The Milky Way Disk and the LAMOST survey

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

2. 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

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

4. How disk forms and evolves? • thedisk (thin) is the primary stellar component

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

6. Some important issues related to the formation and evolution of the disk (thin/thick) • How old are these stellar components? • age dating of stars : an essential element in reconstructing galactic history AMR: age great scatter Nordstrom et al. 2004

7. Some important issues related to the formation and evolution of the disk (thin/thick) • 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. SNIa, SNII Francios et al. 2004

8. (2) The Milky Way disk 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. • Clues from Disk Kinematics • Clues from Chemical Properties

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

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

11. No distinct jump in the velocity dispersion for the oldest stars U V W Nordstrom et al. 2004 Sample about 2800 stars Disk heatingcontinues after 2 Gyr

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

13. Stars within 1 kpc of the Sun, with Hipparcos proper motions Helmi et al. 1999 Substructures in the disk Tidal streams separate in angular momentum – need 3D position and velocity through space.

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

15. Limitations on the kinematics only • 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

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

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

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

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

20. Abundance gradient vs. age and position: Open Clusters Young - 0.037 Older -0.057 Inner - 0.077 Outer - 0.050 Overall: －0.048 dex/kpc Chen, Hou (2008)

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

22. 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 deg2 (200 fibers/deg2.) SDSS/SEGUE:640 fibers in 7 deg2 (90 fibers/deg2.)

23. LEGUELAMOST Experiment for Galactic Understanding and Evolution • Halo (LC Deng) • Disk • Galactic Anti-center (XW Liu)

24. LEGUE • Spheroid (|b|>20°) portion will survey at least 2.5 million objects at R=2000, with 90 minute exposures, during dark/grey time, reaching g0=20 with S/N=10. • 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 g0=16 with S/N=20

25. SEGUE footprint Yanny et al. 2009

26. Basic Idea for the Disk Survey • In the region |b|<20°, 20°< l < 230°~ 8000deg2 (but little data for l < 80°due to weather condition) ~ 6000 deg2 • 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 2000. R=5000 shall be much better to have accurate radial velocity and metallicity, both alpha elements and iron.

27. 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|.

28. 2.5 M halo objects 3 M anticenter objects 3 M disk objects 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 5000

29. 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)

30. SF Regions in the Solar Neighborhood- the Gould Belt • Four SF regions: Per, Tau, Ori, Serp • LAMOST FOV ~ 4 x 5 deg2 • 4000 – 10,000 objects, emission lines • 2-4 pointings

31. ”OC dominated survey” – LOCS project Chen Li

32. A sample of plate field, one of the most crowded Open Clusters field ( 9 OCs ) Yellow circle: rad =2 .5d, 9 OCs covered, L=205d, B=-1.2d NGC 2254 Collinder 111 Collinder 106 Collinder 104 Collinder 107 NGC 2236 Collinder 97 NGC 2252 NGC 2244 Density~2600/d2 Calibration + science

33. 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.

34. ThanksComments are welcome