Towards a physical picture of star-formation quenching: the photometric
  properties of recently-quenched galaxies in the Sloan Digital Sky Survey
  We select a sample of young passive galaxies from the Sloan Digital Sky
Survey Data Release 7 in order to study the processes that quench star
formation in the local universe. Quenched galaxies are identified based on the
contribution of A-type stars to their observed (central) spectra and relative
lack of ongoing star formation; we find that such systems account for roughly
2.5 per cent of all galaxies with log M_sun >= 9.5, and have a space density of
~2.2x10^-4 Mpc^-3. We show that quenched galaxies span a range of morphologies,
but that visual classifications suggest they are predominantly early-type
systems. Their visual early-type classification is supported by quantitative
structural measurements Sersic indices that show a notable lack of
disk-dominated galaxies, suggesting that any morphological transformation
associated with galaxies' transition from star-forming to passive--e.g. the
formation of a stellar bulge--occurs contemporaneously with the decline of
their star-formation activity. We show that there is no clear excess of optical
AGN in quenched galaxies, suggesting that: i) AGN feedback is not associated
with the majority of quenched systems or ii) that the observability of quenched
galaxies is such that the quenching phase in general outlives any associated
nuclear activity. Comparison with classical post-starburst galaxies shows that
both populations show similar signatures of bulge growth, and we suggest that
the defining characteristic of post-starburst galaxies is the efficiency of
their bulge growth rather than a particular formation mechanism.
