NGC 5548

NGC 5548 is a Type I Seyfert galaxy with a bright, active nucleus.[9] This activity is caused by matter flowing onto a 65 million solar mass (M☉) supermassive black hole at the core.[10] Morphologically, this is an unbarred lenticular galaxy with tightly-wound spiral arms, while shell and tidal tail features suggest that it has undergone a cosmologically-recent merger or interaction event.[7] NGC 5548 is approximately 245[5] million light years away and appears in the constellation Boötes. The apparent visual magnitude of NGC 5548 is approximately 13.3 in the V band.[6]

NGC 5548
NGC 5548 image by Hubble.[1]
Observation data (J2000 epoch)
ConstellationBoötes
Right ascension 14h 17m 59.513s[2]
Declination+25° 08′ 12.45″[2]
Redshift0.01651 ± 0.00189[3]
Helio radial velocity5,178[4] km/s
Distance244.6 Mly (75.01 Mpc)[5]
Apparent magnitude (V)13.283[6]
Characteristics
TypeSA0/a pec[7]
Apparent size (V)1.7′ × 1.5′[4]
Notable featuresSeyfert galaxy; radio jet[8]
Other designations
Mrk 1509, UGC 9149[8]

In 1943, this galaxy was one of twelve nebulae listed by American astronomer Carl Keenan Seyfert that showed broad emission lines in their nuclei.[11] Members of this class of objects became known as Seyfert galaxies, and they were noted to have a higher than normal surface brightness in their nuclei.[12] Observation of NGC 5548 during the 1960s with radio telescopes showed an enhanced level of radio emission.[13] Spectrograms of the nucleus made in 1966 showed that the energized region was confined to a volume a few parsecs across, where temperature were around 14000 K and the plasma had a dispersion velocity of ±450 km/s.[14]

Among astronomers, the accepted explanation for the active nucleus in NGC 5548 is the accretion of matter onto a supermassive black hole (SMBH) at the core. This object is surrounded by an orbiting disk of accreted matter drawn in from the surroundings. As material is drawn into the outer parts of this disk, it becomes photoionized, producing broad emission lines in the optical and ultraviolet bands of the electromagnetic spectrum. A wind of ionized matter, organized in filamentary structures at distances of 1–14 light days from the center, is flowing outward in the direction perpendicular to the accretion disk plane.[9]

The mass of the central black hole can be estimated based on the properties of the emission lines in the core region. Combined measurements yield an estimated mass of 6.54+0.26
−0.25×107 M☉. In other words, it is some 65 million times the mass of the Sun. This result is consistent with other methods of estimating the mass of the SMBH in the nucleus of NGC 5548.[10] Matter is falling onto this black hole at the estimated rate of 0.03 M☉ per year, whereas mass is flowing outward from the core at or above the rate of 0.92 M☉ each year.[15] The inner part of the accretion disk surrounding the SMBH forms a thick, hot corona spanning several light hours that is emitting X-rays. When this radiation reaches the optically thick part of the accretion disk at a radius of around 1–2 light days, the X-rays are converted into heat.[16]

References
  1. "Swiftly moving gas streamer eclipses supermassive black hole". ESA/Hubble Press Release. Retrieved 20 June 2014.
  2. Skrutskie, M. F.; et al. (February 2006), "The Two Micron All Sky Survey (2MASS)", The Astronomical Journal, 131 (2): 1163–1183, Bibcode:2006AJ....131.1163S, doi:10.1086/498708.
  3. Adelman-McCarthy, J. K.; et al. (June 2009), "The SDSS Photometric Catalog, Release 7", VizieR On-line Data Catalog: II/294, Bibcode:2009yCat.2294....0A.
  4. Springob, Christopher M.; et al. (September 2005), "A Digital Archive of H I 21 Centimeter Line Spectra of Optically Targeted Galaxies", The Astrophysical Journal Supplement Series, 160 (1): 149–162, arXiv:astro-ph/0505025, Bibcode:2005ApJS..160..149S, doi:10.1086/431550. See footnote 2.
  5. Crook, Aidan C.; et al. (February 2007), "Groups of Galaxies in the Two Micron All Sky Redshift Survey", The Astrophysical Journal, 655 (2): 790–813, arXiv:astro-ph/0610732, Bibcode:2007ApJ...655..790C, doi:10.1086/510201.
  6. Wisniewski, W. Z.; Kleinmann, D. E. (November 1968), "16. Multicolor photometry of Seyfert galaxies and measurement at 1.55 microns of the jet in M 87", Astronomical Journal, 73: 866–867, Bibcode:1968AJ.....73..866W, doi:10.1086/110721.
  7. Slavcheva-Mihova, L.; Mihov, B. (February 2011), "Optical multiband surface photometry of a sample of Seyfert galaxies. I. Large-scale morphology and local environment analysis of matched Seyfert and inactive galaxy samples", Astronomy and Astrophysics, 526: A43, arXiv:1011.1772, Bibcode:2011A&A...526A..43S, doi:10.1051/0004-6361/200913243. See Table 1.
  8. "NED results for object NGC 5548", NASA/IPAC Extragalactic Database, retrieved 2013-05-27.
  9. Kollatschny, W.; Zetzl, M. (March 2013), "Accretion disk wind as explanation for the broad-line region structure in NGC 5548", Astronomy & Astrophysics, 551: L6, arXiv:1301.7704, Bibcode:2013A&A...551L...6K, doi:10.1051/0004-6361/201220923.
  10. Bentz, Misty C.; et al. (June 2007), "NGC 5548 in a Low-Luminosity State: Implications for the Broad-Line Region", Astronomy & Astrophysics, 662 (1): 205–212, arXiv:astro-ph/0702644, Bibcode:2007ApJ...662..205B, doi:10.1086/516724.
  11. Seyfert, Carl K. (January 1943), "Nuclear Emission in Spiral Nebulae", Astrophysical Journal, 97: 28, Bibcode:1943ApJ....97...28S, doi:10.1086/144488. See footnote 2.
  12. Burbidge, E. Margaret; Burbidge, G. R.; Prendergast, K. H. (May 1963), "The Rotation and Physical Conditions in the Seyfert Galaxy NGC 7469", Astrophysical Journal, 137: 1022, Bibcode:1963ApJ...137.1022B, doi:10.1086/147580.
  13. Tovmassian, H. M. (August 1966), "On the radio emission from some peculiar galaxies", Australian Journal of Physics, 19 (4): 565, Bibcode:1966AuJPh..19..565T, doi:10.1071/ph660565.
  14. Dibai, É. A.; Esipov, V. F.; Pronik, V. I. (February 1968), "The Nucleus of the Seyfert Galaxy NGC 5548", Soviet Astronomy, 11: 553, Bibcode:1968SvA....11..553D.
  15. Crenshaw, D. M.; et al. (June 2009), "Mass Outflow in the Seyfert 1 Galaxy NGC 5548", The Astrophysical Journal, 698 (1): 281–292, arXiv:0902.2310, Bibcode:2009ApJ...698..281C, doi:10.1088/0004-637X/698/1/281.
  16. Suganuma, Masahiro; et al. (March 2006), "Reverberation Measurements of the Inner Radius of the Dust Torus in Nearby Seyfert 1 Galaxies", The Astrophysical Journal, 639 (1): 46–63, arXiv:astro-ph/0511697, Bibcode:2006ApJ...639...46S, doi:10.1086/499326.

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