Critical Stellar Central Densities Drive Galaxy Quenching in the Nearby Universe

We study the structural and environmental dependence of star formation on the plane of stellar mass versus central core density (Σ 1 kpc ) in the nearby universe. We study the central galaxies in the sparse environment and find a characteristic population-averaged Σ 1 kpc ∼ 10 9 –10 9.2 M ⊙ kpc −2 , above which quenching is operating. This Σ 1 kpc crit only weakly depends on the stellar mass, suggesting that the mass quenching of the central galaxies is closely related to the processes that operate in the central region rather than over the entire galaxies. For satellites, at a given stellar mass, environment quenching appears to operate in a similar fashion as mass quenching in centrals, also starting from galaxies with high Σ 1 kpc to low Σ 1 kpc , and Σ 1 kpc crit becomes strongly mass-dependent, in particular in dense regions. This is because (1) more low-mass satellites are quenched by the environmental effects in denser regions and (2) at fixed stellar mass and environment, the environment-quenched satellites have, on average, larger Σ 1 kpc , M 1 kpc / M ⋆ , and Sérsic index n , and as well as smaller size. These results imply that either some dynamical processes change the structure of the satellites during quenching or the satellites with higher Σ 1 kpc are more susceptible to environmental effects.