Magnetic Field Configuration at the Galactic Center Investigated by Wide Field Near-Infrared Polarimetry

Shogo Nishiyama(1,2), Motohide Tamura(2), Hirofumi Hatano(3), Saori Kanai(3), Mikio Kurita(3), Shuji Sato(3), Noriyuki Matsunaga(1), Tetsuya Nagata(1), Takahiro Nagayama(1), Ryo Kandori(2), Yasushi Nakajima(2), Nobuhiko Kusakabe(4), Yaeko Sato(4), James H. Hough(5), Koji Sugitani(6), and Haruyuki Okuda(7)

Paper: ApJ, accepted

Weblink: http://www.kusastro.kyoto-u.ac.jp/~shogo/papers/08NishiyamaMagFGC.pdf

EPrint Server: 0809.3089

We present a polarimetric map of a 20' * 20' area toward the Galactic center. The polarization of point sources has been measured in the J, H, and K_S bands using the near-infrared polarimetric camera SIRPOL on the 1.4 m telescope IRSF. One percent or better accuracy of polarization degree is achieved for sources with J<14.5, H<13.5, and K_S<12.0. Comparing the Stokes parameters between high extinction stars and relatively low extinction ones, we have obtained a polarization originating from magnetically aligned dust grains at the central region of our Galaxy of at most 1-2 kpc. The distribution of the position angles shows a peak at 20 DEGr, nearly parallel to the Galactic plane, suggesting a toroidal magnetic configuration. The derived direction of the magnetic field is in good agreement with that obtained from far-infrared/submillimeter observations, which detect polarized thermal emission from dust in the molecular clouds at the Galactic center. Our results show that by subtracting foreground components, near-infrared polarimetry allows investigation of the magnetic field structure at the Galactic center.