Studying MWG structure with VERA Mareki Honma Mizusawa VLBI Observatory, NAOJ Milky Way & VERA Ogasawara station
contents Galaxy scale astrometry with VERA + some more topics future prospect VERA and optical astrometry (GAIA/JASMIEN) Sgr A* observations 2
VLBI Astrometry Arrays VERA, VLBA, EVN, in the Northern hemisphere. LBA, only one in the South
VERA : VLBI Exploration of Radio Astrometry Construction completed in 2002 Regular parallax measurement from 2007 Mizusawa Iriki Ishigaki-jima Ogasawara Target sources : Galactic masers (H2O@22GHz, SiO@43GHz & CH3OH@6.7GHz) New aspect: dual-beam for phase-referencing
Galaxy scale maser astrometry Parallax Sun Galaxy Center Galaxy s center D= 8 kpc π= 125 μas Galaxy scale astrometry requires 10μas accuracy Galaxy scale astrometry = frontier in 21 st century (c.f., astrometric missions like GAIA, JASMINE)
VERA s result: distance to Orion KL Astrometry of H2O masers in Orion KL Hirota et al. (2007) D = 437 +/- 19 pc pi = 2.29 +/- 0.1 mas Orion nebula with Subaru
Perseus molecular cloud NGC 1333 (Hirota+ 2007) L1448C (Hirota+ 2011) c.f. IC 348 at 320 pc seeing depth? 318+/-27 pc HIPPARCOS de Zeeuw +(1999) Sun+(2006) Hirota+(2011)
AGB stars and PL relation AGB stars can be another standard candle Combination with AGB survey at opt/ir will enable us to trace Galaxy s structure. Mira s PL relation (Nakagawa+2014) 8
Another AGB star: R Aqr Symbiotic star: MIRA + compact star (WD?) Showing multi λ activity Astrometry provides distance and orbital information Min+(2015) D ~ 218 pc Radial velocity (~100 yr, including VERA/NRO etc) Orbital motion on the sky plane (~10 yr)
Galaxy s fundamental constants Combined with VLBA/EVN data, we have determined Galactic parameters using 52 sources. First Galactic parameter analysis by using more than 50 sources with VLBI astrometry (Honma et al. 2012)
Fundamental Constants R0 = 8.0 +/ 0.5 kpc (26100 +/ 1600 ly) (curent IAU standard 8.5 kpc 27700 ly) Theta_0 = 240 +/ 14 km/s (IAU standard 220 km/s) Larger rotation velocity 20% larger mass more dark matter (Honma et al. 2012)
Impact on Direct Dark Matter search Dark matter is though to be elementary particle, and there are on going experiments to directly detect DM (Xmass, Xenon 100, DAMA,...) To reveal the nature of DM particle, Galactic parameters (galactic rotation speed and DM density) are crucial. High precision VLBI astrometry can impact not only on Galactic astronomy but also on fundamental physics Xmass detector
More recent results Reid+(2014) 103 sources R0 = 8.34+/-0.16 kpc Θ0 = 240 +/- 8 km/s
Galactic constants Reid+ (2009) Honma+ (2012) Reid+ (2014) N src 18 52 103 R 0 (kpc) 8.4 (+/- 0.6) 8.05 (+/- 0.45) 8.34 (+/- 0.16) Θ 0 (km/s) 247 (+/- 16) 238 (+/- 14) 240 (+/- 8) Galactic constants are already measured at a few percent level!
Most updated data as of 2015 114 sources from VLBA/VERA/EVN (40 sources from VERA)
Spiral structure seen with VLBI astrometry Systematic deviation from circular rotation seen Lag behind the rotation + inward motion Comparison with theories will discriminate if the spiral arms are density wave or material wave (e.g., Sakai et al. 2015, submitted)
Future plan ~60 sources /yr, with a monitoring period of 1.5 2 yr 30 40 sources / yr 250 ~ 300 sources between 2015 2022
Future: East Asia VLBI Network (EAVN) 3C84 X band KaVA+JVN KaVA+JVN+CVN KVN 21m x3 TVN @Chiangmai : JVN : KVN : CVN : VERA Cost effective upgrade of VERA to achive better resolution and sensitivity SHAO 65m
What to do with Southern sky? The first parallax with LBA obtained Krishnan+(2015), G339.88 LBA + AuScope maser project (under discussion with Au, US, Europe & Japan) SKA future radio interferometer in 2020 s (in SA and Au) 19
Toward GAIA/JASMINE era Tracing both gaseous and stellar components are fundamental (gas: collisional, star: collision less) Also important is to compare with simulation Gas orbit in spiral potential (closed) Stellar orbit in spiral potential (non closed) 20
Sgr A* & Event Horizon Telescope (sub mm VLBI) Earth size VLBI operating at ~1mm or shorter To directly image the event horizon scale of black holes (Sgr A*) Green land CARMA ALMA (NRAO/ESO/NAOJ) Hawaii LMT SMTO Pico Veleta ALMA ALMA Phase-up Project is nearly done and ready. Will directly image the black hole shadow soon!?
Concluding remarks MWG Research is and will be wonderful! Collaboration between people with different background should be fundamental. radio / opt IR / X theory and simulation 22