Mapping the dynamics, star-formation rates, and chemical properties of galaxies with integral field spectroscopy

Abstract

Major advances in the development of instruments for eight and ten meter class telescopes are revolutionising our understanding of galaxy formation. In particular, Integral Field Spectrographs (which produce a three dimensional (x, y, velocity) map of a galaxy) now permit studies of distant galaxies in nearly as much detail as local galaxies in our cosmic neighbourhood. These instruments can be employed to investigate specific problems in galaxy formation across 90% of the history of the Universe, and we demonstrate their capabilities by probing galaxy evolution from z=0.l to z=3. Locally, post-starburst (E+A) galaxies are thought to represent the transitional phase of galaxy evolution which links star-forming (late type) galaxies with their quiescent (early type) end products. We demonstrate that integral field spectroscopy can be employed to disentangle the stellar and dynamical structures of this post-star burst phase and therefore constrain the trigger (or triggers) of this phase of galaxy evolution. At higher redshift, (i.e., above z=l), "normal" galaxies are frequently too small and faint to observe via conventional observations. However, gravitational lensing by galaxy clusters provides us with a unique tool to study distant galaxies. By coupling the lensing phenomenon with Integral Field Spectroscopy, we investigate the evolution of the relation between the baryonic and non-baryonic components of galaxies from z=l to the present day through the Tully-Fisher Relation. By reconstructing the source morphologies and velocity fields of lensed galaxies, we find evidence for 0.5mag of brightening in the restframe B-band, but <0.lmag of evolution in the rest frame I-band, suggesting a clear preference for hierarchical growth of structure and increased star-formation activity at z=l. At these high redshifts, some galaxies (such as radio galaxies and SCUBA galaxies) are frequently bright enough and extended enough to study without the boost of a gravitational lens, and therefore can provide important comparison samples with which we can understand how high redshift proto-galaxies evolve into their present day descendants. By targeting the rest frame optical properties of SCUBA galaxies with traditional near-infrared longslit spectroscopy we find that the high redshift sub-mm population share many characteristics with the somewhat less luminous far-infrared galaxies identified in the local Universe. This includes the Ha equivalent widths, the proportion of obvious AGN and the typical spectral classification. Yet there remain important differences, with proportionally more highly-obscured activity in the high-redshift population, apparently larger dynamical mass, lower metallicities and much higher gas fractions on 10-kpc scales. With this sample of far-infrared luminous galaxies in hand, we use integral field spectroscopy to study the structural and dynamical properties of powerful high redshift SCUBA galaxies. We show the power of combining optical and near-infrared integral field spectroscopy to probe the power sources, masses and metallicities of powerful, distant galaxies, as well as understanding the role of AGN- and star-burst driven feedback processes in these high redshift systems.