Publication: GALEX UV color relations for nearby early-type galaxies
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University Chicago Press
We use GALEX/optical photometry to construct color-color relationships for early-type galaxies sorted by morphological type. We have matched objects in the GALEX GR1 public release and the first IR1.1 internal release, with the RC3 early-type galaxies having a morphological type -5.5 ≤ T < − 1.5, with mean error on T < 1.5 and mean error on (B − V)_T < 0.05. After visual inspection of each match, we are left with 130 galaxies with reliable GALEX pipeline photometry in the far-UV and near-UV bands. This sample is divided into ellipticals (-5.5 ≤ T < − 3.5) and lenticulars (-3.5 ≤ T < − 1.5). After correction for Galactic extinction, the color-color diagrams FUV − NUV versus (B − V)_Tc are plotted for the two subsamples. We find a tight anticorrelation between the FUV − NUV and (B − V)Tc colors for ellipticals, with the UV color getting bluer when the (B − V)Tc gets redder. This relationship very likely is an extension of the color-metallicity relationship in the GALEX NUV band. We suspect that the main source of the correlation is metal line blanketing in the NUV band. The FUV − NUV versus B − V correlation has larger scatter for lenticular galaxies; we speculate that this reflects the presence of low-level star formation. If the latter objects (i.e., those that are blue both in FUV − NUV and in B − V) are interpreted as harboring recent star formation activity, this would be the case for a few percent (~4%) of ellipticals and ~15% of lenticulars; this would mean about 10% of early-type galaxies have residual star formation in our full sample of 130 early-type galaxies. We also plot FUV − NUV versus the Mg2 index and central velocity dispersion. We find a tight anticorrelation between FUV − NUV and the Mg2 index; we suspect that this reflects blanketing in the NUV band being correlated with overall metallicity. We find a marginal anticorrelation of FUV − V_T with Mg_2 for elliptical galaxies.
© 2007. The American Astronomical Society. All rights reserved. Artículo firmado por 26 autores. We wish to acknowledge Jakob Walcher for kindly extracting for us useful data from stochastic realizations of star formation models. GALEX (Galaxy Evolution Explorer) is a NASA Small Explorer, launched in 2003 April. We gratefully acknowledge NASA’s support for construction, operation, and science analysis for the GALEX mission, developed in cooperation with the Centre National d’Etudes Spatiales of France and the Korean Ministry of Science and Technology. The grating, window, and aspheric corrector were supplied by France. We acknowledge the dedicated team of engineers, technicians, and administrative staff from JPL/Caltech; Orbital Sciences Corporation; University of California, Berkeley; Laboratory Astrophysique Marseille; and the other institutions who made this mission possible. This work was partly supported by grant R01-2006-000-10716-0 (SKY) from the Basic Research Program of the Korea Science and Engineering Foundation. A. G. d. P. is financed by the MAGPOP EU Marie Curie Research Training Network.
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