| NGC 3998 | |
|---|---|
 SDSS image of NGC 3998 | |
| Observation data (J2000epoch) | |
| Constellation | Ursa Major |
| Right ascension | 11h 57m 56.1333s[1] |
| Declination | +55° 27′ 12.922″[1] |
| Redshift | 0.00350[1] |
| Heliocentric radial velocity | 1048 ± 5 km/s[1] |
| Distance | 45 Mly (13.7 Mpc)[2] |
| Apparent magnitude (V) | 12.10[3] |
| Apparent magnitude (B) | 11.64[4] |
| Absolute magnitude (V) | 2.7′ × 2.3′[5] |
| Characteristics | |
| Type | SA00(r):[1] |
| Other designations | |
| UGC 6946,MCG +09-20-046,PGC 37642[1] | |
NGC 3998 is alenticular galaxy located in theconstellationUrsa Major. It was discovered on April 14, 1789, by the astronomerWilliam Herschel.[5] At a distance of 45 million light-years (13.7 megaparsecs),[2] it is located relatively nearby, making it a well-studied object.[6]
InGérard de Vaucouleurs' atlas ofgalaxy morphological types, NGC 3998 has a classification of SA00(r):, meaning it is unbarred and has an internal ring.[5] It is classified as aLINER-type galaxy.[6] As an early-type galaxy, NGC 3998's stars are relatively old and reddish in color, but its nuclear region may still have signs of star formation with stars less than 10 million years old.[6] The galaxy's shape is very round, and also oblate.[2]
NGC 3998 contains anactive galactic nucleus, or AGN. These aresupermassive black holes that are surrounded by accretion disks that emit large amounts of energy across the electromagnetic spectrum. The supermassive black hole has been modeled to be about8.1+2.0
−1.9×108 M☉[2] The AGN's power is relatively low, and like most other low-power radio galaxies, most of its emission is concentrated near its core. However, it also has some S-shaped lobes of emission, which are quite young and active, at only a few tens of millions of years old.[7]
NGC 3998 has a small disk of ionizedHα radiation that is about roughly 100 parsecs wide, along with a larger, warped disk of neutralhydrogen. It is thought that the gas disk has just started to align with the stellar distribution, which would also explain the warped shape of the radio emission.[6][7]
Media related toNGC 3998 at Wikimedia Commons
