Astronomy and Astrophysics – Astronomy
Scientific paper
Jul 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008iaus..245..391n&link_type=abstract
Formation and Evolution of Galaxy Bulges, Proceedings of the International Astronomical Union, IAU Symposium, Volume 245, p. 391
Astronomy and Astrophysics
Astronomy
Techniques: Spectroscopic, Galaxies: Elliptical And Lenticular, Cd, Galaxies: Evolution, Galaxies: Formation, Galaxies: Stellar Content
Scientific paper
We use a purely data-driven rectified factor analysis to identify early-type galaxies with young (≲ 4 Gyr) stellar populations in the Sloan Digital Sky Survey Spectroscopic Catalogue. We call these galaxies E+F galaxies, analogous to E+A galaxies. These galaxies lie in the ‘Green Valley’, between the blue cloud and the red sequence on the colour-magnitude diagram. As such, these galaxies may represent an important transient stage in the evolution of galaxies from blue and star-forming to red and passive. We investigate the distribution in projected local galaxy surface density of the E+F galaxies, and compare it with the environment of early-type and E+A galaxies. We find that i) the E+A distribution peaks strongly in projected local galaxy surface density, Σ5, at ~ 0.1-0.2 Mpc-2, ii) early-types have a flatter peak at ~ 0.06-0.2 Mpc-2, iii) the E+Fs lie somewhere in between, and iv) the distributions of the models do not agree well with the data, peaking at higher densities, and under-predicting the number of E+As at low (Σ5 < 0.3 Mpc-2) densities. The dearth of E+A and E+F galaxies in dense environments confirms that E+A and E+F galaxies are most likely the products of galaxy-galaxy merging or interactions, rather than star-forming galaxies whose star formation has been quenched by processes unique to dense environments, such as ram-pressure stripping or galaxy harassment. The similarity of the environments in which the E+F population and the E+A galaxy sample are found, together with the spectral evidence, suggests that E+F galaxies are E+A galaxies, which have evolved by a further ~ one to a few Gyr.
Benson Andrew
Harva Markus
Kaban Ata
Nolan Louisa A.
Raychaudhury Somak
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