NGC 7172
NGC 7172 by the Hubble Space Telescope[1]
Observation data (J2000 epoch)
ConstellationPiscis Austrinus
Right ascension22h 02m 01.9s[2]
Declination−31° 52′ 11″[2]
Redshift0.008683 ± 0.000040 [2]
Heliocentric radial velocity2,603 ± 12 km/s[2]
Distance110 Mly (34 Mpc)[2]
Apparent magnitude (V)11.9
Characteristics
TypeSa pec [2]
Apparent size (V)2.5′ × 1.4′[2]
Notable featuresSeyfert galaxy
Other designations
ESO 466- G 038, AM 2159-320, MCG -05-52-007, PGC 67874[2]

NGC 7172 is a spiral galaxy located in the constellation Piscis Austrinus. It is located at a distance of about 110 million light years from Earth, which, given its apparent dimensions, means that NGC 7172 is about 100,000 light years across.[2] It was discovered by John Herschel on September 23, 1834.[3]

Characteristics

NGC 7172 is a spiral galaxy that is seen edge-on. A thick dark dust lane runs across the galaxy, obscuring the nucleus of the galaxy.[1][4] The galaxy appears in deep photographs to be tidally distorted, and a diffuse tail is extending towards the north-west.[5]

Nucleus

The nucleus of NGC 7172 was originally considered to be normal,[6] but later observations revealed that it emitted X-rays[7][8] and was a powerful infrared source, which exhibited variation.[5] These findings indicated that NGC 7172 has an active galactic nucleus which is obstructed in optical wavelengths.[5] The nucleus was classified as a type 2 Seyfert galaxy in the optical, but observations in other wavelengths suggest it is type 1 Seyfert galaxy.[9] The source of activity of the nucleus is an accretion disk around a supermassive black hole. The mass of the supermassive black hole in the centre of NGC 7172 is estimated to be 5.5×107 M☉ based on the MBH–σ⋆ relation[10] or (1.03±0.35)×107 M☉ based on the X-ray scaling method.[11]

NGC 7172 has been found to exhibit variability in X-rays. As observed by the Advanced Satellite for Cosmology and Astrophysics (ASCA), the galaxy exhibited short term variability of about 30% in the time scale of hours, which is common for Seyfert I galaxies. It also exhibits long term variability, as it dimmed three to four times between 1995 and 1996.[12] This was also observed by BeppoSAX.[13] The FeKα line appeared constant when observed with BeppoSAX, but appeared to variate by a factor of two by ASCA, and thus it is associated with an accretion disk.[14] The hard X-ray spectrum appears similar to that of a Seyfert I galaxy, indicating that the nucleus is seen though a Compton-thin absorber.[15]

In infrared observations of the nucleus dominates the spectrum of the active nucleus, with 3.4-μm carbonaceous dust absorption detected, but no 3.3-μm PAH emission, indicating that the nucleus is obstructed. A strong obsurption feature is observed, probably the 9.7-μm silicate dust absorption line.[16] X-rays and mid-infrared have similar absorption columns.[17] It is possible that an outflow towards the southwest is detected in radiowaves.[9]

Nearby galaxies

NGC 7172 is part of the Hickson Compact Group 90. NGC 7172 lies 6 arcminutes north of the core of the compact group, which is comprised by the elliptical galaxies NGC 7173, and NGC 7174, and disturbed spiral galaxy NGC 7176; these three galaxies lie within 6 arcminutes from each other.[18]

The compact group is surrounded by a more loose group, with 19 galaxies of similar redshift within 1.5 degrees from the core group.[18] Garcia identified as members of this group the galaxies NGC 7154, ESO 404- 12, NGC 7163, ESO 466- 36, ESO 466- 46, ESO 404- 27, NGC 7187, IC 5156, ESO 404- 39, and ESO 466- 51.[19] Other nearby galaxies include NGC 7135 and its group, NGC 7204, and NGC 7208.[20]

See also

References

  1. 1 2 "More Than Meets the Eye". www.spacetelescope.org. 28 March 2022. Retrieved 6 May 2023.
  2. 1 2 3 4 5 6 7 8 9 "NASA/IPAC Extragalactic Database". Results for NGC 7172. Retrieved 2023-05-06.
  3. ↑ Seligman, Courtney. "NGC 7172 (= HCG 90A)". Celestial Atlas. Retrieved 19 November 2018.
  4. ↑ Turner, T. J.; George, I. M.; Nandra, K.; Mushotzky, R. F. (November 1997). "ASCA Observations of Type 2 Seyfert Galaxies. I. Data Analysis Results". The Astrophysical Journal Supplement Series. 113 (1): 23–67. arXiv:astro-ph/9608170. doi:10.1086/313053.
  5. 1 2 3 Sharpies, R. M.; Longmore, A. J.; Hawarden, T. G.; Carter, D. (1 May 1984). "NGC 7172: an obscured active nucleus". Monthly Notices of the Royal Astronomical Society. 208 (1): 15–24. doi:10.1093/mnras/208.1.15.
  6. ↑ Rubin, V. C. (August 1974). "Two chains of interesting southern galaxies : NGC 7172-7173-7174-7176and NGC 7201-7203-7204". The Astrophysical Journal. 191: 645. doi:10.1086/153005.
  7. ↑ Marshall, F. E.; Boldt, E. A.; Holt, S. S.; Mushotzky, R. F.; Rothschild, R. E.; Serlemitsos, P. J.; Pravdo, S. H. (July 1979). "New hard X-ray sources observed with HEAO A-2". The Astrophysical Journal Supplement Series. 40: 657. doi:10.1086/190600.
  8. ↑ Turner, T. J.; Pounds, K. A. (1 October 1989). "The EXOSAT spectral survey of AGN". Monthly Notices of the Royal Astronomical Society. 240 (4): 833–880. doi:10.1093/mnras/240.4.833.
  9. 1 2 Smajić, S.; Fischer, S.; Zuther, J.; Eckart, A. (August 2012). "Unveiling the nucleus of NGC 7172". Astronomy & Astrophysics. 544: A105. doi:10.1051/0004-6361/201118256.
  10. ↑ Marinucci, Andrea; Bianchi, Stefano; Nicastro, Fabrizio; Matt, Giorgio; Goulding, Andy D. (1 April 2012). "THE LINK BETWEEN THE HIDDEN BROAD LINE REGION AND THE ACCRETION RATE IN SEYFERT 2 GALAXIES". The Astrophysical Journal. 748 (2): 130. arXiv:1201.5397. doi:10.1088/0004-637X/748/2/130.
  11. ↑ Shuvo, Onic I.; Johnson, Megan C.; Secrest, Nathan J.; Gliozzi, Mario; Fischer, Travis C.; Cigan, Phillip J.; Fernandez, Luis C.; Dorland, Bryan N. (1 September 2022). "FRAMEx. III. Radio Emission in the Immediate Vicinity of Radio-quiet AGNs". The Astrophysical Journal. 936 (1): 76. arXiv:2208.05848. doi:10.3847/1538-4357/ac874a.
  12. ↑ Guainazzi, M.; Matt, G.; Antonelli, L. A.; Fiore, F.; Piro, L.; Ueno, S. (11 August 1998). "The X-ray spectrum and variability of the Seyfert 2 galaxy NGC 7172". Monthly Notices of the Royal Astronomical Society. 298 (3): 824–830. arXiv:astro-ph/9803151. doi:10.1046/j.1365-8711.1998.01702.x.
  13. ↑ Dadina, M.; Bassani, L.; Cappi, M.; Palumbo, G. G. C.; Piro, L.; Guainazzi, M.; Malaguti, G.; Di Cocco, G.; Trifoglio, M. (April 2001). "On the origin of the FeK α line in the Seyfert 2 galaxy NGC 7172". Astronomy & Astrophysics. 370 (1): 70–77. doi:10.1051/0004-6361:20010132.
  14. ↑ Akylas, A.; Georgantopoulos, I.; Comastri, A. (June 2001). "BeppoSAX observations of the Seyfert 2 galaxies NGC 7172 and ESO 103-G35". Monthly Notices of the Royal Astronomical Society. 324 (2): 521–528. doi:10.1046/j.1365-8711.2001.04375.x.
  15. ↑ Awaki, Hisamitsu; Murakami, Hirokatsu; Ogawa, Yuu; Leighly, Karen M. (10 July 2006). "Variability Study of Seyfert 2 Galaxies with XMM-Newton". The Astrophysical Journal. 645 (2): 928–939. doi:10.1086/504405.
  16. ↑ Imanishi, M. (4 April 2002). "The 3.4-μm absorption feature towards three obscured active galactic nuclei: The 3-4-μm absorption feature". Monthly Notices of the Royal Astronomical Society. 319 (1): 331–336. doi:10.1046/j.1365-8711.2000.03873.x.
  17. ↑ Roche, P. F.; Packham, C.; Aitken, D. K.; Mason, R. E. (11 February 2007). "Silicate absorption in heavily obscured galaxy nuclei". Monthly Notices of the Royal Astronomical Society. 375 (1): 99–104. arXiv:astro-ph/0610583. doi:10.1111/j.1365-2966.2006.11207.x.
  18. 1 2 White, P. M.; Bothun, G.; Guerrero, Martin A.; West, Michael J.; Barkhouse, Wayne A. (10 March 2003). "Extraordinary Diffuse Light in Hickson Compact Group 90". The Astrophysical Journal. 585 (2): 739–749. doi:10.1086/346075.
  19. ↑ Garcia, A. M. (1 July 1993). "General study of group membership. II. Determination of nearby groups". Astronomy and Astrophysics Supplement Series. 100: 47–90. Bibcode:1993A&AS..100...47G. ISSN 0365-0138.
  20. ↑ 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. S2CID 119194025. Archived from the original on 31 January 2016. Retrieved 23 December 2018.
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