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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]
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Four supernovae have been observed in M99:
- SN 1967H (type II, mag. 14.0) was discovered by Fritz Zwicky on 1 July 1967.[13][14][15][16]
- SN 1972Q (type unknown, mag. 15.8) was discovered by Leonida Rosino on 14 December 1972.[17]
- SN 1986I (type II, mag. 14) was discovered by Carlton Pennypacker et al. on 17 May 1986.[18][19][20]
- SN 2014L (type Ic, mag. 17.2) was discovered by the THU-NAOC Transient Survey (TNTS) on 26 January 2014.[21][22][23]
- List of Messier objects
- Messier 83 - a similar face-on spiral galaxy
- Pinwheel Galaxy - a similar face-on spiral galaxy
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