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 Hirota et al. (2007) Orion KL D = 437 +/- 19 pc pi = 2.29 +/- 0.1 mas Orion nebula with Subaru
Perseus molecular cloud HIPPARCOS de Zeeuw +(1999) • NGC 1333 (Hirota+ 2007) • L1448C (Hirota+ 2011) c.f. IC 348 at 320 pc seeing depth ? 318+/-27 pc 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 Orbital motion on the sky ‐ plane (~10 yr) (~100 yr, including VERA/NRO etc)
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+ Honma+ Reid+ (2009) (2012) (2014) N src 18 52 103 8.4 8.05 8.34 R 0 (kpc) (+/- 0.6) (+/- 0.45) (+/- 0.16) 247 238 240 Θ 0 (km/s) (+/- 16) (+/- 14) (+/- 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 : VERA : CVN : KVN : JVN SHAO 65m Cost ‐ effective upgrade of VERA to achive better resolution and sensitivity
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 Stellar orbit in spiral potential Gas orbit in spiral potential (non ‐ closed) 20 (closed)
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 SMTO ALMA (NRAO/ESO/NAOJ) Pico Veleta Hawaii LMT 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
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