GALAH view of the Galactic disk - Seoul National Universityastro1.snu.ac.kr/dg2013/presentation/6-6...
Transcript of GALAH view of the Galactic disk - Seoul National Universityastro1.snu.ac.kr/dg2013/presentation/6-6...
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GALAH view of the Galactic disk
Gayandhi De Silva
Australian Astronomical Observatory
Ken Freeman (ANU), Joss Bland-Hawthorn (U. Sydney) and the GALAH Survey team
Dynamics of Disk Galaxies Seoul. 24 October 2013
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What’s a Galah?
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Target: a million stellar spectra at high resolution! 2/13
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HERMES is a High Efficiency and Resolution Multi-Element Spectrograph on the 4m Anglo-Australian Telescope
• SNR = 100 @ V = 14 in 1hr
• R ~28,000 or ~45,000
• 4 channels cover maximum ‘good’ chemical element lines
• Uses 2dF fiber positioner to get 392 stars over 2degree field
Channel Wavelength (Å)
Blue 4708 - 4893
Green 5649 - 5873
Red 6481 - 6739
IR 7590 - 7890
3/13
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Survey Goals
Key GALAH science questions:
(a) When and where were the major episodes of star formation in the disk and what drove them?
(b) To what extent is the Galactic disk composed of stars from merger events?
(c) How have the stars that formed in situ in the disk evolved dynamically since their birth?
(d) Where are the solar siblings that formed together with our Sun?
The major goal of GALAH is to identify chemically similar groups of stars in the Galactic disk, which are most likely ancient disrupted clusters, to decipher the star formation, migration and minor-merger history of the Milky Way.
4/13
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Target Selection
Simple selection criteria: • 2MASS positions, APASS photometry, PPMXL proper motions • Galactic latitudes between ±10° and ±45° up to declination +10 • All targets from 12 < V < 14 • no colour selection
Expected contribution from Galactic components:
−Thin disk ~ 75% −Thick disk ~ 24% −Bulge ~ 1% −Halo ~ 0.1%
With HERMES ~ 350 stars per hour gives > 2000 stars per night
At 100 nights per year for ~5 years gives > 1 million stars
5/13
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Data Analysis
Data reduction pipeline
“2dfrdr” developed at the
AAO handles all their fibre
based instruments and runs
real time between exposures
Automated abundance analysis
pipeline “Theremin” developed
within the GALAH collaboration
(based on MOOG) provides:
• Stellar parameters: effective temperature, gravity, rotation • Radial velocities, variability, multiplicity flags, oddities • Abundances of individual elements: Li, C, O, Na, Al, K, Mg, Si,
Ca, Ti, Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Ba, La, Nd, Ce, Eu
6/13
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Chemical Tagging
Use the chemical information within stars to “tag” them to common formation sites (Freeman & Bland-Hawthorn 2002)
Assumes stars form in clusters and such clusters are chemically homogenous – holds for present day open clusters.
Method verified by identification of moving groups and stellar streams. Chemistry can differentiate origins of kinematical disk substructure, for example: • HR 1614, Argus Association & Wolf 360 group = homogenous clusters De Silva et al. 2007, De Silva et al. 2013, Bubar & King 2010
• Hercules = dynamical stream Bensby et al. 2007
• Hyades = both! Pompeia et al 2011 De Silva et al 2011 Tabernero et al 2011
7/13
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HR 1614 group Hercules stream
Hyades stream
8/13
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Blind chemical tagging of the Bensby et al. 2013 disk stars: Use group finding algorithm to tag 703 disk stars purely using chemical
info
Mitschang et al. 2013a, MNRAS
# st
ars
per
grou
p δ c
(dex
)
9/13
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[Fe/
H]
[α/F
e]
Mitschang et al. 2013b, submitted
Chemical tagging could also provide ages for groups
10/13
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Recover such groups in a million stars to answer key questions:
Chemo-dynamical evolution: What are the dominant nucleosynthetic processes (principle chemical components) as a function of position, velocity and stellar orbital motions. Direct evidence for a physical sequence of disk evolution. Mixing and migration: what will be the distribution of stars in chemically recovered clusters - narrow range in RGC or spread over kpcs in radius? Will depend on migration and mixing efficiencies. Merger history: what will be the frequency of chemically tagged dwarf galaxy signatures vs. homogenous clusters. Will depend on the satellite galaxy infall rate. Solar siblings: chemically tag the solar family – chemical signature of planets, aliens?
11/13
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HERMES commissioning: started, continue till Nov 2013
GALAH pilot survey: Nov 2013 – Jan 2014
GALAH main survey: 2014 – 2019 (?)
Current Schedule
12/13
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The GALAH team on a horizontal branch
More details at: www.aao.gov.au/HERMES/GALAH/
13/13
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GALAH view of the Galactic diskWhat’s a Galah?Target: a million stellar spectra at high resolution! HERMES is a High Efficiency and Resolution Multi-Element Spectrograph on the 4m Anglo-Australian Telescope�Survey Goals�Target SelectionData Analysis�슬라이드 번호 8슬라이드 번호 9슬라이드 번호 10슬라이드 번호 11슬라이드 번호 12슬라이드 번호 13More details at:�www.aao.gov.au/HERMES/GALAH/슬라이드 번호 15