The Scientific Context for NGAO
Mark Morris, representing the NGAO Scientific
Advisory Team (NSAT):
Tommaso Treu, Laird Close, Michael Liu,
& Keith Matthews
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Context for NGAO – growing demand for
LGS-AO on large telescopes
➜ the clear advantage of sky coverage.
Peer-reviewed publications:
Note the dominance of Keck, but other observatories
are knocking hard on the door…
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Adaptive optics usage at WMKO has increased dramatically over the
past decade, and is still rising …
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All major research communities are employing LGS AO …
2010
to date:
6 months
Total LGS
Extragalactic
Galactic
Solar Sys
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Key Science Cases – Requirements Drivers
1. High-redshift galaxies, internal structure and dynamics at z = 1 – 3
2. Black hole masses in nearby AGNs: resolving the Keplerian velocity
increase within the black holes’ sphere of influence
3. General Relativity at the Galactic center: precision stellar orbits to
discover and measure post-Newtonian effects.
4. Planetary companions to low-mass stars & brown dwarfs:
taking advantage of the favorable contrast, & using a coronagraph
5. Asteroid and KBO companions: size, shape, composition & orbits
of companions to minor planets with the aim of reconstructing their history
These push limits of AO system, instrument, and telescope.
Determine the most demanding performance requirements.
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Simulation of radial velocities observed along the major
axis of an emission-line disk surrounding a black hole
in a galaxy center.
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Observational Attributes:
 near-diffraction limited performance in the near-IR (K Strehl ~80%).
On Keck, this provides the highest spatial resolution available at any
of its operating wavelengths.
Very high Strehl  key enabler of the science envisioned with NGAO.
 substantially increased sky coverage, compared to existing AO systems
 AO corrections at wavelengths as short as 7000 Å
 imaging with a reconstructable and only moderately variable PSF
over the entire science field (~20”)  photometry, astrometry, deconvolution
 integral field spectroscopy at R~4000 from 0.7 to 2.4 µm,
with three pixel scales: 10, 35, and 50 (or 70) mas, with 5.6” x 3” FOV
at 50 mas sampling.
- AO-fed medium-resolution NIR IFS unique among AO systems
under development.
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How is NGAO different from
Keck’s AO today?
Calcium
triplet
850 nm
• NGAO: same
Strehl at Ca
Triplet as LGS
today in H band
• NGAO: better
Strehl at J band
than LGS today in
K band
• NGAO: much
higher sky
coverage
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-=- Sky coverage -=-
Many science cases, particularly extragalactic ones
such as Galaxy Assembly and Star Formation
History are strongly affected by NGAO’s sky
coverage
• Need to look at random places in the sky
• Out of the plane of the Galaxy
• In select “Deep Fields” that were chosen by others to have
very few stars
• Need to accumulate a good statistical sample of galaxies in
order to draw conclusions
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MOAO correction of IR tip-tilt stars
has large benefit for sky coverage
• Example: Keck NGAO, galaxy assembly science case,
zenith angle 30 deg, median seeing at Mauna Kea
NGAO EE 50
Current Keck TT
Current Keck EE 50
NGAO TT
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NGAO: dramatic improvements in SNR
for IFU spectra of distant galaxies
Antennae Galaxies
Local Ha image
SNR in H
LGS AO z
=2.5
NGAO z =
2.5
• Cooled AO system to reduce thermal background (K-band)
• Increased instrument throughput (34% vs. 19%)
• Higher spatial resolution means better point source sensitivity
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Advantages of NGAO for
Resolved Stellar Populations
1. Reduced confusion from
halos of adjacent stars:
means better photometry on
more stars
2. Color magnitude diagrams
give better discrimination
using I – K colors than using
J – K or H – K colors (next
slides)
3. Improved astrometry lets
you better determine cluster
membership (next slides)
Olsen Blum and Rigaut 2003
GSMT simulation of NGC 1835
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Resolved Stellar Populations
Visible-light AO = better discrimination between stellar populations due to
longer lever-arm of I-K vs. J-K for color-magnitude diagrams.
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Four Major Wide Field AO Systems
are under Development
Tradeoffs: spatial resolution, strehl, PSF uniformity
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NGAO Will Be the Leader in
High Performance Narrow Field AO
contrast, Strehl, sky
coverage
NGAO more robust
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A broad array of other investigations is enabled by NGAO,
some of which have been used as additional science drivers
 Gravitationally lensed galaxies
 QSO host galaxies
 Circumnuclear disks in galaxies
 Extended gaseous structures at high redshifts
 Resolved stellar populations in extragalactic systems
 The internal dynamics of star clusters, young and old
 Debris disks
 Young stellar objects, protostellar disks, & jets
 Stellar winds: bubbles, bow shocks, & pinwheels
 Planetary & preplanetary nebulae – launching of bipolar flows
 Jovian planet atmospheres: climate and wind dynamics
 Planetary rings, satellites, and their interactions
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So far, 40 astronomers have helped
develop the NGAO Science Cases
New
* Current
NSAT
Members
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Ádámkovics, Mate
Ammons, Mark
Auger, Matt
Barth, Aaron
Bouchez, Antonin
Cameron, Brian
Close, Laird
de Pater, Imke
Eisner, Joshua
Emery, Joshua
Fassnacht, Chris
Ghez, Andrea
Greene, Tom
Hammel, Heidi
Hillenbrand, Lynne
Jonsson, Patrik
Koo, David
Larkin, James
Law, David
Liu, Michael
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Lu, Jessica
Macintosh, Bruce
Marchis, Franck
Marshall, Phil
Matthews, Keith
Max, Claire
McGrath, Liz
Melbourne, Jason
Melling, Laura
Metchev, Stanimir
Morris, Mark
Nierenberg, Anna
Noll, Keith
Novak, Greg
Olsen, Knut
Steidel, Chuck
Suyu, Sherry
Treu, Tommaso
Vegetti, Simona
Weinberg, Nevin
science cases from other scientists
are always welcome
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Competitive Landscape: JWST
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JWST advantages
– JWST will have better sensitivity than NGAO (low
backgrounds) at K band, but lower at J
– Diffraction limited imaging between 2.4 and 5 m
– Multiplexed slit spectroscopy (x 100)
– Spectral resolution R = 2700
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Keck NGAO advantages
– Better spatial resolution than JWST at
wavelengths below 2 m
- JWST pixels under-sample the diffraction limit at
wavelengths shorter than 2 m
– Spectroscopy at spatial resolutions < 0.1”
– Spectroscopy at spectral resolutions R > 2700
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NGAO complementarity to TMT
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Technology groundbreaking for NFIRAOS
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In TMT era, Keck NGAO can play key role in
screening targets for follow-up with scarce TMT time
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TMT advantages
– Higher spatial resolution
– Higher sensitivity
– Wide field with partial correction (IRMS)
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Keck NGAO advantages
– Higher sky coverage (LGS AO corrected tip-tilt stars)
– Half-decade head start
– Synoptic studies
– More CIT & UC community access for NGAO
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For AGN black hole mass measurements, NGAO using Ca II triplet is
comparable with TMT in K band (CO bandhead).
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Summary
 NGAO’s very high Strehl over a substantial field of view,
coupled with a dramatic improvement in sky coverage,
would bring considerable scientific return, and enable
both major progress in existing investigations as well as
new kinds of scientific investigations.
 All areas of astronomy would profit from this capability; the
number of significant science cases so far indicates that
the demand for this capability will be enduring, even into
the era of JWST and TMT.
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