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arXiv · 1501.06588

The GALEX/S4G UV-IR color-color diagram: Catching spiral galaxies away from the Blue Sequence

Alexandre Y. K. Bouquin·Armando Gil de Paz·Samuel Boissier·Juan-Carlos Muñoz-Mateos·Kartik Sheth·Dennis Zaritsky·Jarkko Laine·Jesús Gallego·Reynier F. Peletier·Benjamin R. Röck·Johan H. Knapen
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Abstract

We obtained GALEX FUV, NUV, and Spitzer/IRAC 3.6$μ$m photometry for > 2000 galaxies, available for 90% of the S4G sample. We find a very tight "GALEX Blue Sequence (GBS)" in the (FUV-NUV) versus (NUV-[3.6]) color-color diagram which is populated by irregular and spiral galaxies, and is mainly driven by changes in the formation timescale ($τ$) and a degeneracy between $τ$ and dust reddening. The tightness of the GBS provides an unprecedented way of identifying star-forming galaxies and objects that are just evolving to (or from) what we call the "GALEX Green Valley (GGV)". At the red end of the GBS, at (NUV-[3.6]) > 5, we find a wider "GALEX Red Sequence (GRS)" mostly populated by E/S0 galaxies that has a perpendicular slope to that of the GBS and of the optical red sequence. We find no such dichotomy in terms of stellar mass (measured by $\rm{M}_{[3.6]}$), since both massive ($M_{\star} > 10^{11} M_{\odot}$) blue and red sequence galaxies are identified. The type that is proportionally more often found in the GGV are the S0-Sa's and most of these are located in high-density environments. We discuss evolutionary models of galaxies that show a rapid transition from the blue to the red sequence on timescale of $10^{8}$years.

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Alexandre Y. K. Bouquin, Armando Gil de Paz, Samuel Boissier, Juan-Carlos Muñoz-Mateos, Kartik Sheth, Dennis Zaritsky, Jarkko Laine, Jesús Gallego, Reynier F. Peletier, Benjamin R. Röck, Johan H. Knapen. 2015-01-26. The GALEX/S4G UV-IR color-color diagram: Catching spiral galaxies away from the Blue Sequence. https://doi.org/10.1088/2041-8205%2F800%2F1%2Fl19

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