1 Galactic Science and MOS on the WHT Amina Helmi.
Transcript of 1 Galactic Science and MOS on the WHT Amina Helmi.
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Galactic Science andMOS on the WHT
Amina Helmi
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ESA-ESO report on Galactic populations(Turon, Primas, Binney, Chiappini, Drew, AH, Robin, Ryan)
GCDS: Gaia chemo-dynamical Survey•First meeting: Paris 26 April 2010
GREAT WG3 on Chemical Tagging
Brown, Feltzing, AH, Korn, Walton
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thick disk
stellar halo
bulgethin disk
The Galaxy
How did the Galaxy come to be like this ?
What is the origin/formation epoch/mechanism and relation between the various components?
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ESA-ESO Galaxy WG ESA-ESO meeting, ESTEC, 10 October ESA-ESO 2008 4
The Gaia era
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Gaia• The volume and quality of data that Gaia will provide will
revolutionise the study of the Galaxy
•Full 6D phase-space information only available for a subset
•Not as accurate as proper motions
-> Incomplete dynamical map of the Galaxy e.g. substructures (clusters, resonances) in disk limited to few kpc
from Sun
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Gaia: spectroscopy
• Only gross abundances measurable for a subset of brightest stars
-> MDF only known within few kpc from the Sun, in sections of the bulge or in dwarf galaxies (100 x farther away)
• Detailed elemental abundances missing
-> crucial for chemical history, star formation and assembly history
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Science questions1
• Dynamics of the Milky WayVelocity distributions along the disk; resonance maps; coupling of dark
halo, bar and diskHalo shape, density and granularityStreams as tracers of mass distribution and evolution
• Structure and history of the disksCharacterization of star formation and chemistry as f(R)Models of the formation of thick disk Inter-relation between various components
• Metal-poor componentsStreams in the halo to trace merger historyConstrain the IMF, and star formation in the early Universe (1) not
exhaustive
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A great amount of dark substructure
Sprin
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CDM strong predictions on density profile, shape and granularity
Milky Way Dynamics
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Narrow streams
Thin long streams better probes (more reliable tracers of underlying potential; Eyre & Binney 2009)
Internal velocity dispersions are few km/s
GD-1 stream in SDSS: dissolved cluster
Koposov et al. 2009
•Halo granularity: need very accurate radial velocities
•Distant streams preferred (d ~ 10 – 40 kpc) to isolate other effects-> faint stars
•Low surface brightness -> need to go as far down on RGB
•Need to follow stream across large area on the sky
-> Wide-field, accurate RV, faint magnitudes, multiplex ~ 100
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Chemistry
• Elemental abundances track ISM at formation
• Different elements are produced on different timescales -> their ratio is a clocke.g. -> SNII (short-lived massive stars); Fe: mainly SNI -> [/Fe] enhanced implies fast star formation
r, s processes
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-Very small number of extremely metal-poor stars known to date: 3 with [Fe/H] < -4.5
-Direct counts provide constraints on the IMF at high-redshifte.g. there may be a critical Z below which only very massive stars form
-Currently limited by small number statistics Salvadori et al. 2007
Spectroscopic survey of 105 halo stars at intermediate res. to identify candidates for follow up -> Wide-field, deep & 100 multiplex
Halo metallicity distribution function
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Knowledge of very metal-poor stars detailed abundance patterns•Constraints on the IMF•On the nature of the first stars and explosions (SN or HN)•On the early history of the Galaxy (e.g. why lack of scatter?)
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Cayrel et al. 2004
Chemistry of metal-poor components
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Merger history and streams
Latest cosmological simulations predict much substructure in the halo• 75% of stars near Sun from 3-5 parents
Memory in kinematics -> 100’s streams crossing Solar neighbourhood Should be visible with Gaia!
Cooper et al. 2010
Helmi et al. 2010
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Belokurov et al. 2007
Outer halo:•Clear evidence of substructure•Limited to high-surface brightness features (progenitors/time of events)
Font et al. 2006
Abundance substructure also expected
Characterize the properties of the building blocks of the halo500 streams -> 100*/stream -> 5x104 stars, wide-field (2-3 deg2) 100 multiplex, V ~ 17 for a survey of 2000 deg2 (V ~ 15 for 10000 deg2); HR ~ 20,000
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Global Requirements• Wide-field: 2- 3 deg2
Galaxy is an all-sky object Stars in halo and thick disk are rare -> build up large samples in reasonable time
• Spectral resolution and multiplexing R ~ 5,000 for radial velocities (1 – 2 km/s); #fib < 1000s R ~ 20,000 for metal-weak thick disk, halo studies; #fib ~ 100s
• Survey sizes LR mode for disk: 106 stars for 17< V < 20 HR mode for field populations: 105 stars HR mode for stream characterization: 5 x 104 stars
• Large spectral coverage blue sensitive: well-known region of the spectrum;
many useful lines; little atmospheric lines for metal-poor stars (halo-like): there are fewer lines -> gain
e.g. Eu (r-process) two lines around 6500 A
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The landscape
Recio-Blanco 2009Lamost?
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Structure and history of the disks
• Characterization of star formation and chemistry as f(R)• Test models of the formation of thick disk• Inter-relation between various components
star formation history in galactic thin disk from Solar Neighbourhood:
roughly uniform, with episodic star bursts for ages < 10 Gyr, but lower for ages > 10 Gyr
Rocha-Pinto et al (2000)
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Age-metallicity-velocity relations
Only known for the solar neighbourhood (GCS, d < 100 pc)
Holmberg et al. 2008
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Disentangle histories and relations between thin, thick, bulge and halo
-> abundances as f(R) and f(z)
Samples: • 105 stars with 0.1 dex precision ->
RGB• Local study with MS stars within 2
kpc, with 0.05 dex
Only for Solar neighbourhood
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