Physical Information: Since the pair is obviously interacting, the appropriate estimate of their distance is based on the average of what little distance information is available them, namely a recessional velocity relative to the Cosmic Microwave Background of 15390 km/sec for the western member of the pair (PGC 64801) and 15310 km/sec for the eastern member (PGC 64805), yielding an average value of about 15350 km/sec. Based on that (and
H0 = 70 km/sec/Mpc), a straightforward calculation indicates that the pair is about 715 million light-years away. However, for objects at such distances we should take into account the expansion of the Universe during the time it took their light to reach us. Doing that shows that the pair was about 670 to 675 million light-years away at the time the light by which we see it was emitted, about 690 million years ago (the difference between the two numbers being due to the expansion of the intervening space during the light-travel time). The pair is unusual in that most galaxy mergers involve galaxies of considerably different sizes and a glancing collision, whereas here we see two galaxies of nearly equal size suffering a direct collision of their nuclei, with a chaotic but in some ways surprisingly "regular" result.
Given the estimated distance and the apparent size of about 0.38 by 0.23 arcmin for the nucleus of the western galaxy (including its short spiral arms), about 0.27 by 0.25 arcmin for the nucleus of the eastern galaxy, a separation of 0.25 arcmin between the centers of the two nuclei, 0.98 by 0.67 arcmin for the disorganized "spiral" ring surrounding the pair, 0.27 by 0.18 arcmin for a faint southeastern extension beyond the ring, and an overall size of about 1.1 by 0.71 arcmin for the entire structure (from the images below), at the time the light by which we see the pair left them (almost 700 million years ago), the central part of the western galaxy was about 75 thousand light-years across, that of the eastern one was about 50 to 55 thousand light-years across, the nuclear centers were about 50 thousand light-years apart, the disorganized ring spanned about 195 to 200 thousand light-years, and the entire structure spanned about about 215 thousand light-years. By now, the galaxies are probably well on the way to completely merging, and look considerably different from what we can currently see.
This pair of galaxies is among those in the
Arp-Madore Catalogue of Southern Peculiar Galaxies & Associations, but there is no image of it, and although listed as a member of Category 1: Galaxies With Interacting Companions in an
ASCII file that adds "Ring with Companion in Ring," and "Interacting with Nucleus," there is nothing else in the Catalogue about it (though it does appear in a supposedly complete list of objects in the Catalogue).
Classification Note: The "type" for PGC 64801 is taken from NED and modified according to the HST image below; the "type" for PGC 64805 is based only on the HST image.
