1 research outputs found
A Local Hubble Bubble from SNe Ia?
We analyze the monopole in the peculiar velocities of 44 Type Ia supernovae
(SNe Ia) to test for a local void. The sample extends from 20 to 300 Mpc/h,
with distances, deduced from light-curve shapes, accurate to ~6%. Assuming
Omega_m=1 and Omega_lambda=0, the most significant deviation we find from the
Hubble law is an outwards flow of (6.6+/-2.2)% inside a sphere of radius 70
Mpc/h as would be produced by a void of ~20% underdensity surrounded by a dense
shell. This shell roughly coincides with the local Great Walls. Monte Carlo
analyses, using Gaussian errors or bootstrap resampling, show the probability
for chance occurrence of this result out of a pure Hubble flow to be ~2%. The
monopole could be contaminated by higher moments of the velocity field,
especially a quadrupole, which are not properly probed by the current limited
sky coverage. The void would be less significant if Omega_m is low and
Omega_lambda is high. It would be more significant if one outlier is removed
from the sample, or if the size of the void is constrained a-priori. This
putative void is not in significant conflict with any of the standard
cosmological scenarios. It suggests that the Hubble constant as determined
within 70 Mpc/h could be overestimated by ~6% and the local value of Omega may
be underestimated by ~20%. While the present evidence for a local void is
marginal in this data set, the analysis shows that the accumulation of SNe Ia
distances will soon provide useful constraints on elusive and important aspects
of regional cosmic dynamics.Comment: 21 pages, 3 figures. Slightly revised version. To appear in ApJ, 503,
Aug. 20, 199