NGC 3998
Coordinates: 
11h 57m 56.1333s, +55° 27′ 12.922″
11h 57m 56.1333s, +55° 27′ 12.922″| NGC 3998 | |
|---|---|
J2000 epoch) | |
| 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 a
Ursa Major. It was discovered on April 14, 1789, by the astronomer William 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]
In
LINER-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]
Structure
NGC 3998 contains an active galactic nucleus, or AGN. These are supermassive 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 about 8.1+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 ionized
Hα radiation that is about 100 parsecs wide, along with a larger, warped disk of neutral hydrogen. 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]
References
- ^ a b c d e f "Results for object NGC 3998 (NGC 3998)". NASA/IPAC Extragalactic Database. California Institute of Technology. Retrieved 2021-04-25.
- ^ S2CID 16506695.
- .
- ^ "NGC 3998". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2021-04-25.
- ^ a b c Seligman, Courtney. "New General Catalogue objects: NGC 3950 - 3999". cseligman.com. Retrieved 2021-04-25.
- ^ S2CID 73593876.
- ^ S2CID 209140612.
External links
Media related to NGC 3998 at Wikimedia Commons
