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Understanding our Galaxy: from the center to outskirts

Published online by Cambridge University Press:  01 October 2007

Z. Q. Shen ,
Y. Xu ,
J. L. Han  and
X. W. Zheng
Z. Q. Shen
Affiliation:
Shanghai Astronomical Observatory, Shanghai 200030, China email: [email protected]
Y. Xu
Affiliation:
Purple Mountain Observatory, Nanjing 210008, China email: [email protected]
J. L. Han
Affiliation:
National Astronomical Observatories, Beijing 100012, China email: [email protected]
X. W. Zheng
Affiliation:
Department of Astronomy, Nanjing University, Nanjing 210093, China email: [email protected]
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Abstract

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We describe the efforts to understand our Milky Way Galaxy, from its center to outskirts, including (1) the measurements of the intrinsic size of the galactic center compact radio source Sgr A*; (2) the determination of the distance from the Sun to the Perseus spiral arm; and (3) the revealing of large scale global magnetic fields of the Galaxy.

With high-resolution millimeter-VLBI observations, Shen et al. (2005) have measured the intrinsic size of the radio-emitting region of the galactic center compact radio source Sgr A* to be only 1 AU in diameter at 3.5 mm. When combined with the lower limit on the mass of Sgr A*, this provides strong evidence for Sgr A* being a super-massive black hole. Comparison with the intrinsic size detection at 7 mm indicates a frequency-dependent source size, posing a tight constraint on various theoretical models.

With VLBI phase referencing observations, Xu et al. (2006) have measured the trigonometric parallax of W3OH in the Perseus spiral arm with an accuracy of 10 μas and also its absolute velocity with an accuracy of 1 km s−1. This demonstrates the capability of probing the structure and kinematics of the Milky Way by determining distances to 12 GHz methanol (CH3OH) masers in star forming regions of distant spiral arms and Milky Way's outskirts.

With pulsar dispersion measures and rotation measures, Han et al. (2006) can directly measure the magnetic fields in a very large region of the Galactic disk. The results show that the large-scale magnetic fields are aligned with the spiral arms but reverse their directions many times from the most inner Norma arm to the outer Perseus arm.

Keywords

Galaxy: centerGalaxy: structureblack hole physicsmaserspulsars: generaltechniques: high angular resolutionastrometrystars: distancesstars: kinematicsISM: magnetic fieldsISM: structure
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 3 , Symposium S248: A Giant Step: from Milli- to Micro-arcsecond Astrometry , October 2007 , pp. 470 - 473
Copyright
Copyright © International Astronomical Union 2008

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