“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

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

SDSS DR4: 849,920 spectra, 6670 sq degs Extension ( ): Legacy, SNe, Galaxy

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

Experimental Set-up See also: Nolta et al, Boughn and Crittenden, Myers et al, Ashfordi et al

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

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)

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

positive correlation more sources come in than area diluted: positive correlation negative correlation less sources come in than area diluted: negative correlation Effects cancel

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 <5% contamination (Richards et al. 2004): photometric QSO catalogs

Blue points = data Black line = best fit Red line = best fit + alpha Grey shading = 1sigma 195,000 quasars 13.5 million galaxies 8  detection Now fully consistent with  CDM model Ideal for next generation imaging surveys like DES

Baryon Acoustic Oscillation Gravity squeezes the gas, pressure pushes back. They oscillate Gravity squeezes the gas, pressure pushes back. They oscillate When the Universe cools below 3000K, these baryonic acoustic oscillations are frozen in When the Universe cools below 3000K, these baryonic acoustic oscillations are frozen in Courtesy of Wayne Hu

BAO observations   Effect of these oscillations already seen in the CMB   Can we see them today in the distribution of galaxies? LRG

LRG Correlation Function The correlation function is the probability of finding pairs at a given separation, above that of a random distribution. Excess of galaxies separated by 500 million light years

What does it mean?   We have detected the BAO at two different epochs consistent with our theory of gravitational structure formation   BAO provide a fixed scale, or “standard ruler”   BAO are consistent with LCDM model   Assuming LCDM model, then BAO constrain flatness of universe to 1% - break the degeneracy between w & curvature

WFMOS 3000 thousands of fibers over a 1.5 degree field- of-view on an 8-meter class telescope (Subaru/Gemini) z~1 survey with 2 million galaxies with twice LRG volume 1% accuracy Taken from WFMOS Feasibility Study by NOAO, JHU, AAO, Oxford, Durham, Portsmouth, UA w ~ 5% dw/dz ~ 20%

WFMOS will also be a user instrument and have significant archival value-added science eg. Baldry et al. (2004) SDSS color bimodality as fn(L,  at z~1  mod =  5 + L/L -20 Red Fraction