The morphological transformation and the quenching of galaxies
  We study the morphological transformation from late types to early types and
the quenching of galaxies with the seventh Data Release (DR7) of the Sloan
Digital Sky Survey (SDSS). Both early type galaxies and late type galaxies are
found to have bimodal distributions on the star formation rate versus stellar
mass diagram ($\lg SFR - \lg M_*$). We therefore classify them into four types:
the star-forming early types (sEs), the quenched early types (qEs), the
star-forming late types (sLs) and the quenched late types (qLs). We checked
many parameters on various environmental scales for their potential effects on
the quenching rates of late types and early types, as well as the early type
fractions among star-forming galaxies and those among quenched galaxies. These
parameters include: the stellar mass $M_*$, and the halo mass $M_{halo}$; the
small-scale environmental parameters, such as the halo centric radius
$R_p/r_{180}$ and the third nearest neighbor distances ($d_{3nn}$); the
large-scale environmental parameters, specifically whether they are located in
clusters, filaments, sheets, or voids. We found that the morphological
transformation is mainly regulated by the stellar mass. Quenching is mainly
driven by the stellar mass for more massive galaxies and by the halo mass for
galaxies with smaller stellar masses. In addition, we see an overall stronger
halo quenching effect in early type galaxies, which might be attributed to
their lacking of cold gas or earlier accretion into the massive host halos.
