NGC 4861

NGC 4861, also known as Arp 266, is a galaxy in the constellation Canes Venatici. It was discovered by William Herschel on May 1, 1785.^[4]

NGC 4861
Hubble Space Telescope image of NGC 4861, taken using the Advanced Camera for Surveys
Observation data (J2000 epoch)
Constellation	Canes Venatici
Right ascension	12h 59m 02.340s[1]
Declination	+34° 51′ 33.98″[1]
Redshift	0.002785[2]
Heliocentric radial velocity	835[2]
Distance	34.77 ± 15.99 Mly (10.662 ± 4.903 Mpc)[2]
Group or cluster	Virgo Cluster
Apparent magnitude (V)	12.32
Apparent magnitude (B)	12.90
Characteristics
Type	SB(s)m[2] Im/BCD
Apparent size (V)	0.797′ × 0.692′[1]
Other designations
Arp 266, UGC 8098, MCG+06-29-003, PGC 44536[3]

Morphological classification of NGC 4861 has proved relatively difficult. Its mass, size, and rotational velocity are consistent with it being a spiral galaxy. However, due to its highly irregular shape, it may also be classified as a dwarf irregular galaxy.^[5] In fact, since dwarf galaxies are less massive and have lower gravitational potentials, gases and other material for star formation can move within them much faster, causing the galaxy to become a specific type of starburst galaxy, called a blue compact dwarf galaxy.^[5][3] It has also been described as a "comet-like" galaxy due to its resemblance to a comet.^[6]

Two ultraluminous X-ray sources (ULXs) have been found within NGC 4861. The first, NGC 4861 X1, is associated with a dense H II region. The second, NGC 4861 X2, seems to be within a small star cluster near the "comet head" of NGC 4861. Assuming it is a star cluster, it has a mass of 400±80 M_☉ and an age of 5 million years. Compared to other star clusters with which ULXs are associated, its mass is quite low.^[6]

See also

• Dwarf irregular galaxy