The Milky Way Disk and the LAMOST survey Jinliang HOU Shanghai Astronomical Observatory, CAS Workshop on Galactic Studies with the LAMOST Survey KIAA-PKU, Beijing, July 18-23, 2010

Contents ( 1 ) Basic components of The MW Galaxy ( 2 ) The Milky Way Disk (MWD) ▲ kinematics – disk formation ▲ chemical – star formation history ( 3 ) LAMOST Survey for the Milky Way Disk ▲ Basic idea of the disk survey ▲ Possible early sciences in disk survey

(1) Basic Components of the MW Galaxy dark halo stellar halo thin disk thick disk bulge We would like to understand how our Galaxy came to look like this. Figure From Ken Freeman

How disk forms and evolves?  the disk (thin) is the primary stellar component

 In what pattern stars move in the disk? kinematics of stars: clues to the merger or galaxies interacting (ex. Sgr dwarf ) Some important issues related to the formation and evolution of the disk (thin/thick) Ibata et al. 1994, 1995 Sgr was discovered as a velocity inhomogeneity

 How old are these stellar components? age dating of stars : an essential element in reconstructing galactic history Some important issues related to the formation and evolution of the disk (thin/thick) Nordstrom et al AMR: age great scatter

 What are their chemical abundances [Fe/H]? chemical evolution of the galaxy: an essential element in understanding the enrichment history of the galaxy, that is the star formation history. Some important issues related to the formation and evolution of the disk (thin/thick) Francios et al SNIa, SNII

The thin disk is the defining stellar component of disk galaxies. End product of the dissipation of most of the baryons, contains almost all of the baryonic angular momentum Understanding its formation is the most important goal of galaxy formation theory. (2) The Milky Way disk  Clues from Disk Kinematics  Clues from Chemical Properties

Clues from Disk Kinematics Observations: Velocity dispersions of nearby dwarf stars Velocity dispersions of stars increase with the stellar age.  search for the kinematic signature of thick disk

Edvardsson et al 1993; Quillen & Garnett 2001 Velocity dispersions of nearby F stars (about 289) old disk thick disk Disk heating saturates at 2-3 Gyr 2Gyr

No distinct jump in the velocity dispersion for the oldest stars Nordstrom et al U V W Sample about 2800 stars Disk heating continues after 2 Gyr

Clues from Angular Momentum Observations: 3 Dimensional Positions and Velocities of stars structures will separate in angular momentum space  search for the substructures in the disk

Stars within 1 kpc of the Sun, with Hipparcos proper motions Tidal streams separate in angular momentum – need 3D position and velocity through space. Helmi et al Substructures in the disk

Moving groups from SDSS/SEGUE stars within 5 kpc of the Sun. Significant velocity substructure in the Solar neighborhood. Smith et al. 2009

 The ancient star forming history lost in the dynamical identity, dispersed by phase- mixing (not heating)  Velocity-Age Relation not well constructed, more sample needed, age determinations  Angular momentum need 6-D parameters of stars, large sample needed History may be retained in the chemical identities: Abundance Pattern Limitations on the kinematics only

The detailed abundance pattern reflects the chemical evolution of the gas from which stars formed. Observations: Abundance Pattern Clues from Chemical Properties Observed properties in the Milky Way disk  MDF - Metallicity Distribution Function  AMR – Age-Metallicity Relation  Abundance Gradient along the disk  ……

Dwarf stars in the solar neighborhood  G–dwarf problem, closed box ruled out Observed evidences Metallicity Distribution Function (MDF) Nordstrom et a. 2004

MDF: Model vs. Observation Model: Gas infall in the early epoch of galaxy formation Inside-out: disk formation Yin et al. 2009

To understand the Milky Way disk, we need to survey the entire disk, not just in the solar neighborhood. Solar nearby Other disk places Anti-center Bulge region

Abundance gradient vs. age and position: Open Clusters Young Older Inner Outer Chen, Hou (2008) Overall: － dex/kpc

We need very large samples of stellar kinematics and abundances data ( both solar nearby and other locations in the Galactic disk ) (3) LAMOST Survey for Milky Way Disk in order to better understanding the formation and evolution of our Galaxy

LAMOST facts Aperture: ~4 m Field of view: 5 degree diameter Size of focal plane: 1.75 m Sky coverage: Dec>-10 d, 1.5 hours around meridian Wavelength range: 370 nm to 900 nm, R=1000/2000 Number of fibers: 4000, 16 spectrographs, 250 fibers each Spectra: >10,000 spectra/night ( > 2m / year) 2-3 gigabytes/night LAMOST: 4000 fibers in 20 deg 2 (200 fibers/deg 2.) SDSS/SEGUE:640 fibers in 7 deg 2 (90 fibers/deg 2.)

LEGUE LAMOST Experiment for Galactic Understanding and Evolution 1.Halo (LC Deng) 2.Disk 3.Galactic Anti-center (XW Liu)

LEGUE (1)Spheroid (|b|>20°) portion will survey at least 2.5 million objects at R=2000, with 90 minute exposures, during dark/grey time, reaching g 0 =20 with S/N=10. (2)Anticenter (|b|<30°, 150°<l<210°) portion will survey about 3 million objects at R=2000 with 40 minute exposures, during bright time (and some dark/grey time), reaching J=15.8 with S/N=20. (3) Disk (|b|<20°, 20°<l<230°) and will survey about 3 million objects at R=2000 and R=5000, with 10 and 30 minute exposures, respectively, during bright time, reaching g 0 =16 with S/N=20

Yanny et al SEGUE footprint

Basic Idea for the Disk Survey  In the region |b|<20°, 20°< l < 230°~ 8000deg 2 (but little data for l < 80°due to weather condition) ~ 6000 deg 2  Using all the bright times for disk survey  Try to be magnitude complete (R~16)  Target densities need to be lowered, so selection probability should be vary smoothly with color and/or magnitude  We need resolution about R=5000 shall be much better to have accurate radial velocity and metallicity, both alpha elements and iron.

Disk Survey – input Select bright stars (V<16) from GSC II, with positions from 2MASS and proper motions from UCAC3. Use de-reddened magnitudes for bright stars near the Galactic plane (?). Very important to have a homogeneous optical photometry catalogue for the disk |b| < 30 deg (can be combined with 2MASS) Galactic Anti-center: XUYI telescope doing very good photometry (Liu XW talk) If possible – extend to disk lower |b|.

Survey footprint (just for illustration), shown as an Aitoff projection in Galactic coordinates. The region with filled circles at low Galactic latitude will be surveyed with shorter, bright time exposures including R=2000 and M halo objects 3 M anticenter objects 3 M disk objects

Disk Survey – Possible Early Science projects  Star forming regions in the solar neighborhood (Wang HC etc. - PMO)  Regions with open clusters dominated (Chen Li etc. - SHAO)

SF Regions in the Solar Neighborhood - the Gould Belt Four SF regions: Per, Tau, Ori, Serp LAMOST FOV ~ 4 x 5 deg – 10,000 objects, emission lines 2-4 pointings

”OC dominated survey” – LOCS project Chen Li

A sample of plate field, one of the most crowded Open Clusters field ( 9 OCs ) NGC 2236 Collinder 97 NGC 2252 NGC 2244 NGC 2254 Collinder 111 Collinder 106 Collinder 104 Collinder 107 Yellow circle: rad =2.5d, 9 OCs covered, L=205d, B=-1.2d Density~2600/d 2 Calibration + science

Summary  We need to observe a large sample of disk stars to clarify some important problems in the disk  LAMOST is very efficient in observing the disk stars spectroscopy  Disk survey only using the bright time, not competitive against extra-galactic and halo survey  Optical photometry for disk |b|<30 is very helpful.

Thanks Comments are welcome

Press release, November 4, 2003 Blue – model Milky Way Pink – model planar stream Tidal Stream in the Plane of the Milky Way Sun Canis Major or Argo Navis Monoceros, stream in the Galactic plane, Galactic Anti-center Stellar Stream (GASS) If it’s within 30° of the Galactic plane, it is tentatively assigned to this structure TriAnd,TriAnd2 Explanations: (1)One or more pieces of tidal debris; could have puffed up, or have become the thick disk. (2)Disk warp or flare (3)Dark matter caustic deflects orbits into ring

2.5 M halo objects 3 M anticenter objects 3 M disk objects

Spectroscopic surveys of stars RAVE: I 25°, 1 M stars, in progress SEGUE: g 0 -10°, 400,000 stars, nearing completion APOGEE: H -10°,100,000 stars, infrared, in fabrication HERMES: V<14, R=30,000, 1.5 M stars, in fabrication WFMOS: in planning stages None of these surveys probe the Galactic plane. Except for possibly WFMOS, LEGUE: g 0 -10°, 7.5 M stars, expected