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 Template:Convert from the Milky Way.<ref name=Tully2016/> 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.<ref name="jonesbook1991" /><ref>Template:Cite journal</ref>

This galaxy has a morphological classification of SA(s)c,<ref name=vaucoulerus1991/> 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°.<ref name="Vollmer2005" />

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.<ref name="Vollmer2005"/> 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.<ref name="Chyży2007" /> 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.<ref name="Vollmer2005"/>

Supernovae

Four supernovae have been observed in M99:

• SN 1967H (type II, mag. 14.0) was discovered by Fritz Zwicky on 1 July 1967.<ref>{{#invoke:citation/CS1|citation

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• SN 1972Q (type unknown, mag. 15.8) was discovered by Leonida Rosino on 14 December 1972.<ref>{{#invoke:citation/CS1|citation

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• SN 1986I (type II, mag. 14) was discovered by Carlton Pennypacker et al. on 17 May 1986.<ref>Template:Cite journal</ref><ref>{{#invoke:citation/CS1|citation

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• SN 2014L (type Ic, mag. 17.2) was discovered by the THU-NAOC Transient Survey (TNTS) on 26 January 2014.<ref>Template:Cite journal</ref><ref>{{#invoke:citation/CS1|citation

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See also

• List of Messier objects
• Messier 83 – a similar face-on spiral galaxy
• Pinwheel Galaxy – a similar face-on spiral galaxy

External links

• SEDS: Spiral Galaxy M99
• UniverseToday: Dark Matter Galaxy?
• PPARC: New evidence for a Dark Matter Galaxy
• Template:Cite journal
• Template:WikiSky