Unveiling Galactic Structures with Astrometry using ODI

1. Galactic Structure and Near-field Cosmology via Astrometry with ODI Dana Casetti, Terry Girard, Bill van Altena - Yale • Orbits of MW: • • satellites • • globular clusters • • stars in tidal steams and overdensities • • stars in the thin, thick disk, and halo

2. Satellites -Spatial alignment of the traditional 11 dwarf sph. (Lynden-Bell 1976, 1982, Kunkel & Deemers 1976). -Newly found ultra-faint dwarfs follow this alignment (Metz et al. 2009). -Proper motions of 6 dwarf satellites indicate that their orbital angular momenta are aligned -> rotationally supported disk of satellites (Metz et al. 2008). Metz et al. 2009, 2008 Only 7 satellites have p.m. measured (with 0.04 to 0.25 mas/yr errors). HST and ground-based observations do not agree.

3. Satellites: current proper motions. How good are they? A case study: Fornax - 140 kpc Piatek et al. 2002 (before CTI correction) Dinescu et al. 2004  Piatek et al. 2006

4. Satellites - summary • The formation of the MW satellite system: is it consistent with CDM predictions? • Need to properly quantify: • the input of tides into mass estimates of dwarfs (missing satellite problem, nature of dwarfs) • spatial and associated kinematical alignments • Key observables: orbital eccentricities and angular momenta Add-on project - 9 dwarf galaxies; some need both epochs with ODI, and some only 2nd epoch with ODI (existing 1st-epoch material, OPTIC and plates).

5. Globular Clusters Clusters with very extended blue horizontal branches (EHBs) appear to have multiple main sequences, subgiant branches. NGC 2808: EHB-strong Piotto 2007 Castellani et al. 2006

6. Globular Clusters From 94 clusters with HB classification (Lee et al. 2007): - There are 26 EHB clusters that make up 53% of the total mass of the GC system. - 65% of the EHBs (58%, excluding 2 poor measurements*) have orbits measured. EHB clusters :17 Everything else: 29 with [Fe/H] < -1 7 with [Fe/H] > -1.0 (star symbols)

7. Tidal Streams/Overdensities (Sgr.) Sagittarius stream: measuring the LSR velocity LSR vel: Main survey: the 2h region Vel. difference => 0.3 mas/yr => need p.m. of ~0.1 mas/yr => @0.5mas/yr/star need ~30 stream stars To V ~ 20 in a 40x40 arcmin area: 10 RV members => for 9 sq. deg ~ 200 members. 180 km/s 220 km/s 260 km/s Sgr core Extensions Main: 2h region Law et al. 2005, Majewski et al. 2006

8. Tidal Streams/Overdensities The Monoceros/Anticenter stream: main survey region at R.A. ~ 8 or 9h, Dec = 0. 9h 8h Grillmair et al. 2006, 2008

9. Tidal Streams/Overdensities • Their origin and disruption history, the MW potential, the LSR velocity, the lumpiness of the MW halo • Need to properly quantify: • membership to a stream ( sky overlap between different streams) • 3D kinematics along large angular extensions of a stream • Key observables: proper motions, radial velocities, orbits Add-on project - Sgr stream, Monoceros stream, Virgo overdensity, possibly a few others. Fields separated by 5 deg in the equatorial stripe (58 fields ), the dec=+15deg stripe (8), and the dec=-15 deg stripe (13). Of 79 fields, 27 have 1st epoch plate material.

10. Observing Plan 5+3 dithered exposures of 5 min each in i and g per field => 45 min/field for 114 fields => in all ~ 11 nights to obtain single-epoch data.