| NGC 7213 | |
|---|---|
 NGC 7213 by theHubble Space Telescope | |
| Observation data (J2000epoch) | |
| Constellation | Grus |
| Right ascension | 22h 09m 16.3s[1] |
| Declination | −47° 09′ 59″[1] |
| Redshift | 0.005839 +/- 0.000019[1] |
| Heliocentric radial velocity | 1,750 ± 6 km/s[1] |
| Distance | 72Mly (22Mpc)[1] |
| Apparent magnitude (V) | 10.1 |
| Characteristics | |
| Type | SA(s)0^0[1] |
| Apparent size (V) | 3.1′ × 2.8′[1] |
| Notable features | Seyfert galaxy, LINER |
| Other designations | |
| ESO 288- G043, AM 2206-472,PGC 68165[1] | |
NGC 7213 is alenticular galaxy located in the constellationGrus. It is located at a distance of circa 70 millionlight-years from Earth, which, given its apparent dimensions, means that NGC 7213 is about 75,000 light-years across.[1] It was discovered byJohn Herschel on September 30, 1834.[2] It is an active galaxy with characteristics between a type ISeyfert galaxy andLINER.
The nucleus of NGC 7213 features activity and belongs to the low-luminosityactive galactic nuclei (LLAGN). The opticalspectrum features broadH-alpha lines and has similar characteristics to a type ISeyfert galaxy, however it is considerably less luminous than other similar galaxies.[3] It also features [Ne V] λ3426, He II λ4686, [O II] λ3726, 3729, 7319, 7330, [O III] λ4363, 4959, and 5007 emission lines. However the intensity ratios of many of these lines is similar to aLINER.[4] Observed inradio waves, NGC 7213 looks like a point-like source that could feature two jets that bend between one 1 arcsec (150 pc) and 10 arcsec (1.5 kpc). It is categorised as a radio-intermediate galaxy, lying between radio-quiet and radio-loud sources.[5] The source of activity in the AGNs is asupermassive black hole (SMBH) lying at the centre of the galaxy. The mass of the SMBH at the centre of NGC 7213 is estimated to be between8×107 M☉[6] and9.6+6.1
−4.1×107 M☉ based on the meanvelocity dispersion[5] or (3-47) × 106 (106.83+0.84
−0.33)M☉ based on the polarization of broad Hα emission.[7]
NGC 7213 has been found to be a low-luminosityX-ray source. The 2-10 keV spectrum of NGC 7213 resembles the spectrum of Seyfert I galaxies, but also contains significant emission lines from FeXXV and FeXXVI, which are observed in LINERs and are not present in most classical Seyfert galaxies. Also, the soft X-ray spectrum of NGC 7213 features collisionally ionized thermal plasma, one more characteristic of LINERs. In addition, there is no X-ray emission detected that can be attributed to anaccretion disk.[8] Observations byNuSTAR at 3-79 keV showed no evidence for a Compton-reflected continuum. The observations suggest that the accretion disc is truncated in the inner region, with the black hole being fed via radiative-inefficient accretion flows.[9]
The X-ray flux of NGC 7213 is fluctuating, presenting a sharp flare, larger than the others, in the 1980s with the flux reducing steadily after for more than 20 years. This flare showed a fast-rise-exponential-decay pattern and has been suggested to be caused by the tidal disruption of amain sequence star by the black hole at the centre of NGC 7213.[10] Smaller scale flares are also observed. The emission variability is also observed in other wavelengths with a time lag. The lag is 24 ± 12 days for 8.4 GHz radio and 40 ± 13 days for the 4.8 GHz radio.[11]
Surrounding the nucleus is a ring ofstarforming regions, lying at a radius of circa 20 arcseconds. Closer to the nucleus can be observed a dustyspiral pattern, with two arms, with the northwest arm being on the near side of the galaxy, and the southeast one to the far side. The ionised gas inflow rate towards the nucleus is estimated to be 0.2 M☉ per year.[6] Although NGC 7213 appears undisturbed in visible light, it shows signs of having undergone acollision or merger when viewed at longer wavelengths, with disturbed patterns of ionized hydrogen including a filament of gas around 64,000 light-years long, itself being part of a larger HI tidal tail southwest of the nucleus.[12]
NGC 7213 is the foremost galaxy in agalaxy group known as the NGC 7213 group. Other members of the group include IC 5170, IC 5181,NGC 7232, andNGC 7233. A bit further away lies the NGC 7144 group, which includesNGC 7144,NGC 7145,NGC 7151, andNGC 7155.[13] These galaxies group are part of the Pavo-Indus cloud and the Grus cloud, which lie between theLocal Supercluster andPavo–Indus Supercluster.[14]
Other Seyfert galaxies include:
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