Download Extragalactic AO Science

Extragalactic AO Science
James Larkin
AOWG Strategic Planning Meeting
September 19, 2004
Fundamental motivations

Galaxies quickly shrink below 1” in size making ground-based
observations difficult, but their sub-structures like bulges remain
above the Keck diffraction limit to arbitrary redshift.
2
Angular Size(arcsec)
WM=0.25, WL=0.75, Ho=70 km/s/Mpc
1”
1.5
1
5 kpc
Good Optical/NIR Seeing
0.5
2 kpc
0.5 kpc
Keck Diffraction Limit @ 1.6mm
Sb Galaxy @ z=0.5
0
0
1
2
3
Redshift
4
5
Fundamental motivations

At high redshift, optical spectral lines shift into the infrared where AO
correction is best and HST has had limited impact.

Magic redshift ~ 2.3








Ha & NII in K band
OIII & Hb in H band
OII, 4000 Break in J band
This is probably the formation epoch of MW-like disks (1” diameter).
Most gravitational lenses occur in areas under a couple of
arcseconds, and weakly lensed galaxies are elongated by of order
an arcsecond.
Even for extended sources, AO on Keck provides increased
sensitivity. Especially powerful in identifying point-like sources within
galaxy.
Crowding of stars in nearby systems prevents accurate analysis of
stellar populations.
The internal structure of most nearby active nuclei is unresolved with
one arcsecond resolution.
Fundamental Problems

Guide star brightness




Very few galaxies have sufficiently bright cores for high-order AO
systems.
Only ~10-4 of objects are near bright foreground stars
Curvature systems are currently doing most of the extragalactic
science, but with limited Strehl.
Surface Brightness



Sensitivity increases rapidly with Strehl for point sources, but
extended targets gain much less.
AO systems produce additional background in Near-IR and
reduce throughput further making it difficult to observe faint
extended sources.
Normal galaxy disks only achieve a maximum SB of K~16
mag/sq arcsec and this fades as (1+z)4. This means all normal
disks are fainter than 22.5 mag within 0.05x0.05”.


Galaxy evolution improves this affect.
Observations take hours even for imaging.
What will the laser do…



Provide consistent performance on variety of sources.
Allow for target selection by characteristics.
Open up HST deep fields and ground based redshift
fields.





Brightest star within ultra deep field is R~15 mag
Opens up the study of rare but important objects such as
Lyman-break galaxies, sub-mm galaxies, and
ultraluminous infrared galaxies.
Allow studies of stellar populations as a controlled
function of radius.
Improves Strehl since extragalactic sources have
depended on off-axis guide stars.
Generally beneficial to all areas of extragalactic science.
What would higher order do for you
without a laser
Reduce fraction of sky available, probably
becoming totally dependent on foreground
off-axis stars.
 Increased sensitivity to point sources, and
better contrast.
 Probably only beneficial to a few areas of
stellar population studies if still dependent
on natural guide stars.

Other areas that will benefit
extragalactic science…

Cleaner (or better coatings) and colder AO systems, and
better throughput.



K–band is probably the most important filter
Local thermal background can devastate faint object work.
Integral field spectroscopy




Avoids slit losses.
Samples complex geometry.
Multiplex advantage on resolved stellar populations.
SINFONI is commissioned on VLT.

9 out of 12 approved science verification programs are extragalactic
Some big questions future AO could address





Assembly of galaxy masses. Complex kinematics at z~1,
Lyman break kinematics at z~3. Modern mass disks at
z~2?
Variations within NLR of individual AGN, and detailed
comparisons of many AGN. Testing standard paradigm.
Evolutionary (or not) linkages between ULIRGS,
Quasars and normal galaxies.
Cosmological constant – High redshift type-Ia
supernovae.
Formation of bulges and tie to central black hole.



Central velocity dispersions in local galaxies.
Bulge formation tied to quasar epoch?
Test new CDM models of galaxy formation.
Technology with biggest impact
Laser, especially with faint TT magnitudes
 PSF Characterization (stability,telemetry)–
accurate photometry and morphology
 General improvements: better wavefront
sensor CCD, faster reconstructor, cleaner
optics.
