ELT Stellar Populations Science

•Near IR photometry and spectroscopy of resolved stars in nearby galaxies provides a way to extract their entire star formation and chemical enrichment histories

Crowding is the limiting factor for photometry of bulges, disks, and the main bodies of elliptical galaxies; sensitivity will be limiting factor for regions with lower surface brightness

(independent of aperture size)M31 observed with Gemini N+NIRI/Altair (Olsen et al. 2006)

KHB~23.5

Issues addressed through simulations

Scientific Issues:

Sample size needed

Field size needed

Filters needed

Photometric Issues:

Spatial variability of PSF

Time variability of PSF

Absolute calibration

PSF Simulation

• AO Error sources included

1. Finite number of guide stars and DMs

2. Finite spatial resolution of wavefront sensors and DMs

• Sampled on 7x7 20” wide grid in IJHK for 20-m, 30-m, 50-m, and 100-m telescopes

• Sampled over 12-minute average intervals from hour-long “typical” observation with TMT MASS/DIMM

• 5 atmospheric profiles 4 filters 49 positions 4 telescopes = 3920 PSFs

30-m J PSF grid, profile 1

Simulating a realistic observation

Courtesy of Richard Clare

Simulation procedure

•Select appropriate population mix

•Pick stars from stellar isochrones and place in image, making sure to simulate stars well below crowding limit

•Convolve image with PSFs (495 convolutions, combine through weighted average)

•Add sky background and noise

•Perform PSF-fitting photometry

•Correct photometry for Strehl ratio using profile 1 or average of profiles 1 and 5

•Derive best-fit population mix

“Raw” photometry With 1 PSF observationWith 2 PSF observations“Perfect” photometry

20-m to 100-m: M31 Bulge

KHB~23.5, KMSTO~27

20-m to 100-m: M31 Bulge20-m 30-m

50-m 100-m

An M31 Survey: 20-m

Local Group Survey (Massey et al. 2002) image

Name r() K B/D Klim Time(s)F1 1.97 15.0 7.4 24.1 21.8Bulge1 2.05 15.1 6.7 24.1 24.9F177 2.79 15.4 5.5 24.4 38.3F174 2.59 15.4 5.3 24.4 38.3F3 3.80 15.8 3.8 24.7 66.9Bulge2 3.83 16.0 3.1 24.9 87.8F4 3.98 16.1 2.7 25.0 100F5 5.84 16.4 2.0 25.2 147F170 6.08 16.5 1.9 25.3 168Disk2 9.09 17.1 1.1 25.7 348F2 11.9 17.8 0.3 26.1 776F280 20.5 18.4 0.2 26.6 1767Disk1 56.9 19.6 0.0 27.8 17476

1 hour exposure, S/N=5:J: 28.9H: 28.0K: 27.0

KHB~23.5, KMSTO~27