Charling Tao

, NAOC August 2006

Dark Energy Constraints from BA0Wang Yun astro/ph 0601163

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!

Charling Tao

, NAOC August 2006

21 cm redshift survey to constrain dark energy

Jeff Peterson and Ue-Li Pen (March 2006 Moriond)

Use acoustic oscillations from z = 0 to z = 1.5 to detail the transition from deceleration to acceleration.

Survey 2 Pi steradians from 500 to 1500 MHZ with a 250,000 sq m fixed-pointed meridian-scan radio telescope.

Cylindrical reflectors allow for ultra-wide field observations, and inexpensive FFT based beam forming.

Modest cost--$20M--$0.02/redshift

Charling Tao

, NAOC August 2006

Four Cylinders each 2 (3?) km long

N

2 (3 )km

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

Charling Tao

, NAOC August 2006

Existing cylinders

MOLONGLO

Cost:$12/m^2 (current dollars)

OOTY

Both rotate in one dimension

Molonglo

AUSTRALIABrisbane

Darwin

PerthCanberra

Hobart

AdelaideMelbourne

Sydney

+

Charling Tao

, NAOC August 2006

Cylinder History

Illinois 400 ftTelescope ca. 1960

Popular 1960-1980

Lost favor with advent of cryogenically cooled pre-amplifiers.

Room temp amplifiers with 20K noise temp now available.

Charling Tao

, NAOC August 2006

Dark Energy Constraint vs. redshift limit

Blake and Glazebrook

Charling Tao

, NAOC August 2006

Conclusions Peterson

w=w0+w1z

Many questions on feasability and price!

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

Will cover 100 times the SDSS volume

Will constrain w1 to ~0.1

????200 M

????=SKA/10

Why not use existing facilities? Han JinLin

- EVLA

- FAST: need to develop fast correlators