NGC 7172 explained

NGC 7172
Epoch:J2000
Type:Sa pec [1]
Dist Ly:110 Mly (34 Mpc)
Z:0.008683 ± 0.000040
H Radial V:2,603 ± 12 km/s
Appmag V:11.9
Size V:2.5 × 1.4
Constellation Name:Piscis Austrinus
Notes:Seyfert galaxy
Names:ESO 466- G 038, AM 2159-320, MCG -05-52-007, PGC 67874

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. It was discovered by John Herschel on September 23, 1834.[2]

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.[3] The galaxy appears in deep photographs to be tidally distorted, and a diffuse tail is extending towards the north-west.[4]

Nucleus

The nucleus of NGC 7172 was originally considered to be normal,[5] but later observations revealed that it emitted X-rays[6] [7] and was a powerful infrared source, which exhibited variation.[4] These findings indicated that NGC 7172 has an active galactic nucleus which is obstructed in optical wavelengths.[4] 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.[8] 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 based on the MBH–σ⋆ relation[9] or based on the X-ray scaling method.[10]

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.[11] This was also observed by BeppoSAX.[12] 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.[13] 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.[14]

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.[15] X-rays and mid-infrared have similar absorption columns.[16] It is possible that an outflow towards the southwest is detected in radiowaves.[8]

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.[17]

The compact group is surrounded by a more loose group, with 19 galaxies of similar redshift within 1.5 degrees from the core group.[17] 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.[18] Other nearby galaxies include NGC 7135 and its group, NGC 7204, and NGC 7208.[19]

See also

External links

Notes and References

  1. Web site: NASA/IPAC Extragalactic Database . Results for NGC 7172 . 2023-05-06 .
  2. Web site: Seligman . Courtney . NGC 7172 (= HCG 90A) . Celestial Atlas . 19 November 2018.
  3. Turner . T. J. . George . I. M. . Nandra . K. . Mushotzky . R. F. . ASCA Observations of Type 2 Seyfert Galaxies. I. Data Analysis Results . The Astrophysical Journal Supplement Series . November 1997 . 113 . 1 . 23–67 . 10.1086/313053. astro-ph/9608170 . 1997ApJS..113...23T .
  4. Sharpies . R. M. . Longmore . A. J. . Hawarden . T. G. . Carter . D. . NGC 7172: an obscured active nucleus . Monthly Notices of the Royal Astronomical Society . 1 May 1984 . 208 . 1 . 15–24 . 10.1093/mnras/208.1.15. free .
  5. Rubin . V. C. . Two chains of interesting southern galaxies : NGC 7172-7173-7174-7176and NGC 7201-7203-7204. . The Astrophysical Journal . August 1974 . 191 . 645 . 10.1086/153005. 1974ApJ...191..645R .
  6. Marshall . F. E. . Boldt . E. A. . Holt . S. S. . Mushotzky . R. F. . Rothschild . R. E. . Serlemitsos . P. J. . Pravdo . S. H. . New hard X-ray sources observed with HEAO A-2 . The Astrophysical Journal Supplement Series . July 1979 . 40 . 657 . 10.1086/190600. 1979ApJS...40..657M .
  7. Turner . T. J. . Pounds . K. A. . The EXOSAT spectral survey of AGN . Monthly Notices of the Royal Astronomical Society . 1 October 1989 . 240 . 4 . 833–880 . 10.1093/mnras/240.4.833. free . 1989MNRAS.240..833T .
  8. Smajić . S. . Fischer . S. . Zuther . J. . Eckart . A. . Unveiling the nucleus of NGC 7172 . Astronomy & Astrophysics . August 2012 . 544 . A105 . 10.1051/0004-6361/201118256. free .
  9. Marinucci . Andrea . Bianchi . Stefano . Nicastro . Fabrizio . Matt . Giorgio . Goulding . Andy D. . The Link Between the Hidden Broad Line Region and the Accretion Rate in Seyfert 2 Galaxies . The Astrophysical Journal . 1 April 2012 . 748 . 2 . 130 . 10.1088/0004-637X/748/2/130. 1201.5397 . 2012ApJ...748..130M .
  10. Shuvo . Onic I. . Johnson . Megan C. . Secrest . Nathan J. . Gliozzi . Mario . Fischer . Travis C. . Cigan . Phillip J. . Fernandez . Luis C. . Dorland . Bryan N. . FRAMEx. III. Radio Emission in the Immediate Vicinity of Radio-quiet AGNs . The Astrophysical Journal . 1 September 2022 . 936 . 1 . 76 . 10.3847/1538-4357/ac874a. free . 2208.05848 . 2022ApJ...936...76S .
  11. Guainazzi . M. . Matt . G. . Antonelli . L. A. . Fiore . F. . Piro . L. . Ueno . S. . The X-ray spectrum and variability of the Seyfert 2 galaxy NGC 7172 . Monthly Notices of the Royal Astronomical Society . 11 August 1998 . 298 . 3 . 824–830 . 10.1046/j.1365-8711.1998.01702.x. free . astro-ph/9803151 . 1998MNRAS.298..824G .
  12. Dadina . M. . Bassani . L. . Cappi . M. . Palumbo . G. G. C. . Piro . L. . Guainazzi . M. . Malaguti . G. . Di Cocco . G. . Trifoglio . M. . On the origin of the FeK α line in the Seyfert 2 galaxy NGC 7172 . Astronomy & Astrophysics . April 2001 . 370 . 1 . 70–77 . 10.1051/0004-6361:20010132. free . astro-ph/0101324 . 2001A&A...370...70D .
  13. Akylas . A. . Georgantopoulos . I. . Comastri . A. . BeppoSAX observations of the Seyfert 2 galaxies NGC 7172 and ESO 103-G35 . Monthly Notices of the Royal Astronomical Society . June 2001 . 324 . 2 . 521–528 . 10.1046/j.1365-8711.2001.04375.x. free . astro-ph/0101079 . 2001MNRAS.324..521A .
  14. Awaki . Hisamitsu . Murakami . Hirokatsu . Ogawa . Yuu . Leighly . Karen M. . Variability Study of Seyfert 2 Galaxies with XMM-Newton . The Astrophysical Journal . 10 July 2006 . 645 . 2 . 928–939 . 10.1086/504405. free . 2006ApJ...645..928A .
  15. Imanishi . M. . 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 . 4 April 2002 . 319 . 1 . 331–336 . 10.1046/j.1365-8711.2000.03873.x. free .
  16. Roche . P. F. . Packham . C. . Aitken . D. K. . Mason . R. E. . Silicate absorption in heavily obscured galaxy nuclei . Monthly Notices of the Royal Astronomical Society . 11 February 2007 . 375 . 1 . 99–104 . 10.1111/j.1365-2966.2006.11207.x. free . astro-ph/0610583 . 2007MNRAS.375...99R .
  17. White . P. M. . Bothun . G. . Guerrero . Martin A. . West . Michael J. . Barkhouse . Wayne A. . Extraordinary Diffuse Light in Hickson Compact Group 90 . The Astrophysical Journal . 10 March 2003 . 585 . 2 . 739–749 . 10.1086/346075. free . 2003ApJ...585..739W .
  18. Garcia . A. M. . General study of group membership. II. Determination of nearby groups. . Astronomy and Astrophysics Supplement Series . 1 July 1993 . 100 . 47–90 . 1993A&AS..100...47G . 0365-0138.
  19. Makarov. Dmitry. Karachentsev. Igor. Galaxy groups and clouds in the local (z~ 0.01) Universe. Monthly Notices of the Royal Astronomical Society. 21 April 2011. 412. 4. 2498–2520. 10.1111/j.1365-2966.2010.18071.x. free . 2011MNRAS.412.2498M. 1011.6277. 119194025.

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