Abstract
Peculiar velocities are one of the only probes of very large-scale mass density fluctuations in the nearby Universe. We present new "minimal variance" bulk flow measurements based upon the "First Amendment" compilation of 245 Type Ia supernovae (SNe) peculiar velocities and find a bulk flow of 249 +/- 76 km/s in the direction l= 319 +/- 18 deg, b = 7 +/- 14 deg. The SNe bulk flow is consistent with the expectations of \Lambda CDM. However, it is also marginally consistent with the bulk flow of a larger compilation of non-SNe peculiar velocities (Watkins, Feldman, & Hudson 2009). By comparing the SNe peculiar velocities to predictions of the IRAS Point Source Catalog Redshift survey (PSCz) galaxy density field, we find \Omega_{m}^{0.55} \sigma_{8,lin} = 0.40 +/- 0.07, which is in agreement with \Lambda CDM. However, we also show that the PSCz density field fails to account for 150 +/- 43 km/s of the SNe bulk motion.
Highlights
In the standard cosmological model, gravitational instability causes the growth of structure and peculiar velocities
In order to reduce the impact of these nearby SNe, it is interesting to redetermine the bulk flow excluding nearby objects
We have shown that the PCSz does not account for all of the motion of the Local Group (LG), it is plausible that some of the missing signal comes from within the survey volume in the form of extra infall into the highest density superclusters
Summary
In the standard cosmological model, gravitational instability causes the growth of structure and peculiar velocities. An alternate method for removing the effects of small-scale structure on flow measurements is to assume gravitational instability and linear perturbation theory equation (1). The result is a model-dependent correction to measured peculiar velocities which can separate local effects from large-scale density waves from outside the survey volume. Feldman et al (2010) measured the tidal and higher order terms for the ‘Composite’ sample of Watkins et al (2009), but found them to be small. We neglect these terms here and model the residual as a simple bulk flow U
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