TESTING FOR A LARGE LOCAL VOID BY INVESTIGATING THE NEAR-INFRARED GALAXY LUMINOSITY FUNCTION

Abstract

Recent cosmological modeling efforts have shown that a local underdensity on\nscales of a few hundred Mpc (out to z ~ 0.1), could produce the apparent\nacceleration of the expansion of the universe observed via type Ia supernovae.\nSeveral studies of galaxy counts in the near-infrared (NIR) have found that the\nlocal universe appears under-dense by ~25-50% compared with regions a few\nhundred Mpc distant. Galaxy counts at low redshifts sample primarily L ~ L*\ngalaxies. Thus, if the local universe is under-dense, then the normalization of\nthe NIR galaxy luminosity function (LF) at z>0.1 should be higher than that\nmeasured for z<0.1. Here we present a highly complete (> 90%) spectroscopic\nsample of 1436 galaxies selected in the H-band to study the normalization of\nthe NIR LF at 0.1<z<0.3 and address the question of whether or not we reside in\na large local underdensity. We find that for the combination of our six fields,\nthe product phi* L* at 0.1 < z < 0.3 is ~ 30% higher than that measured at\nlower redshifts. While our statistical errors in this measurement are on the\n~10% level, we find the systematics due to cosmic variance may be larger still.\nWe investigate the effects of cosmic variance on our measurement using the\nCOSMOS cone mock catalogs from the Millennium simulation and recent empirical\nestimates. We find that our survey is subject to systematic uncertainties due\nto cosmic variance at the 15% level ($1 sigma), representing an improvement by\na factor of ~ 2 over previous studies in this redshift range. We conclude that\nobservations cannot yet rule out the possibility that the local universe is\nunder-dense at z<0.1.\n