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Critical Stellar Central Densities Drive Galaxy Quenching in the Nearby Universe

We study the structural and environmental dependence of the star formation on the plane of stellar mass versus central core density ($Σ_{\rm 1\ kpc}$) in the nearby universe. We study the central galaxies in the sparse environment and find a characteristic population-averaged $\rm Σ_{1\ kpc} \sim 10^9-10^{9.2}\ M_{\odot}\ kpc^{-2}$, above which quenching is operating. This $\rm Σ^{crit}_{1\ kpc}$ only weakly depends on the stellar mass, suggesting that the mass-quenching of the central galaxies is more closely related to the processes that operate in the central regions 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 $\rm Σ_{1\ kpc}$ to low $\rm Σ_{1\ kpc}$, and $\rm Σ^{crit}_{1\ kpc}$ 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 $Σ_{\rm 1\ kpc}$, $\rm M_{1\ kpc}/M_{\star}$ and Sersic 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 $Σ_{\rm 1\ kpc}$ are more susceptible to the environmental effects.