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

Sep 23, 2006 Seoul Collaboration Meeting

Brian Yanny Fermilab

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.

SEGUE: Sloan Extension for Galactic Understanding and Exploration

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,...?

➔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

Imaging Survey Design

8 kpc

KV

G

MSTO/F

BHB/BS

K IIISEGUE uses stellar probes of increasingabsolute brightness to probeincreasing distances in the disk, thick disk and Milky Way halo.

d < 1 kpc

d < 6 kpc

d < 15 kpc

d < 50 kpc

d < 100 kpc

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.

r = 1.5kpc

Streams and outer halo stars

Inner and outer halo stars

thin, thickdisk stars

8 kpc

KV

G

MSTO/F

BHB/BS

K IIISEGUE uses stellar probes of increasingabsolute brightness to probeincreasing distances in the disk, thick disk and Milky Way halo.

d < 1 kpc

d < 6 kpc

d < 15 kpc

d < 50 kpc

d < 100 kpc

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.

r = 1.5kpc

Streams and outer halo stars

Inner and outer halo stars

thin, thickdisk stars

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

➔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

Spectroscopic Survey Design

WDA/BHBF TurnoffG III +VLow MetalsK IIIK VM VAGBCool Wds

SEGUE target selection currently has 12 categories, (not shown are Proper motion selected sdMs and Brown Dwarfs/hi-z QSOs).

g-r

u-g

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.

SEGUE science example#1:

Use stellar atmospheric parameters(velocity, metalicity and gravity)of a large number of stars in thesame direction on the sky to isolate astream from the background andforeground.

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

Field of Streams result

SCIENCE with SEGUE `Field of Streams'

Heliocentric Radial Velocity distribution

Strategy:Pick out starswhich stand outin velocity clump,and exploretheir stellarparameters.

SEGUE/SDSS-I science example #2:

Constrain the shape ofthe Dark Matter Potentialof the Galaxy (in progress...)

Clowe et al astro-ph/0608407

Dark Matter traces non-dissipational galaxies, notdominant X-ray gas! Implies bad news for MOND.

Good news for further studies into the nature ofdark matter!

Baryons are here!

But Dark Matter is centered here!!!!

If MOND is true,expect con-centricBaryon+ “DM”

A Disk Galaxylike the Milky Wayand its dark matterhalo.

Q=1.0

q=0.75

Offcenteror

mis-aligneddark haloesare possible!

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

1Mpc

Flattened HaloFlattened Disk (centered)

Satellites orbits determined by Halo and Disk potentials.

Field of Streams result Bootes dwarf

The Bootes Satellite: One of about 10 new dwarf Milky Way companions (2006 Belokurov et al. astro-ph/0604355)

Very faintsparseMilky Waydwarf galaxy ordisruptedclustercompanion,d=45 kpc from sun.

New Connections made with SDSS-II:

A: Orphan Stream on same orbit asHI High Velocity clouds!

B: UMa-II dwarf (d=30 kpc) has same line of sight as High Velocity cloud complexA!

A.

B.

Belokurov et al. astro-ph/0605705

Zucker et al. astro-ph/0606633:

Z Z

Y

X

X

Y

Modeling the orbit of the orphan streamand other halo streams can helpto discriminate various halo potentials.

This particular (over-simple model)uses q=1 (i.e. Spherical potential – noflattening).

Orphan streamfiducial points

ComplexA H-I gas

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?

Stellar parameter pipeline focuses on three regions of the spectrumfor metalicity indications:

Ca K (3933A) H-delta/gamma+CH(G band) Mg triplet

We show here an extremely low-metal F sub dwarf (top)[Fe/H] = -3.39 and a more moderate metalicity thick diskF/G star: [Fe/H] = -0.84 (lower plot)

Stellar Parameter Pipeline: Beers, Y. S. Lee, C. Allende,R. Wilhelm, J. Norris, S. Thirupathi, C. Bailer-Jones, P. re Fiorentin et al.

SEGUE Target Selection tuned for lower metalicityHalo and Thick Disk stars:

Summary:

SEGUE has completed the first year of its threeyear observing program. The data are availableNOW to all collaborators, and will become publicwith DR6 in July 2007.

There are many interesting science projectsto be pursued with the SEGUE spectroscopicand imaging data bases.

We welcome new collaborators who wish topursue a science project, and to help assure thequality of the data.

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 welcomenew collaborators!

1. Subscribe tothe `sdss-stars'e-mailing list!

2. Contact us by e-mail!Brian Yannyyanny@fnal.govConnie Rockosicrockosi@ucolick.org

http://www.astro.princeton.edu:81/sdss-stars/INDEX.html

What is the nature/origin of the thick disk???

Thin disk scale length = 3 kpc

Thick disk scale length?? 6 kpc???

Or is thick disk scale length only 3kpc (same as thin disk)?

We don't knowthe answer tothe question:What is thethick disk scale length?

Distinguishes twoformationscenarios.

Is thicka puffed upthin disk,or a 'separateentity'????

SEGUE/SDSS canhelp!

8 kpc

r=1.5kpc

d = 5.7 kpch = 1.5kpc

SEGUE is uniquely able to use photometry and spectra of low-latitude sightlines to probe the distant thick disk.

Questions SEGUE will address:

Is the scale length of thethick disk the same as thatof the thin disk? (origin of Thick disk) Does a single exponential scaleheight account for all of the thick diskpopulation in all directions?

Thick Disk/Halo interface

Surface mass density of Galactic disk

MSTO star at g=18

b=15 o

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

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!

SEGUE Status as of Sept 1, 2006 (end of Year 1 of 3)

2271/3500 square degrees of imaging completed (64%), most remaining stripes inlate South (winter observing),

146/400 plates completed (36%), more remaining tiles in North (spring observing).

Due to Legacy scheduling,remaining SEGUE plates areweighted towards the first half (Jan-Jun) ofthe year (100 < RA< 250).

J F M A M J J A SO N D

Month transits at Midnight

Old: Spectro v4has spectrophotometricnormalization problemat the very blue end(note rollover).

New: Correctedin spectro v5.

Relative Radial Velocityreproducibility for1028 SEGUE Q/A targets, g < 19, is 7.5 km/s.

Preliminarywork on ABSOLUTERV calibrationshows we have color dependentsystematics atabout the 10 km/s level.

Stellar Parameter Pipeline (T. Beers of MSU heads effort, withY. 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.

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].

Photometric calibration and spectroscopic <<-->> photometric tiein effort: (D. Tucker, FNAL, J. Johnson, OSU, H. Morrison, CWRU lead)

Goals:

Determine ugriz <---> u'g'r'i'z' <---> UBVRI filter transformsto 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) SDSSstellar 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.

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 processcrowded fields with DAOPHOT, doPhot, PanStarrs codes, and matchzeropoints 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.

One of three low-latitude selection areas: The AGB/M-giant box.

u-g

g-r

Stellar locus atlow-latitude (note larger width)

Database population and data distribution (Heads: Yanny, FNAL, Ani Thakar, JHU)

Status: Data model changes defined and signed off onin 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 anyextra stellar parameters such as [Fe/H], log g, etc.

Next: Need progress on Data model changesby early fall 2006 to meet DR6 deadline,as this is a long lead time item.

Next: Some early SEGUE science....

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).

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 BHBspectra, 24,000 G spectra, 15,000 F-turnoff stars, and over 1,000K 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

Two stars with nearly identical photometry may be separatedspectroscopically: One is a distant giant, the other a local dwarf.