Note About Classification: The type is taken from the Spitzer Survey of Stellar Structure in Galaxies. "sp" means that the galaxy is a "spindle" (that is, an edge-on galaxy), which makes determining its structure more difficult than usual. The "/ E(d)3" indicates that (at least in infrared images) the galaxy is enveloped in a disklike elliptical outer region, but that doesn't change the fact that it is a spiral galaxy.

Physical Properties: PGC 16643 is part of a study of fifty nearby star-forming galaxies, whence the HST image of the galaxy shown below. In DSS and PanSTARRS images the hot young stars recently formed in it give it a bluish cast, whereas an HST image which emphasizes the clouds of gas and dust out of which those stars formed and new stars will eventually form has a pinkish tone. Based on a recessional velocity of 835 km/sec (and H₀ = 70 km/sec/Mpc), PGC 16643 is about 35 to 40 million light years away, in reasonable agreement with a redshift-independent distance estimate (per the press release accompanying the HST image below) of about 30 million light years. Given that and its apparent size of about 1.15 by 0.7 arcmin (from the images below), the galaxy is about 10 to 13 thousand light years across, making it a dwarf spiral (or perhaps, given its peculiar structure, a dwarf irregular) galaxy.

Note About Classification: The type is taken from the Spitzer Survey of Stellar Structure in Galaxies.

Note About Classification: The type is taken from the Spitzer Survey of Stellar Structure in Galaxies.

Note About Classification: The type is taken from the Spitzer Survey of Stellar Structure in Galaxies. The colon after the "m" means that part of the classification is not as certain as the authors would have liked.