http://arxiv.org/abs/1412.7310
We investigate the impact of cosmic flows and density perturbations on Hubble constant $H_0$ measurements using nonlinear phase-space reconstructions of the Local Universe (LU). We rely on a set of 25 N-body simulations which are constrained to resemble the LU within distances of about 90 Mpc/h. These have been randomly extended up to volumes enclosing distances of 360 Mpc/h with augmented Lagrangian perturbation theory (=750 simulations), accounting in this way for effects from from larger scales ($\sigma_{\rm large}=134$ km/s). We report on Local Group (LG) speed reconstructions, which are compatible with those derived from the CMB-dipole: $|v_{\rm LG}|=685\pm137$ km/s. The direction $(l,b)=(260.5\pm 13.3,39.1\pm 10.4)^\circ$ is found to be compatible with observations. We use the CMB-dipole information to estimate the missing large scale bulk flow component, indicating that we miss a closely perpendicular flow with a magnitude corresponding to $1.4 \sigma_{\rm large}$. Considering this, our bulk flow estimations assuming a $\Lambda$CDM model are compatible with the most recent estimates based on the Tully-Fisher relation. We focus on low redshift supernova (SN) measurements out to $0.01<z<0.025$, which have been found to disagree with CMB estimates, as well as with SN samples at larger distances. Our analysis indicates that there are two effects related to cosmic variance contributing to this tension. The anisotropic distribution of SNe, which aligns with the velocity dipole and hence induces a systematic boost in $H_0$. The second is due to inhomogeneous matter fluctuations in the LU. In particular a divergent region surrounding the Virgo Supercluster is responsible for an additional positive bias in $H_0$. This yields a correction of $\Delta H_0= -2.13 \pm 0.27$ km/s/Mpc, thereby reducing the tension between local and more distant probes. Effectively $H_0$ is lower by about 3%.
S. Hess and F. Kitaura
Wed, 24 Dec 14
20/37
Comments: submitted to MNRAS 10 pages, 7 figures
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