ARP23 (NGC 4618/4625) One Armed Dwarf Galaxy in HaLRGB (David Payne)

Celestial hemisphere: Northern · Constellation: Canes Venatici (CVn) · Contains: IC 3668 · IC 3675 · NGC 4618 · NGC 4625 · PGC 2176077 · PGC 2177330 · PGC 2177776 · PGC 2180478 · PGC 2180781 · PGC 42575

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ARP23 (NGC 4618/4625) One Armed Dwarf Galaxy in HaLRGB

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ARP23 (NGC 4618/4625) One Armed Dwarf Galaxy in HaLRGB

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.

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Status	Advanced success
Started	...
Astrometry.net job	7470990
PixInsight job	9DYD8AGE6ODF29W3L78KFBBIVCQGMV0K
PixInsight queue size	n/a
PixInsight stage	TASK_LOG

RA (center)	12h41m06s.739
RA (top/left)	12h40m28s.452
RA (top/right)	12h39m24s.542
RA (bottom/right)	12h41m44s.745
RA (bottom/left)	12h42m49s.276

Dec (center)	+41°11′46″.66
Dec (top/left)	+41°30′35″.80
Dec (top/right)	+41°05′38″.89
Dec (bottom/right)	+40°52′52″.83
Dec (bottom/left)	+41°17′50″.40

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ARP23 (NGC 4618/4625) One Armed Dwarf Galaxy in HaLRGB

ARP23 (NGC 4618/4625) One Armed Dwarf Galaxy in HaLRGB

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ARP23 (NGC 4618/4625) One Armed Dwarf Galaxy in HaLRGB

ARP23 (NGC 4618/4625) One Armed Dwarf Galaxy in HaLRGB

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