The connection between the UV colour of early-type galaxies and the stellar initial mass function revisited

This article has been accepted for publication in Monthly notices of the Royal Astronomical Society © 2014 RAS. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. DZ acknowledges financial support from NASA ADAP NNX12AE27G and NYU CCPP for its hospitality during long-term visits. The authors acknowledge the support from the FP7 Marie Curie Actions of the European Commission, via the Initial Training Network DAGAL under REA grant agreement PITN-GA-2011-289313. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA.
We extend our initial study of the connection between the UV colour of galaxies and both the inferred stellar mass-to-light ratio, Upsilon(*), and a mass-to-light ratio referenced to Salpeter initial mass function (IMF) models of the same age and metallicity, Upsilon(*)/Upsilon(Sal), using new UV magnitude measurements for a much larger sample of early-type galaxies, ETGs, with dynamically determined mass-to-light ratios. We confirm the principal empirical finding of our first study, a strong correlation between the GALEX FUV-NUV colour and Upsilon(*). We show that this finding is not the result of spectral distortions limited to a single passband (e.g. metallicity-dependent line-blanketing in the NUV band), or of the analysis methodology used to measure Upsilon(*), or of the inclusion or exclusion of the correction for stellar population effects as accounted for using Upsilon(*)/Upsilon(Sal). The sense of the correlation is that galaxies with larger Upsilon(*), or larger Upsilon(*)/Upsilon(Sal), are bluer in the UV. We conjecture that differences in the low-mass end of the stellar IMF are related to the nature of the extreme horizontal branch stars generally responsible for the UV flux in ETGs. If so, then UV colour can be used to identify ETGs with particular IMF properties and to estimate Upsilon(*). We also demonstrate that UV colour can be used to decrease the scatter about the Fundamental Plane and Manifold, and to select peculiar galaxies for follow-up with which to further explore the cause of variations in Upsilon(*) and UV colour.
Unión Europea. FP7
NASA ADAP
Depto. de Física de la Tierra y Astrofísica
Fac. de Ciencias Físicas
TRUE
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