NGC 7213

NGC 7213 is a lenticular galaxy located in the constellation Grus. It is located at a distance of circa 70 million light years from Earth, which, given its apparent dimensions, means that NGC 7213 is about 75,000 light years across.[1] It was discovered by John Herschel on September 30, 1834.[2] It is an active galaxy with characteristics between a type I Seyfert galaxy and LINER.

NGC 7213
NGC 7213 by the Hubble Space Telescope
Observation data (J2000 epoch)
ConstellationGrus
Right ascension 22h 09m 16.3s[1]
Declination−47° 09′ 59″[1]
Redshift0.005839 +/- 0.000019 [1]
Helio radial velocity1,750 ± 6 km/s[1]
Distance72 Mly (22 Mpc)[1]
Apparent magnitude (V)10.1
Characteristics
TypeSA(s)0^0 [1]
Apparent size (V)3′.1 × 2′.8[1]
Notable featuresSeyfert galaxy, LINER
Other designations
ESO 288- G043, AM 2206-472, PGC 68165[1]

Characteristics

The nucleus of NGC 7213 features activity and belongs to the low luminosity Active Galactic Nuclei (LLAGN). The optical spectrum features broad H-alpha lines and has similar characteristics to a type I Seyfert 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 a LINER.[4] Observed in radio 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 a supermassive 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 between 8×107 M☉[6] and 9.6+6.1
−4.1×107 M☉ based on the mean velocity 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-luminosity X-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 an accretion disk.[8] Observations by NuSTAR 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 a main 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 of starfoming regions, lying at a radius of circa 20 arcseconds. Closer to the nucleus can be observed a dusty spiral 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 a collision 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]

Nearby galaxies

NGC 7213 is the foremost galaxy in a galaxy group known as the NGC 7213 group. Other members of the group include IC 5170, IC 5181, NGC 7232, and NGC 7233. A bit further away lies the NGC 7144 group, which includes NGC 7144, NGC 7145, NGC 7151, and NGC 7155.[13] These galaxies group are part of the Pavo-Indus cloud and the Grus cloud, which lie between the Local Supercluster and Pavo-Indus Supercluster.[14]

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References
  1. "NASA/IPAC Extragalactic Database". Results for NGC 7213. Retrieved 2016-01-18.
  2. Seligman, Courtney. "NGC 7213 (= PGC 68165)". Celestial Atlas. Retrieved 19 November 2018.
  3. Phillips, M. M. (February 1979). "Optical Spectrophotometry of the Suspected X-Ray Galaxies NGC 6221 and NGC 7213". The Astrophysical Journal. 227: L121. Bibcode:1979ApJ...227L.121P. doi:10.1086/182881.
  4. Filippenko, A. V.; Halpern, J. P. (October 1984). "NGC 7213 - A key to the nature of liners?". The Astrophysical Journal. 285: 458. Bibcode:1984ApJ...285..458F. doi:10.1086/162521.
  5. Blank, D. L.; Harnett, J. I.; Jones, P. A. (January 2005). "An 8.4-GHz Long Baseline Array observation of the unusual Seyfert galaxy NGC 7213". Monthly Notices of the Royal Astronomical Society. 356 (2): 734–736. Bibcode:2005MNRAS.356..734B. doi:10.1111/j.1365-2966.2004.08506.x.
  6. Schnorr-Müller, Allan; Storchi-Bergmann, Thaisa; Nagar, Neil M.; Ferrari, Fabricio (11 March 2014). "Gas inflows towards the nucleus of the active galaxy NGC 7213". Monthly Notices of the Royal Astronomical Society. 438 (4): 3322–3331. arXiv:1401.5650. Bibcode:2014MNRAS.438.3322S. doi:10.1093/mnras/stt2440.
  7. Piotrovich, M. Yu.; Gnedin, Yu. N.; Silant'ev, N. A.; Natsvlishvili, T. M.; Buliga, S. D. (30 September 2015). "A polarimetric method for measuring black hole masses in Active Galactic Nuclei". Monthly Notices of the Royal Astronomical Society. 454 (1): 1157–1160. arXiv:1509.01028. Bibcode:2015MNRAS.454.1157P. doi:10.1093/mnras/stv2047.
  8. Starling, R. L. C.; Page, M. J.; Branduardi-Raymont, G.; Breeveld, A. A.; Soria, R.; Wu, K. (January 2005). "The X-ray spectrum of NGC 7213 and the Seyfert-LINER connection". Monthly Notices of the Royal Astronomical Society. 356 (2): 727–733. arXiv:astro-ph/0410333. Bibcode:2005MNRAS.356..727S. doi:10.1111/j.1365-2966.2004.08493.x.
  9. Ursini, F.; Marinucci, A.; Matt, G.; Bianchi, S.; Tortosa, A.; Stern, D.; Arévalo, P.; Ballantyne, D. R.; Bauer, F. E.; Fabian, A. C.; Harrison, F. A.; Lohfink, A. M.; Reynolds, C. S.; Walton, D. J. (3 August 2015). "The NuSTAR X-ray spectrum of the low-luminosity active galactic nucleus in NGC 7213". Monthly Notices of the Royal Astronomical Society. 452 (3): 3266–3272. arXiv:1507.01775. Bibcode:2015MNRAS.452.3266U. doi:10.1093/mnras/stv1527.
  10. Yan, Zhen; Xie, Fu-Guo (March 2018). "A decades-long fast-rise-exponential-decay flare in low-luminosity AGN NGC 7213". Monthly Notices of the Royal Astronomical Society. 475 (1): 1190–1197. arXiv:1712.05272. Bibcode:2018MNRAS.475.1190Y. doi:10.1093/mnras/stx3259.
  11. Bell, M. E.; Tzioumis, T.; Uttley, P.; Fender, R. P.; Arévalo, P.; Breedt, E.; McHardy, I.; Calvelo, D. E.; Jamil, O.; Körding, E. (11 February 2011). "X-ray and radio variability in the low-luminosity active galactic nucleus NGC 7213". Monthly Notices of the Royal Astronomical Society. 411 (1): 402–410. arXiv:1009.2430. Bibcode:2011MNRAS.411..402B. doi:10.1111/j.1365-2966.2010.17692.x.
  12. Hameed, Salman; Blank, David L.; Young, Lisa M.; Devereux, Nick (10 January 2001). "The Discovery of a Giant Hα Filament in NGC 7213". The Astrophysical Journal. 546 (2): L97–L100. arXiv:astro-ph/0011208. Bibcode:2001ApJ...546L..97H. doi:10.1086/318865.
  13. Makarov, Dmitry; Karachentsev, Igor (21 April 2011). "Galaxy groups and clouds in the local (z∼ 0.01) Universe". Monthly Notices of the Royal Astronomical Society. 412 (4): 2498–2520. arXiv:1011.6277. Bibcode:2011MNRAS.412.2498M. doi:10.1111/j.1365-2966.2010.18071.x.
  14. Fouque, P.; Proust, D.; Quintana, H.; Ramirez, A.; Proust, D.; Quintana, H.; Ramirez, A. (1993). "Dynamics of the Pavo-Indus and Grus Clouds of Galaxies". Astronomy and Astrophysics Supplement Series. 100 (3): 493–500. Bibcode:1993A&AS..100..493F.CS1 maint: multiple names: authors list (link)


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