Evolution of the Milky Waya look at just some of the bigger issues we don’t know

and future prospects for progress: Gaia

Gerry GilmoreIoA Cambridge

Stellar populations: 4.5 `types’• Kinematically cold, high-J (angular momentum), wide age-

range, narrow abundance range - dG-`problem’ late gas accretion? -- thin disk POP I• Old, high-J, discrete? intermediate PopII, thick disk I.5• Hot, low-J, old?, metal-rich, related to SMBH? – pseudo+bulge• Hot, low-J(???), old(??) metal-poor(?), late accretion(?),

probably itself 2-component – halo classical POPII• The first early stars POPIII? +POPIV +....

• CONCLUSION: We know little about unbiased samples• BUT each type shows surprisingly little element scatter • focus has been on extremes

The complexity we have available to study

The Galactic disks• disk (late type) galaxies are (too?) common• Most, perhaps all, are double disks • – thin disk plus thick disk• Most disks are big – too big? • Most disks are old – too old?• Most/all are metal-rich – too metal-rich?• All have complex secular dynamical evolution

g-dwarf `problem’

Big challenge:understand the DFof metal-poor disk stars

What created the elements at -1.5dexand high angularmomentum?

Where are the ancestors?Where are the minor mergerconsequences?

Solar cylinder metallicity DF

What came before the thin disk? The thick disk? The halo? Both? Neither?

Both the Thin and the Thick Disk look very homogeneous locally: hard to understand! Do few components imply few

origins?

Chemical evolution modelsallow very large element ratioscatter – not seenThis model from Wyse + gg

Element ratio data from Fuhrmann

Burnett, Binney etal 2011: RAVE data

Vertical metallicity DF with Z-height

Looks like a two-component thin+thickseparate population model fits best.

A very old model! (Wyse&GG 1995)

Consistent with thick disk formationending prior to thin disk, and gas retained.

Z>500pc

Z<500pc

Age Age-metallicity DF, from RAVE

The thin disk shows very smallchemical evolution over 8Gyr;the thick disk has a narrow age

Similar to Ohta results from Subaru/FMOS

Tight element ratios efficient ISM mixing

SFR ISM fountains

Burnett etal 2011andBinney, nipoti, fraternali MN 2009 397 1804

Thick disk merges into inner halo??

galactic field stars all see a mass-average yield, which is spatially well mixed.

This continuity tells us nothing about MWG merger/assembly duilding blocks – except they perhaps did not exist.

Derived ratios of several key α-elements to iron, for 215 red giants

Blue = HaloRed = Thick Disk Black = Thin DiskOrange = Thick/HaloGreen = Thin/Thick

Ruchti et al 2010, 2011. RAVE sample follow-up

MgI/FeI

SiI/FeI

CaI/FeI

TiI/FeI

TiII/FeII

Bulge—halo —disk connection? Which first?

Wyse & gg 1992

Bulge angular momentum distribution consistent with dissipational collapse of gaseous ejecta from stellar halo star-forming regions -- mass ratios also agree with low metallicity of stellar halo Hartwick 1979: impossible with significant late halo accretion or secular growth

Bulge, halo

Thick, thin disks

The first zero [Fe]stars should be in the bulge: are they?

SMBH connection??

Renzini 2008

Current data show the power of chemistry to measure `history’NB- ongoing star formation in very inner disk – Arches, etc – creating a pseudo-bulge?

Standard IMF (#1)Well-mixed (#2)Fast recycling (#3)

VISTA VHS data,b=40deg

Much focus on inner (pseudo-) bulge, not much on the very extendedBut it exists! Recall Ibata/Gilmore survey

Most of the stars here are halo, or disc(s)

Plateau universal IMFPlateau efficient mixingSharp break narrow timeSmall scatter good mixing..........

Lots and lots of physicsHALO

EMP stars are criticalprobes of the stellar IMFin the early UniverseTheir use to probe galaxy formation models is not clear-- lots of recent models.Current accretion – Sgr, SMCis making a young metal-richPop-II halo

Roederer 2009:Red=inner halo orbitsBlue=outer halo orbits

Stellar metallicity distributionsappear sequential:Halo thick disk thin disk

Halo MDF consistent with monolithic formation in situ,with gas loss into early disk.[ELS]

But this is not modern LCDMexpectation.

Coincidence or information?

We do not know the [Fe/H]DFs of any stellar ppulation

We do not know the [Fe/H]DFs of any stellar ppulation

The new “field of streams”double Sgr stream, much complexity

how does this relate to the “typical” halo?

Koposov, Belokurov, et al 2011

RAVE meeting Coonabarabran 1525 June 2011

• Gaia astrometric mission due for launch 2013– parallaxes and proper motions

for ~1 billion stars to mG<20 mag

– spectra for radial velocities and metallicities for 150 million stars

– Variability alerts from 2014– Full source data from 2016– Precise astrometry later

The coming revolution: GaiaGaia needs spectroscopy

16

Gaia Focal Plane

Star motion in 10 s4.4s per CCD

Total field: - active area: 0.75 deg2

- CCDs: 14 + 62 + 14 + 12

- 4500 x 1966 pixels (TDI)

- pixel size = 10 µm x 30 µm

= 59 mas x 177 mas

Astrometric Field CCDs

Blue Photometer CCDs

Sky Mapper CCDs

104.26cm

Red Photometer CCDs

Radial-Velocity Spectrometer CCDs

Basic Angle Monitor

Wave Front Sensor

Basic Angle Monitor

Wave Front Sensor

Sky mapper: - detects all objects to 20 mag

- rejects cosmic-ray events

- FoV discriminationAstrometry: - total detection noise: ~6 e-

Photometry: - spectro-photometer - blue and red CCDsSpectroscopy: - high-resolution spectra - red CCDs

42.3

5cm

Figure courtesy Alex Short

Science Alertsaims: •detect unexpected and rapid changes in the flux, spectrum or position•or appearance of new objects•trigger ground-based follow-up•provide targets to the community to be studied at peculiar states methods:•run in near-real-time: between couple of hours and 24h after observation•use photometric, spectroscopic and astrometric Gaia data•cross-match against existing information •Gaia spatial resolution makes for a real challenge – crowded fields•Motivation•Collaboration interests in special cases, esp rare objects

Advantage of spatial resolution: Gaia detects all sources with FWHM <0.65arcsecSo all the AGN, compact galaxies,.multi-lensed QSOs, kiler asteroids,...

R136 at 0.1”, 0.5”, 1.0”

Gaia is so many orders better than no win every parameter it is hard to appreciate,

Photometry selection – complete to V=20, drop to 50% at G=20.5Even in crowded fields – this is R136 (HST data) as seen by one Gaia CCDGreen box = Gaia will measure that source.

Co-PIsGerry Gilmore

(IoA, Cambridge)&

Sofia Randich(INAF-Arcetri)

plus......

The Gaia-ESO Spectroscopic Survey

• VLT-FLAMES public survey of all stellar populations of the MWG: Halo; Bulge; Thick & Thin disks; open clusters and associations

•240+60 nights (30n/semester) over 5 (4+1) years; start 1/ 2012 (P88), end 9/2016 (P97)+; visitor mode

• will yield: >105 Giraffe spectra (R~20,000); • > 104 UVES spectra (R~47,000)

[Mg,Ca,Ti, Si, Cr, Mn, Ni]

Gaia-ESO survey overview

Summary: we don’t know what “stellar population” means: dispersions in element ratios are always very small

• Big picture: pure disk formation problem• Disks are old – thick disks very common – Angular momentum disks link? • Vertical chemistry DF seems separate – also element ratios – why? • dG problem – chemistry DF narrow in Fe and element ratios - limits gradients and secular

effects??• Chemical evolution – none seen over 8Gyr: winds etc move gas round? • continuity to thick disk and halo? – constant IMF, efficient mixing, minimal or no local self-

enrichment. Short-lived star formation formed thick disk. • Q: how much scatter in elements in OCs at same age, radius? • Massive GC age/Na-O problems! MDF => not primordial building blocks• Secular models very uncertain – don’t know history of disk spiral/bar structure. Comparing

SFR and cluster survival numbers might help.• Merger models ditto – tough to test.• Turbulent disk formation – leads to thick disks but bulges – not dominant • Clusters – OCs only in thin disk – just age? Red GCs? But then inner halo/bulge link – opposite

to angular momentum relation?• .................. • Gaia will be here soon, to help – and challenge• Gaia-ESO spectroscopic survey an example of those to come.