NGC 4939 by Hubble Space Telescope
|Observation data (J2000 epoch)|
|Right ascension||13h 04m 14.4s|
|Declination||−10° 20′ 22″|
|Redshift||0.010374 +/- 0.000013 |
|Helio radial velocity||3,110 ± 4 km/s|
|Distance||118 ± 30 Mly (36.1 ± 9.4 Mpc)|
|Apparent magnitude (V)||11.3|
|Apparent size (V)||5′.5 × 2′.8|
|Notable features||Seyfert galaxy|
|MCG -02-33-104, PGC 45170|
NGC 4939 is a spiral galaxy located in the constellation Virgo. It is located at a distance of circa 120 million light years from Earth, which, given its apparent dimensions, means that NGC 4939 is about 190,000 light years across. It was discovered by William Herschel οn March 25, 1786.
NGC 4939 has been characterised as a Seyfert galaxy, a galaxy category which features bright point-like nuclei. NGC 4939 is a type II Seyfert galaxy. Its X ray spectrum is more consistent with a Compton-thick cold reflection source, which means that the source is hidden behind dense material, mainly gas and dust, and the X-ray observed have been reflected, but a Compton-thin transmission model could not be ruled out. The equivalent width of the FeKα line is large, indicating too that it is a Compton-thick source. Further observations by Swift Observatory confirmed its Compton-thick nature. The source of activity in the active galactic nuclei is a supermassive black hole (SMBH) lying at the centre of the galaxy. The SMBH at the centre of NGC 4939 is accreting material with a rate of 0.077 M☉ per year. The black hole has been detected in hard X-rays, which are not absorbed by the Compton-thick column, by INTEGRAL.
The galaxy has a large elliptical bulge and maybe a weak bar. It is a grand design spiral galaxy, with two tightly wrapped arms emanating from the bulge. The arms are thin, smooth and well defined and can be traced for nearly one and a half revolutions before fading. Two symmetric arm sections or arcs are observed in the central part of the galaxy. The galaxy is seen with an inclination of 56 degrees. The rotational speed of the galaxy is about 270 km/s.
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