La compleja vida de las galaxias elípticas

We present a simple phenomenological model of feedback in early-type galaxies that tracks the evolution of the gas content, 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. This departure from a standard scenario of passive evolution implies significantly younger luminosity-weighted ages for the stellar population in low-mass galaxies at moderate redshifts, even though the more physically meaningful mass-weighted ages are changed only slightly. Such secondary bursts of star formation 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 X-ray vs optical 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.