Galaxies and the Universe - Evolution of galaxies

Galaxies and the Universe - Evolution of galaxies - 1/15/12...

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1/15/12 Gala[ieV and Whe UniYeuVe - EYolXWion of gala[ieV 1/2 ZZZ.aVWu.Xa.edX/keel/gala[ieV/galeYolYe.hWml Evolution of Galaxies There are several senses in which galaxies evolve with time, not all necessarily running at the same rates for various kinds of galaxy. We may distinguish for convenience evolution of stellar populations, chemical abundances, and dynamics of a galaxy, remembering that in real galaxies these are all tied together at some level. I will cover the basic principles needed to understand modelling these processes, and observational approaches to each one. The likelihood of observing galaxy evolution can be seen from comparing several relevant timescales. The Hubble time is in the range 1-2 î 10 10 years. This matches the main-sequence lifetime of solar-mass stars, making it many generations of more luminous massive stars. And dynamically, the rotation period on our part of the Milky Way is 0.25 Gyr, so the relaxation time for a massive galaxy to form structure should be several Gyr. PopXlaWion eYolXWion combines the history of star formation in a galaxy and stellar evolution of its constituents, giving changes in the HR diagram of a galaxy (generally changing from place to place in the galaxy) with time. To predict the population at some time, we thus need the SFR at all previous times and an understanding of stellar evolution for all relevant masses; see the discussion under spectrum and population synthesis . Elliptical galaxies, or the bulges of spirals, are popular tests of synthesis models, since they are assumed to have had most of their
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Galaxies and the Universe - Evolution of galaxies - 1/15/12...

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