1. Comparative Performance of a 30m Groundbased GSMT and a 6
Comparative Performance of a 30m Groundbased GSMT and a 6.5m (and 4m) NGST NAS Committee of Astronomy & Astrophysics 9th April Matt Mountain Gemini Observatory/AURA NIO

2. Overview Science Drivers for a GSMT Performance Assumptions Results
Backgrounds, Adaptive Optics and Detectors
Results
Imaging and Spectroscopy
compared to a 6.5m & 4m NGST
A special case,
high S/N, R=100,000 spectroscopy
Conclusions

3. GSMT Science Case “The Origin of Structure in the Universe”
Najita et al (2000,2001)
From the Big Bang… to clusters, galaxies, stars and planets

4. Mass Tomography of the Universe
z~3
Hints of Structure at z=3
(small area)
z~0.5
Existing Surveys + Sloan
100Mpc (5Ox5O), 27AB mag (L* z=9), dense sampling
GSMT 1.5 yr
Gemini 50 yr
NGST 140 yr

5. Tomography of Individual Galaxies out to z ~3
Determine the gas and mass dynamics within
individual Galaxies
Local variations in starformation rate
Multiple IFU spectroscopy
R ~ 5,000 – 10,000
GSMT 3 hour, 3s limit
at R=5,000
0.1”x0.1” IFU pixel
(sub-kpc scale structures)
J H K

6. Probing Planet Formation with High Resolution Infrared Spectroscopy
Planet formation studies in the infrared (5-30µm):
Planets forming at small distances (< few AU) in warm region of the disk
Spectroscopic studies:
Residual gas in cleared region emissions
Rotation separates disk radii in velocity
High spectral resolution high spatial resolution
S/N=100, R=100,000, >4m
Gemini out to 0.2pc sample ~ 10s
GSMT kpc ~100s
NGST X
8-10m telescopes with high resolution (R~100,000) spectrographs can detect the formation of Jupiter-mass planets in disks around nearby stars (d~100pc).

7. 30m Giant Segmented Mirror Telescope concept
GEMINI
30m F/1 primary, 2m adaptive secondary

8. GSMT Control Concept LGSs provide full sky coverage
Deformable M2 : First stage MCAO, wide field seeing improvement and M1 shape control
LGSs provide full sky coverage
M2: rather slow, large stroke DM to compensate ground layer and telescope figure,
or to use as single DM at >3 m. (~8000 actuators)
Dedicated, small field (1-2’) MCAO system (~4-6DMs).
Active M1 (0.1 ~ 1Hz)
619 segments on 91 rafts
10-20’ field at ” seeing
1-2’ field fed to the MCAO module
Focal plane

9. GSMT Implementation concept - wide field (1 of 2)
Barden et al (2001)

10. GSMT Implementation concept - MCAO/AO foci and instruments
Oschmann et al (2001)
MCAO optics moves with telescope
elevation axis
MCAO Imager
at vertical
Nasmyth 4m
Narrow field AO or
narrow field seeing limited port

11. MCAO Optimized Spectrometer
Baseline design stems from current GIRMOS d-IFU tech study occurring at ATC and AAO
~2 arcmin deployment field
µm coverage using 6 detectors
IFUs
12 IFUs total ~0.3”x0.3” field
~0.01” spatial sampling R ~ 6000 (spectroscopic OH suppression)

12. Quantifying the gains of NGST compared to a groundbased telescope
Assumptions (Gillett & Mountain 1998)
SNR = Is . t /N(t): t is restricted to 1,000s for NGST
Assume moderate AO to calculate Is , Ibg
N(t) = (Is . t + Ibg. t + n . Idc .t + n . Nr2)1/2
For spectroscopy in J, H & K assume “spectroscopic OH suppression”
When R < 5, SNR(R) = SNR(5000).(5000/R)1/ and 10% of the pixels are lost
Source noise background dark-current read-noise

13. Space verses the Ground
Takamiya (2001)

14. Adaptive Optics enables groundbased telescopes to be competitive
For background or sky noise limited observations:
S  Telescope Diameter 
N Delivered Image Diameter B
Where:  is the product of the system throughput and detector QE
B is the instantaneous background flux

15. Adaptive Optics
works well

16. Modeling verses Data GEMINI AO Data Model Results 2.5 arc min.
20 arcsec
2.5 arc min.
Model Results
M15: PSF variations and stability
measured as predicted

17. Quantitative AO Corrected Data
AO performance can be well modeled
Quantitative predictions confirmed by observations
AO is now a valuable
scientific tool:
predicted S/N gains now being realized
measured
photometric errors in crowded fields ~ 2%
Rigaut et al 2001

18. Multi-Conjugate Adaptive Optics
2.5 arc min.
Model results
Tomographic calculations correctly
estimated the measured atmospheric phase
errors to an accuracy of 92%
better than classical AO
MCAO can be made to work
MCAO

19. AO Technology constraints (50m telescope)
r0(550 nm) = 10cm No. of Computer CCD pixel
Actuator pitch S(550nm) S(1.65mm) actuators power rate/sensor
(Gflops) (M pixel/s)
10cm % % , x
25cm % % , x
50cm % % , , SOR (achieved) ~ x 4.5
Early 21st Century technology will keep AO confined to l > 1.0 mm
for telescopes with D ~ 30m – 50m

20. MCAO on a 30m: summary
MCAO on 30m telescopes should be used l > 1.25 mm
Field of View should be < 3.0 arcminutes,
Assumes the telescope residual errors ~ 100 nm rms
Assumes instrument residual errors ~ nm rms
Equivalent Strehl from focal plane to detector/slit/IFU > 1 micron
Instruments must have:
very high optical quality
very low internal flexure
l(mm) Delivered Strehl
~ 0.4
~ 0.6
~ 0.8
Rigaut & Ellerbroek (2000)
9 Sodium laser constellation
4 tip/tilt stars (1 x 17, 3 x 20 Rmag) PSF variations < 1% across FOV

21. Modeled characteristics of a 30m GSMT with MCAO (AO only, l>3mm) and a 6.5m NGST
Assumed encircled-energy diameter (mas) containing energy fraction h
30M mm 1.6mm 2.2mm 3.8mm 5.0mm 10mm 17mm 20mm
(mas)
h % % % % % 56% % %
NGST mm 1.6mm 2.2mm 3.8mm 5.0mm 10mm mm 20mm
(mas)
h % % % % % % % %
Assumed detector characteristics
1mm < l < 5.5mm mm < l < 25mm
Id Nr qe Id Nr qe
0.01 e/s 4e % e/s e %

22. Comparative performance of a 30m GSMT with a 6.5m NGST
Assuming a detected S/N of 10 for NGST on
a point source, with 4x1000s integration
R = 10,000
R = 1,000
R = 5
advantage
GSMT
NGST advantage

23. Comparative performance of a 30m GSMT with a 4m NGST
Assuming a detected S/N of 10 for NGST on
a point source, with 4x1000s integration
R = 10,000
R = 1,000
R = 5
advantage
GSMT
NGST advantage

24. Observations with high Signal/Noise, R>30,000 is a new regime - source flux shot noise becomes significant

25. High resolution, high Signal/Noise observations
Detecting the molecular gas from gaps swept
out by a Jupiter mass protoplanet, 1 AU
from a 1 MO young star in Orion (500pc) (Carr & Najita 1998)
GSMT observation ~ 40 mins
(30 mas beam)

26. Conclusions NGST Comments X X X X X X X NGST advantage
GSMT advantage X
6.5m
4.0m
Comments 1.
Camera
0.6 – 5 mm
Deep imaging from space; consistent image quality, IR background, even for l < 2.5mm if D>4.0m 2.
MOS
R=1,000
1.2 – 2.5mm
2.5 – 5.0 mm
NGST MOS still competitive for l < 2.5mm only if D~6.0m (consistent image quality, l coverage) 3.
Spec. R=1500
5 – 28 mm
Clear IR background advantage observing from space, even for D~4m
and R< 30,000 4.
IFU
R=5,000
Detector noise limited for l < 2.5mm D2 advantage for groundbased GSMT
For l >2.5mm, NGST wins even D~4m
D2 advantage for groundbased GSMT
For l <12mm
AW advantage of GSMT,technology challenges from space (fibers) X
NGST Instrument X X X X
High S/N, R~100,000 spectroscopy
WF MOS Spectroscopy l < 2.5mm X X