Extragalactic AO Science

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Extragalactic AO Science

• James Larkin
• AOWG Strategic Planning Meeting
• September 19, 2004

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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.

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Sb Galaxy _at_ z0.5
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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.

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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
  K16 mag/sq arcsec and this fades as (1z)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.

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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 R15
  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.

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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.

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Other areas that will benefit extragalactic
science

• Cleaner (or better coatings) and colder AO
  systems, and better throughput.
• Kband 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

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Some big questions future AO could address

• Assembly of galaxy masses. Complex kinematics at
  z1, Lyman break kinematics at z3. Modern mass
  disks at z2?
• 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.

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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.