Sunday, August 4, 2013

1308.0054 (Daniel H. McIntosh et al.)

Massive blue early-type galaxies in the SDSS. I. A new population of recently quenched elliptical galaxies    [PDF]

Daniel H. McIntosh, Cory Wagner, Andrew Cooper, Eric F. Bell, Dusan Keres, Frank C. van den Bosch, Anna Gallazzi, Tim Haines, Justin Mann, Anna Pasquali, Allison M. Christian
We use the SDSS to explore early-type galaxies (ETGs) that are plausibly in transition between the red sequence and the blue cloud. Through careful morphological inspection, we identify 1500 unusually blue elliptical galaxies among a larger sample of blue ETGs with 0.011e10 h^{-2} M_sun. Blue ellipticals comprise 3.7% of all ETGs with 1e1050% of the expected quiescent growth at z~0 assuming this phase lasts 0.5Gyr. Based on color, stellar M/L ratios and metallicity estimates, we argue that RQEs have recent SFHs that differ from rejuvenated ETGs. Yet, a significant but small incidence (5%) of RQEs with E+A spectra implies that the quenching of most RQEs did not involve a large starburst. Most (90%) RQEs reside at the centers of 3x10^{12}h^{-1} M_sun groups, which agrees well with the `small group scale' in which spiral merging onto the halo center is maximally efficient. The preferred RQE environment rules out satellite-specific quenching processes for most. Under the assumption that most RQEs were quenched by a hot halo atmosphere impeding efficient gas cooling, we discuss the incidence of Seyfert and LINER activity with regards to the maintenance-mode feedback needed to keep star formation shut off at the centers of such small halos. (abridged)
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