Mon. Not. R. Astron. Soc., 442, 533-557 (2014/July-3)
A new population of recently quenched elliptical galaxies in the SDSS.
McINTOSH D.H., WAGNER C., COOPER A., BELL E.F., KERES D., VAN DEN BOSCH F.C., GALLAZZI A., HAINES T., MANN J., PASQUALI A. and CHRISTIAN A.M.
Abstract (from CDS):
We use the Sloan Digital Sky Survey to investigate the properties of massive elliptical galaxies in the local Universe (z ≤ 0.08) that have unusually blue optical colours. Through careful inspection, we distinguish elliptical from non-elliptical morphologies among a large sample of similarly blue galaxies with high central light concentrations (cr ≥ 2.6). These blue ellipticals comprise 3.7 per cent of all cr ≥ 2.6 galaxies with stellar masses between 1010 and 1011h-2M☉. Using published fibre spectrum diagnostics, we identify a unique subset of 172 non-star-forming ellipticals with distinctly blue urz colours and young (<3Gyr) light-weighted stellar ages. These recently quenched ellipticals (RQEs) have a number density of 2.7-4.7x10^- 5^h3Mpc- 3 and sufficient numbers above 2.5x1010h-2M☉ to account for more than half of the expected quiescent growth at late cosmic time assuming that this phase lasts 0.5Gyr. RQEs have properties that are consistent with a recent merger origin (i.e. they are strong `first-generation' elliptical candidates), yet few involved a starburst strong enough to produce an E+A signature. The preferred environment of RQEs (90 per cent reside at the centres of <3x1012h-1M☉ groups) agrees well with the `small group scale' predicted for maximally efficient spiral merging on to their halo centre and rules out satellite-specific quenching processes. The high incidence of Seyfert and LINER activity in RQEs and their plausible descendants may heat the atmospheres of small host haloes sufficiently to maintain quenching.