Probing the history of star formation in the Local Group using the galactic fossil record

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1 Probing the history of star formation in the Local Group using the galactic fossil record Brian O Shea (Michigan State University) Collaborators: Tim Beers, Carolyn Peruta, Monica Derris (MSU), Jason Tumlinson (STScI) Monica Valluri (UMich), Christine Allen (UNAM)

2 What is the galactic fossil record? Very old, low-metallicity stars in the Milky Way bulge, disk, and halo (including stars in MW satellite dwarf galaxies) Age indicates these stars formed at high redshift, in galaxies that were ancestors to the Milky Way

3 Who cares about the fossil record? Provides both chemical and dynamical information on stars: probe the star formation AND merger history of the Milky Way! Can address questions about the IMF at high z and low Z Can investigate reionization, (some) properties of whole populations of high-z galaxies (who needs JWST?)

4 Who cares about the fossil record? Provides both chemical and dynamical information on stars: probe the star formation AND merger history of the Milky Way! Can address questions about the IMF at high z and low Z Can investigate reionization, (some) properties of whole populations of high-z galaxies (who needs JWST?) Image c/o Paul Harding, CWRU

5 image c/o Vasily Belokurov, SDSS-IICollaboration Who cares about the fossil record? Provides both chemical and dynamical information on stars: probe the star formation AND merger history of the Milky Way! Can address questions about the IMF at high z and low Z Can investigate reionization, (some) properties of whole populations of high-z galaxies (who needs JWST?) Image c/o Paul Harding, CWRU

6 Current and (near) future observations SDSS (+SEGUE-I and -II) ugriz photometry for 300,000,000 stars in the galactic halo medium-resolution spectroscopy of ~500K stars already, another 100K soon. proper motions for ~50K stars Dataset provides proper motions, vr, and abundances APOGEE: near-ir spectra of 100K stars in bulge, halo, disk (get vr and abundances)

7 Current and (near) future observations LAMOST: medium-resolution spectra of ~5 million stars over next few years SkyMapper: ugriz photometry, astrometry of ~5e9 stars in southern sky GAIA: astrometry, low-resolution spectroscopy of ~1e9 stars (launch late 2011/early 2012) LSST: 20,000 square degrees to m > 27 (billions and billions and billions...)

8 Ivezic et al. 2008

9 New version of Ivezic et al result (unpublished) Two halo components are kinematically distinct (Carollo et al. 2007, 2010) ugriz photometry, SDSS Stripe 82

10 Detection of substructure in SEGUE data Schlaufman et al. 2009

11 SDSS local calibration stars \ #/Bin [Fe/H]

12 #/Bin [C/Fe]

13 20% of stars have [C/Fe] > 0.5: similar to SDSS ultra-faint dwarfs! #/Bin [C/Fe]

14 Representative orbits of 4 SDSS calibration stars (halo stars) (work w/ Christine Allen, Monica Valluri)

15

16 How to make sense of it all?

17 How to make sense of it all?

18 Cosmological simulations of the fossil record Cosmological simulations are needed to accurately model dynamical history of MW-like galaxy and its satellites We have developed a set of population synthesis models that follow the abundance outputs of populations of stars as a function of IMF, formation redshift, metallicity These are being incorporated into high-resolution AMR simulations of structure formation that include DM, gas, cooling+ionization, star formation+feedback

19 Feedback from all stars, Salpeter IMF, M, Z = Z.

20 Summary The galactic fossil record is a very useful probe of the evolution of the Milky Way and its progenitors that is complementary to observations of distant galaxies Structure in abundance, phase space can clearly be seen in the galactic halo: multiple stellar populations, progenitors! Tantalizing hints that old populations in stellar halo have systematically different properties than disk stars: CMBregulated IMF? Stellar evolution? Theoretical models are crucial to making sense of these results and constraining the high-z/low-z IMF, and more generally star formation in distant galaxies