  We present a phenomenological model of feedback in early-type galaxies that
tracks the evolution of the interstellar medium gas mass, metallicity, and
temperature. Modeling the star formation rate as a Schmidt law with a
temperature-dependent efficiency, we find that intermittent episodes of star
formation are common in moderate-size ellipticals. Our model is applicable in
the case in which the thermalization time from SN is sufficiently long that
spatial variations are relatively unimportant, an appropriate assumption for
the empirical parameters adopted here. The departure from a standard scenario
of passive evolution implies significantly younger luminosity-weighted ages for
the stellar populations of low-mass galaxies at moderate redshifts, even though
the more physically meaningful mass-weighted ages are changed only slightly.
Secondary bursts of star formation also lead to a natural explanation of the
large scatter in the NUV-optical relation observed in clusters at moderate
redshift and account for the population of E+A galaxies that display a
spheroidal morphology. As the late-time formation of stars in our model is due
to the gradual cooling of the interstellar medium, which is heated to
temperatures ~1 keV by the initial burst of supernovae, our conclusions do not
rely on any environmental effects or external mechanisms. Furthermore, a simple
estimate of the X-ray emission from this supernova heated gas leads to an L_X
vs L_B correlation that is in good agreement with observed values. Thus
feedback processes may be essential to understanding the observed properties of
early-type galaxies from the optical to the X-ray.
