2005A&A...438..103M

We present I-band Surface Brightness Fluctuation (SBF) measurements for 16 early-type galaxies (3 giants, 13 dwarfs) in the central region of the Hydra cluster, based on deep photometric data in 7 fields obtained with VLT FORS1. From the SBF-distances to the galaxies in our sample we estimate the distance of the Hydra cluster to be 41.2±1.4Mpc ((m-M)=33.07±0.07mag). Based on an improved correction for fluctuations from undetected point sources, we revise the SBF-distance to the Centaurus cluster from Mieske & Hilker (2003A&A...410..445M) upwards by 10% to 45.3±2.0Mpc ((m-M)=33.28±0.09mag). The relative distance modulus of the two clusters then is (m-M)_Cen-(m-M)_Hyd=0.21 ±0.11mag. With H₀=72±4km/s/Mpc, we estimate a positive peculiar velocity of 1225±235km/s for Hydra and 210±295km/s for the Cen30 component of Centaurus. Allowing for a thermal velocity dispersion of 200km/s, this rules out a common peculiar flow velocity for both clusters at 98% confidence. We find that the 9x10¹⁵M_☉ ``Great Attractor'' at a distance of ≃45Mpc can explain the observed peculiar velocities if shifted about 15° towards the Hydra cluster position. Our results are inconsistent at 94% confidence with a scenario where the Centaurus cluster is identical to the GA. In order to better restrict partially degenerate Great Attractor parameters like its mass and distance, a recalculation of the local flow model with updated distance information over a larger area than covered by us would be needed.