Large-scale Bulk Flows from the Cosmicflows-2 Catalog

We calculate the large-scale bulk flow from the Cosmicflows-2 peculiar velocity catalog (Tully et al. 2013) using the minimum variance method in-troduced in Watkins et al. (2009). We find a bulk flow of 262 ± 60 km/sec on a scale of 100h−1Mpc, a result somewhat smaller than that found from the COMPOSITE catalog introduced in Watkins et al. (2009), a com-pendium of peculiar velocity data that has many objects in common with the Cosmicflows-2 sample. We find that distances are systematically larger in the Cosmicflows-2 catalog for objects in common due to a different approach to bias correction, and that this explains the difference in the bulk flows de-rived from the the two catalogs. The bulk flow result from the Cosmicflows-2 survey is consistent with expectations from ΛCDM, and thus this catalog po-tentially resolves an important challenge to the standard cosmological model.