The Milky Way Disk and the LAMOST

survey

Jinliang HOUShanghai Astronomical Observatory, CAS

Workshop on Galactic Studies with the LAMOST SurveyKIAA-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. 2004

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. 2004

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 dispersionsof nearby F stars(about 289)

old disk

thickdisk

Disk heating saturates at 2-3 Gyr2Gyr

No distinct jump in the velocity dispersion for the oldest stars

Nordstrom et al. 2004

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. 1999

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.

ObservationModel: 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- 0.037

Older-0.057Inner

- 0.077

Outer- 0.050

Chen, Hou (2008)

Overall: － 0.048 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 factsAperture : ~4 mField of view : 5 degree diameterSize of focal plane : 1.75 mSky coverage : Dec>-10 d, 1.5 hours around meridianWavelength range : 370 nm to 900 nm, R=1000/2000Number of fibers : 4000, 16 spectrographs, 250 fibers eachSpectra : >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.)

LEGUELAMOST Experiment for Galactic

Understanding and Evolution

1.Halo (LC Deng)2.Disk3.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 g0=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 g0=16 with S/N=20

Yanny et al. 2009

SEGUE footprint

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.

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 5000

2.5 M halo objects3 M anticenter objects3 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 deg2

4000 – 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 2236Collinder 97NGC 2252 NGC 2244

NGC 2254 Collinder 111Collinder 106 Collinder 104 Collinder 107

Yellow circle: rad =2 .5d, 9 OCs covered, L=205d, B=-1.2d

Density~2600/d2

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