Supervisor: Bodo Ziegler (Department of Astrophysics)

Funding Situation: potentially via a VISESS PhD fellowship

Project outline: The interconnected components of a galaxy – stars, gas, dust, central supermassive black hole (SMBH), and dark matter halo – are subject to a variety of feedback mechanisms. Stellar feedback is a key regulator of how efficiently gas is converted into stars. An accreting SMBH turns into an active galactic nucleus (AGN) with enough energy output to affect the full host galaxy, so-called AGN feedback. When a galaxy falls into a cluster, the hot cluster gas can start removing the galaxy's gas reservoir via ram-pressure and subsequently quench star formation, so-called external feedback. Previously, we found that the stellar populations in disk galaxies up to z~1 reflect “down-sizing”: stars in more massive galaxies formed earlier and on shorter timescales than in less massive ones. The reason is, however, unclear: does stellar feedback keep the star formation efficiency in lower-mass galaxies low, or does AGN feedback drive an early and efficient conversion of gas into stars in higher-mass galaxies? To distinguish both we combine different galaxy scaling relations: stellar and AGN feedback cause galaxies to become outliers, but not the same way in each scaling relation, while field versus cluster disk galaxies allows to examine environmental feedback.

Covering galaxies with total stellar masses from 109 to 1011 solar masses, we will determine stellar versus AGN feedback as cause for the observed “down-sizing”. Our samples are located in different environments, so that we can control for, as well as constrain, the effect of environmental feedback. Ultimately, we will quantify the importance of stellar feedback versus external and AGN feedback over the past ~10 Gyr.