Post on 21-Dec-2015
Surveying the Galaxy:classical methods applied to topical science
and the role of the ING
Gerry GilmoreInstitute of Astronomy
Cambridge University
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