1. Dark Energy BAO Intensity Mapping T. Chang, UP, J. Peterson, P. McDonald PRL 100, 091303 (March 5, 2008) UP, L. Staveley-Smith, J. Peterson, T. Chang arXiv:0802.3239

2. Baryon Acoustic Oscillations – Dark Energy Probe CMB acoustic oscillations: imprinted standard ruler, 100 Mpc. Present in current matter distribution WMAP5 and other, Nolta et al (2008)

3. Large Scale Structure BAO Blake and Glazebrook, Seo & Eisenstein et al: standard ruler measures H(z) and D(z). From Percival et al:

4. Present LSS BAO Detections Percival et al 2007 Eisenstein et al 2005

5. Mapping Large Scale Structure Measure individual galaxy redshifts – SDSS(3), SKA, ADEPT, WFMOS (radio/optical), etc. OR measure collective emission from galaxies without resolving individual objects. Hundreds of galaxies in each BAO pixel! Prototype observations and analysis in progress – CMU cylinder, GBT, VLBA, ATA, Parkes, GMRT. (Bandura, Staveley-Smith, Briggs)

6. Radio Mapping Experiments Redshifted 21cm Hydrogen transition: 300MHz-1.4 GHz, radio maps Large area survey, large field of view, low surface brightness: like CMB. Signal ~ 50 µK Foregrounds large -- ~K, but smooth (spatially and spectrally).

7. First Intensity Mapping Detection Archival analysis of Parkes HIPASS data 21cm Survey of 68% of the sky, at dec<22 deg z<0.04, median detected galaxy z=0.01 Cross correlate with 6dF

9. Pen et al 2008

10. Prospects with existing telescopes Cross correlation detected with µK noise. CMB-like scan strategy for extended source mapping. Parkes multibeam: perfect for all sky z<0.13 (receiver limit). Redo SDSS volume, fill in zone of avoidance (?). Strengthen low z BAO signal. GBT: pencil beam surveys to z=2.5, in progress (April 23-May 1, 2008). May detect BAO at z=1.5 with major campaign. ATA (used as single dishes): northern sky, z<0.2.

11. Dedicated Survey Experiment Low frequency technology cheap, modest collecting area Large field of view: receiver arrays High surface brightness sensitivity: compact arrays Stable, reliable: no moving parts Technologies: aperture arrays (Wyithe, Loeb, Geil 2008), cylinders (Peterson et al)

12. Existing cylinders MOLONGLO OOTY Molonglo AUSTRALIA Brisbane Darwin Perth Canberra Hobart Adelaide Melbourne Sydney + NORTHERN CROSS Cambridge

13. CMU cylinder under construction: U. Seljak, J. Peterson, K. Bandura.

15. Mapping LSS

16. Cosmic Variance Limited Hubble Surveys Chang, UP, Peterson, McDonald, PRL 100, 091303, March 5, 2008

17. Conclusions Baryon Acoustic Oscillations – geometric measure of the universe and dark energy First detections reported – 2dF, SDSS Intensity Mapping: unresolved galaxies. First detection of IM through cross correlation in archival HIPASS data. Prototypes and observations under way. Cylinder telescopes a promising technology.