Keck NGAO Science Case Requirements Claire Max and Liz McGrath NGAO Team Meeting 13 January 25, 2008

2 Topics Overview of SCRD Release 2 Discuss three science cases (the ones that have evolved the most) –Extrasolar planets around low-mass stars (key) –Gravitational lensing –Backup Science New version of Rainbow Chart Other considerations

3 SCRD Release 2 Overview For each science case section: –Scientific background –Results from science simulations or calculations –Requirements: text and tables (tables will go into SRD, FRD) “Key Science Drivers”: tables in good shape “Science Drivers”: –New or substantially revised sections: gas giant planets, ice giant planets, backup science, minor planet size shape and composition, gravitational lensing –Beginnings of section on QSO Host Galaxies –Some cases put off till next SCRD Release or PDR Astrometry in sparse fields, resolved stellar populations, debris disks and young stellar objects,

4 Key Science Case: Extrasolar planets around low-mass stars General goals (unchanged) –Direct imaging of extrasolar planets allows measurement of colors, temperatures, and luminosities: test theoretical models of planetary evolution and atmospheres. –Spectroscopic follow-up will be an important means to characterize the planet atmospheres Discovery space for NGAO is nice complement to Gemini GPI –Enabled by laser guide stars: look for planets around faint low-mass stars

5 Target sample now differentiated into three scientific questions Target sample 1: Old brown dwarf stars, to 20 pc –Old field brown dwarfs Target sample 2: Young brown dwarf stars, to 80 pc –Young (<100 Myr) field brown dwarfs and low-mass stars Target sample 3: Young solar-mass stars, pc –Solar type stars in nearby star forming regions such as Taurus and Ophiuchus, and young clusters at distance of 100 to 150 pc. Separated samples because each has different requirements on contrast ratio, astrometry

7 Issues regarding the planets around low-mass stars science case(s) Target sets 1, 2, and 3 get increasingly hard Should they all be “requirements”? Tentative answers: –Target Set 1: keep as “requirement” –Target Set 3: move to “goal” –Target Set 2: Analyze further Philosophy: –GPI, SPHERE etc are specialized instruments –Don’t torque whole NGAO design around these science cases, but let’s see how well we can do with reasonable level of effort

Science Requirements: Gravitational Lensing by Galaxies E. McGrath and C. Max

9 Outline I.Background a.Strong lensing: Einstein rings, multiply imaged sources b.Gravitational telescopes II.Scientific Goals, Galaxies Lensed by Galaxies a.Determine mass profile of foreground deflector galaxy by studying the geometry of multiply imaged sources b.Utilize magnification power of the lens to obtain detailed kinematical and morphological information about distant galaxies III.Scientific Goals, Galaxies Lensed by Clusters a.Find high-z galaxies around clusters, lensed with high magnification IV.NGAO Derived Requirements a.Near-IR IFU b.Near-IR imager c.d-IFS

10 Galaxies Lensed by Galaxies

11 Galaxies Lensed by Galaxies: Mass Profile of Deflector Galaxy Predominantly early-type, massive elliptical galaxies Questions of interest: Mass profile of dark-matter halo Fraction of DM as a function of radius, redshift, mass Substructure in DM halos? Combine with scaling relations (e.g., Fundamental Plane) to disentangle their stellar-population and mass- assembly histories

12 Galaxies Lensed by Galaxies: Properties of Background Galaxies Predominantly late-type, faint spirals and irregular galaxies Super-resolution (from lens + NGAO) allows one to address the following issues: Morphology (surface brightness profile) Kinematics (velocity profile) Stellar population information star formation history as a function of z

13 Kinematic Lensing Exploits achromaticity of galaxy-galaxy lensing –(traditional lensing exploits surface brightness preservation to construct model of lens potential)

14 Galaxies Lensed by Galaxies: NGAO vs. HST and LGS AO Pre-NGWFC

15 Cluster-scale lensing science Structure of cluster dark matter halos Detection of very high-z galaxies and determining the luminosity function and size distribution of such objects. –Since clusters are large, we have longer caustic lines, which means a better chance to observe a high-z galaxy in the region of highest magnification d-IFU application –Place multiple arms along caustic lines to find high-z targets and to obtain spectra of multiple lensed sources simultaneously Imaging? –Can mosaic narrow fields –Is acquisition camera useful? –Y/z/J-band drop-outs

16 Galaxies Lensed by Galaxies: Near-IR IFU Requirements The shorter the wavelength the better (better resolution, better astrometry) –J-band (would use z-band if available, for closer sources) Higher-z sources require longer FOV needs to be large enough to fit lens (alternatively, mosaic) –Typical lens sizes are ~1” in radius (e.g., deflector galaxy at z~0.5 and background galaxy at z~1) –Some are up to a ~2” in radius, requiring larger fields of view (or mosaicing). PSF knowledge and stability –In order to subtract out the deflector galaxy. Easier when observing a specific line (H  ) where foreground galaxy will be faint

17 Gravitational Lensing: More NGAO Instrument Requirements Near-IR imager –Shorter wavelengths are better (z, J-band) –FOV slightly larger Want to be able to dither For cluster-scale lensing, FOV is up to 1 arcmin (due to anisoplanatism, will certainly want to mosaic smaller regions) –PSF knowledge and stability even more important, since we are not focusing on a narrow emission line (more contamination from deflector galaxy). Need to model the surface brightness profile of the galaxy convolved with the PSF, and subtract off Near-IR d-IFS (Clusters) –Longer wavelengths will likely be key, here –Used for cluster-scale lensing to obtain spectra of multiple arcs. –May need to place several IFUs along one arc –Field of regard should be at least 30” in radius in order to observe arcs around the entire cluster

18 Backup Science Backup Science requirements largely involve science preparation and operations, but there are some important considerations in NGAO design that will help ensure we get the most out of backup programs (and the least amount of wasted shutter time) Two main scenarios when conditions do not allow propagation of lasers: 1.NGS observations 2.Seeing-limited observations Also, less demanding LGS science that can be accomplished with less laser power.

19 Backup Science NGS observations –Requirements driven by most demanding science cases, which are likely to be Extragalactic backup cases Currently very difficult to do extragalactic science with LGS AO Minimal sky coverage, faint targets and faint TT guide stars –Tentative requirement that performance and sky coverage in NGS mode should not be worse than current LGS-mode operations Ensures that current science is still do-able as a backup program in NGS mode with NGAO –Sky coverage ~5% 1/6th of the 30% sky coverage we get with LGS NGAO 1/6th the number of observations (e.g, only 1 IFU available for NGS) Requires: –R=14 mag guide star with a 60” diameter FOR, or –R=15 mag guide star with a 45” diameter FOR –Fast switching between LGS and NGS mode in case conditions improve ~15 min.

20 Backup Science Seeing-limited observations –Acquisition camera used for seeing-limited surveys of large region of sky (~3’)? –Could provide follow-up targets for future NGAO observing runs Question –Is the acquisition camera sensitive enough to produce meaningful results?

21 Rainbow Chart Revisions (in red)

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23 Other Considerations: Role of “Science Drivers” Role of “Science Drivers” (as opposed to “Key Science Drivers”) Many of the “Science Drivers” will take advantage of whatever AO capabilities flow down from the “Key Science Drivers” –Don’t impose strong new requirements on AO performance, for example But “Science Drivers” often do highlight additional operational scenarios, coordination, software, or simulations needed

24 Examples Gas Giant and Ice Giant Planets –Requirements for non-sidereal tracking (≤ 50 arc sec/hr or 14 mas/sec), field of view of NIR imager (imager field of view ≥ 30” diam. at K) Backup Science –Motivates requirement on field of regard for high-order NGS wavefront sensor –Sky coverage ≥ 5% R=14 mag guide star with 60” diameter field of regard (FOR) R=15 mag guide star with 45” diameter FOR Quasar host galaxies –Emphasizes analysis of requirements for accurate PSF subtraction (to be able to image host galaxy without light from central point source). Will serve other science cases as well.

25 Other Considerations: Future Science Team Tasks Short term: add tables to SRD, FRD Rest of System Design Phase –Include remaining “Science Drivers” in SCRD –Iterate with Rich’s Wavefront Error spreadsheets At the minimum analyze for every Key Science Driver Also for one or more selected Science Drivers? –Issue Release 3 of SCRD PDR phase: –Develop astrometry error budget as a quantitative tool for the Key Science Driver cases –Analyze PSF issues quantitatively –Science simulations that address key design choices –Serious progress on instrument concepts, requirements