Astronomy Tea Talk

The Tully-Fisher (luminosity-rotational velocity) relation is a powerful tool to probe the evolution of galaxies, particularly their stellar populations and dark matter content. Here, we briefly review and propose methods to extend its use across all galaxy morphological types and to significant redshifts. First, and although they are not rotationally-supported, we show how good photometry and stellar kinematics can be used to generate a Tully-Fisher relation for early-type galaxies. This yields direct constraints on the stellar mass-to-light (M/L) ratios and dark matter, but is very time-consuming. We simultaneously show that spiral galaxies can not simply passively evolve into lenticular (S0) galaxies, but must also compactify in the process. Second, we demonstrate that CO is, unexpectedly, an excellent kinematic tracer in early-type galaxies, and analyse potential pitfalls. We verify that CO molecular gas can thus be used trivially for Tully-Fisher studies across all galaxy types, and recover more time-consuming results. Third, we describe an ongoing NANTEN2 project to establish a reliable z=0 CO Tully-Fisher benchmark, and discuss how this can be extended to intermediate redshifts with ALMA. We also introduce the second generation VLT instrument KMOS, a near-infrared spectrograph with multiple deployable integral-field units. We discuss how KMOS guaranteed time will be used to probe the Tully-Fisher relation of disk galaxies at intermediate redshifts, using ionised gas. A bright, renewed future for Tully-Fisher studies thus emerges, promising studies to significant redshifts and the elimination of the systematic errors usually arising when comparing galaxies of different morphological types.