High Redshift Galaxies: Encircled energy performance budget and IFU spectroscopy Claire Max Sept 14, 2006 NGAO Team Meeting

Agenda Discuss each of the first series of science cases Come up with preliminary “figures of scientific merit” Discuss the AO design issues most affecting the science case Lay out “next steps”

Focus on science requirements for IFU spectroscopy of high-z galaxies We need to decide on a few key science issues. –One example (from June proposal): mergers of high-z galaxies –Let’s come up with several other science issues, then narrow down –Understand what we need to learn from spectroscopic measurements What are the key things to measure? Examples: –Redshifts –Morphologies –Spatially resolved kinematics –Star formation rates –Compare AGNs with quiescent galaxies –Gas content and outflow properties

Potential science cases: example from June NGAO proposal Mergers of hi-z galaxies. Implications for: –Balance of early to late type galaxies, formation of bulges, destruction of disks –Formation of LIRGs, ULIRGs –Possible role in AGN life cycle –Gas injection into IGM Top: Images. An order of magnitude more pixels with with SNR  10 (yellow) for NGAO Bottom: Kinematic maps. Current LGS AO: Hard to determine if galaxy has ordered rotation. NGAO: Spatially complex velocity distribution characterizing major merger.

What alternative potential science cases can we write down?

Surveys are the name of the game We need to characterize key survey parameters for a few specific science cases –What kind of galaxies are we going to study? –How many of these galaxies are needed? –How far apart are these galaxies on the sky? –How bright are they? –What spatial extent/structure do we expect? Sky coverage fraction, observing efficiency, and throughput are 3 potential figures of merit for surveys –Are these the right ones?

Figures of merit for surveys of high-z galaxies

Discuss the AO design issues most affecting the science case Trade between encircled energy diameter and sky coverage fraction –Key AO design issues are tip-tilt correction, desired encircled energy diameter, backgrounds –More on this later Spatial and spectral resolution vs. signal to noise –Key AO and instrument design issues are FWHM or encircled energy diameter, slitlet size, backgrounds What else?

Role of encircled energy Example from Law, Steidel, Erb for Keck AO, OSIRIS: For given background level, SNR increases (up to a point) as slitlet or lenslet size gets larger Encircled energy diameter (e.g.  80 ) and background levels determine when you start getting diminishing returns from using larger slitlets Slitlet too small or encirled energy diam. too big: lose signal Slitlet too large: high background Larger slitlets mean lower spatial resolution as well Exposure time 1 hr, star formation rate 1 M  / yr

Trade-off between encircled energy diameter and sky coverage fraction For tomographic wavefront measurements, encircled energy diameter is determined by the quality of the tip- tilt correction –If there are enough bright tip-tilt stars w/in field, tip-tilt correction will be good, encircled energy diameter will be small But the more bright tip-tilt stars you require nearby, the lower the sky coverage fraction (statistically) –Tip-tilt stars are in short supply To achieve a minimum required level of sky coverage (e.g. 50%), the average  80 may be several times the diffraction limit

Expected NGAO sky coverage fraction, from June proposal In GOODS N field, predicted H-band FWHM is <50 mas over half the sky < 100 mas almost everywhere Implies that a slitlet diameter of mas could be optimum, but will depend on background levels GOODS N Need to repeat for encircled energy diameter, for other deep fields, other ’s R. Dekany

Next steps