1. CELT Science Case

2. CELT Science Justification Process Put together a Science Working Group –Bolte, Chuck Steidel, Andrea Ghez, Mike Brown, Judy Cohen, Mike Jura, Richard Ellis, Wal Sargent –Identified areas and solicited work from various members of the UC/CIT community –Made a presentation at a workshop in Feb 2001 and gathered useful feedback. –Final result is Chapter 2 of the CELT Conceptual Design `Greenbook’

3. SWG Goals Answer questions: –Is it worthwhile building a next generation large telescope based on science drivers? –What is the minimum size for `breakthrough’ capability –Where does a 30m O/IR telescope fit into the ALMA/NGST/multiple 8m picture Make the science case Guide conceptual design of telescope and proposed 1st generation instruments and the site

4. Emphasize capabilities, rather than specific science projects. –Lesson from Keck is that it is difficult to anticipate the most exciting science areas a decade in advance. –Developing workhorse capabilities in general areas pays large scientific dividends. Anticipated Science Areas: –The development and evolution of structure in the universe –The emergence of the first galaxies –The physics of star formation –The formation and evolution of planetary systems –Physical processes in the Solar System –The star formation and chemical evolution history of galaxies in the local universe. New discovery space

5. Greenbook Examples Spectral studies of Solar System objects Extra-solar planets –Extend searches to lower L/M –Spectroscopic studies of ESP atmospheres –Direct detection Star formation Chemical Evolution/star formation histories of galaxies to 20Mpc Black hole demographics Evolution of galaxies and the IGM from z=1-5

6. Seeing-limited optical/near-IR spectroscopy of faint objects over wide fields (0.3-2.5 microns) –Much of the highest-impact Keck science to date has been in this area. –This capability provides much of the synergy with other observatories working at other wavelengths. Near-IR diffraction-limited imaging and spectroscopy (1- 2.5 microns) –Science applications from the nearest star-forming region to the most distant galaxies. –Raw sensitivity competitive even with NGST for imaging (but with 5 times the spatial resolution). –New dimension is spectroscopy. R>5000 allows astrophysics– kinematics, chemistry, measurement of physical properties Thermal-IR diffraction limited imaging and spectroscopy –Spatial resolution coupled with high spectral resolution complements the sensitivity of SIRTF, NGST –Similar spatial resolution to ALMA, at shorter wavelengths.

7. Seeing-Limited Observations One illustrative example: Sloan Digital Sky Survey survey at a lookback time of 10 billion years (z~2.5) –20 arc minute seeing limited field of view: equivalent at z=2.5 to a 3.4 degree field at the mean redshift of the SDSS– CELT is a wide-field telescope for the distant universe. –There are 50,000 galaxies (in the z=2-3.5 range) per square degree accessible to low-resolution optical spectroscopy with CELT (R=26.5) –The CELT aperture allows one to use the brightest high redshift galaxies, rather than rare quasars, as background sources that can be used to perform tomography on the diffuse intergalactic medium. Surface density of objects for which R>5000 spectra could be obtained increases by 2 orders of magnitude Detailed physics, chemistry of baryonic material, relative distribution of galaxies, diffuse hydrogen, and metals in the young universe.

8. Example: Baryonic Structure at High Redshift The 3-D Structure of the diffuse IGM can be probed using “tomography” via multiple sightlines through the survey volume Keck/HIRES hydrogen carbon

9. Where to next? Database of night-sky emission and detector characteristics Develop a simulator Identify few key science questions and do a detailed evaluation of 30m capability (assist in tradeoff discussions) Expand the science baseline of ideas for 30m science - e.g. astrometry

10. Diffraction-limited Observations For many diffraction-limited observations, the signal scales as D 4 –Gains factors of 60- 80 for unresolved sources –Crucial for spatial dissection accompanied by astrophysical spectroscopy near-IR mid-IR

11. Thermal IR (3-30 microns) Point source sensitivity is not a primary driver, although it is respectable relative to all but NGST. This is the realm of highly obscured regions, star and planet formation Spatial Resolution would be unprecedented –80 mas at 10  m –160 mas at 20  m Unique high-resolution spectroscopic capabilities Figure courtesy of James Graham