ARP23 or NGC4618/4625 - HaLRGB (Canes Venatici), March 2023
Planewave CDK12.5" telecope and A-P 1100GTO AE mount
ASI6200MM, Antlia Pro BB & 3nm Ha Filters
Lum (26 x 160s exposures, Bin 2x2, Gain 100)
RGB (3 x 20 x 160s exposures, Bin 2x2 Gain 100)
Ha (13 x 420s exposures, Bin 2x2, Gain 200)
Total Integration Time = 5.3 hours

ARP23 is included in the Arp catalogue of peculiar galaxies as the dwarf galaxy NGC4618 (the larger of the two) is only one of a few spirals with only 1 arm. To me it looks like a cinnamon bun, with Ha sprinkles. The intense red hydrogen areas indicate that it is likely undergoing intense star formation. Also the galaxy is quite blue with very bright and young stars.
Why it only has one arm is unknown, but it has been postulated that this is due to an interaction with its companion NGC4618. Interestingly, NGC4618 was the site of a supernova recorded in 1985.