The Tully-Fisher relation of intermediate redshift field and cluster galaxies from Subaru spectroscopy

We have carried out spectroscopic observations in four cluster fields using Subaru's FOCAS multislit spectrograph and obtained spectra for 103 bright disc field and cluster galaxies at 0.06 ≤ z ≤ 1.20. 77 of these show emission lines, and 33 provide reasonably secure determinations of the galaxies' rotation velocity. The rotation velocities, luminosities, colours and emission-line properties of these galaxies are used to study the possible effects of the cluster environment on the star formation history of the galaxies. Comparing the Tully-Fisher relations of cluster and field galaxies at similar redshifts we find no measurable difference in rest-frame B-band luminosity at a given rotation velocity (the formal difference is 0.18 ± 0.33 mag). The colours of the cluster emission line galaxies are only marginally redder in rest-frame B - V (by 0.06 ± 0.04 mag) than the field galaxies in our sample. Taken at face value, these results seem to indicate that bright star-forming cluster spirals are similar to their field counterparts in their star formation properties. However, we find that the fraction of disc galaxies with absorption-line spectra (i.e. with no current star formation) is larger in clusters than in the field by a factor of ∼3-5. This suggests that the cluster environment has the overall effect of switching off star formation in (at least) some spiral galaxies. To interpret these observational results, we carry out simulations of the possible effects of the cluster environment on the star formation history of disc galaxies and thus their photometric and spectroscopic properties. This allows us to create mock samples of unperturbed 'field' galaxies [with approximately constant star formation rates (SFRs)] and perturbed 'cluster' galaxies with different star formation histories, including star formation truncation, with or without an associated starburst. We show that, if we select only bright galaxies with current star formation (i.e. with emission lines strong enough for rotation-curve measurements), the average colours and luminosities of the 'cluster' galaxies may not be very different from those of galaxies in the 'field' sample, even though their star formation histories may be significantly different. However, the fraction of emission and absorption-line galaxies would change significantly. We also use these simulations to estimate the size of field and cluster galaxy samples that would allow us to differentiate the different star formation scenarios considered. Finally, we find that the rest-frame absolute B-band magnitude of the field galaxies in our sample shows an evolution of -1.30 ± 1.04 mag per unit redshift at fixed rotation velocity. This indicates that the average SFR of bright disc galaxies evolves more slowly than the universal SFR as determined from ultraviolet, Hα, far-infrared and radio studies. This suggests the evolution of the universal SFR density is not dominated by bright star-forming disc galaxies, in agreement with previous studies.