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Structure (and Substructure) of the Galactic Halo from SDSS-I and SEGUE

Structure (and Substructure) of the Galactic Halo from SDSS-I and SEGUE Sep 23, 2006 Seoul Collaboration Meeting Brian Yanny Fermilab. SEGUE: Sloan Extension for Galactic Understanding and Exploration. The SEGUE experiment combines accurate low-latitude

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Structure (and Substructure) of the Galactic Halo from SDSS-I and SEGUE

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  1. Structure (and Substructure) of the Galactic Halo from SDSS-I and SEGUE Sep 23, 2006 Seoul Collaboration Meeting Brian Yanny Fermilab

  2. SEGUE:Sloan Extension for Galactic Understanding and Exploration The SEGUE experiment combines accurate low-latitude stellar photometry with radial velocities and chemical abundance information from spectroscopy to answer questions about the global structure of the Milky Way.

  3. SEGUE Imaging Science – mapping the Galaxy • Old stellar populations carry the signature of the Galaxy's formation and evolution in their kinematic, spatial and metallicity distributions. • What is the global structure of the thin disk, thick disk, bulge and spheroid? • Are they smooth, regular structures on the laragest scales? • Metallicity gradients? • Are there other streams like Sgr, Mon/Canis Major? • Is there a metal-weak thick disk, a flattened inner halo,...?

  4. Imaging Survey Design • 3500 sq. degrees • |b| < 35° and South Galactic sky • 20° grid in Gal. longitude • sample Galactic components, spatially coherent substructure • photometric accuracy: 2% in gri, 3% in u,z • calibration of stellar parameter estimates from photometry, spectroscopy • photometric parallax • star count uniformity • necessary for any study of stellar populations over large angle on the sky • 1% calibration enables more stellar population science, e.g., metallicity gradients

  5. SEGUE uses stellar probes of increasing absolute brightness to probe increasing distances in the disk, thick disk and Milky Way halo. K III d < 100 kpc BHB/BS d < 50 kpc Streams and outer halo stars MSTO/F d < 15 kpc G thin, thick disk stars d < 6 kpc Inner and outer halo stars KV d < 1 kpc r = 1.5kpc Other spectroscopic surveys will not probe as deep, for instance, Blue Horizontal Branch Stars (BHBs) from a survey with V< 12 are from a volume within 1.5 kpc of the sun. 8 kpc

  6. SEGUE uses stellar probes of increasing absolute brightness to probe increasing distances in the disk, thick disk and Milky Way halo. K III d < 100 kpc BHB/BS d < 50 kpc Streams and outer halo stars MSTO/F d < 15 kpc G thin, thick disk stars d < 6 kpc Inner and outer halo stars KV d < 1 kpc r = 1.5kpc Other spectroscopic surveys will not probe as deep, for instance, Blue Horizontal Branch Stars (BHBs) from a survey with V< 12 are from a volume within 1.5 kpc of the sun. 8 kpc

  7. SEGUE Spectroscopic Science – kinematics and chemical evolution • What is the shape, extent and smoothness of the Milky Way's dark matter halo • position, velocity dispersion of Sgr, Mon/Canis Maj, (other?) streams • velocity ellipsoid in the halo • The chemical abundance distribution of the Galaxy is a product of its enrichment history and contains clues to its origins. • Globular cluster vs. halo [Fe/H] distributions • Metal-poor tail of the halo

  8. Spectroscopic Survey Design • 240,000 stars • 200 lines of sight, 14.5<g<20 • Target evenly in log(distance) to 100 kpc+ • 11 categories • large volume of Galaxy • probe distant halo, anticenter • 3800Å – 9100Å, 3Å • good leverage for parameter estimates • Radial velocities to 7 km/s @ g=18.2 • Teff, log(g), [Fe/H] • Teff 150K, [Fe/H] 0.3 dex, log(g) 0.5 dex • requirements based on separating populations, giants/dwarfs, measuring distances

  9. WD A/BHB F Turnoff G III +V Low Metals K III K V M V AGB Cool Wds u-g g-r SEGUE target selection currently has 12 categories, (not shown are Proper motion selected sdMs and Brown Dwarfs/hi-z QSOs).

  10. Examples of Important Science with SEGUE 1. Characterize streams in the halo (separate them, determine age, metalicity, mass, surface density) 2. Constrain the Dark Matter halo potential using stellar tidal streams positions and kinematics 3. Explore the distribution of the oldest “Pop III?” stars in the halo, what does this say about how the Galaxy formed.

  11. SEGUE science example#1: Use stellar atmospheric parameters (velocity, metalicity and gravity) of a large number of stars in the same direction on the sky to isolate a stream from the background and foreground.

  12. S Select all G-colored stars (0.45 < g-r < 0.55) from SEGUE plates in this area of sky, within 10 degrees of Sag. Dwarf tidal stream crossing. Explore the stellar populations in vicinity of a stream....

  13. Field of Streams result SCIENCE with SEGUE `Field of Streams'

  14. Heliocentric Radial Velocity distribution

  15. Strategy: Pick out stars which stand out in velocity clump, and explore their stellar parameters.

  16. SEGUE/SDSS-I science example #2: Constrain the shape of the Dark Matter Potential of the Galaxy (in progress...)

  17. If MOND is true, expect con-centric Baryon+ “DM” Clowe et al astro-ph/0608407 Dark Matter traces non-dissipational galaxies, not dominant X-ray gas! Implies bad news for MOND. Baryons are here! But Dark Matter is centered here!!!! Good news for further studies into the nature of dark matter!

  18. A Disk Galaxy like the Milky Way and its dark matter halo. Q=1.0

  19. q=0.75

  20. Offcenter or mis-aligned dark haloes are possible!

  21. 1Mpc Kravstov dark matter numerical simulation, Each blue patch shows a lump of dark matter.

  22. Flattened Halo Flattened Disk (centered) Satellites orbits determined by Halo and Disk potentials.

  23. Bootes dwarf Field of Streams result

  24. The Bootes Satellite: One of about 10 new dwarf Milky Way companions (2006 Belokurov et al. astro-ph/0604355) Very faint sparse Milky Way dwarf galaxy or disrupted cluster companion, d=45 kpc from sun.

  25. Belokurov et al. astro-ph/0605705 A. B. New Connections made with SDSS-II: A: Orphan Stream on same orbit as HI High Velocity clouds! B: UMa-II dwarf (d=30 kpc) has same line of sight as High Velocity cloud complex A! Zucker et al. astro-ph/0606633:

  26. Modeling the orbit of the orphan stream and other halo streams can help to discriminate various halo potentials. This particular (over-simple model) uses q=1 (i.e. Spherical potential – no flattening). Y Orphan stream fiducial points Complex A H-I gas X Z Z Y X

  27. SEGUE science example #3: (a non-expert's [i.e. my] view) Explore the lowest metalicity stars in the halo Baade's Two Populations. Pop I: The sun, solar metalicity and slightly below, [Fe/H] ~ = -0.3 Pop II: Typified by halo stars, [Fe/H] = -1.5 or so. Still, -1.5 is still some Iron, where did is originate???? Pop III: The earliest generation of stars, [Fe/H] < -3 or -4 or ??? [These have not been observed yet in great numbers, if they exist at all] Do we have any Pop III stars??? How are they distributed?

  28. Stellar parameter pipeline focuses on three regions of the spectrum for metalicity indications: Ca K (3933A) H-delta/gamma+CH(G band) Mg triplet Stellar Parameter Pipeline: Beers, Y. S. Lee, C. Allende, R. Wilhelm, J. Norris, S. Thirupathi, C. Bailer-Jones, P. re Fiorentin et al. We show here an extremely low-metal F sub dwarf (top) [Fe/H] = -3.39 and a more moderate metalicity thick disk F/G star: [Fe/H] = -0.84 (lower plot)

  29. SEGUE Target Selection tuned for lower metalicity Halo and Thick Disk stars:

  30. Summary: SEGUE has completed the first year of its three year observing program. The data are available NOW to all collaborators, and will become public with DR6 in July 2007. There are many interesting science projects to be pursued with the SEGUE spectroscopic and imaging data bases. We welcome new collaborators who wish to pursue a science project, and to help assure the quality of the data.

  31. SEGUE participants and management: Brian Yanny [Co-leader], D. Tucker+ *student (FNAL) Connie Rockosi (UC Santa Cruz, Lick) [Co-leader] Heidi Newberg and *student (RPI) *J. A. Smith (Austin Peay State,TN) Hugh Harris, Jeff Munn (USNO) Heather Morrison, Paul Harding, and *student (CWRU) *James Clem (LSU) Jennifer Johnson (OSU) Tim Beers, S. Thirupathi, Y. S. Lee (MSU) *Carlos Allende Prieto (UTexas, Austin) *Ron Wilhelm (Texas Tech) Peregrine McGehee (LANL) Kyle Cudworth, Evalyn Gates (U. Chicago) G. Knapp, J. Gunn (Princeton) Craig Loomis, Robert Lupton (Princeton) Dan Zucker, G. Gilmore, V. Belokurov (Cambridge) Eric Bell, H. W. Rix, V. Smolcic (Max Planck Heidelberg) S. Lepine, M. Shara (Am. Museum Nat. History,NY) M. Steinmetz, M. Schrieber (AIP, Potsdam) Andreas Just, A. Belikov(ARI, Heidelberg) Z. Ivezic, J. Bochanski (U Washington) R. Wyse, A. Thakar (JHU) E. Grebel, K. Jordi (Basel) Steph Snedden, Kurt Anderson (APO, NMSU) * = External Participant We welcome new collaborators! 1. Subscribe to the `sdss-stars' e-mailing list! 2. Contact us by e-mail! Brian Yanny yanny@fnal.gov Connie Rockosi crockosi@ucolick.org http://www.astro.princeton.edu:81/sdss-stars/INDEX.html

  32. What is the nature/origin of the thick disk??? Thin disk scale length = 3 kpc Thick disk scale length?? 6 kpc??? We don't know the answer to the question: What is the thick disk scale length? Distinguishes two formation scenarios. Is thick a puffed up thin disk, or a 'separate entity'???? SEGUE/SDSS can help! Or is thick disk scale length only 3kpc (same as thin disk)?

  33. SEGUE is uniquely able to use photometry and spectra of low-latitude sightlines to probe the distant thick disk. MSTO star at g=18 d = 5.7 kpc Questions SEGUE will address: Is the scale length of the thick disk the same as that of the thin disk? (origin of Thick disk) Does a single exponential scale height account for all of the thick disk population in all directions? Thick Disk/Halo interface Surface mass density of Galactic disk h = 1.5kpc o b=15 r=1.5kpc 8 kpc

  34. Distinguishing David (K-dwarfs) from Goliath (K-giant)

  35. Giants have narrow, weak lines (low surface gravity), dwarfs have strong Mg triplets (though watch out for metals) Note that the photometry got it backwards!

  36. SEGUE Status as of Sept 1, 2006 (end of Year 1 of 3) 2271/3500 square degrees of imaging completed (64%), most remaining stripes in late South (winter observing), 146/400 plates completed (36%), more remaining tiles in North (spring observing).

  37. Month transits at Midnight Due to Legacy scheduling, remaining SEGUE plates are weighted towards the first half (Jan-Jun) of the year (100 < RA< 250). O N D J F M A M J J A S

  38. Old: Spectro v4 has spectrophotometric normalization problem at the very blue end (note rollover). New: Corrected in spectro v5.

  39. Relative Radial Velocity reproducibility for 1028 SEGUE Q/A targets, g < 19, is 7.5 km/s. Preliminary work on ABSOLUTE RV calibration shows we have color dependent systematics at about the 10 km/s level.

  40. Stellar Parameter Pipeline (T. Beers of MSU heads effort, with Y. S. Lee, S. Thirupathi (MSU), C. Allende (UT), R. Wilhelm (TT): Goal: Automate determination of [Fe/H], log g, Teff, for all SEGUE spectra. (Enhanced goal: [alpha/Fe] measures, individual elemental abundances, rare element abundances). Status: First version (v1_0) of Pipeline is checked in to Code Repository (CVS) at FNAL. Testing underway. Application: Pipeline being used to create Value Added Catalog of stellar parameters for SDSS-I stars. Application: Used to identify [Fe/H] < -3 stars in Milky Way halo. Application: determine carbon enhanced star frequency, Application: search for evidence of abundance gradient in halo. Next: In preparation for DR6, this version must be run independently (not by authors) at FNAL, be documented with outputs vetted and inserted into database.

  41. Three F-type turnoff stars from SEGUE data, analyzed with the stellar parameter pipeline (SPP). Note the correlation of depth of Ca K (3933) line vs. [Fe/H].

  42. Photometric calibration and spectroscopic <<-->> photometric tie in effort: (D. Tucker, FNAL, J. Johnson, OSU, H. Morrison, CWRU lead) Goals: Determine ugriz <---> u'g'r'i'z' <---> UBVRI filter transforms to 2% accuracy, esp. for Giant Branches of known globulars, (J. A. Smith, APSU, TN, and J. Clem, LSU external participants). Determine feasibility of using u-g, g-r, r-i photometric colors as 'photometric metalicity' and 'photometric luminosity' classifiers. If possible, allows stellar population work to extend from SEGUE sample of 240,000 spectra to much larger (N > 10^7) SDSS stellar imaging catalog. Status: Photometry (USNO, PT) and Hi-res spectroscopy (HET, Keck) for many faint stars (g > 15) obtained at numerous other telescopes, data being analyzed. Next: Assemble data, match to existing SEGUE data, derive transforms. Will evolve beyond DR6.

  43. Crowded, reddened target selection and processing of low-latitude (|b| < 20 degrees), crowded field regions (Robert Lupton (Princeton), Jennifer Johnson (OSU), V. Smolcic (MPH), P. Harding (CWRU) are co-investigators). Status of Target selection: Low-latitude algorithm signed off on by collab at Santa Fe meeting (Mar 2006). Basically: because of reddening uncertainties, low-lat algorithm reduces number of targeting categories from 12 to 3 (blue objects, K-M giants, and high-proper motion objects). About 6 plates obtained on-sky with this algorithm, currently being analyzed. Status of Crowded field photometry: Parallel efforts to process crowded fields with DAOPHOT, doPhot, PanStarrs codes, and match zeropoints onto photo (default SDSS code) in uncrowded realms. Will not be complete for DR6, but on-going effort through 2008. Hooks being inserted into database.

  44. One of three low-latitude selection areas: The AGB/M-giant box. Stellar locus at low-latitude (note larger width) g-r u-g

  45. Database population and data distribution (Heads: Yanny, FNAL, Ani Thakar, JHU) Status: Data model changes defined and signed off on in meetings; Change requests filed; code changes in progress. Early SEGUE plates (obtained under SDSS-I), have been included in DR5 data release, as is, i.e. without any extra stellar parameters such as [Fe/H], log g, etc. Next: Need progress on Data model changes by early fall 2006 to meet DR6 deadline, as this is a long lead time item. Next: Some early SEGUE science....

  46. Spectro 2d pipeline upgrade (C. Loomis at Princeton heads effort): Goals: Improve sky subtraction in red (Ca triplet), and spectrophotometric flux calibration in blue (better EqW. measures of Ca K, H-delta, et al.). Improve zeropoints of radial velocity templates across all spectral types. Status: Sky subtraction work completed, tested at Princeton. Zeropoint work underway, futher refinement needed. Next: Need Pipeline operational by this fall to facilitate reprocessing of all SEGUE spectra for DR6 release in July 2007 (this step has a long lead time of several months).

  47. SEGUE observing status at end of year 1: 2271/3500 square degrees of imaging completed (64%) 146/400 plates completed (36%), including over 7,000 BHB spectra, 24,000 G spectra, 15,000 F-turnoff stars, and over 1,000 K giants. With over 33% of the imaging and spectroscopy complete, we are on track to meet the program baseline in the 3 scheduled years. Status of development work for SEGUE: • Spectro 2d pipeline upgrade • Stellar parameter pipeline • Photometric and spectroscopic calibration efforts • Crowded,reddened field target selection and low-|b| photometry • SEGUE database population and distribution

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