NGC 4157

NGC 4157 is a spiral galaxy in the constellation Ursa Major. The galaxy lies about 55 million light years away from Earth, which means, given its apparent dimensions, that NGC 4157 is approximately 125,000 light years across. It was discovered by William Herschel on March 9, 1788.

Characteristics
NGC 4157 seen nearly edge-on, with an inclination of 84° based on CO imaging. The total stellar mass of NGC 4157 is $2.92 M_solar$, while the dust mass is estimated to be $2.1 M_solar$. The hydrogen disk of NGC 4157 is symmetric and slightly wrapped, indicating no strong interaction with other galaxies, and extends to twice the size of the optical disk. The total H I mass in the galaxy is estimated to be $M_solar$.

The star formation rate of the galaxy is $1.76 M_solar$ per year. A star formation area is visible beyond the end of the optical disk and is also visible in X-ray and ultraviolet imaging. It could probably be the result of a recent accretion.

The galaxy has radio emission extending above and below the optical disk, indicating the presence of a radio halo. There is also radio emission extending southwards from the north-eastern end of the disk.

Supernovae
Three supernovae have been observed in NGC 4157: SN 1937A (mag. 16.2), SN 1955A (mag. 16), and SN 2003J. SN 2003J was a type II supernova which had an apparent magnitude of 16.7 upon discovery.

Nearby galaxies
NGC 4157 is the foremost galaxy of the NGC 4157 Group. Other members of the group include NGC 4085, NGC 4088, UGC 6992, and UGC 7176. UGC 7176 is a companion of NGC 4157, lying 12 arcminutes away. The group is part of the Ursa Major Cluster, a large association of mostly spiral galaxies lying north of the Virgo Cluster, that is part of the Local Supercluster. NGC 4157 is one of the dominant galaxies in the cluster, along with NGC 3769, NGC 3877, NGC 3992, NGC 4111, NGC 4217 and NGC 4346.