1. Charling Tao, NAOC August 2006 Dark Energy Constraints from BA0 Wang Yun astro/ph 0601163

2. Charling Tao, NAOC August 2006 Need good z resolution Cosmos (HST) Ground optical follow-up for photoz  z/(1+z)=0.031! What about space and radiotelescopes? Wang Yun astro/ph 0601163 Need factor 10 improvement for w’ measurement to 0.1!

3. Charling Tao, NAOC August 2006 21 cm redshift survey to constrain dark energy Jeff Peterson and Ue-Li Pen (March 2006 Moriond) n Use acoustic oscillations from z = 0 to z = 1.5 to detail the transition from deceleration to acceleration. n Survey 2 Pi steradians from 500 to 1500 MHZ with a 250,000 sq m fixed-pointed meridian-scan radio telescope. n Cylindrical reflectors allow for ultra-wide field observations, and inexpensive FFT based beam forming. n Modest cost--$20M--$0.02/redshift

4. Charling Tao, NAOC August 2006 Four Cylinders each 2 (3?) km long N 2 (3 )km

5. Charling Tao, NAOC August 2006 Cylindrical reflectors use suspended mesh, with a line of feed points Reflector Cost: ~$20/m^2 Survey Speed~A*N

6. Charling Tao, NAOC August 2006 Existing cylinders MOLONGLO Cost:$12/m^2 (current dollars) OOTY Both rotate in one dimension Molonglo AUSTRALIA Brisbane Darwin Perth Canberra Hobart Adelaide Melbourne Sydney +

7. Charling Tao, NAOC August 2006 Cylinder History Illinois 400 ft Telescope ca. 1960 n Popular 1960-1980 n Lost favor with advent of cryogenically cooled pre- amplifiers. n Room temp amplifiers with 20K noise temp now available.

8. Charling Tao, NAOC August 2006 Projected w and w’ sensitivity Blake and Glazebrook

9. Charling Tao, NAOC August 2006 Dark Energy Constraint vs. redshift limit Blake and Glazebrook

10. Charling Tao, NAOC August 2006 Conclusions Peterson w=w 0 +w 1 z Many questions on feasability and price! n Using off the shelf technology, a redshift survey telescope can be built for modest cost ($20M) which will yield 10^9 redshifts to z~1.5 n Will cover 100 times the SDSS volume n Will constrain w 1 to ~0.1 ???? 200 M ???? =SKA/10 Why not use existing facilities? Han JinLin - EVLA - FAST: need to develop fast correlators