# Presentation: 093365

##    Structure (and Substructure)

-    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
- 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      

**  ****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,...?

## Imaging Survey Design

- |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

## KV

- 8 kpc

- G

- MSTO/F

- BHB/BS

- K III

- SEGUE uses stellar probes of increasing
- absolute brightness to probe
- increasing 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, thick
- disk stars

## KV

- 8 kpc

- G

- MSTO/F

- BHB/BS

- K III

- SEGUE uses stellar probes of increasing
- absolute brightness to probe
- increasing 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, thick
- disk 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

## Spectroscopic Survey Design

- 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

## WD

- A/BHB
- F Turnoff
- G III +V
- Low Metals
- K III
- K V
- M V
- AGB
- Cool 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 the
- same direction on the sky to isolate a
- stream from the background and
- foreground.

## 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....

## Field of Streams result

- SCIENCE with SEGUE

- `Field of Streams'

## Heliocentric Radial Velocity distribution 

- Heliocentric Radial Velocity distribution

## Strategy:

- Pick out stars
- which stand out
- in velocity clump,
- and explore
- their stellar
- parameters.

## Slide 16

## Slide 17

## SEGUE/SDSS-I science example #2:

- Constrain the shape of
- the Dark Matter Potential
- of the Galaxy (in progress...)

## Clowe et al astro-ph/0608407

- Dark Matter traces non-dissipational galaxies, not
- dominant X-ray gas!  Implies bad news for MOND.

- Good news for further studies into the nature of
- dark matter!

- Baryons are here!

- But Dark Matter is centered here!!!!

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

## A Disk Galaxy

- like the Milky Way
- and its dark
- matter
- halo.

- Q=1.0

## q=0.75

## Offcenter

- 	or
- mis-aligned
- dark haloes
- are possible!

## Kravstov dark matter numerical simulation,

- Each blue patch shows a lump of dark matter.

**1Mpc**

## Flattened Halo

- Flattened Disk
-    (centered)

- Satellites orbits determined by Halo and Disk potentials.

## Bootes dwarf

- Field of Streams result

## 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.

## 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!

- 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 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).

- Orphan stream
- fiducial points

- Complex
- A 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 spectrum

- for 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 disk
- F/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 metalicity

- Halo and Thick Disk stars:

## Slide 32

## Summary:  

- 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.

## We welcome

- 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

- new collaborators!
- 1. Subscribe to
- the `sdss-stars'
- e-mailing list!
- 2. Contact us by
- e-mail!
- Brian Yanny
- _[yanny@fnal.gov](mailto:yanny@fnal.gov)_
- Connie Rockosi
- crockosi@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 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!

## 8 kpc

- r=1.5kpc

- d = 5.7 kpc

- h  = 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 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

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

## Due to Legacy scheduling,

- remaining SEGUE plates are
- weighted towards the first half (Jan-Jun) of
- the year (100 < RA< 250).

- J       F      M     A     M     J       J       A      S

- O       N     D

- Month transits at Midnight

## Old:  Spectro v4

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

## 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.

## 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.

## 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 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.

## 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.

## One of three low-latitude selection areas:

-    The AGB/M-giant box.

- u-g

- g-r

- Stellar locus at
- low-latitude (note
- larger width)

## 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....

## Spectro 2d pipeline upgrade (C. Loomis at Princeton heads effort):  

- 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 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

## Two stars with nearly identical photometry may be separated

- spectroscopically:  One is a distant giant, the other a local dwarf.