The MASSIVE Survey - VII. The Relationship of Angular Momentum, Stellar Mass and Environment of Early-Type Galaxies

We analyze the environmental properties of 370 present-day early-type galaxies in the MASSIVE and ATLAS3D surveys, two complementary volume-limited integral-field spectroscopic (IFS) galaxy surveys spanning absolute $K$-band magnitude $-21.5 > M_K > -26.6$, or stellar mass $6 \times 10^{9} < M_* < 2 \times 10^{12} M_\odot$. We find these galaxies to reside in a diverse range of environments measured by four methods: group membership (whether a galaxy is a brightest group/cluster galaxy, satellite, or isolated), halo mass, large-scale mass density (measured over a few Mpc), and local mass density (measured within the $N$th neighbor). The spatially resolved IFS stellar kinematics provide robust measurements of the angular momentum parameter $\lambda_e$ and enable us to examine the relationship among $\lambda_e$, stellar mass, and environment of ETGs. We find a strong correlation between $\lambda_e$ and stellar mass, where the average $\lambda_e$ decreases from $\sim 0.5$ to less than 0.1 with increasing galaxy mass, and the fraction of slow rotators increases correspondingly from $\sim 10$% to 90%. While we see weak trends between environment and both $\lambda_e$ and slow rotator fraction, this kinematic morphology-density relation is fully accounted for by the strong correlation between the slow rotator fraction and stellar mass; due to the correlation between stellar mass and environment, it naturally results in a correlation between slow/fast classification and environment as well. A possible exception is that the increased fraction of slow rotators at high local density is slightly more than expected based only on these joint correlations. Our results suggest that the physical processes responsible for building up the present-day stellar masses of massive galaxies are also very efficient at reducing their angular momentum, in any environment.