The pair is made up of two galaxies, NGC 2444 (also known as UGC 4016) and NGC 2445 (UGC 4017), both members of the esteemed NGC 2415 galaxy group. NGC 2444 is a lenticular galaxy spanning approximately 85,000 light-years, while its counterpart, NGC 2445, is an irregular galaxy stretching nearly 90,000 light-years, given its distance from us.
Arp 143 is part of a unique and infrequent class of galaxies referred to as collisional ring galaxies. Characterized by a distinctive ring-shaped arrangement of gas and stars replacing the usual spiral structure, these galaxies typically form when a gas-rich spiral galaxy collides with a small early-type galaxy dominated by older stars.
What sets Arp 143 apart is the highly distorted ring system of NGC 2445, bearing a trapezoidal appearance. Observations have shown that NGC 2445's surrounding structure comprises multiple areas of intense star formation filled with relatively youthful stars.
Arp 143 showcases another fascinating feature: a tidal tail extending northwards made up of molecular hydrogen, nearly 500,000 light-years long. This points to a collision between NGC 2445 and its partner, disrupting the galaxy's disk and resulting in the observed features.
It's also plausible that NGC 2445 collided and merged with another small early-type galaxy before its encounter with NGC 2444, which could explain the observed features in NGC 2445, including the ring structure and the northern tidal tail.
Lastly, a composite optical image of Arp 143 captured by the Hubble Space Telescope provides an awe-inspiring view. The image was created using broadband filters centered at 475 nm (g-band, blue), 606 (V-band, green), and 814 nm (I-band, orange), along with a narrow band filter that is focused on the emission of ionized hydrogen (Hα, red). NGC 2445 can be seen on the right, while NGC 2444 is on the left.
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