NGC 3445

Lore & Background

NGC 3445 was discovered by William Herschel on April 8, 1793. The galaxy is included in Halton Arp's Atlas of Peculiar Galaxies in the one-armed spiral galaxies category. It has a thick arm pattern with many HII regions. A large spiral arm is visible at the south part of the galaxy while a weaker one is visible in infrared at the north. Radio emission is observed along the arms. At the end of the main spiral arm there is a smaller galaxy, lying 1.2 arcminutes from the nucleus of NGC 3445, connected with a weak bridge.

In the infrared are visible four bright locations of active star formation. The brightest of these infrared knots hosts five young massive star clusters, all being formed by a single giant molecular cloud. The age of the clusters was determined to be 3 to 5 million years and their mass to be around 105 M☉. Another large star cluster lies at the nucleus of the galaxy and could be in the process of forming a bulge. The total star formation rate of the galaxy is estimated to be around 1 M☉ per year. The star formation as well as the shape of the galaxy could be the result of interaction with other galaxies.

NGC 3445 forms a triplet with NGC 3440, which lies 9.9 arcminutes away, and NGC 3458, which lies 14 arcminutes away. These galaxies comprise the LGG 226 group. It belongs to the same galaxy cloud as NGC 3610.

Reader's Guide

NGC 3445 is significant as a Magellanic spiral galaxy that exhibits a peculiar one-armed spiral structure, earning it a place in Halton Arp's Atlas of Peculiar Galaxies. Its thick arm pattern, rich in HII regions, and the presence of a weaker infrared arm highlight its asymmetric morphology. The galaxy's interaction with a smaller companion, connected by a weak bridge at the end of the main spiral arm, is a key feature that likely drives its star formation and shape. The infrared observations reveal four bright knots of active star formation, with the brightest hosting five young massive star clusters formed from a single giant molecular cloud, aged 3 to 5 million years and with a mass around 105 M☉. A large star cluster at the nucleus may be forming a bulge. The total star formation rate of about 1 M☉ per year underscores its ongoing activity. As part of the LGG 226 group with NGC 3440 and NGC 3458, and belonging to the same galaxy cloud as NGC 3610, NGC 3445 provides insight into galaxy interactions and star formation processes in a group environment.

Did You Know?

• NGC 3445 is a Magellanic spiral galaxy about 75 million light years away.
• The galaxy has a large spiral arm at the south and a weaker infrared arm at the north.