Constraints on cosmic hemispherical power anomalies from quasars

Recent analyses of the cosmic microwave background (CMB) maps from the WMAP satellite have uncovered evidence for a hemispherical power anomaly, i.e. a dipole modulation of the CMB power spectrum at large angular scales with an amplitude of +/- 14 percent. Erickcek et al. have put forward an inflationary model to explain this anomaly. Their scenario is a variation on the curvaton scenario in which the curvation possesses a large-scale spatial gradient that modulates the amplitude of CMB fluctuations. We show that this scenarion would also lead to a spatial gradient in the amplitude of perturbations sigma 8, and hence to a diple asymmetry in any highly biased traced of the underlying density field. Using the high-redshift quasars from the Sloan Digital Sky Survey, we find an upper limit on such a gradient of vertical bar del sigma 8 vertical bar/sigma 8 < 0.027 gamma(-1)(lss) (99% posterior probability), where gamma(lss) is the comoving distance to the last-scattering surface. This rules out the simplest version of the curvation spatial gradient scenario.