The GALEX/S4G UV–IR Color–Color Diagram: Catching Spiral Galaxies Away from the Blue Sequence

Bouquin, A. Y. K.; Gil de Paz, Armando; Boissier, Samuel; Muñoz-Mateos, Juan-Carlos; Sheth, Kartik; Zaritsky, Dennis; Laine, Jarkko; Gallego, Jesús; Peletier, Reynier F.; Röck, B. R.; Knapen, J. H.
Referencia bibliográfica

The Astrophysical Journal Letters, Volume 800, Issue 1, article id. L19, 6 pp. (2015).

Fecha de publicación:
2
2015
Número de autores
11
Número de autores del IAC
2
Número de citas
16
Número de citas referidas
14
Descripción
We obtained GALEX FUV, NUV, and Spitzer/IRAC 3.6 μm photometry for \gt 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]) \gt 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 {{M}[3.6]}) since both massive ({{M}\star }\gt {{10}11}{{M}ȯ }) blue- and red-sequence galaxies are identified. The type that is proportionally more often found in the GGV is 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 a timescale of 108 yr.
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