An estimation of local bulk flow with the maximum-likelihood method

Abstract

A maximum-likelihood method, tested as an unbiased estimator from numerical simulations, is used to estimate cosmic bulk flow from peculiar velocity surveys. The likelihood function is applied to four observational catalogues (ENEAR, SFI++, A1SN and SC) constructed from galaxy peculiar velocity surveys and Type-Ia supernovae data at low redshift ($z \leq 0.03$). We find that the Spiral Field {\it I}-band catalogue constrains the bulk flow to be $V=290 \pm 30 {\,{\rm km}\,{\rm s}^{-1}}$ towards $l=281^{\circ} \pm 7^{\circ}$, $b=8^{\circ +6^{\circ}}_{-5^{\circ}}$ on effective scales of $ 58 {\,{h^{-1} {\rm Mpc}}}$, which is the tightest constraints achievable at the present time. By comparing the amplitudes of our estimated bulk flows with theoretical prediction, we find excellent agreement between the two. In addition, directions of estimated bulk flows are also consistent with measurements in other studies.