1. The Need for Contiguous Fields NGAO Team Meeting, Waimea January 22, 2007 Claire Max

2. 2 Outline Background Science cases Calibration issues Summary

3. 3 Background Many NGAO science cases need only a small field of view (e.g. 10” or less) A few important science cases are looking at larger objects or fields (e.g. 0.5 - 2 arc min) Here we are asking which of the latter require contiguous coverage of these larger fields, and which can do as well or better with many smaller (e.g. a few - 10”) non-contiguous fields

4. 4 Background, continued We are posing this as a geometry question In reality it’s more complex For example: –Quality of PSF knowledge may differ between contiguous (MCAO) and non-continuous (MOAO) field –Absolute value of Strehl may differ –PSF variability may differ In this discussion we will not focus on these items. We will ask: “all other things being equal, can this science case be done with a contiguous field? With a non-contiguous field?”

5. 5 Science Cases: Narrow Field* NameImagingSpectroscopy Asteroids and TNOs  Moons of giant planets  Young stellar objects  Debris disks  Companions to low mass stars  ? Galactic Center (near Sag A*)  Grav. lensing by galaxies  Black hole masses, nearby gals  Extragalactic globular cluster *s  * For example 10” or less

6. 6 Large-field science cases that do not benefit from a contiguous field Gravitational lensing by clusters –Several lensed objects per square arc min (in a cluster) –Each a few arc sec across –Field of regard 30” - 40” Field galaxies at high redshift (z ≥ 0.5) –5 - 10 galaxies per square arc min, each a few arc sec across –Field of regard as big as possible –Galaxy assembly and internal kinematics –History of disk and bulge growth –Internal color gradients and star formation history MOAO would be a fine solution for these

7. 7 Large-field science cases which could benefit from contiguous field Galactic Center stellar populations, kinematics (in regions beyond the central 10 arc sec) –How did the young stars get there? –Are there multiple stellar disks? –Clusters such as the Arches Initial mass function in the Orion star forming region Stellar populations in nearby dwarf galaxies Intergalactic stars in the Virgo cluster Do these require a contiguous field, or could they be done instead with multiple non-contiguous fields?

8. 8 Some common characteristics All need stable PSF Crowded fields of point sources: possible (to varying degrees) to extract PSF from data themselves All are confusion limited –Hence benefit strongly if Strehl is higher All are large enough that field could be broken up into smaller pieces for non-contiguous AO

9. 9 Specific issues: IMF in Orion For photometry, can break into smaller non-contiguous pieces (e.g. MOAO) Issue: how to determine if a star is in the Orion cluster, or a field star? Astrometry is one method (cluster stars all move together) Need to connect to wide cluster reference frame Issues: –MCAO: astrometry “breathes” –MOAO: how do you anchor postage stamps to larger reference frame? Both: do large-scale astrometry with MOSFIRE?

10. 10 Specific issues: Intergalactic stars in Virgo cluster This is hard. –Stars are faint. J=26.5, H=25.8, K=25.5 Need high AO and instrument throughput, high QE on detector, excellent background subtraction, etc Gemini MCAO decided this was too hard for their GSAOI imager. Probably too hard for any incarnation of Keck NGAO.

11. 11 Issues to pursue How to best do astrometry (work is under way; here are some further thoughts) Problems generic to both MCAO and MOAO –Static and dynamic distortions, residual turbulence close to (or in) AO system,..... Issue for MCAO: “breathing” of field. –Can adequate mitigations be developed? Issue for MOAO (for some science cases): how to tie in astrometric measurements within one postage-stamp to the larger-scale reference frame. –Is it adequate to use MOSFIRE imaging for the larger scales, and to tie MOAO postage stamps to MOSFIRE’s frame?

12. 12 Design considerations Many of the wide-field science cases for which MOAO would work well need imaging –We need to think about design of MOAO imagers as well as IFUs If we have MOAO imagers, need to develop methods to cross-calibrate the various units for photometry –e.g. Use internal sources during the afternoon to cross-calibrate all of the deployable imagers with respect to a reference unit. Then do photometric standard with the reference unit.

13. 13 Summary A large number of NGAO science cases need a narrow field (e.g. 10 arc sec or less) Several key Galactic and extragalactic science cases seem best suited for non-contiguous fields –Objects of interest are separated and have space density of order 10 per square arc minute A few science cases could use either contiguous or non- contiguous fields Issues to address: –Astrometry with both MCAO and MOAO –Concept for MOAO imagers –Photometric calibration of multiple units with respect to each other