Halo Histories vs. Galaxy Properties at z=0, I: The Quenching of Star Formation

Understand

We test whether halo age and galaxy age are correlated at fixed halo and galaxy mass.

• The formation histories, and thus ages, of dark matter halos correlate with their large-scale density $\rho$, an effect known as assembly bias.
• We test whether this correlation extends to galaxies by measuring the dependence of galaxy stellar age on $\rho$.
• To clarify the comparison between theory and observation, and to remove the strong environmental effects on satellites, we use galaxy group catalogs to identify central galaxies and measure their quenched fraction, $f_Q$, as a function of large-scale environment.