  The three-point correlation function (3PCF) for galaxies provides an
opportunity to measure the non-Gaussianity generated from nonlinear structure
formation and also probes information about galaxy formation and evolution that
is generally not available from the two-point correlation function (2PCF). We
measure the 3PCF of the Sloan Digital Sky Survey DR7 main sample galaxies in
both redshift and projected spaces on scales up to 40Mpc/h. We explore the
dependence of the 3PCF on galaxy stellar mass and color in order to constrain
the formation and evolution for galaxies of different properties. The study of
the dependence on these properties also helps better constrain the relation
between galaxy stellar mass and color and the properties of their hosting
dark-matter halos. We focus on the study of the reduced 3PCF, Q, defined as the
ratio between the 3PCF and the sum of the products of the 2PCFs. We find a very
weak stellar mass dependence of Q in both redshift and projected spaces. On
small scales, more massive galaxies tend to have slightly higher amplitudes of
Q. The shape dependence of Q is also weak on these small scales, regardless of
stellar mass and color. The reduced 3PCF has a strong color dependence for the
low-mass galaxies, while no significant dependence on color is found for the
high-mass galaxies. Low-mass red galaxies have higher amplitudes and stronger
shape dependence of the reduced 3PCF than the blue galaxies, implying that
these low-mass red galaxies tend to populate filamentary structures. The linear
galaxy bias model fails to interpret the color dependence of Q, emphasizing the
importance of a nonvanishing quadratic bias parameter in the correct modeling
of the galaxy color distribution.
