Extragalactic AO Science

1. Extragalactic AO Science James Larkin AOWG Strategic Planning Meeting September 19, 2004

2. WM=0.25, WL=0.75, Ho=70 km/s/Mpc 5 kpc Good Optical/NIR Seeing 2 kpc 0.5 kpc Keck Diffraction Limit @ 1.6mm 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. 1” Sb Galaxy @ z=0.5

3. 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.

4. 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.

5. 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.

6. 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.

7. 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

8. 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.

9. 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.