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Abstract: We present an analysis of the stellar populations in a sample of ~7000galaxies from the 6dF Galaxy Survey 6dFGS. We derive ages and metallicitiesusing stellar population models. We also derive dynamical masses and dynamicalmass-to-light ratios by combining central velocity dispersions with globalphotometry in B, R and K bands. Together, these data allow to reduce thedegeneracies between age, metallicity and star formation burst-strength thathave limited previous studies. We find old galaxies exhibit a mass-metallicityrelation with slope dFe-H-dlogM = 0.25, while young galaxies show slopesconsistent with zero. When we account for the effects of the mass-metallicityrelation, we obtain a single, consistent relation between mass-to-light ratioand mass for old galaxies in all passbands. As we have accounted for stellarpopulation effects, this relation must have a dynamical origin. However, wedemonstrate that any simple trend between mass-to-light-ratio and mass orluminosity is inconsistent with the observations, and that a more complexrelationship must exist. We find the central regions of galaxies often exhibityoung stellar populations. However it is only in the lowest-mass galaxies~10^{10} M$ {\odot}$ that these populations are evident in the globalphotometry. In higher-mass galaxies, young central populations have decreasinginfluence on the global photometry, with there being no discernible impact ingalaxies more massive than ~2x10^{11} M$ {\odot}$. We conclude that the youngstellar populations detected in spectroscopic studies are generally centrallyconcentrated, and that there is an upper limit on the mass of star-formingevents in massive galaxies. These results have ramifications for mass-to-lightratios estimated from photometric observations.

Author: Robert N. Proctor, Philip Lah, Duncan A. Forbes, Matthew Colless, Warrick Couch


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