SkyMapper SEDs of nearby galaxies: quenching and bursting probed by a
  change index for star formation
  The wish list of astronomers includes a tool that reveals quenching of star
formation in galaxies directly as it proceeds. Here, we present a
proof-of-concept for a new quenching-and-bursting diagnostic, a "change index"
for star formation, that requires only photometric data, provided they include
filters such as the violet $uv$ bands used by SkyMapper. The index responds
mostly to changes in star-formation rate on a timescale of 20 to 500 Myr and is
nearly insensitive to dust extinction. It works effectively to distances of 100
to 150 Mpc. We explore its application to eight example galaxies in SkyMapper
DR2, including known E+A and Seyfert-1 galaxies. Owing to the degeneracies
inherent in broad-band photometry, the change index can only be a qualitative
indicator of changes in star-formation rate. But once the SkyMapper Southern
Survey is complete, the change index will be available for every spatial
resolution element of every galaxy in the Southern sky within its working
distance range.
