The e-MERLIN Legacy programme
AGATE: Astrophysics of Galaxy Transformation and Evolution
Chris Simpson (Liverpool John Moores) and Ian Smail (Durham)
Rob Beswick (JBCA, Manchester), Richard Bower (Durham), Dave Carter (LJMU), Scott Chapman (Cambridge), Chris Collins (LJMU), Harald Ebeling (IfA, Hawaii), Alastair Edge (Durham), James Geach (Durham), Phil James (LJMU), Matt Jarvis (Hertfordshire), Tadayuki Kodama (NAOJ), Yuichi Matsuda (Durham), Steve Rawlings (Oxford), Dan Smith (LJMU) and John Scott (LJMU)
In the local Universe, some of the most fundamental properties of galaxies are found to be a strong function of environment, such as their morphologies or star-formation histories. Yet it is still unclear whether these trends reflect the initial conditions of galaxy formation (nature) or more recent environmental processing of galaxies (nurture), and answering this question is essential for unravelling the physics of galaxy formation and evolution. Massive clusters of galaxies represent some of the most extreme environments experienced by galaxies and are therefore ideal laboratories for differentiating the physical processes which can affect and transform the morphologies and star-formation properties of galaxies, efficiently providing large samples of galaxies over a wide range of local environment. Although most work has focused on the suppression of star-formation activity in galaxies as they become part of the cluster population, recent evidence has increasingly demonstrated that there must also be a period of star-formation enhancement to explain the growth of the galactic bulges. This is likely to be accompanied by a period of AGN activity to ensure the central supermassive black hole remains on the M_bulge:M_BH relation. e-MERLIN provides a unique capability to study these processes since (a) it is sensitive to the radio continuum emission produced by both AGN and star-formation activity; (b) it has a sufficiently wide field of view to image a cluster beyond the virial radius and out to where infalling groups lie; and (c) it has the angular resolution required to separate the compact AGN activity from the >~ kpc-scale circumnuclear star formation.
We therefore request 590 hours of e-MERLIN time (not including the Lovell Telescope) to undertake 1.4-GHz continuum mapping observations of six z~0.5 rich galaxy clusters which possess a wealth of complementary multi-wavelength data. These systems are some of the most massive clusters known and are therefore excellent laboratories for studying the astrophysical processes which occur in dense environments, as well as being observed at a cosmic epoch when galaxy transformation is occurring. These observations will morphologically and spectrally chart the co-evolution of star formation and AGN activity in cluster galaxies, expected to trace the transformation of bulge-weak, star-forming disc populations into the bulge-strong, passive spheroids which dominate rich cluster populations today. The extensive multi-wavelength data available for all our cluster fields will ensure prolonged Legacy value for our dataset and complement "blank-field" e-MERLIN surveys.