Galaxy formation and evolution with a GSMT: The z=0 fossil record 17 March, 2003

Current Landscape The star formation, chemical evolution and dynamical histories of the Galaxy have been largely (though not completely) pieced together from studies of the kinematics and abundances of field stars and clusters. Starting with 4m-based photometry and now with 8 and 10m high-dispersion spectroscopy similar studies have been extended to the Milky Way dwarf galaxy complement.

Color-magnitude Studies of Star- Formation Histories Fornax Carina

Current Landscape The star-formation histories of the Galaxy’s dSph have proven to be surprisingly diverse and so-far unexplained. To date, beyond the Local Group inferences about SFH and chemical evolution history have been based on integrated spectroscopy and photometry. 8/10m AO-based studies in their infancy.

The role of a 30m Extend `fossil record’ studies of resolved stellar populations to 15Mpc. –Vastly larger samples across full Hubble Sequence. –Environments ranging from field to Virgo Cluster-like density (core of the Coma I group).

The Big Questions What are the star formation histories for M31 & M81 and their dwarf complements? –Did star formation commence simultaneously throughout the Local Group? –What are the key factors that govern dwarf galaxy star formation episodes? What are the complete chemical enrichment histories of Local Group galaxies? –Fe/alpha/r-process compared to Galaxy. Inferences for IMF and feedback differences

Big Questions cont. Directly measured star formation histories of giant elliptical galaxies. –Is there a significant population of young stars in giant elliptical galaxies? (JWST?) –Detailed mix of elements with different nucleosynthetic origins in a gE

Big Questions cont. Did star formation commence at the same time throughout the volume of space to Virgo? Cosmic variance in SFH as a function of Hubble type/environment z=0 population census is crucial for matching populations at larger z

The role of a 30m: Analysis Techniques Establish distance scale to Virgo Cluster to 10% via RR Lyrae,TRGB observations CMD studies –Main-sequence turnoff ages –[Fe/H] and [Fe/H] spread from RGB morphology –Horizontal branch morphology inferences for ages R=5000 to spectroscopic studies –Kinematics –Detailed chemical compositions

MSTO (10Gyr) V HB V RGB tip V Absolute M M NGC Virgo

MSTO (10Gyr) V/I/K HB level V/I/K RGB tip V/I/K Absolute4.5/3.8/3.20.8/0/-1.2-1/-4/-7.5 M3128.8/28.1/ /24.3/ /20.3/16.8 M8132.3/31.5/ /27.8/ /24.8/20.3 NGC /33.8/ /30/28.829/26/22.5 Virgo36/35.2/ /31.5/ /27.5/24 What you shade in a table like this depends strongly on MCAO performance

I= M81 Group M31 Group Nearby GGC Galactic dSph Old MSTO magnitude 4m 10m 30m

Useful type of plot?

Relevant numbers to collect Sample sizes broken down by Hubble Type as a function of distance (easy) S/N vs science for different studies (easy) Surface brightness/crowding limits and effects (hard). Olsen/Rigout work is an important contribution. Good MCAO simulations are crucial to this area

Capabilities requirements list Instrumentation –R~40000 optical/Near-IR spectroscopy –MCAO/ modest-field JHK photometry AO –PSF stability/strehl requirements require simulations Lambda regimes –B through K

What might be missing from current discussions? Real simulations –Crowding –Effects of realistic PSF for AO photometry and spectroscopy Tools required for using diagnostics in the near-IR (CMD/abundances) - most of the gains will require AO with moderate or better strehl -- likely only possible longward of 1 micron for the next few decades) Young stellar populations Slide from November are we getting anywhere?

Would you build an ELT to do this? Perhaps not. 8/10m +AO will make excellent progress throughout the Local Group and probably out the the M81 Group. –Will we learn fundamentally new things extending to the 10Mpc groups and Virgo? –If an ELT is there, these are excellent areas and excellent astronomy will be available. –MSTO photometry throughout Local Group and stellar pops in a gE may be the greatest potential Sub-mas astrometry of faint objects