Galactic Structure and Near-field Cosmology Galactic Structure and Near-field Cosmology via Astrometry with ODI via Astrometry with ODI

Dana Casetti, Terry Girard, Bill van Altena - YaleDana Casetti, Terry Girard, Bill van Altena - Yale

Orbits of MW:Orbits of MW:

• • satellites satellites

• • globular clustersglobular clusters

• • stars in tidal steams and overdensitiesstars in tidal steams and overdensities

• • stars in the thin, thick disk, and halo stars in the thin, thick disk, and halo

Satellites Satellites

Metz et al. 2009, 2008

-Spatial alignment of the traditional 11 -Spatial alignment of the traditional 11 dwarf sph. (Lynden-Bell 1976, 1982, dwarf sph. (Lynden-Bell 1976, 1982, Kunkel & Deemers 1976).Kunkel & Deemers 1976).

-Newly found ultra-faint dwarfs follow -Newly found ultra-faint dwarfs follow this alignment (Metz et al. 2009).this alignment (Metz et al. 2009).

-Proper motions of 6 dwarf satellites -Proper motions of 6 dwarf satellites indicate that their orbital angular indicate that their orbital angular momenta are aligned -> rotationally momenta are aligned -> rotationally supported disk of satellites (Metz et al. supported disk of satellites (Metz et al. 2008).2008).

Only 7 satellites have p.m. measured (with 0.04 to 0.25 mas/yr errors). Only 7 satellites have p.m. measured (with 0.04 to 0.25 mas/yr errors). HST and ground-based observations do not agree.HST and ground-based observations do not agree.

Satellites: current proper motions. How good are they? Satellites: current proper motions. How good are they?

Piatek et al. 2002 (before CTI correction)

Dinescu et al. 2004

Piatek et al. 2006

A case study: Fornax - 140 kpcA case study: Fornax - 140 kpc

Satellites - summarySatellites - summary

•The formation of the MW satellite system: is it consistent with The formation of the MW satellite system: is it consistent with CDM CDM predictions?predictions?

•Need to properly quantify: Need to properly quantify:

-the input of tides into mass estimates of dwarfs (missing satellite the input of tides into mass estimates of dwarfs (missing satellite problem, nature of dwarfs)problem, nature of dwarfs)

-spatial and associated kinematical alignmentsspatial and associated kinematical alignments

•Key observables: orbital eccentricities and angular momentaKey observables: orbital eccentricities and angular momenta

Add-on project - 9 dwarf galaxies; some need both epochs with ODI, Add-on project - 9 dwarf galaxies; some need both epochs with ODI, and some only 2nd epoch with ODI (existing 1st-epoch material, and some only 2nd epoch with ODI (existing 1st-epoch material, OPTIC and plates).OPTIC and plates).

Globular Clusters Globular Clusters

Clusters with very extended blue horizontal branches (EHBs) Clusters with very extended blue horizontal branches (EHBs) appear to have multiple main sequences, subgiant branches.appear to have multiple main sequences, subgiant branches.

Piotto 2007

NGC 2808: EHB-strongNGC 2808: EHB-strong

Castellani et al. 2006

Globular Clusters Globular Clusters

From 94 clusters with HB classification (Lee et al. 2007):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 - There are 26 EHB clusters that make up 53% of the total mass of the GC system. GC system.

- 65% of the EHBs (58%, excluding 2 poor measurements- 65% of the EHBs (58%, excluding 2 poor measurements**) have orbits ) have orbits measured.measured.

EHB clusters :17EHB clusters :17

Everything else:Everything else:

29 with [Fe/H] < -129 with [Fe/H] < -1

7 with [Fe/H] > -1.0 7 with [Fe/H] > -1.0 (star symbols)(star symbols)

Tidal Streams/Overdensities (Sgr.) Tidal Streams/Overdensities (Sgr.)

260 km/s260 km/s

220 km/s220 km/s

180 km/s180 km/s

Sgr coreSgr core

LSR vel:LSR vel:

Main: 2Main: 2hh region regionExtensionsExtensions

Law et al. 2005, Majewski et al. 2006

Sagittarius stream: measuring the LSR velocitySagittarius stream: measuring the LSR velocity

Main survey:Main survey: the 2 the 2hh region region

Vel. difference => 0.3 mas/yr => Vel. difference => 0.3 mas/yr =>

need p.m. of ~0.1 mas/yr => need p.m. of ~0.1 mas/yr => @0.5mas/yr/star need ~30 stream stars@0.5mas/yr/star need ~30 stream stars

To V ~ 20 in a 40x40 arcmin area: 10 To V ~ 20 in a 40x40 arcmin area: 10 RV members => for 9 sq. deg ~ 200 RV members => for 9 sq. deg ~ 200 members.members.

Tidal Streams/Overdensities Tidal Streams/Overdensities

The Monoceros/Anticenter stream: The Monoceros/Anticenter stream:

main survey region at R.A. ~ 8 or 9main survey region at R.A. ~ 8 or 9hh, Dec = 0., Dec = 0.

Grillmair et al. 2006, 2008 88hh99hh

Tidal Streams/Overdensities Tidal Streams/Overdensities

•Their origin and disruption history, the MW potential, the LSR Their origin and disruption history, the MW potential, the LSR velocity, the lumpiness of the MW halovelocity, the lumpiness of the MW halo

•Need to properly quantify: Need to properly quantify:

-membership to a stream ( sky overlap between different streams)membership to a stream ( sky overlap between different streams)

-3D kinematics along large angular extensions of a stream3D kinematics along large angular extensions of a stream

•Key observables: proper motions, radial velocities, orbitsKey observables: proper motions, radial velocities, orbits

Add-on project - Sgr stream, Monoceros stream, Virgo overdensity, Add-on project - Sgr stream, Monoceros stream, Virgo overdensity, possibly a few others. Fields separated by 5 deg in the equatorial 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 (58 fields ), the dec=+15deg stripe (8), and the dec=-15 deg stripe (13). Of 79 fields, 27 have 1st epoch plate material.stripe (13). Of 79 fields, 27 have 1st epoch plate material.

Observing PlanObserving Plan

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