The distance to Hydra and Centaurus from surface brightness fluctuations: Consequences for the Great Attractor model

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 +/- 1.4 Mpc (( m - M) = 33.07 +/- 0.07 mag). Based on an improved correction for fluctuations from undetected point sources, we revise the SBF-distance to the Centaurus cluster from Mieske & Hilker ( 2003, A&A, 410, 455) upwards by 10% to 45.3 +/- 2.0 Mpc ((m- M) = 33.28 +/- 0.09 mag). The relative distance modulus of the two clusters then is (m- M)(Cen)-(m- M)(Hyd) = 0.21 +/- 0.11 mag. With H-0 = 72 +/- 4 km s(-1) Mpc(-1), we estimate a positive peculiar velocity of 1225 +/- 235 km s(-1) for Hydra and 210 +/- 295 km s(-1) for the Cen30 component of Centaurus. Allowing for a thermal velocity dispersion of 200 km s(-1), this rules out a common peculiar flow velocity for both clusters at 98% confidence. We find that the 9 x 10(15) M-circle dot Great Attractor at a distance of similar or equal to 45 Mpc can explain the observed peculiar velocities if shifted about 15 degrees 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.