The LAMOST Galactic Structure Working Group

1. LAMOST Experiment for Galactic Understanding and Evolution (LEGUE) The LAMOST Galactic Structure Working Group

2. Overview • Constraints and suitability of the LAMOST Telescope (2) Scientific justification for a Galactic survey of millions of stars (3) LEGUE Survey Strategy - a survey of 2.5 million spheroid stars, and 5 million disk stars

3. LAMOST facts Aperture: ~4 m Type: Schmidt, Alt-Az Focal length: 20m Relative aperture: f/5 Field of view: 5 degree diameter Size of focal plane: 1.75 m Sky coverage: Dec>-10 degrees, 1.5 hours around meridian Wavelength range: 370 nm to 900 nm, R=1000/2000 Number of fibers: 4000, 16 spectrographs with 250 fibers each >10,000 spectra per night (>2 million spectra/year), 2-3 gigabytes/night LAMOST: 4000 fibers in 20 square degrees (200 fibers/sq. deg.) UKST: 250 fibers in 28 square degrees (5 fibers/sq. deg.) SDSS: 640 fibers in 7 square degrees (90 fibers/sq. deg.)

4. LAMOST Constraints (1) Pointing - Light lost with distance from the meridian, declinations away from the optical axis of the telescope. (2) Fibers - must be uniformly distributed. (3) Weather – poor summer weather limits view of Galactic center.

5. Optical System MA is the Schmidt corrector, 5.72m x 4.40m, with 24 hexagonal plane sub-mirrors, each with 1.1m diagonal and 2.5 cm thickness. MB is the spherical primary, 6.67m x 6.05m, with a radius of curvature of 40m, 37 hexagonal spherical sub-mirrors, each with 1.1m diagonal and 7.4 cm thickness. Active control for aspheric shape of corrector (34 force actuators plus 3 mount points per submirror). Optimal shape changes with declination and hour angle. Active control for MB is just 3 mount points plus three actuators per submirror. Optical axis is 25° from horizontal. The focal plane has a radius of curvature of 20m.

6. LAMOST effective aperture as a function of declination

7. δ = 90° δ = -10° δ = 40° δ = -10° δ = 40° δ = 90° with atmosphere with atmosphere with atmosphere Spot sizes (80% of light) for central 3° field

8. 1.5 hours of tracking atmosphere included The plots above show the largest linear extent of the spot size containing 80% of the light, as a function of declination. Above declination of 60°, the field of view has been reduced from 5 degrees to 3 degrees in diameter, which is the reason for the apparent sudden reduction in spot size. The spot size at the edge of the field (5°) at δ=60° is the same as the spot size at δ=90° at the edge of the 3° field.

9. In one pointing, fewer than 20 LAMOST fibers can be placed inside the 10’ tidal radius of a globular cluster. Fewer than 50 LAMOST fibers can be placed within 20’ of the center of an open cluster. 3.15 arc minutes 4.7 arc minutes

10. The combination of site weather patterns and the need to look at the meridian puts strong constraints on the footprint of the LAMOST survey.

11. Potential Worries • Sky brightness • Scattered light • Dust/pollution • Temperature • Calibration But note that we already have a spectrum of similar quality to SDSS.

12. 6660 Å, bandwidth 480 Å

13. Sky brightness measured by BATC in dark photometric nights New CCD chip

14. Comments on sky brightness • BATC measurements avoid sky emissions (as of KPNO) therefore somewhat fainter than true values; • There is a scatter ~1mag in each night. The scatter has a weak dependence on direction.

16. The LAMOST spectrum (top) is comparable to the SEGUE spectrum (bottom) of the same star, with similar exposure time. The LAMOST sky subtraction and response function still need more work (note O2 line at 6880Å and 7600Å), but it can already achieve simlar S/N as SDSS.

17. Monoceros stream, Stream in the Galactic Plane, Galactic Anticenter Stellar Stream, Canis Major Stream, Argo Navis Stream Newberg et al. 2002 Vivas overdensity, or Virgo Stellar Stream Pal 5 Stellar Spheroid? Sagittarius Dwarf Tidal Stream

18. Belokurov et al. 2007 Hercules-Aquila Cloud Areal density of SDSS stars with 0.1<g-i<0.7 and 20<i<22.5 in Galactic coordinates. The color plot is an RGB composite with colors representing regions of the CMD as shown in the inset. The estimated distance to the cloud is 10-20 kpc.

19. Belokurov et al. 2007 Hercules-Aquila Cloud The large scale lumpiness of the stellar halo density has made it difficult to determine whether the outer parts of the Galaxy are axisymmetric (Xu, Deng & Hu 2006, 2007).

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

21. Summary of Spheroid Substructure Dwarf galaxy streams: (1) Sagittarius: Ibata et al. 2001a, Ibata et al. 2001b, Yanny et al. 2000 (2) Canis Major/Argo Navis? Monoceros (Newberg et al. 2002, Yanny et al. 2003), GASS (Frinchaboy et al. 2004), TriAnd (Majewski et al. 2004), TriAnd2 (Martin, Ibata & Irwin 2007), tributaries (Grillmair 2006) (3) ?? Orphan stream, Grillmair 2006, Belokurov et al. 2006 (4) ?? Virgo Stellar Stream, Vivas et al. 2001, Newberg et al. 2002, Zinn et al. 2004, Juric et al. 2005, Duffau et al. 2006, Newberg et al. 2007 (5) Styx, Grillmair 2009 (6) Cetus Polar Stream, Newberg, Yanny & Willett 2009 • Globular cluster streams: • Pal 5: Odenkirchen et al. 2003 • (2) GD-1 Grillmair & Dionatos 2006 • (3) NGC 5466: Grillmair & Johnson 2006 • (4-6) Acheron, Cocytos, and Lethe: • Grillmair 2009 Sino-Western collaborations on spheroid substructure: Xue, X.X., Rix, H.-W., Zhao, G., et al. 2008, ApJ, 684, 1143 Liu, C., Hu, J.Y. Newberg, H.J., & Zhao, Y.H. 2008, A&A, 477, 139 • Other: • Hercules-Aquila Cloud • Virgo Overdensity?

22. density selected sky density of SDSS spectra velocity selected velocity selected Sgr stream The Cetus Polar Stream

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

24. Smith et al. 2009 Klements et al. 2009 Moving groups found from 22,321 low metallicity ([Fe/H]<-0.5) SDSS/SEGUE stars within 2 kpc of the Sun, from SEGUE data (above). Moving groups from SDSS /Segue stars within 5 kpc of the Sun (right). Both analyses show significant velocity substructure in the Solar neighborhood.

25. GAIA Astrometric Satellite Magnitude limit: 20 1 billion Galactic stars Astrometry and radial velocities 2012-2020 Will only get precise radial velocities for stars brighter than 15th magnitude! With LAMOST, radial velocities can be obtained for the most interesting magnitude range of 15<V<20 Other large spectroscopic surveys of stars include RAVE (I<12), SDSS III/ SEGUE II (400,000 stars), APOGEE (infrared bulge), HERMES (V<14, in fabrication), and WFMOS (in planning stages).

26. Metal-poor stars t Metal-poor stars See also: Zhao, G., Butler, K., Gehren, T. 1998, A&A, 333, 219 Zhao, G. et al. 2006, ChJAA, 6, 265 MPIA, January 09 35/37 Norbert Christlieb

27. Number of contributing SNe Karlsson & Gustafsson (2005, IAU 238) Norbert Christlieb MPIA, January 09 MPIA, January 09 36/49

28. The halo metallicity distribution function HE 01075240 HE 13272326 HE 05574840 Norbert Christlieb MPIA, January 09 MPIA, January 09 37/49

29. EMP and HMP stars expected to be found Norbert Christlieb Heidelberg, April 2009 MPIA, January 09 38/48

30. Outstanding Problems • Describe the chemical evolution of the Galactic disk(s), and especially the first generation of stars. • What is the detailed structure of the Milky Way’s disk? How is it related to Monoceros/ Canis Major? • What does the dark matter potential of the Milky way look like? We have yet to successfully extract information about the Galactic potential from tidal streams. • How many stellar components are there in the Milky Way, and how do we describe them? • Galactic stellar data in all Galactic components is more complex than the models in structure and in dynamics. How do we compare them? • How many small galaxies merged to create the Milky Way, and when? • So far, advances have primarily come from reducing the data size to analyze very clean samples. How do we utilize all of the partial chemical, kinematic, and spatial information at the same time?

31. The Future of Galactic structure In the Milky Way, we have the opportunity to learn the whole history of one galaxy instead of comparing snapshots of many. It is only now that we have large surveys of the whole sky that we are able to comprehend the Milky Way as a whole. Unlike external galaxies, the picture we are building is in three dimensions of position and velocity, with much higher accuracy information for each star. Many surveys currently in progress will provide multi-color imaging of the sky. However, there is a great need for spectroscopic surveys of millions of stars. Twenty years ago, when the idea for the SDSS was born, large scale structures of galaxies had just been discovered. But there was structure on all scales of the largest surveys of the day. There was a pressing need for a larger spectroscopic survey. We are at the same place now in the study of the Milky Way. Spatial substructure and moving groups are found in every spectroscopic sample of spheroid stars that is well constrained in position and stellar type. It is guaranteed that a larger survey will reveal more substructure.

32. LAMOST Experiment for Galactic Understanding and Exploration (LEGUE) Science Goals • Discovery of spheroid substructure • Constrain Galactic potential • Disk/spheroid interface near Galactic anticenter • Search for extremely metal poor stars • Identify smooth component of spheroid • Structure of thin/thick disks, including chemical abundance and kinematics • Search for hypervelocity stars • Survey OB stars and 3D extinction in Galaxy • Globular cluster environments • Properties of open clusters • Complete census of young stellar objects across the Galactic plane

33. LAMOST Experiment for Galactic Understanding and Exploration (LEGUE) Survey Strategy (five years) Three subsets: • 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

34. Survey footprint, shown as an Aitoff projection in Galactic coordinates. The region with open circles will be observed at R=2000. The region with filled circles at low Galactic latitude will be surveyed with shorter, bright time exposures including R=5000 and R=2000. There is a small region that is part of both the anticenter and speroid surveys. The Celestial Equator is shown as a solid line. This illustrates the footprint, but not the exact placement of the survey plates.

35. Spheroid Survey Use SDSS, PanSTARRS, or SuperCOSMOS photometry, in that order, as available. A u-band survey is planned on the 2.3 meter Bok telescope of Arizona’s Steward Observatory; a camera is currently being fabricated. This survey can be used in conjunction with PanSTARRS or SuperCOSMOS • Select as many 0.1<(g-r)0<1.0, g0<17 stars as possible (a nearly complete sample where surveyed, except below b=40°, randomly sample to g0<18 • Randomly sample stars with (g-r)0<0.4 in the magnitude range 17<g0<20 If u-band photometry is available, we will deselect QSOs. The subsampling will be about one in two or one in three at higher latitudes.

36. Additional Criteria for spheroid • We will observe a sample of high proper motion stars with colors of M dwarfs in the magnitude range 16<g0<20 (local spheroid stars) • If u-band available, subsample K and M giant candidates with 17<g0<20 • Within 3 tidal radii of 40 selected GCs, we will use a completely different selection algorithm to select stars with color/magnitude of the GC stars • We will include bright (V<12) K and M stars from the Tycho-2 catalog, without regard to their proper motion.

37. Deng Licai, Liu Chao Simulation of LAMOST stellar spectral density in a five year survey, using an Aitoff projection in Galactic coordinates, using *all* of the clear weather. The result is 7.5 million halo objects, 5 million anticenter objects, and 3 million disk objects.

38. 7.5 M halo objects 5 M anticenter objects 3 M disk objects Deng Licai, Liu Chao Sample survey coverage in fibers per square degree, shown as an Aitoff projection in Equatorial coordinates (Galactic coordinates shown in blue). The survey simulation was done assuming all of the time for a five year period, including moon and likely weather conditions as a function of season.

39. 2.5 M halo objects 3 M anticenter objects 3 M disk objects Deng Licai, Liu Chao Sample survey coverage in fibers per square degree, shown as an Aitoff projection in Equatorial coordinates (Galactic coordinates shown in blue). The survey simulation was done assuming 1/3 of the dark/grey time and all of the bright time for a five year period, including moon and likely weather conditions as a function of season.

40. Deng Licai, Liu Chao Number of spectra winter summer Survey footprint covered Accumulation of data as a function of time assuming all of the dark and grey time for a five year survey. After the first year, we begin to re-observe parts of the sky that have already been covered.

41. Deng Licai, Liu Chao Number of spectra winter summer Survey footprint covered Accumulation of data as a function of time assuming 1/3 of the dark/grey time and all of the bright time for a five year survey. After the first year, we begin to re-observe parts of the sky that have already been covered.

42. 2.5 M halo objects 3 M anticenter objects 3 M disk objects LEGUE Science Working Group: DENG Licai, HOU Jinliang, NEWBERG Heidi, CHRISTLIEB Norbert, LIU Xiaowei, HAN Zhanwen, CHEN Yuqin, ZHU Zi., PAN Kaike, LEE Hsu-Tai, WANG Hongchi

43. Recent development • We learnt last week that the telescope can point 2 hour away from the meridian without loosing much efficiency; • The survey plan may change a lot. • The expected data size for LEGUE will not change. • Site quality decays quickly, if we want to do the survey, we should act fast!