Messier 99

Messier 99 or M99, also known as NGC 4254 or St. Catherine's Wheel, is a grand design spiral galaxy in the northern constellation Coma Berenices approximately 15,000,000 parsecs (49,000,000 light-years) from the Milky Way.^[5] It was discovered by Pierre Méchain on 17 March 1781. The discovery was then reported to Charles Messier, who included the object in the Messier Catalogue of comet-like objects. It was one of the first galaxies in which a spiral pattern was seen. This pattern was first identified by Lord Rosse in the spring of 1846.^[10][11]

Messier 99
Galaxy Messier 99, Schulman Telescope[1]
Observation data (J2000 epoch)
Constellation	Coma Berenices[2]
Right ascension	12h 18m 49.625s[3]
Declination	+14° 24′ 59.36″[3]
Redshift	0.008029[4]
Heliocentric radial velocity	2,404 km/s[5]
Distance	45.2 Mly (13.87 Mpc)[5]
Group or cluster	Virgo Cluster[6]
Apparent magnitude (V)	9.9[7]
Characteristics
Type	SA(s)c[8]
Apparent size (V)	5.4′ × 4.7′[4]
Other designations
Coma Pinwheel Galaxy, Virgo Cluster Pinwheel, M99, NGC 4254, PGC 39578, UGC 7345[9]

This galaxy has a morphological classification of SA(s)c,^[8] indicating a pure spiral shape with loosely wound arms. It has a peculiar shape with one normal looking arm and an extended arm that is less tightly wound. The galaxy is inclined by 42° to the line-of-sight with a major axis position angle of 68°.^[6]

A bridge of neutral hydrogen gas links NGC 4254 with VIRGOHI21, an HI region and a possible dark galaxy. The gravity from the latter may have distorted M99 and drawn out the gas bridge, as the two galaxy-sized objects may have had a close encounter before parting greatly. However, VIRGOHI21 may instead be tidal debris from an interaction with the lenticular galaxy NGC 4262 some 280 million years ago.^[6] It is expected that the drawn out arm will relax to match the normal arm once the encounter is over.

While not classified as a starburst galaxy, M99 has a star formation activity three times larger than other galaxies of similar Hubble type that may have been triggered by the encounter.^[12] M99 is likely entering the Virgo Cluster for the first time bound to the periphery of the cluster at a projected separation of 3.7°, or around one megaparsec, from the cluster center at Messier 87. The galaxy is undergoing ram-pressure stripping of much of its interstellar medium as it moves through the intracluster medium.^[6]

Four supernovae have been observed in this galaxy: SN 1967H (type II, mag. 14.6),^[13] SN 1972Q (type unknown, mag. 15.8), SN 1986I (type II, mag. 14),^[14] and SN 2014L (type Ic, mag. 15.4).^[15]