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تسجيل مستخدم جديدA new population of recently quenched elliptical galaxies in the SDSS
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Daniel H. McIntosh
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We use the Sloan Digital Sky Survey to investigate the properties of massive elliptical galaxies in the local Universe (zleq0.08) that have unusually blue optical colors. Through careful inspection, we distinguish elliptical from non-elliptical morphologies among a large sample of similarly blue galaxies with high central light concentrations (c_rgeq2.6). These blue ellipticals comprise 3.7 per cent of all c_rgeq2.6 galaxies with stellar masses between 10^10 and 10^11 h^{-2} {rm M}_{sun}. Using published fiber spectra diagnostics, we identify a unique subset of 172 non-star-forming ellipticals with distinctly blue urz colors and young (< 3 Gyr) light-weighted stellar ages. These recently quenched ellipticals (RQEs) have a number density of 2.7-4.7times 10^{-5},h^3,{rm Mpc}^{-3} and sufficient numbers above 2.5times10^{10} h^{-2} {rm M}_{sun} to account for more than half of the expected quiescent growth at late cosmic time assuming 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 centers of < 3times 10^{12},h^{-1}{rm M}_{sun} groups) agrees well with the `small group scale predicted for maximally efficient spiral merging onto their halo center and rules out satellite-specific quenching processes. The high incidence of Seyfert and LINER activity in RQEs and their plausible descendents may heat the atmospheres of small host halos sufficiently to maintain quenching.
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