Proceedings of the International Astronomical Union

Contributed Papers

Mass distribution of the Galaxy with VERA

Nobuyuki Sakaia1, Mareki Honmaa1a2, Hiroyuki Nakanishia3, Hirofumi Sakanouea3, Tomoharu Kurayamaa3 and VERA project members

a1 The Graduate University for Advanced Studies (Sokendai), Mitaka, Tokyo 181-8588, Japan

a2 Mizusawa VLBI Observatory, NAOJ, Mitaka, Tokyo 181-8588

a3 Faculty of Science, Kagoshima University, 1-21-35 Korimoto, Kagoshima, Kagoshima 890-0065 email: nobuyuki.sakai@nao.ac.jp

Abstract

We aim to reveal the mass distribution of the Galaxy based on a precise rotation curve constructed using VERA observations. We have been observing Galactic H2O masers with VERA. We here report one of the results of VERA for IRAS 05168+3634. The parallax is 0.532 ± 0.053 mas which corresponds to a distance of 1.88+0.21 −0.17 kpc, and the proper motions are (μαcosδ, μδ) = (0.23 ± 1.07, −3.14 ± 0.28) mas yr−1. The distance is significantly smaller than the previous distance estimate of 6 kpc based on a kinematic distance. This drastic change places the source in the Perseus arm rather than in the Outer arm. Combination of the distance and the proper motions with the systemic velocity provides a rotation velocity of 227+9 −11 km s−1 at the source assuming Θ0 = 240 km s−1. The result is marginally slower than the rotation velocity at LSR with ~ 1−σ significance, but consistent with previous VLBI results for six sources in the Perseus arm. We also show the averaged disk peculiar motion over the seven sources in the Perseus arm as (U mean, V mean) = (11 ± 3, −17 ± 3) km s−1. It suggests that the seven sources in the Perseus arm are systematically moving toward the Galactic center, and lag behind the Galactic rotation with more than 3-σ significance.

Keywords

  • astrometry — ISM: individual (IRAS 05168+3634) — techniques: interferometric — VERA