摘要
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 10 <sup>10</sup> and 10 <sup>11</sup> h <sup>-2</sup> M⊙. Using published fibre spectrum diagnostics, we identify a unique subset of 172 non-star-forming ellipticals with distinctly blue urz colours and young (<3Gyr) lightweighted stellar ages. These recently quenched ellipticals (RQEs) have a number density of 2.7-4.7 × 10 <sup>-5</sup> h3 Mpc <sup>-3</sup> and sufficient numbers above 2.5 × 10 <sup>10</sup> h <sup>-2</sup> M⊙ to account for more than half of the expected quiescent growth at late cosmic time assuming that this phase lasts 0.5 Gyr. 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 <3 × 10 <sup>12</sup> h <sup>-1</sup> M⊙ 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. © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.