Surveying the Galaxy:classical methods applied to topical science

and the role of the ING

Gerry GilmoreInstitute of Astronomy

Cambridge University

Our requirement is really very simple

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• Probably discrete? intermediate PopII, thick disk I.5• Hot, low-J, old?, metal-rich, related to SMBH – bulge• Hot, low-J(???), old(??) metal-poor(?), late accretion(?),

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

• PLUS, most important of all?:• All these in an evolving dark-matter potential: POP 0?• Justification is observed relation to physics

What stars we have available to study

Complexity, richness• All these “populations” means complexity,• large samples• no single “answer”• no single approach is sufficient

• many types of survey are needed:• Imaging, kinematic, spectroscopic (various R),• and Gaia.• R~5000 most science, most critical, cf other talks

Stellar orbit-abundance correlation: yellow band is ELS relation

A simple example of the power of large samples, with understood biasses

8,600 faint F/G dwarfs, several kpc above the plane, spectroscopic metallicities from AAOmega/AAT data

[Fe/H]

(g-r)o

Wyse, Gilmore, Norris 2008: Thick disk is OLD

Old stars here

Young stars would be here

12Gyr turn-off points

Power of huge samples, low dispersion

Chemical evolution models allow x100 element ratioscatter – not seen

The scatter is 2-3 ordersless than the range.

This implies efficient large-scale mixing, or uniform sub-units

Element ratio data from Fuhrmann, see also Nissen.

Local volume-complete sample

The OUTER halo is only 10% of the halo, perhaps 1% of the stellar GalaxyMOST of the halo POPII is old, and has very clearly defined chemical element ratiosNot at all like the surviving dSph

Renzini 2008

Current data show the power of chemistry to measure `history’, fig from Renzini

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

Carretta etal 2009 A&A 505 117

There are very many complications,which need lots of data to “understand” – eg, why do giantsshow different elementpatterns/ratios in star clustersthan in the field??

Yet again, this is suggesting oursurvivor structures are not theimportant building blocks.

Why not??

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

Lots and lots of physics

Blue=outer haloRed = inner halo

How much of that scatter is real??

How were those stars selected for analysis?

Nissen & Schuster 2010 : 1002.4514

Our current samples are small, and very biased: there is obviously vastly moreto learn before we are sure we are even asking the right questions.

Majority of data sets suggest remarkably small scatter in low-abundance starsBUT: one recent survey provides a quite different result – two low-scatter relationsAnd much increased richness/complexity for [m/h]-1

The thick disk/halostate of the art:many more metal-poorstars at bright magnitudes,high angular momentumextends to low metallicity(pace ELS).

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

Ruchti, Fulbright, Wyse,GG, in prep, based onRAVE survey

What role does ING have to play in these big challenges?

Very many exciting science cases are presented here. Very interesting, but“all of the above” and “people want us” is not an intelligent reaction. One needs to look at sharing, coordinating, off-loading

SDSS and RAVE are an excellent example of a practical way forward:Focussed use of a cheap facility (UKST) to do a very few things very well,while focussing on big science questions.

The Gaia-related follow-up projects are a superb example of optimalscience use of a wide-field 4m telescope, with data serving a huge range of science and a huge science community.

Coordination inside the GREAT initiative (coordinated by Nic Walton andthe GAIA project DPAC community) is an obvious way forward.

Scale of people, scale of science, focus of technical demands.

And this is highly likely to be a non-negotiable requirement for continuing financial support

What role does ING have to play in these big challenges?

Very many exciting science cases are presented here.Attempting all (or even many) of them is foolish, and will fail

We are an age of big statisticsWe have many small telescopes: all of them doing everything is stupid

2-4m telescopes are like clever students:doing a very small number of things well is a smart future

Coordinated major Gaia-related science is smart, to be somewhere.

There is a wide-field spectroscopic AstroNet review panel underwayLikely outcome: share the 3 top priorities around the best facilities,Each doing 1-2 things only, and optimally

Make a clear choice, then commit to do it well.

dSphs vs. halo abundancesdSphs vs. halo abundances

Shetrone et al. (2001, 2003): 5 dSphs

Letarte (2007): Fornax

Sadakane et al. (2004): Ursa Minor

Koch et al. (2007, 2008, 2009): Carina

Monaco et al. (2005): Sagittarius

Koch et al. (2008): Hercules

Shetrone et al. (2008): Leo II

Aoki et al. (2009): Sextans

Frebel et al. (2009): Coma Ber, Ursa Major

Tolstoy et al. (2009): Sculptor

Cohen & Huang (2009): Draco

Feltzing et al. (2009): Boo IFrebel et al. (in prep.): Sculptor

Looking again near the Sun: the RAVE survey –UKST – 1million bright stars, to see what is really there.Kinematic `populations’ and chemistry follow-up