NGC 3081 is a barred lenticular ring galaxy in the constellation of Hydra. NGC 3081 is located about 85 million light-years away from Earth, which means, given its apparent dimensions, that NGC 3081 is approximately 60,000 light years across. It is a type II Seyfert galaxy, characterised by its bright nucleus. It was discovered by William Herschel on 21 December 1786.
NGC 3081 is seen nearly face-on. The galaxy's barred spiral centre is surrounded by a bright loop known as a resonance ring. This ring is full of bright clusters and bursts of new star formation, and frames the supermassive black hole thought to be lurking within NGC 3081 — which glows brightly as it gobbles up infalling material.
NGC 3081 by Hubble Space Telescope
|Observation data (J2000 epoch)|
|Right ascension||09h 59m 29.5s|
|Declination||−22° 49′ 35″|
|Redshift||0.007976 ± 0.000010 |
|Helio radial velocity||2,391 ± 3 km/s|
|Distance||83 Mly (25.3 Mpc)|
|Apparent magnitude (V)||13.5|
|Apparent size (V)||2′.1 × 1′.6|
|Notable features||Seyfert galaxy|
|IC 2529, ESO 499-G31, AM 0957-223, MCG -04-24-012, PGC 28876|
NGC 3081 is known to feature an active galaxy nucleus which is categorised as type II Seyfert galaxy. Even though NGC 3081 shows significant absorption, it is Compton thin. Also it does not show spectral variability on monthly timescales in X-rays. In the nucleus of the galaxy is thought to exist a supermassive black hole whose mass upper limit is estimated to be between 8.5 and 37 millions M☉, based on the intrinsic velocity dispersion as measured by the Hubble Space Telescope.
Observations obtained with the GMOS integral field spectrograph on the Gemini North telescope show a gas flow is present in the inner ≈ 2arcsec (200pc) of the galaxy, whose appearance is consistent with a bipolar outflow oriented along the north–south direction. Its outflow rate in ionized gas is estimated to be between 1.9 ×10−3M☉/year and 6.9 ×10−3 M☉/year. There was also observed residual gas motion which is interpreted as gas following non-circular orbits in the barred potential, which may lead to gas inflow up to 1.3 ×10−2 M☉/year.
NGC 3081 features four well defined rings; a misaligned nuclear ring with angular radius 14", an aligned inner ring with angular radius 35", an outer ring with radius 90", and an outer pseudoring with radius 105". Each ring is a well-defined zone of active star formation, while little or no star formation is observed between the rings. The rings lie at periodic orbits, known as resonances, certain positions where gravitational effects throughout the galaxy cause gas to pile up and accumulate in. These can be caused by the presence of a bar within the galaxy, as with NGC 3081, or by interactions with other nearby objects. It is not unusual for rings like this to be seen in barred galaxies, as the bars are very effective at gathering gas into these resonance regions, causing pile-ups which lead to active and very well-organised star formation. As external interactions could prevent the material from becoming sufficiently well organized in rings to trace the orbits so clearly, it is believed that NGC 3081 evolved in a relatively undisturbed manner.
Within the nuclear ring has been obseverd a spiral structure with two arms. Some parts of the nuclear ring and discrete knots in the arms feature higher numbers of younger stars than the rest of the nuclear ring interior, which suggests that they are sites of recent or ongoing star formation. They also feature emission indicative of HII regions. The inner ring, which is intrinsically elongated, features a gas cloud formed by the perturbation of a rotating bar at the location where the ring crosses the bar major axis, resulting to star formation.
The outer ring features a dimpling near the bar axis, being aligned nearly perpendicular to it. The pseudoring is formed by two faint spiral arms beyond the outer ring that nearly close into another ring. The presence of both an outer ring and a pseudoring is rarely seen in barred galaxies.
The galaxy features a complex double-barred structure as seen in optical and infrared wavelengths. The primary bar is weak and it is located within the inner ring. The secondary bar lies within the nuclear ring and is misaligned with the primary bar by 71 degrees. The secondary bar is also surrounded by a lens extending to the radius of the nuclear ring. In the residual image created by Laurikainen et al. the secondary bar shows an ansae-type morphology.
NGC 2273 is a barred spiral galaxy located in the constellation Lynx. It is located at a distance of circa 95 million light years from Earth, which, given its apparent dimensions, means that NGC 2273 is about 100,000 light years across. It was discovered by Nils Dunér οn September 15, 1867.NGC 3821
NGC 3821 is a low surface brightness spiral galaxy and a ring galaxy about 270 million light-years away in the constellation Leo. The galaxy was discovered by astronomer William Herschel on April 26, 1785 and is a member of the Leo Cluster.Seyfert galaxy
Seyfert galaxies are one of the two largest groups of active galaxies, along with quasars. They have quasar-like nuclei (very luminous, distant and bright sources of electromagnetic radiation) with very high surface brightnesses whose spectra reveal strong, high-ionisation emission lines, but unlike quasars, their host galaxies are clearly detectable.Seyfert galaxies account for about 10% of all galaxies and are some of the most intensely studied objects in astronomy, as they are thought to be powered by the same phenomena that occur in quasars, although they are closer and less luminous than quasars. These galaxies have supermassive black holes at their centers which are surrounded by accretion discs of in-falling material. The accretion discs are believed to be the source of the observed ultraviolet radiation. Ultraviolet emission and absorption lines provide the best diagnostics for the composition of the surrounding material.Seen in visible light, most Seyfert galaxies look like normal spiral galaxies, but when studied under other wavelengths, it becomes clear that the luminosity of their cores is of comparable intensity to the luminosity of whole galaxies the size of the Milky Way.Seyfert galaxies are named after Carl Seyfert, who first described this class in 1943.
New General Catalogue 3000 to 3499