GSMT: Stellar Populations
04 December 2002
• This is an example of an area with many
topics of interest to the astronomical
community, but perhaps not good
candidates for the `elevator’ talk.
What are the main topics
• Extending `fossil record’ studies of resolved stellar
populations to Virgo Cluster galaxies
• CMD studies
– Main-sequence turnoff ages
– HB/red clump morphology
– [Fe/H] and [Fe/H] spread from RGB morphology
• R=5000 to 50000 spectroscopic studies
– Kinematics
– Detailed chemical compositions
Top Level Goals
• Directly determine star formation and chemical
evolution histories for very large sample of
galaxies throughout the Hubble sequence.
– Did star formation comence at the same time
thoughout the volume of space to the Virgo Cluster?
– What are the star-formation histories for gE galaxies?
– Is there a Universal `floor’ to the MDF?
– Are there IMF variations as evidenced by element
mixes in different galaxies?
– Detailed understanding of galaxies at z=0 is crucial to
interpretation of integrated properties of galaxies at
larger z
Key Measurements
• CMD studies: Derive age/metallicity mix of
a population
– to HB (current limit, M31 group)
– to 12Gyr main-sequence turnoff (current limit,
Milky Way Galaxy companions)
Key Performance Drivers: CMD
Studies
• See next figure. Requires modest-field, moderate
Strehl AO.
• Understanding of photometry in AO corrected
images is crucial.
• Best age/metallicity diagnostics are for optical and
near -IR combinations.
• Maybe be better done with NGST (background,
psf stability) but crowding could be a key
Spectroscopic Studies
• R>5000 spectroscopy is where 30m brings a
new dimension in capability compared to
NGST.
• Extend traditional Galactic stellar
abundance work fainter by 2.5 mag
– In situ RGB stars everywhere
– Rare populations
– Globular cluster main-sequence stars
Spectroscopic Studies
• AO-fed spectroscopy opens up star-by-star
studies to M31/M81 groups
– MDF for a large sample of galaxies
– Relative contributions of r-, s-process elements
and SNII - SN1a with implications for IMF and
SF histories.
Progress with Current facilities
• There is going to be a lot of progress on
these problems with the current generation
of telescopes.
– Near-IR abundances studies just getting started
– AO-photometry and spectroscopy just now
beginning to be put to work
What might be missing from
current discussions?
• Real simulations (Olsen, Rigaut)
– 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)
• Detailed NGST/30m tradeoffs for photometric
studies
Aperture trade-offs
• Matt Mountain/NIO document
• Real simulations
Galactic Astrometry
• For gaussian-like images, centroiding is
easy to FWHM/70
• 30m @ 1micron -> 0.1 milliarcsecond
• Trig parallax @10kpc to faint apparent
magnitudes
• 100 km/sec@3kpc proper motion in a week.
Short Summary
• Probably no topics in this area for WvC four
viewgraphs
• To go forward requires some significant
simulation work (Olsen, Rigaut)