| 词条 | NGC 6951 |
| 释义 |
| name = NGC 6951 | image = Ngc6951-hst-R814GB658.jpg | image_size = 250px | caption =NGC 6951 by Hubble Space Telescope | credit = NASA/ESA | epoch = J2000 | type = SAB(rs)bc [1] | ra = {{RA|20|37|14.1}}[1] | dec = {{DEC|+66|06|20}}[1] | dist_ly = 75 ± 12 Mly (23.1 ± 3.5 Mpc)[1] | z = 0.004750 ± 0.000005 [1] | h_radial_v = 1,424 ± 1 km/s[1] | appmag_v = 11.0[2] | size_v = 3′.9 × 3′.2[1] | constellation name = Cepheus | notes = Seyfert galaxy | names = NGC 6952, UGC 11604, CGCG 325-003, MCG +11-25-002, PGC 65086[1] }}NGC 6951 (also catalogued as NGC 6952) is a barred spiral galaxy located in the constellation Cepheus. It is located at a distance of circa 70 million light years from Earth, which, given its apparent dimensions, means that NGC 6951 is about 100,000 light years across. It was discovered by Jérôme Eugène Coggia in 1877 and independently by Lewis Swift in 1878.[3] CharacteristicsThe nucleus of NGC 6951 is active. It has been classified both as a type 2 Seyfert galaxy and a LINER 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.[4] A supermassive 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 million {{solar mass|link=yes}} based on velocity dispersion.[5] Molecular gas, most probably a circumnuclear dust disk or torus less than 50 parsec in radius, has been detected around the nucleus.[6] Around the nucleus of NGC 6951 has been observed a star formation ring with a radius of 5 arcseconds.[4] It also emits radio waves.[7] The total gas mass at and inside the ring is estimated to be {{val|3|e=8|u=M_solar}}.[8] 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 by Hubble Space Telescope. The central part of the nuclear area contains red supergiant stars.[4] The ring is complete and features HII regions. It is characterised by a gradient in stellar population ages, with the younger stars being a few million years old while the older are more than a hundred million years old.[9] The stars in the ring form star clusters with masses between {{val|e=4}} and {{val|e=6.8|u=M_solar}}. 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.[10] NGC 6951 has a large stellar bar with dust lanes running across it. These lanes come in contact with the circumnuclear ring at its north and south points.[10] Gas is channeled inwards, towards the ring, through the bar. Observations in CO revealed also the presence of molecular gas with inflow motion towards the galactic nucleus. Since there are no signs of interaction with another galaxy in the isolated NGC 6951 for the last one billion years, it is believed that the origin of the gas is internal.[11] Gas kinematics have also been observed for the rest of the galaxy, where the gravitational torques caused by the bar have a dominant role.[12] Four supernovae have been observed in NGC 6951; SN 1999el (Type IIn, mag 15.4), SN 2000E (type Ia, mag 14.3), SN 2015G (type Ibn, mag 15.5),[13] and AT2016ejj (mag 16.0).[14][15] References1. ^1 2 3 4 5 6 7 {{cite web | title=NASA/IPAC Extragalactic Database | work=Results for NGC 6951 | url=http://ned.ipac.caltech.edu/cgi-bin/nph-objsearch?objname=NGC+6951 | accessdate=2016-01-18 }} 2. ^{{cite web |title=Revised NGC Data for NGC 6951 |url=http://spider.seds.org/ngc/revngcic.cgi?NGC6951 |website=spider.seds.org |accessdate=25 November 2018}} 3. ^{{cite web |last1=Seligman |first1=Courtney |title=NGC 6951 (= PGC 64650) |url= http://cseligman.com/text/atlas/ngc69a.htm#6951 |website=Celestial Atlas |accessdate=19 November 2018}} 4. ^1 2 {{cite journal |last1=Pérez |first1=E. |last2=Márquez |first2=I. |last3=Marrero |first3=I. |last4=Durret |first4=F. |last5=González Delgado |first5=R. M. |last6=Masegosa |first6=J. |last7=Maza |first7=J. |last8=Moles |first8=M. |title=Circumnuclear structure and kinematics in the active galaxy NGC 6951 |journal=Astronomy and Astrophysics |date=1 January 2000 |volume=353 |pages=893–909 |issn=0004-6361 |bibcode=2000A&A...353..893P|arxiv=astro-ph/9909495 }} 5. ^{{cite journal |last1=Beifiori |first1=A. |last2=Sarzi |first2=M. |last3=Corsini |first3=E. M. |last4=Bontà |first4=E. Dalla |last5=Pizzella |first5=A. |last6=Coccato |first6=L. |last7=Bertola |first7=F. |title=Upper Limits on the Masses of 105 Supermassive Black Holes from Hubble Space Telescope/Space Telescope Imaging Spectrograph Archival Data |journal=The Astrophysical Journal |date=10 February 2009 |volume=692 |issue=1 |pages=856–868 |doi=10.1088/0004-637X/692/1/856|bibcode=2009ApJ...692..856B |arxiv=0809.5103 }} 6. ^{{cite journal |last1=Krips |first1=M. |last2=Neri |first2=R. |last3=García-Burillo |first3=S. |last4=Combes |first4=F. |last5=Schinnerer |first5=E. |last6=Baker |first6=A. J. |last7=Eckart |first7=A. |last8=Boone |first8=F. |last9=Hunt |first9=L. |last10=Leon |first10=S. |last11=Tacconi |first11=L. J. |title=Molecular gas in NUclei of GAlaxies (NUGA): VI. Detection of a molecular gas disk/torus via HCN in the Seyfert 2 galaxy NGC 6951? |journal=Astronomy & Astrophysics |date=11 January 2007 |volume=468 |issue=3 |pages=L63–L66 |doi=10.1051/0004-6361:20066785}} 7. ^{{cite journal |last1=Saikia |first1=D. J. |last2=Phookun |first2=B. |last3=Pedlar |first3=A. |last4=Kohno |first4=K. |title=Radio observations of the circumnuclear ring in NGC 6951 |journal=Astronomy & Astrophysics |date=15 February 2002 |volume=383 |issue=1 |pages=98–103 |doi=10.1051/0004-6361:20011710|bibcode=2002A&A...383...98S |arxiv=astro-ph/0201079 }} 8. ^{{cite journal |last1=García-Burillo |first1=S. |last2=Combes |first2=F. |last3=Schinnerer |first3=E. |last4=Boone |first4=F. |last5=Hunt |first5=L. K. |title=Molecular gas in NUclei of GAlaxies (NUGA) |journal=Astronomy & Astrophysics |date=23 September 2005 |volume=441 |issue=3 |pages=1011–1030 |doi=10.1051/0004-6361:20052900}} 9. ^{{cite journal |last1=Mazzuca |first1=Lisa M. |last2=Knapen |first2=Johan H. |last3=Veilleux |first3=Sylvain |last4=Regan |first4=Michael W. |title=A Connection between Star Formation in Nuclear Rings and Their Host Galaxies |journal=The Astrophysical Journal Supplement Series |date=February 2008 |volume=174 |issue=2 |pages=337–365 |doi=10.1086/522338|bibcode=2008ApJS..174..337M |arxiv=0709.2915 }} 10. ^1 {{cite journal |last1=van der Laan |first1=T. P. R. |last2=Schinnerer |first2=E. |last3=Emsellem |first3=E. |last4=Hunt |first4=L. K. |last5=McDermid |first5=R. M. |last6=Liu |first6=G. |title=How does star formation proceed in the circumnuclear starburst ring of NGC 6951? |journal=Astronomy & Astrophysics |date=26 February 2013 |volume=551 |pages=A81 |doi=10.1051/0004-6361/201220285|bibcode=2013A&A...551A..81V |arxiv=1301.2621 }} 11. ^{{cite journal |last1=van der Laan |first1=T. P. R. |last2=Schinnerer |first2=E. |last3=Boone |first3=F. |last4=García-Burillo |first4=S. |last5=Combes |first5=F. |last6=Haan |first6=S. |last7=Leon |first7=S. |last8=Hunt |first8=L. |last9=Baker |first9=A. J. |title=Molecular gas in NUclei of GAlaxies (NUGA) |journal=Astronomy & Astrophysics |date=29 March 2011 |volume=529 |pages=A45 |doi=10.1051/0004-6361/201014488}} 12. ^{{cite journal |last1=Haan |first1=Sebastian |last2=Schinnerer |first2=Eva |last3=Emsellem |first3=Eric |last4=García-Burillo |first4=Santiago |last5=Combes |first5=Francoise |last6=Mundell |first6=Carole G. |last7=Rix |first7=Hans-Walter |title=Dynamical Evolution of AGN Host Galaxies - Gas In/Out-Flow Rates in 7 NUGA Galaxies |journal=The Astrophysical Journal |date=20 February 2009 |volume=692 |issue=2 |pages=1623–1661 |doi=10.1088/0004-637X/692/2/1623}} 13. ^List of Supernovae IAU Central Bureau for Astronomical Telegrams. Retrieved 29 December 2015. 14. ^{{cite web |title=Bright Supernova pages - Most prolific galaxies |url=http://www.rochesterastronomy.org/snimages/sndupe.html |website=www.rochesterastronomy.org}} 15. ^{{cite web |title=AT 2016ejj |url=https://wis-tns.weizmann.ac.il/object/2016ejj |website=Transient Name Server |publisher=weizmann.ac.il}} External links{{wikiSky}}
8 : Barred spiral galaxies|Seyfert galaxies|Cepheus (constellation)|NGC objects|UGC objects|Principal Galaxies Catalogue objects|Astronomical objects discovered in 1877|Discoveries by Jérôme Coggia |
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