Mario Juric Institute for Advanced Study, Princeton

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1 Mapping Galactic density, metallicity and kinematics. Mario Juric Institute for Advanced Study, Princeton with Zeljko Ivezic, Nick Bond, Branimir Sesar, Robert Lupton and the SDSS Collaboration

2 Dissecting the Milky Way Program :: Goals 1. Directly measure the distribution of stellar number density, kinematics, and metallicity in a representative volume of the Galaxy. 2. Use the distributions to learn about [Gg]alaxy formation, evolution, interactions with environment, and the distribution of dark matter.

3 Mapping the Milky Way with S DS S Input: Data Reduction: S DS S photometry: ~1 5 0 M ugriz observations of stars, deg2, ~5 0 M stars >2 0 0 x larger area than pre-s DS S samples Keeping it simple and clean: Model-free mapping first, modeling second Metallicity: ug,gr + calibration from S DS S spectra Distances: ( u) gri + photometric parallax relation ( r<2 1.5 ) P roper Motions / Velocities: S DS S +P OS S, S DS S +S DS S Output: Distribution of stars in (X,Y,Z,Mr,[Fe/H],Y ly b) space

4 Visualizing the Hypercube R Z Y X Y Z R X

5 Juric et al. (2008) Dissecting the Milky Way: Density

6 Density Maps: D < 3 kpc ( Late K, M stars) Right: X -Y maps of number density distribution at Z=+/ and +/ pc for 1 < r-i < 1.1 stars ( ~M1 M2 ) Face-on view of the Galaxy Bottom: Density contours around the axis of symmetry

7 Density Maps: D > 3 kpc ( F, G, early K) Right: X -Y maps of number density distribution at Z=5, 4, 1 2, 1 0 kpc for.1 < r-i <.1 5 stars ( ~F /G S pt) S ignatures of overdensities

8 E dge-on View ( R -Z density distribution) Right: e (R, Z) density distribution ( edge-on view ) 1 kpc ( bottom right; M dwarfs) to ~2 0 kpc ( top left; F dwarfs) scales Map Analysis Summary: Smooth, axisymmetric, background consistent with exponentials (disk) and power laws (halo) Overlayed by localized overdensities: clumps and streams Most major overdensities at D > 3kpc

9 The S DS S Galactic Density Model Juric et al. (2008) Best fit exponential disk, with all biases accounted for Comparison with prior measurements Siegel et al. 2002, Figure 1

10 The Value of S DS S I: Breaking the Degeneracy NGP line of sight only: H1 =2 6 0 pc H1 =2 4 5 pc H2 = pc H2 =7 5 0 pc f=4 % f=1 3 % Two substantially different fits describe the NGP line of sight equally well A number of prior studies are NGP only Wide area survey is necessary to break the degeneracy In our case, the fit always converged to the same minimum ( or did not converge at all)

11 The Value of S DS S II: S eeing/avoiding the S ubstructure If left unremoved, overdensities will influence the fits The only way to know where they are is to have a wide area survey ( Pencil beams considered harmful ) Overdensity removal is an iterative process ( Fit check remove fit check ) requiring considerable effort and care See also: Heidi Newberg s talk

12 Ivezic et al. (2008) Dissecting the Milky Way: Metallicity

13 P hotometric Metallicity: Calibration P recision and accuracy: S tellar parameters from S E GUE Teff ~ K spectra ( ~2 8 0,0 0 0 stars; Beers et al, Allende P rieto et al, Lee et al.) [Fe/H] ~ dex ( calibration), per star estimate bound by ( u-g, g-r) colors strongly correlate photometry ( ~0.2 dex, better than with spectroscopic metallicity and spectroscopic determination!) temperature See also: Tim Beers 2:55pm talk

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15 Metallicity Map Ivezic et al. (2008) Metallicity does not follow density Features in density space features in metallicity space

16 Vertical Variation of Metallicity Distribution Clear disk/halo separation

17 Halo Metallicity Distribution Halo Model: Well described by a Gaussian metallicity distribution e = dex e = 0.3 dex Mean and the dispersion independent of position

18 Disk Metallicity Distribution Detection of metallicity gradient Disk metallicity distribution: Approximately fitted with a gaussian with Zdependent mean, e ([Fe/H]) ~ G(e D, e = 0.16) Best fit by an asymmetric distribution with a slight low-metallicity tail

19 Ivezic et al. (2008) Metallicity of the Monoceros S tream Monoceros stream ( Newberg et al ) clearly distinct in metallicity space Metal poor compared to the disk, but metal rich compared to the halo ([Fe/H] = dex) Disk only Disk w. Mon. S trong evidence for external origin ( merger remnant, as opposed to disk flaring or excitation) Alternative view: see Heather Morrison s 11:35am talk

20 Ivezic et al. (2008), Bond et al., in prep. Dissecting the Milky Way: Kinematics

21 Completing the Census: P roper Motions ~1955 (POSS) Munn et al ( ) catalog Recalibrated P OS S astrometry using galaxies E rrors: Random: 3 mas/yr to r < 1 8, 6 mas/yr at r=2 0 S ystematic: ~0.3 mas/yr ( using k quasars) P ublicly available as part of DR 6 Over 3 0 M main sequence stars, entire S DS S footprint DR 6 sample ( Dmax ~ 10 kpc) Measure the proper motions towards the NGP E asy to interpret: ve =e D b is the rotational velocity ~2002 (SDSS)

22 Halo/Disk Components, Disk Rotational Velocity Lag Top panels: small dots are individual stars, large symbols are the median values Top left: disk stars show clear rotational velocity lag Top right: halo stars ve ~ 220 km/s, no significant rotation Disk Halo Halo Disk Halo Bottom left: disk velocity lag not linear Bottom right: halo velocity dispersion increase consistent with being due to photometric errors only

23 Two-component Disk? Ivezic et al. (2008) Left: E xpected rotational velocity-metallicity correlation at 1 kpc < Z < kpc ( for a simple gaussian velocity model) Right: Observed metallicity-rotational velocity correlation In general, we were unable to find a bimodality in distribution of any property we looked at ( velocities,

24 Detailed maps of velocity distribution Bond et al., in preparation

25 Features in velocity space Bond et al., in preparation Dehnen (1998) moving groups

26 Reduced P roper Motion Diagrams Juric et al., in preparation Local halo LF ( x 200) Halo Disk WDs Left: Data Right: Model (J08 disk/halo model + Disk LF)

27 Juric et al., in preparation Luminosity Functions Local disk LF Local halo LF ( x 200) See also: Independent disk K/M-dwarf LF measurement by Bochanski et al. (4:30pm talk, today)

28 Instead of a S ummary: S DS S Long-term Legacy S DS S I+II/S E GUE : measurements of density/metallicity/velocity distribution with 2 orders of magnitude larger samples than pre-s DS S studies ( e.g., in ~1 0 % of Galactic disk volume) Ahead of theory S etting a benchmark for simulations for the years to come Clumps/streams are an integral part of Milky Way structure, both halo and the disk. Methods and codes directly applicable to future wide-field surveys ( S kymapper+rave, P ans TARRS, DE S, LS S T) The Milky Way Tomography with SDSS. I. Stellar Number Density Distribution, J uric et al., 2008, ApJ, 673, 864 The Milky Way Tomography with SDSS. II. Stellar Metallicity, Ivezic et al., ApJ, in press (arxiv: ) Candidate Wide Binaries in the Sloan Digital Sky Survey, Sesar et al., ApJ, subm. The Milky Way Tomography with SDSS. III. Stellar Kinematics, Bond et al., in prep. The Luminosity Function of Galactic Disk and Halo, J uric et al., in prep.

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