Maser Astrometry with VLBIand Galactic Structure

Mareki Honma

Mizusawa VLBI Observatory, NAOJ

Milky Way & VERA Ogasawara station

Back to 115 years ago …

ILO Mizusawa: now Mizusawa VLBI Observatory

ILO Carlo Forte: now Cagliari Astron. Observatory

Mizusawa

Carlo Forte

International Latitude Observatory (ILO), founded in 1899

both working on radio/VLBI

Galaxy-scale maser astrometry

GC distance D= 　 8 kpc, π= 　 125 μasrequires 10-μas accuracy

Galaxy scale astrometry : frontier in 21st century (e.g. GAIA)

•Relative VLBI astrometry certainly can measure this

δx ~ θ sep c δt / B δx ~ 10 μas for reasonable parameters

Sun Galaxy Center

Parallax

Arrays• VERA, VLBA, EVN. All in the Northern

hemisphere.

• LBA, only one in the South

Astrometry examples• Chibueze+(2014) NGC6334I(N) D ~ 1.27 kpc

• Min+(2014) R Aqr D ~ 218 pc

EVN astrometry

Rygl+(2012), astrometry of masers in Cygnus X complex

Galactic structure• Reid+(2009): Early results based on 18 sources

• R0 = 8.4 +/- 0.6 kpc, Θ0 = 247 +/- 16 km/s• 489 citations as of Oct 2014, good demonstration

of impacts of VLBI astrometry in this field

Galactic structure II: Honma+(2012)• 52 sources from VERA/VLBA/EVN

R0=8.05 +/- 0.45 kpc, Θ0=238 +/- 14 km/s

III. Reid+(2014)

• 103 sources

R0 = 8.34+/-0.16 kpc

Θ0 = 240 +/- 8 km/s

Galactic constants

Reid+(2009)

Honma+(2012)

Reid+(2014)

Nsrc 18 52 103

R0 (kpc) 8.4(+/- 0.6)

8.05(+/- 0.45)

8.34(+/- 0.16)

Θ0 　

(km/s)247

(+/- 16)238

(+/- 14)240

(+/- 8)

Galactic constants are already measured at a few percent level !

Most updated data as of Oct 2014

114 sources from VLBA/VERA/EVN

Tracing spiral arms

• Non-circular systematic motion has been detected

• Slow-rotation along the Perseus arm

Useful for testing the spiral arm scenario --- density wave or material wave ?

Broader impacts beyond astronomy• Direct Dark Matter search

Galactic rotation is the key to know the flux of dark matter particles on Earth.

• Gravitational wave

Until recently the largest uncertainty in the Hulse-Taylor pulsar was Galactic acceleration.

• Mass extinction on the Earth !!??

There is a claim that Sun’s spiral-arm passage

could have caused the global climate change (!?)

Concluding remarks

• VLBI can certainly do 10-uas level 　astrometry.

• Parallax and proper motions are obtained for more than 100 source.

• VLBI astrometry readily provides excellent results on the Galactic structure and beyond.

East Asian VLBI

Array extension to East Asia regions

Better sensitivity, better imaging capability -> better astrometry

SHAO 65m

KVN 21m x3

202x ~ ?

Mizusawa

Carlo Forte

1899~

Corresponding to ~7% SKA in collecting area !

Thank you for attention!

And let’s keep collaboration for next 100 years !