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STScI Webcast

2016 Fall Science Colloquia

Galaxy Assembly and Mergers through Cosmic Time

Presented by: Jennifer Lotz  (STScI)
Category: Science Colloquia   Duration: 1 hour   Broadcast date: September 21, 2016
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Deep HST observations have revealed galaxies fainter than ever seen before, at look-back times when the universe was less than a billion years old. These first galaxies grow throughout cosmic time via the accretion of gas and dark matter, and via mergers with other galaxies. The detailed structures of galaxies provide direct insight into their most recent assembly events. From SDSS and HST imaging surveys, we now have a broad-brush picture of how galaxy shapes and sizes have evolved over the past 10 billion years. But the role of galaxy mergers in galaxy evolution is poorly understood, particularly at early times. More subtle morphological tracers are needed to track the complex processes responsible for the transformation of galaxies. I use new machine learning classifications of galaxy morphology at 0 < z < 3 to identify galaxy mergers and galaxies transitioning to today's Hubble types. Numerical simulations are used to inform the interpretation of these morphological classes, and to constrain the precise merger states of local systems. I track the evolution of galaxies as a function these new measures, and discuss the role of mergers in the size growth of galaxies. Finally, I discuss the prospects for studying galaxy assembly with JWST, LSST, and WFIRST in the coming decade.