The SPLASH survey: Quiescent galaxies are more strongly clustered but
  are not necessarily located in high-density environments
  We use the stellar-mass-selected catalog from the Spitzer Large Area Survey
with Hyper-Suprime-Cam (SPLASH) in the COSMOS field to study the environments
of galaxies via galaxy density and clustering analyses up to $z \sim 2.5$. The
clustering strength of quiescent galaxies exceeds that of star-forming
galaxies, implying that quiescent galaxies are preferentially located in more
massive halos. When using local density measurement, we find a clear positive
quiescent fraction--density relation at $z < 1$, consistent with earlier
results. However, the quiescent fraction--density relation reverses its trend
at intermediate redshifts ($1 < z < 1.5$) with marginal significance
(<1.8$\sigma$) and is found to be scale dependent (1.6$\sigma$). The lower
fraction of quiescent galaxies seen in large-scale dense environments, if
confirmed to be true, may be associated with the fact that the star formation
can be more easily sustained via cold stream accretion in `large-scale'
high-density regions, preventing galaxies from permanent quenching. Finally, at
$z > 1.5$, the quiescent fraction depends little on the local density, even
though clustering shows that quiescent galaxies are in more massive halos. We
argue that at high redshift the typical halo size falls below $10^{13}$
$M_{\odot}$, where intrinsically the local density measurements are so varied
that they do not trace the halo mass. Our results thus suggest that in the
high-redshift Universe, halo mass may be the key in quenching the star
formation in galaxies, rather than the conventionally measured galaxy density.
