Slide 1

The Dark Side of the SDSS Bob Nichol ICG, Portsmouth Chris Miller, David Wake, Brice Menard, Idit Zehavi, Ryan Scranton, Gordon Richards, Daniel Eisenstein, all my SDSS colleagues Slide 2 Outline Brief overview of the SDSS Brief overview of the SDSS New paths to the Dark Side New paths to the Dark Side ISW effect Cosmic magnification Baryon Acoustic Oscillations WFMOS WFMOS Slide 3 SDSS DR4: 849,920 spectra, 6670 sq degs Extension (2005-2008): Legacy, SNe, Galaxy Slide 4 Late-time Integrated Sachs Wolfe (ISW) Effect DE also effects the growth of structure i.e. Poisson equation with dark energy: DE also effects the growth of structure i.e. Poisson equation with dark energy: In a flat, matter-dominated universe (CMB tells us this), then density fluctuations grow as: In a flat, matter-dominated universe (CMB tells us this), then density fluctuations grow as: Therefore, for a flat geometry, changes in the gravitational potential are a direct physical measurement of Dark Energy Therefore, for a flat geometry, changes in the gravitational potential are a direct physical measurement of Dark Energy Slide 5 Experimental Set-up See also: Nolta et al, Boughn and Crittenden, Myers et al, Ashfordi et al Slide 6 ISW and the SDSS Searching for a detection Searching for a detection LRG selection to z~0.8 (Eisenstein et al. 2001) LRG selection to z~0.8 (Eisenstein et al. 2001) 5300 sq degrees 5300 sq degrees Achromatic (no contamination) Achromatic (no contamination) Errors from 5000 CMB skies Errors from 5000 CMB skies Compared to a null result Compared to a null result >95% for all samples Data prefers DE model over null hypothesis at the >99% confidence for all combinations Data prefers DE model over null hypothesis at the >99% confidence for all combinations Yellow: smoothed clean, Black: Clean, Red: Q, Blue: W, Green: V Slide 7 Future ISW directions Probe of DE sound speed (Hu & Scranton 2004; Pogosian 2004) and highly complementary to geometrical measures of DE Probe of DE sound speed (Hu & Scranton 2004; Pogosian 2004) and highly complementary to geometrical measures of DE Circa 2006 (SDSS) Circa 2006 (SDSS) 8000 sq degrees (3 per redshift) Tighter redshift intervals (> 5 bins) Beyond Beyond ASTRO-F all-sky out to z~1.5 UKIDSS+VISTA all-sky (LRG selection to z>1) QSO catalogs (z out to 3) DES & LSST will provide competitive DE constraints from ISW for Kink models of DE (Pogosian et al. 2005) Slide 8 Cosmic Magnification Gravitational magnification increases flux received from galaxies and hence allows us to see fainter galaxies, resulting in an increased apparent galaxy number density. But, it also magnifies the solid angle of the projected lensed sky which results in a decrease in the apparent galaxy number density. Therefore a competition between the two! more flux more solid angle Slide 9 positive correlation more sources come in than area diluted: positive correlation negative correlation less sources come in than area diluted: negative correlation Effects cancel Slide 10 Hunting for quasars Traditional UVX approach to finding quasars uses hyper- planes (Richards et al. 2002). However, significant contamination (~40%), thus demanding spectroscopic follow-up. New bayesian technique provides