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In this paper we present a new statistic for quantifying galaxy morphology based on measurements of the Gini coefficient of galaxy light distributions. This statistic is easy to measure and is commonly used in econometrics to measure how wealth is distributed in human populations. When applied to galaxy images, the Gini coefficient provides a quantitative measure of the inequality with which a galaxy's light is distributed amongst its constituent pixels. We measure the Gini coefficient of local galaxies in the Early Data Release of the Sloan Digital Sky Survey and demonstrate that this quantity is closely correlated with measurements of central concentration, but with significant scatter. This scatter is almost entirely due to variations in the mean surface brightness of galaxies. By exploring the distribution of galaxies in the three-dimensional parameter space defined by the Gini coefficient, central concentration, and mean surface brightness, we show that all nearby galaxies lie on a well-defined two-dimensional surface (a slightly warped plane) embedded within a three-dimensional parameter space. By associating each galaxy sample with the equation of this plane, we can encode the morphological composition of the entire SDSS g * -band sample using the following three numbers: {22.451, 5.366, 7.010}. The i * -band sample is encoded as: {22.149, 5.373, and 7.627}.

In this paper we compare the properties of three subsystems of Galactic globular clusters, which are defined according to metallicity and horizontal branch morphology. We specifically focus on cluster luminosities, structures, surface brightnesses and ellipticities. It is shown that the so‐called ‘young’ halo (YH) clusters, which are thought to have formed in external satellite galaxies, exhibit characteristics which are clearly distinct from those of the ‘old’ halo (OH) and bulge/disc (BD) clusters, the majority of which are believed to be Galactic natives. The properties of the YH objects are, in many respects, similar to those of clusters belonging to a number of present‐day satellite dwarf galaxies. The OH and BD populations have apparently been strongly modified by destructive tidal forces and shocks in the inner Galaxy. By comparing the properties of the three cluster subsystems, we estimate that the present population of native Galactic clusters may only represent approximately two‐thirds of the original population. Several clusters with low surface brightnesses are observed to be highly flattened. We briefly speculate on the possibility that this ellipticity reflects the intrinsic flattening of dark matter mini‐haloes in which these optically dim clusters might be embedded. Finally, we examine the distribution of clusters on the size (log Rh) versus luminosity (MV) plane. Three objects are seen to fall well above the sharp upper envelope of the main distribution of clusters on the size–luminosity plane: ω Centauri, M54 and NGC 2419. All three of these objects have previously, and independently, been suggested to be the stripped cores of former dwarf galaxies. This suspicion is strengthened by the additional observation that the massive cluster G1 in M31 plus a number of the most luminous clusters in NGC 5128 also fall in the same region of the log Rh versus MV plane. All of the latter objects have previously been suggested as the stripped cores of now defunct dwarf galaxies.

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