Changes: The Past, Present, and Future of the Nearby Dwarf Galaxy NGC 55
  Spectra that cover wavelengths from 0.6 to 1.1um are used to examine the
behavior of emission and absorption features in a contiguous 22 x 300 arcsec
region centered on the nearby dwarf galaxy NGC 55. Based on the relative
strengths of various emission features measured over spatial scales of many
tens of parsecs, it is concluded that the ionization states and sulphur
abundances in most of the star-forming regions near the center of NGC 55 are
similar. A large star-forming region is identified in the north west part of
the disk at a projected distance of ~1 kpc from the galaxy center that has
distinct ionization properties. Fossil star-forming regions are also identified
using the depth of the near-infrared Ca triplet. One such area is identified
near the intersection of the major and minor axes, and it is suggested that
this area is a proto-nucleus. The spectra of bright unresolved sources that are
blended stellar asterisms, compact HII regions, and star clusters are also
discussed. The spectra of some of the HII regions contain Ca triplet absorption
lines, signalling a concentration of stars in the resolution element that span
many Myr. Six of the unresolved sources have spectroscopic characteristics that
are indicative of C stars embedded in intermediate age clusters. The peculiar
properties of NGC 55 have been well documented in the literature, and it is
argued that these may indicate that NGC 55 is transforming into a dwarf
lenticular galaxy.
