PI: Amy J. Barger, University of Wisconsin, Madison, email@example.com
Address: Astronomy Department, 475 N. Charter St., Madison, WI 53706, United States
CoI: Ryan C. Keenan, ASIAA, Taiwan
CoI: Lennox L. Cowie, Institute for Astronomy, Hawaii
CoI: Isak G. B. Wold, University of Wisconsin
Title: Is the Universe Underdense at z < 0.1?
Abstract: Recent cosmological modeling efforts have shown that a local underdensity on scales of a few hundred Mpc (out to z ~ 0.1) could produce the apparent acceleration of the expansion of the universe observed via type Ia supernovae. Several studies of galaxy counts in the near-infrared (NIR) have found that the local universe appears underdense by ~ 25-50% compared with regions a few hundred Mpc distant (e.g. Keenan et al., 2010). If the space density of galaxies is rising as a function of redshift, then the luminosity density, as measured via the NIR galaxy luminosity function (LF), should be rising as well. In Keenan et al. (2012), we presented a study of the NIR LF at z ~ 0.2 and found that the product \phi^*L^* (the peak of the luminosity density distribution) at z ~ 0.2 is roughly ~ 30% higher than that measured at z ~ 0.05. Using simulations and recent empirical estimates of cosmic variance, we found that our survey is subject to systematics due to cosmic variance at the ~ 15% level. We showed that increasing our survey volume by roughly a factor of four will reduce these uncertainties to < 5%, allowing a robust test for a local underdensity. Here we propose to use the AAOmega + 2dF instrument to expand our survey to cover four fields of 2 deg^2 each to K_\rmAB=18. This study will serve as the first robust direct test of whether or not we reside in a large local underdensity. An accurate measurement of any such underdensity will be important to experiments seeking to understand the nature of dark energy.
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