Edmond Cheung

Bars are thought to be the major drivers of secular evolution. They are also present in up to two thirds of the local disk population, suggesting that they significantly affect galaxy evolution, at least at z~0.

Using Galaxy Zoo 2, I've lead a project in which we searched for evidence of bar-driven secular evolution. Specifically, we explored the behavior of bars as a function of several parameters that are predicted to significantly affect bar-driven secular evolution. The above plot is Figure 3 from Cheung et al. 2013. It shows that the bar likelihood, i.e., the likelihood a bar exists, is related to the properties of a galaxy, indicating that the existence of bars are connected to galaxy properties.

Moreover, these trends match the predictions of bar-driven secular evolution, strongly supporting the theory of secular evolution. This implies that bars are important drivers of galaxy evolution. See Cheung et al. 2013. for more details.

Quenching

The number of red sequence galaxies has doubled since z~1 while the number of blue cloud galaxies has remained relatively constant. A natural interpretation is that galaxies evolve from blue to red with time, i.e., from star forming to 'quenched.'

In Cheung et al. 2012, I led a project to discover what the underlying physical processes are behind quenching. While we were unable to identify the quenching mechanism, we were able to place strong constraints on the quenching process. We found that red and blue galaxies were best separated by the central stellar surface mass density (see above figure, which is Figure 7 from Cheung et al. 2012), suggesting that whatever quenches galaxies must also significantly increase the central stellar mass of galaxies.