Oh, Chungsik The university of Tokyo, Mizusawa VERA observatory

1. Study of the Galactic rotation curve with VERA Oh, Chungsik The university of Tokyo, Mizusawa VERA observatory

2. Overview • Previous studies of the Galactic rotation curve. • Source selection. • Measurements of distance and proper motion of three massive star forming regions. • Constraint of the Galactic rotation curve. • Detailed structure of the Galactic rotation curve.

3. Intro : Previous studies of the Galactic rotation curve • The Galactic rotation curve tracemass distribution of the Galaxy. - bulge - disk - dark matter : flat profile • HI & CO line observation - constrain the flat rotation curve in outer region of the Galaxy. • Only 1-dimensional (los) obser- vation  large uncertainty and Θ0 dependence of the rotation curve in the outer region. Sofue et al. (2008) Honma & Sofue (1997)

4. Recent : VLBI observation with phase referencing method. (VERA, VLBA ・・・) - Honma et al. (2007) : distance measurement with high accuracy. using 3-dimensional observation, estimate the Galactic rotation velocity.  flat rotation curve with small error.

5. Source selection： From the VERA H2O maser Survey • Survey : maser & reference source 158 pairs(2004~2006) - detected maser : 50 - reference : 53  19 pair are detected in both beam at the same time • From 19-pairs of maser-reference source - massive star forming region - previous study with multi-frequency - molecular outflow  three star forming regions are selected IRAS 06058+2138, AFGL 2789, IRAS 19213+1723

6. <IRAS 06058+2138> • Massive YSO、the brightest object in IR cluster • Galactic Coordinate : 188.95 +0.89 (Perseus arm) • distance :3.5 kpc (Moffat et al. 1979), 1.5 kpc (Tofani et al. 1995), 2 kpc (Klein et al. 2005, Bik et al. 2006).　 <IRAS 19213+1723> • Massive YSO • Galactic Coordinate : 52.1 + 1.04 • distance : 4.1kpc or 10.5 kpc (Sridharan et al. 2002, Zhang et al. 2005). <AFGL 2789> • Young O7e type within a polarized optical nebula(Cohen 1977) • Herbig Ae/Be type star with dense circumstellar disc (Goodrich 1986, Hamann & Persson 1989) • Galactic Coordinate : 94.60 –1.80 • Distance : 3.5 kpc (Humphreys et al. 1976, Goodrich 1986) 6 kpc (Cohen 1977) (Perseus arm)

7. Observations <IRAS 06058+2138> • Epoch ：DOY 118, 321, 351 in 2006 DOY019, 053, 272, 306, 351 in 2007 DOY34, 99, 186 in 2008 • Station ：　VERA（Mizusawa, Iriki, Ogasawara, Ishigaki-jima) • Frequency : 22GHz (H2O maser emission line) • Velocity resolution ：0.21km/s (bandwidth:8MHz, 512channel） • Objects

8. <IRAS 19213+1723> • Epoch ：DOY293, 326, 355 in 2007 • DOY 40, 81, 110, 152, 185, 214 in 2008 • Station ：　VERA（Mizusawa, Iriki, Ogasawara, Ishigaki-jima) • Velocity resolution ：0.21km/s (bandwidth:8MHz, 512channel） • Objects <AFGL 2789> • Epoch ：DOY83, 112, 151, 248, 318, 351 in 2007 DOY 21, 53, 102, 146 in 2008 • Station ：　VERA（Mizusawa, Iriki, Ogasawara, Ishigaki-jima) • Velocity resolution ：0.42km/s (bandwidth:16MHz, 512channel） • Objects

9. Result-IRAS 06058+2138 1. Spectrum & map • Spectrum : Mizusawa-Iriki baseline at DOY 351 in 2007. • Maser were detected in MM1 and MM2.

10. 2. Annual parallax & proper motion Distance  F: blue, H: pink, K: sky-blue, L: green

11. Result-IRAS 19213+1723 1. Spectrum & map • Spectrum : Mizusawa-Iriki baseline at DOY 293 in 2007. • Masers are concentrated in compact region less than 1 mas.

12. 2. Annual parallax & proper motion Distance  A: blue, B: pink, C: sky-blue, D: green

13. Result - AFGL 2789 1. Spectrum & map • Spectrum : Mizusawa-Iriki baseline at DOY 318 in 2007

14. 2. Annual parallax & proper motion Distance  A: pink, G: blue, H: green

15. Discussions 1. The Galactic rotation curve • Proper motion of maser features and systemic velocity  3-dimensional velocity components. • Constrain the Galactic rotation from 3-dimensional velocity components

16. Assume Θ0 = 200km/s, R0= 8 kpc, combining with S269 (Honma et al. 2007).  flat rotation curve in the region of 6.4 kpc≤ R ≤ 13 kpc. • Not depend on Θ0 with 3-dimensional velocity components.

17. Discussions 2. dip-profile • From HI & CO line observation, a dip profile from flat rotation curve is seen.(∼8.5 < R <11 kpc）。 • VLBI observation with phase referencing method also confirm the dip profile. 1) another gravitational structure except disk and dark matter? 　 - massive ring of amplitude as large as 0.3 to 0.4 times the disk density with the density peak at radius 11 kpc. (Sofue et al. 2008)。 2) From systematic motion of objects in Perseus arm,these objects may trace peculiar motion of Perseus arm itself.

18. Discussions 3. Peculiar motion toward the Galactic Center • Three objects + previous results ( four massive star forming regions with VLBA;Xu et al. 2006, Brunthaler et al. 2008 )  all objects are moving toward the Galactic Center. - Local motion in the Galactic plane. 　　　A : trace peculiar motion of the Perseus arm itself. B : near to central bar of the Galaxy, and moving toward G.C. by gravit ational effect of the central bar. - Possibility that LSR system is moving against the G.C.  LSR value from Hipparcos is not correct？

19. Summary • The first VLBI observations with phase referencing method have performed toward three massive star forming regions. • Distance to these sources (IRAS 06058+2138, IRAS 19213+1723, AFGL 2789)were measured with high accuracy. • From 3-dimensional velocity components of maser features, flat rotation curve is constrained. • From a dip-profile, existence of ring-like local disk region or peculiar motion of the Perseus arm itself are suggested. • Peculiar motion toward the G.C., local motion of objects in the Galactic plane (peculiar motion of the Perseus arm, gravitation effect of central bar) or motion of the LSR system itself are suggested.