  Large-scale asymmetries in the stellar mass distribution in galaxies are
believed to trace non-equilibrium situations in the luminous and/or dark matter
component. These may arise in the aftermath of events like mergers, accretion,
and tidal interactions. These events are key in the evolution of galaxies. In
this paper we quantify the large-scale lopsidedness of light distributions in
25155 galaxies at z < 0.06 from the Sloan Digital Sky Survey Data Release 4
using the m = 1 azimuthal Fourier mode. We show that the lopsided distribution
of light is primarily due to a corresponding lopsidedness in the stellar mass
distribution. Observational effects, such as seeing, Poisson noise, and
inclination, introduce only small errors in lopsidedness for the majority of
this sample. We find that lopsidedness correlates strongly with other basic
galaxy structural parameters: galaxies with low concentration, stellar mass,
and stellar surface mass density tend to be lopsided, while galaxies with high
concentration, mass, and density are not. We find that the strongest and most
fundamental relationship between lopsidedness and the other structural
parameters is with the surface mass density. We also find, in agreement with
previous studies, that lopsidedness tends to increase with radius. Both these
results may be understood as a consequence of several factors. The outer
regions of galaxies and low-density galaxies are more susceptible to tidal
perturbations, and they also have longer dynamical times (so lopsidedness will
last longer). They are also more likely to be affected by any underlying
asymmetries in the dark matter halo.
