Observing Correlations Between Dark Matter Accretion and Galaxy Growth:
  I. Recent Star Formation Activity in Isolated Milky Way-Mass Galaxies
  The correlation between fresh gas accretion onto haloes and galaxy star
formation is critical to understanding galaxy formation. Different theoretical
models have predicted different correlation strengths between halo accretion
rates and galaxy star formation rates, ranging from strong positive
correlations to little or no correlation. Here, we present a technique to
observationally measure this correlation strength for isolated Milky Way-mass
galaxies with $z < 0.123$. This technique is based on correlations between dark
matter accretion rates and the projected density profile of neighbouring
galaxies; these correlations also underlie past work with splashback radii. We
apply our technique to both observed galaxies in the Sloan Digital Sky Survey
as well as simulated galaxies in the UniverseMachine where we can test any
desired correlation strength. We find that positive correlations between dark
matter accretion and recent star formation activity are ruled out with $\gtrsim
85\%$ confidence. Our results suggest that star formation activity may not be
correlated with fresh accretion for isolated Milky Way-mass galaxies at $z=0$
and that other processes, such as gas recycling, dominate further galaxy
growth.
