Mapping our Milky Way with Methanol Masers

Collaborator:

M. J. Reid (CFA, US) , K. M. Menten (MPIR, Germany)

A. Brunthaler (MPIR, Germany), L. Moscadelli (Italy)

Y. Xu (PMO, China), B. Zhang (NJU, China)

M. Sato (VERA), M. Honma (VERA), T. Hirota (VERA)

K. Hachsuka (SHAO, China), Y. K. Choi (MPIR, Germany)

G. A. Moellenbrock (NRAO, US), A. Bartkiewicz (Poland)

A. Nakagawa(Japan), Y. Asaki (Japan)

Xingwu Zheng

Astronomy Department,Nanjing University,China

outline

• progress of the project

• preliminary results

• Further work

Radio instruments of mapping the Galactic structure:VLBA (Very large Baseline Arry)VERA (VLBI Exploration Radio Astrometry)

VLBAArray beam Astrometry accuracy

VERAArray beam Astrometry accuracy

Distance measurement 10 kpc (parallax 0.1 mas)

0.5θ / SNR 5μas

/ 1cm / 8000km 0.25masD

/ 1cm / 2300km 0.87masD

0.5θ / SNR μas

Milky Way Parallaxes

W3OH:

= 0.512 mas

+/- 0.010 mas

Xu, Reid, Zheng & Menten (2006)

Milky Way ParallaxesHonma et al. (2007)

S269:

= 0.189 mas

+/- 0.016 mas

Milky Way ParallaxesHachisuka et al. (2009)

S269:

= 0.189 mas

+/- 0.016 mas

WB89-437:

= 0.167 mas

+/- 0.006 mas

Orion Nebular Cluster Parallax

D = 414 +/- 7 pc

Menten, Reid, Forbrich & Brunthaler (2007)

S Per -34 0.399+/-0.014 -0.38 -1.54 -34 9

S Car 2.33+/-0.13 -1.56 -5.16 34.7 10

Methanol maser parallax measurementswith VLBA

First phase result:

project from 2004 to 2008

CH3OH, SiO and H2O maser parallax with VLBA and VERA

The model Thin disk disk rotation speed

R

0 0( ) ( )d

R R RdR

0

0R

frame system: Cartesian Galactic coordinate

1 1 1, ,HelioD D U V W v ,v ,v（ ） （ ）

LSR Heliov v( sin cos )cos sinStd Std Std

Helio LSR V l U l b W b v v

1

1

1

U

V G N N S

W

Helio

v

v

v

1

0 1

0sin

cos

Hs U

HVs

U U U

VVV

＋ ＋

dataModel values

Least-squarses Fitting

2 2

1( )

N

i iid m

0( , , , , )R R D l b

2.3km/s

14.7km/ss

s

U

V

1 12.3kms kpcd

dR

0

0

8.4kpc

254km/s

R

00d

ordR

0d

dR

Average motion:

Best fitting:

Discrepancy: kinematic distance? ? pecular motion?

0 0,R

The Milky Way may have more mass

0 0

0 0

8.4, 254)1.3

8.5, 220)gal

gal

M R

M R

（（

20

0galM

GR

Total dynamical mass of the Milky Way

1 12.3kms kpcd

dR

Need more data

2.3km/s

14.7km/ss

s

U

V

Dust lanes?Shocks?

Second phase: 8 methanol sources data available until May 2009Third phase: 6 H2O sources data available until the end of 2009

More 10 SiO & H2Osources with VERA

summary

• Measured ~20 CH3OH, H2O & SiO maser sources parallax and proper motion

• Have very interesting preliminary results of galactic rotation and important parameters

• Model need more data

• Need southern sky data

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