The Tully-Fisher relation at intermediate redshift

Using the Very Large Telescope in Multi Object Spectroscopy mode, we have observed a sample of 113 field spiral galaxies in the FORS Deep Field (FDF) with redshifts in the range 0.1<1.0. The galaxies were selected based oil apparent brightness (R<23(m)) and encompass all late spectrophotometric types from Sa to Sdm/Im. Spatially resolved rotation curves have been extracted for 77 galaxies and fitted with synthetic velocity fields taking into account all observational effects from inclination and slit misalignment to seeing and slit width. We also compared different shapes for the intrinsic rotation Curve. To obtain robust values of V-max, our analysis is focused on galaxies with rotation curves that extend well into the region of constant rotation velocity at large radii. If the slope of the local Tully-Fisher relation (TFR) is held fixed, we find evidence for a mass-dependent luminosity evolution which is as large as up to Delta M-B approximate to-2(m) for the lowest-mass galaxies, but is small or even negligible for the highest-mass systems in our sample. In effect, the TFR slope is shallower at z approximate to 0.5 in comparison to the local sample. We argue for a mass-dependent evolution of the mass-to-light ratio. An additional population of blue, low-mass spirals does not seen, a very appealing explanation. The flatter tilt we find for the distant TFR is in contradiction to the predictions of recent semi-analytic simulations.