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Evidence for a ~300 Mpc Scale Local Under-density in the Distribution of Galaxies | Ryan C. Keenan
; Amy J. Barger
; Lennox L.Cowie
; | Date: |
10 Apr 2013 | Abstract: | Galaxy counts and recent measurements of the luminosity density in the
near-infrared (NIR) have indicated the possibility that the local universe may
be under-dense on scales of several hundred megaparsecs. The presence of a
large-scale under-density in the local universe could introduce significant
biases into the interpretation of cosmological observables, and, in particular,
into the inferred effects of dark energy on the expansion rate. Here we measure
the K-band luminosity density as a function of redshift to test for such a
local under-density. We find that the overall shape of the z = 0 rest-frame
K-band luminosity function (M* = -21.6 +/- 0.04 and alpha = -0.99 +/- 0.03)
appears to be relatively constant as a function of environment and redshift out
to z ~0.2. We find a local (z < 0.07) luminosity density that is in good
agreement with previous studies. At z > 0.07 we detect a rising luminosity
density, and at z > 0.1, it is roughly ~1.5 times higher than that measured
locally. This suggests that the stellar mass density as a function of redshift
follows a similar trend. Assuming that luminous matter traces the underlying
dark matter distribution, this implies that the local mass density of the
universe may be lower than the global value on a scale and amplitude sufficient
to introduce significant biases into the determination of basic cosmological
observables, such as the expansion rate. An under-density on this scale and
amplitude, for example, would be more than sufficient to resolve the apparent
tension between direct measurements of the Hubble constant and those inferred
by Planck. | Source: | arXiv, 1304.2884 | Services: | Forum | Review | PDF | Favorites |
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