/0.5]? Uncertainty in Hmag
121-126 F6.3 mag Ksmag [7.2/16.5]? The Ks band magnitude
128-132 F5.3 mag e_Ksmag [0.002/0.3]? Uncertainty in Ksmag
134-157 A24 --- Class Classification (2)
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Note (1): The uncertainties in the polarization angles are not accounted for
overall angular calibration uncertainty of 3 degrees, which is a
systematic uncertainty which would affect all the measured
polarization angles.
Note (2): Classification as follows:
Class I = Class I stars (7 occurrences)
Class II = Class II stars (40 occurrences)
foreground = confirmed foreground star (121 stars).
background = confirmed background star or cluster member (189 stars).
foreground d = probable foreground star with PH>3%
(see section 3.3; 18 stars).
background d d = probable background star or cluster member with
excess polarization (see section 3.3; 52 stars).
background DD = probable background star or cluster member with
depolarization (see section 3.3; 11 stars).
NIR excess = stars with NIR excess ([J-H]<1.69[H-Ks]; 86 occurrences)
L-band excess = stars with L-band excesses (Maercker+ 2006, J/A+A/450/253 ;
38 occurrences)
Nebulous background = stars with nebulous background (46 occurrences)
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 03-Jul-2018