  Extended stellar clusters with effective radii larger than 10 pc have been
found in various environments. Objects with masses comparable to globular
clusters (GCs) are called extended clusters (ECs), while objects with masses in
the dwarf galaxy regime are called ultra-compact dwarf galaxies (UCDs). The
paper analyses the observational parameters luminosity, effective radius, and
projected distance to the host galaxy, of all known ECs and UCDs and the
dependence of these parameters on the type and the luminosity of their host
galaxy. We searched the available literature to compile a catalog of star
clusters larger than 10 pc. As there is no clear distinction between ECs and
UCDs, both types of objects will be called extended stellar objects (EOs). In
total, we found 813 EOs of which 171 are associated with late-type and 642 with
early-type galaxies. EOs cover a luminosity range from about MV = -4 to -14
mag. However, the vast majority of EOs brighter than -10 mag are associated
with elliptical galaxies. At each magnitude EOs are found with effective radii
between 10 pc and an upper size limit, which shows a clear trend: the more
luminous the object the larger is the upper size limit. For EOs associated with
early-and late-type galaxies, the luminosity functions peak at -6.40 and -6.47
mag, respectively, which is about one magnitude fainter than the peak of the GC
luminosity function. EOs and GCs form a coherent structure in the reff vs. MV
parameter space, while there is a clear gap between EOs and early type dwarf
galaxies. However, there is a small potential overlap at the high-mass end,
where the most extended EOs are close to the parameters of compact elliptical
galaxies. We compare the EO sample with numerical models and conclude that the
parameters of the EO sample as a whole can be very well explained by a star
cluster origin, where EOs are the results of merged cluster complexes.
