Astrophys. J., Suppl. Ser., 173, 597-606 (2007/December-0)
GALEX UV color relations for nearby early-type galaxies.
DONAS J., DEHARVENG J.-M., RICH R.M., YI S.K., LEE Y.-W., BOSELLI A., GIL DE PAZ A., BOISSIER S., CHARLOT S., SALIM S., BIANCHI L., BARLOW T.A., FORSTER K., FRIEDMAN P.G., HECKMAN T.M., MADORE B.F., MARTIN D.C., MILLIARD B., MORRISSEY P., NEFF S.G., SCHIMINOVICH D., SEIBERT M., SMALL T., SZALAY A.S., WELSH B.Y. and WYDER T.K.
Abstract (from CDS):
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 Mg2index; we suspect that this reflects blanketing in the NUV band being correlated with overall metallicity. We find a marginal anticorrelation of FUV-VT with Mg2for elliptical galaxies.
Galaxies: Elliptical and Lenticular, cD - Galaxies: Photometry - Galaxies: Stellar Content - Ultraviolet: Galaxies
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