The nature of the Sloan Digital Sky Survey galaxies in various classes
  based on morphology, colour and spectral features - III. Environments
  We present a study on the environments of the SDSS galaxies divided into fine
classes based on their morphology, colour and spectral features. The SDSS
galaxies are classified into early-type and late-type; red and blue; passive,
HII, Seyfert and LINER, which returns a total of 16 fine classes of galaxies.
We estimate the local number density, target-excluded local luminosity density,
local colour, close pair fraction and the luminosity and colour of the
brightest neighbour, which are compared between the fine classes
comprehensively. The morphology-colour class of galaxies strongly depends on
the local density, with the approximate order of high-density preference: red
early-type galaxies (REGs) -- red late-type galaxies (RLGs) -- blue early-type
galaxies (BEGs) -- blue late-type galaxies (BLGs). We find that high-density
environments (like cluster environments) seem to suppress AGN activity. The
pair fraction of HII REGs does not show statistically significant difference
from that of passive REGs, while the pair fraction of HII BLGs is smaller than
that of non-HII BLGs. HII BLGs show obvious double (red + blue) peaks in the
distribution of the brightest neighbour colour, while red galaxies show a
single red peak. The brightest neighbours of Seyfert BLGs tend to be blue,
while those of LINER BLGs tend to be red, which implies that the difference
between Seyfert and LINER may be related to the pair interaction. Other various
environments of the fine classes are investigated, and their implication on
galaxy evolution is discussed.
