1. 21CMA 21 Centimeter Array a.k.a. PAST

2. Reionization 21cm: hyperfine transition of neutral Hydrogen

3. 21CMA a.k.a. PAST Basic ideas: an experiment, not an observatory use cheap, off-the -shelf technology (i.e. TV+PC) simple design (looking at NCP) choose site with minimal EM interference to become operational before MWA/LOFAR Xiang-Ping Wu (NAOC) Ue-Li Pen (CITA) Jeff Peterson (Carnegie)

4. VLBI Map of 21CMA site 21CMA

5. E N Urumuqi Ulastai

6. Log-Periodic antenna

7. 20m A pod (127 antenna)

8. correlator arrayLNAfilteramplifier Optical transmitter Opt. fibre Optical receiver ADC 21CMA data collection system

9. Basic Design of 21CMRA At z=9, 10 comoving Mpc  ~ 0.6 MHz,  ~ 3.6 arcmin frequency range 70-200 MHz (6.1<z<19.3) baseline: 2 km, (at 140 MHz, 3.6 arcmin) Collecting Area 10 4 m 2 A/L 2 ~ 0.01

10. Schedule & Status summer 2003 Ue-Li, Jeff, Xiang-Ping discussed the idea autumn 2003 site search began, Ulastai chosen March 2004 7-antennae prototype, first image August 2004 array design finished January 2005 batch I (first 20 pods) constructed summer 2005 batch II (60 pods) construction, data collecting electronics installation January 2006 fully operational Total cost estimate: 15-30 M yuan, now borrowing from other groups in NAOC, will apply a grant, please support!

11. January 1, 2005

12. First skymap (dirty) 3C061.1 3CR390.3 NCP 3CR061.1

13. Dark Energy? AP test power spectrum measurement lensing...

14. Discussion on dark energy observation

15. Dark Energy? Observation Data Theoretical Assumptions General RelativityCosmo Principle Model IModel II Model III

16. Ways to measure dark energy Gravitational test: luminosity distance angular diameter distance growth of perturbation solar system & beyond Non-Gravitational test: variation of constants dark energy interaction supernovae & GRB gravitational lensing cluster large scale structure CMB 21cm gravitational wave micro-gravity, solar system & lab

17. What can we do in China Existing projects: LAMOST, 21CMA New Projects: ?