Transcript segue - Himastron

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 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
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
SEGUE uses stellar probes of increasing
absolute brightness to probe
increasing distances in the disk, thick
BHB/BS
disk and Milky Way halo.
K III
d < 100 kpc
d < 50 kpc
MSTO/F
Streams and outer halo stars
d < 15 kpc
thin, thick
disk stars
G
d < 6 kpc
KV
Inner and outer halo stars
d < 1 kpc
r = 1.5kpc
8 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.
SEGUE uses stellar probes of increasing
absolute brightness to probe
increasing distances in the disk, thick
BHB/BS
disk and Milky Way halo.
K III
d < 100 kpc
d < 50 kpc
MSTO/F
Streams and outer halo stars
d < 15 kpc
thin, thick
disk stars
G
d < 6 kpc
KV
Inner and outer halo stars
d < 1 kpc
r = 1.5kpc
8 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.
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
240,000 stars
➔
200 lines of sight, 14.5<g<20
➔
Target evenly in log(distance) to 100 kpc+
➔
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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
u-g
WD
A/BHB
F Turnoff
G III +V
Low Metals
K III
KV
MV
AGB
Cool Wds
g-r
SEGUE target selection currently has 12 categories, (not shown are
Proper motion selected sdMs and Brown Dwarfs/hi-z QSOs).
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.
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
Strategy:
Pick out stars
which stand out
in velocity clump,
and explore
their stellar
parameters.
SEGUE/SDSS-I science example #2:
Constrain the shape of
the Dark Matter Potential
of the Galaxy (in progress...)
If MOND is true,
Clowe et al astro-ph/0608407
expect con-centric
Baryon+ “DM”
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!
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!
1Mpc
Kravstov dark matter numerical simulation,
Each blue patch shows a lump of dark matter.
Flattened Halo
Flattened 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 faint
sparse
Milky Way
dwarf
galaxy or
disrupted
cluster
companion,
d=45 kpc
from sun.
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:
Modeling the orbit of the orphan stream
and other halo streams can help
to discriminate various halo potentials.
Y
This particular (over-simple model)
uses q=1 (i.e. Spherical potential – no
flattening).
Orphan stream
Complex
fiducial points
A H-I gas
X
Z
Z
Y
X
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
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)
SEGUE Target Selection tuned for lower metalicity
Halo and Thick Disk stars:
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.
SEGUE participants and management:
We welcome
new collaborators!
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) 1. Subscribe to
*James Clem (LSU)
the `sdss-stars'
Jennifer Johnson (OSU)
Tim Beers, S. Thirupathi, Y. S. Lee (MSU)
e-mailing list!
*Carlos Allende Prieto (UTexas, Austin)
*Ron Wilhelm (Texas Tech)
http://www.astro.princeton.edu:81/sdss-stars/INDEX.html
Peregrine McGehee (LANL)
Kyle Cudworth, Evalyn Gates (U. Chicago)
G. Knapp, J. Gunn (Princeton)
Craig Loomis, Robert Lupton (Princeton)
2. Contact us by
Dan Zucker, G. Gilmore, V. Belokurov (Cambridge)
Eric Bell, H. W. Rix, V. Smolcic (Max Planck Heidelberg)
e-mail!
S. Lepine, M. Shara (Am. Museum Nat. History,NY)
M. Steinmetz, M. Schrieber (AIP, Potsdam)
Brian Yanny
Andreas Just, A. Belikov(ARI, Heidelberg)
Z. Ivezic, J. Bochanski (U Washington)
[email protected]
R. Wyse, A. Thakar (JHU)
E. Grebel, K. Jordi (Basel)
Connie Rockosi
Steph Snedden, Kurt Anderson (APO, NMSU)
* = External Participant
[email protected]
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?
Is thick
a puffed up
thin disk,
or a 'separate
entity'????
Distinguishes two
SEGUE/SDSS can
formation
help!
scenarios.
Or is thick disk scale length only 3kpc (same as thin disk)?
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
h = 1.5kpc
r=1.5kpc
b=15
o
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
8 kpc
Surface mass density of Galactic disk
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).
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
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.
g-r
Stellar locus at
low-latitude (note
larger width)
u-g
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):
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.