Cosmic flows in the nearby universe from Type Ia Supernovae

TL;DR

This paper measures the bulk flow of nearby universe using Type Ia supernovae, finding results consistent with DM predictions but also indicating some discrepancies with galaxy density field models.

Contribution

It introduces new bulk flow measurements from a large supernova dataset and compares them with galaxy survey predictions, highlighting both agreement and discrepancies.

Findings

Bulk flow of 249 1 76 km/s in a specific direction.

Consistency of supernova bulk flow with DM expectations.

Discrepancy between supernova bulk motion and galaxy density field predictions.

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.