NGC 6951 (also catalogued asNGC 6952) is abarred spiral galaxy located in the constellationCepheus. It is located at a distance of about 75 millionlight-years from Earth, which, given its apparent dimensions, means that NGC 6951 is about 100,000 light-years across. It was discovered byJérôme Eugène Coggia in 1877 and independently byLewis Swift in 1878.[3]
Image of NGC 6951 taken by theGALEX ultraviolet telescope.
NGC 6951 has a largestellar bar with dust lanes running across it. These lanes come in contact with the circumnuclear ring at its north and south points.[4] Gas is channeled inwards, towards the ring, through the bar. Observations in CO revealed also the presence ofmolecular gas with inflow motion towards the galactic nucleus. Since there are no signs of interaction with another galaxy in theisolated NGC 6951 for the last one billion years, it is believed that the origin of the gas is internal.[5] Gas kinematics have also been observed for the rest of the galaxy, where the gravitationaltorques caused by the bar have a dominant role.[6]
The nucleus of NGC 6951 isactive. It has been classified both as atype 2 Seyfert galaxy and aLINER and it has been suggested that it is in transition form, between a Seyfert galaxy and a very-high-excitation LINER, with very strong [N II] and [S II] lines.[7] Asupermassive black hole which accretes material in the centre of the galaxy is believed to be the cause of the nuclear activity. The upper mass limit of the supermassive black hole at the centre of NGC 6951 is estimated to be between 6 and 14 millionM☉ based onvelocity dispersion.[8] Molecular gas, most probably a circumnuclear dust disk ortorus less than 50 parsec in radius, has been detected around the nucleus.[9]
Around the nucleus of NGC 6951 has been observed astar formation ring with a radius of 5 arcseconds.[7] It also emitsradio waves.[10] The total gas mass at and inside the ring is estimated to be3×108M☉.[11] Inside the ring is detected a spiral-like structure, with two spiral arms, that extends up to 0.5 arcseconds from the nucleus, while no inner bar was detected in the images obtained byHubble Space Telescope. The central part of the nuclear area contains redsupergiant stars.[7] The ring is complete and featuresH II regions. It is characterised by a gradient instellar population ages, with the younger stars being a few million years old while the older are more than a hundred million years old.[12]
The stars in the ring formstar clusters with masses between104 and106.8M☉. Although there have been observed clusters with ages as little as 4 million years or over one billion years, the star clusters predominantly have intermediate ages, with average ages of 200–300 million years, and are massive. Based on the ages of the clusters it is suggested that the most intense star formation in the ring took place 800 million years ago, then lowered, only to increase again 400 million years ago.[4]
^van der Laan, T. P. R.; Schinnerer, E.; Boone, F.; García-Burillo, S.; Combes, F.; Haan, S.; Leon, S.; Hunt, L.; Baker, A. J. (29 March 2011). "Molecular gas in NUclei of GAlaxies (NUGA)".Astronomy & Astrophysics.529: A45.arXiv:1102.5104.doi:10.1051/0004-6361/201014488.S2CID37172955.
^abcPérez, E.; Márquez, I.; Marrero, I.; Durret, F.; González Delgado, R. M.; Masegosa, J.; Maza, J.; Moles, M. (1 January 2000). "Circumnuclear structure and kinematics in the active galaxy NGC 6951".Astronomy and Astrophysics.353:893–909.arXiv:astro-ph/9909495.Bibcode:2000A&A...353..893P.ISSN0004-6361.
^Beifiori, A.; Sarzi, M.; Corsini, E. M.; Bontà, E. Dalla; Pizzella, A.; Coccato, L.; Bertola, F. (10 February 2009). "Upper Limits on the Masses of 105 Supermassive Black Holes from Hubble Space Telescope/Space Telescope Imaging Spectrograph Archival Data".The Astrophysical Journal.692 (1):856–868.arXiv:0809.5103.Bibcode:2009ApJ...692..856B.doi:10.1088/0004-637X/692/1/856.S2CID54903233.
^Krips, M.; Neri, R.; García-Burillo, S.; Combes, F.; Schinnerer, E.; Baker, A. J.; Eckart, A.; Boone, F.; Hunt, L.; Leon, S.;Tacconi, L. J. (11 January 2007). "Molecular gas in NUclei of GAlaxies (NUGA): VI. Detection of a molecular gas disk/torus via HCN in the Seyfert 2 galaxy NGC 6951?".Astronomy & Astrophysics.468 (3):L63 –L66.arXiv:astro-ph/0701403.Bibcode:2007A&A...468L..63K.doi:10.1051/0004-6361:20066785.S2CID62785358.
^Mazzuca, Lisa M.; Knapen, Johan H.; Veilleux, Sylvain; Regan, Michael W. (February 2008). "A Connection between Star Formation in Nuclear Rings and Their Host Galaxies".The Astrophysical Journal Supplement Series.174 (2):337–365.arXiv:0709.2915.Bibcode:2008ApJS..174..337M.doi:10.1086/522338.S2CID9188872.
^"SN 1999el".Transient Name Server.IAU. Retrieved28 December 2024.
^Valentini, G.; Di Carlo, E.; Guidubaldi, D.; Brocato, E.; Di Paola, A.; d'Alessio, F.; Speziali, R.; Li Causi, G.; Pedichini, F. (2000)."Supernova 2000E in NGC 6951".International Astronomical Union Circular (7351): 1.Bibcode:2000IAUC.7351....1V.
^"SN 2000E".Transient Name Server.IAU. Retrieved28 December 2024.
^Yusa, T.; Buczynski, D.; Noguchi, T.; Nakano, S.; Kiyota, S.; Masi, G.; Ayani, K.; Foley, R. J.; Zheng, W.; Filippenko, A. V.; Van Dyk, S. D. (2015). "Supernova 2015G in NGC 6951 = PSN J20372558+6607115".Central Bureau Electronic Telegrams.4087: 1.Bibcode:2015CBET.4087....1Y.
^"SN 2015G".Transient Name Server.IAU. Retrieved28 December 2024.
^"SN 2020dpw".Transient Name Server.IAU. Retrieved28 December 2024.
^"SN 2021sjt".Transient Name Server.IAU. Retrieved28 December 2024.
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