J/ApJS/213/22 NIR polarimetry in the Central Molecular Zone (Yoshikawa+, 2014)
Young stellar object search toward the boundary of the Central Molecular Zone
with near-infrared polarimetry.
Yoshikawa T., Nishiyama S., Tamura M., Kwon J., Nagata T.
<Astrophys. J. Suppl. Ser., 213, 22 (2014)>
=2014ApJS..213...22Y 2014ApJS..213...22Y
ADC_Keywords: Polarization ; Milky Way ; YSOs ; Infrared sources
Keywords: Galaxy: center; polarization; stars: formation;
stars: pre-main sequence
Abstract:
We have carried out near-infrared polarimetry toward the boundary of
the Central Molecular Zone, in the field of (-1.°4≲l≲-0.°3
and 1.°0≲l≲2.°9,|b|≲0.°1), using the near-infrared
polarimetric camera SIRPOL on the 1.4m Infrared Survey Facility
telescope. We have selected 112 intrinsically polarized sources on the
basis of the estimate of interstellar polarization on Stokes Q/I-U/I
planes. The selected sources are brighter than KS=14.5mag and have
polarimetric uncertainty δP<1%. Ten of these distinctive
polarized sources are fit well with spectral energy distributions of
young stellar objects when using the photometry in the archive of the
Spitzer Space Telescope mid-infrared data. However, many sources have
spectral energy distributions of normal stars suffering from heavy
interstellar extinction; these might be stars behind dark clouds. Due
to the small number of distinctive polarized sources and candidates of
young stellar objects, we cannot judge if they are declining in number
outside the Central Molecular Zone. Many massive candidates for young
stellar objects in the literature have only small intrinsic
polarization. This might suggest that their masses are 4-15M☉,
whose intrinsic polarization has been expected to be small.
Description:
We conducted near-infrared (NIR) polarimetric observations of the
Central Molecular Zone (CMZ) with the SIRPOL camera attached to the
1.4m telescope IRSF (Infrared Survey Facility). This enables
simultaneous observations in the J (central wavelength
λJ=1.25um), H (λH=1.63um), and Ks
(λKs=2.14um) bands. The image scale of the arrays is
0.45"/pixel, yielding a field of view of 460"x460". From 2010 to 2012,
we observed 35 fields toward the boundary of the CMZ (See Figures 1-3).
We obtain the data of point sources at 3.6um, 4.5um, 5.8um, 8.0um
(Ramirez et al. 2008, Cat. II/295), and 24um (Hinz et al. 2009,
Cat. J/ApJS/181/227) from the Spitzer archive, and we merge the
mid-infrared data with our data matching within radii of 1" for 3.6um,
4.5um, 5.8um, and 8.0um, and 3" for 24um.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 79 112 Distinctive polarized sources
table3.dat 37 10 Properties of YSO candidates
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See also:
II/319 : UKIDSS-DR9 LAS, GCS and DXS Surveys (Lawrence+ 2012)
II/316 : UKIDSS-DR6 Galactic Plane Survey (Lucas+ 2012)
II/295 : Spitzer IRAC survey of the galactic center (Ramirez+, 2008)
J/A+A/563/A68 : CH3OH and H2O Galactic center masers (Chambers+, 2014)
J/ApJ/736/133 : Spitzer-IRS study of massive YSOs in GC (An+, 2011)
J/ApJS/181/227 : Catalog of 24um sources toward Galactic Center (Hinz+, 2009)
J/ApJ/702/178 : YSOs in the central 400pc of the Galaxy (Yusef-Zadeh+, 2009)
J/ApJ/697/1741 : Warped disks of YSOs in Galactic center (Bartko+, 2009)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq [1/112] Running sequence number
5- 12 F8.5 deg GLON [-1.45/2.9] Galactic longitude
14- 21 F8.5 deg GLAT [-0.07/0.15] Galactic latitude
23- 27 F5.2 mag Ksmag [9.5/14.5] Ks-band magnitude
29- 35 F7.4 --- Q/I [-0.2/0.2] Relative Stokes parameter Q/I
37- 42 F6.4 --- e_Q/I [0.0008/0.02] Q/I uncertainty
44- 50 F7.4 --- U/I [-0.2/0.2] Relative Stokes parameter U/I
52- 57 F6.4 --- e_U/I [0.0006/0.05] U/I uncertainty
59- 63 F5.2 % Pol [2.3/20] Degree of polarization
65- 68 F4.2 % e_Pol [0.06/4] Pol uncertainty
70- 74 F5.1 deg theta [0.7/180] Polarisation position angle θ
76- 79 F4.1 deg e_theta [0.4/21] theta uncertainty
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq [10/112] Identification number
5- 8 F4.2 mag H-Ks [2/4.1]? H-Ks color index
10- 13 F4.2 mag [3.6/4.5] [0.4/1.5]? IRAC (3.6-4.5) micron band color index
15- 18 F4.2 mag [5.8/8] [0.1/1]? IRAC (5.8-8.0) micron band color index
20- 22 A3 --- Class YSO class (1)
24- 29 A6 --- SED SED class (2)
31 A1 --- Pol Polarization type (3)
33- 37 F5.2 mag <DH-Ks> [-0.5/2.5]? Difference of observed H-KS colors
between distinctive polarized sources and the
surrounding sources (<Δ(H-KS)>) (4)
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Note (1): YSO classification in a [3.6]-[4.5] vs. [5.8]-[8.0] color-color
diagram. I, II, and III represent class I, II, and III YSOs.
Note (2): "Normal" means that only a photosphere component can explain the SED
of the source with fitting method of Robitaille et al.
(2007ApJS..169..328R 2007ApJS..169..328R). In contrast, "YSO" means that a disk or/and
envelope component is necessary.
Note (3): "a" and "b" mean panels (a) and (b) in Figure 16, respectively.
Note (4): This is represented by <(H-Ks)pol-(H-Ks)sur>, where
(H-Ks)pol is the H-Ks color of a distinctive polarized source, and
(H-Ks)sur is the H-Ks color of the surrounding sources. The positive
value means that the distinctive polarized source is redder than the
surrounding sources.
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History:
From electronic version of the journal
(End) Emmanuelle Perret [CDS] 04-Sep-2014