3C 120

File:3C120LightCurve.png for 3C 120, adapted from Pollock et al. (1979){{cite journal |last1=Pollock |first1=J. T. |last2=Pica |first2=A. J. |last3=Smith |first3=A. G. |last4=Leacock |first4=R. J. |last5=Edwards |first5=P. L. |last6=Scott |first6=R. L. |title=Long-term optical variations of 20 violently variable extragalactic radio sources |journal=Astronomical Journal |date=November 1979 |volume=84 |pages=1658-1676 |bibcode=1979AJ.....84.1658P |doi=10.1086/112591 |url=https://articles.adsabs.harvard.edu/pdf/1979AJ.....84.1658P |access-date=1 April 2025}}]]

The galaxy was discovered in 1940 by Harlow Shapley and C. M. Hanley to be a variable in visual light, with an apparent magnitude varying between 13.7 and 14.6 in irregular intervals, and was given the variable star designation BW Tauri.{{cite journal |last1=Penston |first1=M. V. |title=BW Tau = 3C 120 |journal=Information Bulletin on Variable Stars |date=1 February 1968 |volume=255 |pages=1 |url=https://articles.adsabs.harvard.edu/pdf/1968IBVS..255....1P |issn=0374-0676}} The radio emission of the galaxy was detected during the third radio research of Cambridge and was added in the Third Cambridge Catalogue of Radio Sources, published in 1959. The name signifies that it was the 120th object (ordered by right ascension) of the Catalog. The galaxy was catalogued as peculiar by Boris Vorontsov-Velyaminov and V. P. Arkhipova in the 1964 Morphological Catalogue of Galaxies.

Variability of 1.1 magnitudes in the ultraviolet was detected in observations obtained in 1974-1977 by the International Ultraviolet Explorer.{{cite journal |last1=Oke |first1=J. B. |last2=Zimmerman |first2=B. |title=IUE and visual spectrophotometry of 3C 120 and Markarian 79 |journal=The Astrophysical Journal |date=July 1979 |volume=231 |pages=L13 |doi=10.1086/182996|bibcode=1979ApJ...231L..13O |doi-access=free }} In X-rays, changes in luminosity by a factor of 2.5 within days or months were detected by Einstein Observatory in 1979–1981, along with changes in spectral slope.{{cite journal |last1=Halpern |first1=J. P. |title=X-ray spectrum and variability of 3C 120 |journal=The Astrophysical Journal |date=March 1985 |volume=290 |pages=130 |doi=10.1086/162967|bibcode=1985ApJ...290..130H }} Large variability in the infrared was detected in the 1970s.{{cite journal |last1=Rieke |first1=G. H. |title=The infrared emission of Seyfert galaxies |journal=The Astrophysical Journal |date=December 1978 |volume=226 |pages=550 |doi=10.1086/156639|bibcode=1978ApJ...226..550R }} Superluminal motion in the radio jet was detected in observations between 1975 and 1977, along with flux variability.{{cite journal |last1=Seielstad |first1=G. A. |last2=Cohen |first2=M. H. |last3=Linfield |first3=R. P. |last4=Moffet |first4=A. T. |last5=Romney |first5=J. D. |last6=Schilizzi |first6=R. T. |last7=Shaffer |first7=D. B. |title=Further monitoring of the structure of superluminal radio sources |journal=The Astrophysical Journal |date=April 1979 |volume=229 |pages=53 |doi=10.1086/156929|bibcode=1979ApJ...229...53S |doi-access=free }}

3C 120 is a lenticular galaxy with an extended structure that looks like spiral arms, while there is also emission extending southeast and northwest of the nucleus. In the optical images are visible extensive HII regions which are likely photoionised by the nucleus.{{cite journal |last1=Zirbel |first1=Esther L. |last2=Baum |first2=Stefi A. |title=The Ultraviolet Continuum Emission of Radio Galaxies. I. Description of Sources from the Hubble Space Telescope Archives |journal=The Astrophysical Journal Supplement Series |date=February 1998 |volume=114 |issue=2 |pages=177–235 |doi=10.1086/313070|bibcode=1998ApJS..114..177Z |s2cid=122958826 |doi-access=free }}{{cite journal |last1=Baldwin |first1=J. A. |last2=Carswell |first2=R. F. |last3=Wampler |first3=E. J. |last4=Boksenberg |first4=A. |last5=Smith |first5=H. E. |last6=Burbidge |first6=E. M. |title=The nebulosity associated with 3C 120 |journal=The Astrophysical Journal |date=March 1980 |volume=236 |pages=388 |doi=10.1086/157756|bibcode=1980ApJ...236..388B }} Two shell structures are visible about one arcsecond from the bright nucleus. It has been suggested that photoionised nebulae are part of a tidal tail and the galaxy has undergone a galaxy merger.{{cite journal |last1=Garcia-Lorenzo |first1=B. |last2=Sanchez |first2=S. F. |last3=Mediavilla |first3=E. |last4=Gonzalez-Serrano |first4=J. I. |last5=Christensen |first5=L. |title=Integral Field Spectroscopy of the Central Regions of 3C 120: Evidence of a Past Merging Event |journal=The Astrophysical Journal |date=March 2005 |volume=621 |issue=1 |pages=146–166 |doi=10.1086/427429|arxiv=astro-ph/0411298 |bibcode=2005ApJ...621..146G |s2cid=53654291 }} The star formation rate of 3C 120 is estimated to be about 2.8 solar masses per year.{{cite journal |last1=Westhues |first1=Christian |last2=Haas |first2=Martin |last3=Barthel |first3=Peter |last4=Wilkes |first4=Belinda J. |last5=Willner |first5=S. P |last6=Kuraszkiewicz |first6=Joanna |last7=Podigachoski |first7=Pece |last8=Leipski |first8=Christian |last9=Meisenheimer |first9=Klaus |last10=Siebenmorgen |first10=Ralf |last11=Chini |first11=Rolf |title=Star formation in 3CR radio galaxies and quasars at z < 1 |journal=The Astronomical Journal |date=21 April 2016 |volume=151 |issue=5 |pages=120 |doi=10.3847/0004-6256/151/5/120 |arxiv = 1602.07443 |bibcode=2016AJ....151..120W |doi-access=free }}

It is a Fanaroff and Riley class I radio galaxy. The emission lines in the radiowaves are broad, and 3C 120 is the brightest broad-line radio galaxy.{{cite journal |last1=Osterbrock |first1=Donald |title=Optical Emission-Line Spectra of Seyfert Galaxies and Radio Galaxies |journal=Physica Scripta |date=1 March 1978 |volume=17 |issue=3 |pages=137–143 |doi=10.1088/0031-8949/17/3/002|bibcode=1978PhyS...17..137O |s2cid=250889982 }}

The nucleus of 3C 120 has been found to be active and it has been categorised as a type I Seyfert galaxy. The most accepted theory for the energy source of active galactic nuclei is the presence of an accretion disk around a supermassive black hole. The mass of the black hole in the centre of 3C 120 is estimated to be {{val|6.3|0.5|0.3|e=7|ul=M_solar}} based on reverberation mapping,{{cite journal |last1=Hlabathe |first1=Michael S |last2=Starkey |first2=David A |last3=Horne |first3=Keith |last4=Romero-Colmenero |first4=Encarni |last5=Crawford |first5=Steven M |last6=Valenti |first6=Stefano |last7=Winkler |first7=Hartmut |last8=Barth |first8=Aaron J |last9=Onken |first9=Christopher A |last10=Sand |first10=David J |last11=Treu |first11=Tommaso |last12=Diamond-Stanic |first12=Aleksandar M |last13=Villforth |first13=Carolin |title=Robotic reverberation mapping of the broad-line radio galaxy 3C 120 |journal=Monthly Notices of the Royal Astronomical Society |date=21 September 2020 |volume=497 |issue=3 |pages=2910–2929 |doi=10.1093/mnras/staa2171|doi-access=free |arxiv=2007.11522 }} or {{val|2.29e7|u=M_solar}} based on stellar velocity dispersion.{{cite journal |last1=Nelson |first1=Charles H. |title=Black Hole Mass, Velocity Dispersion, and the Radio Source in Active Galactic Nuclei |journal=The Astrophysical Journal |date=1 December 2000 |volume=544 |issue=2 |pages=L91–L94 |doi=10.1086/317314|arxiv=astro-ph/0009188 |bibcode=2000ApJ...544L..91N |doi-access=free }}

The X-ray emission is highly variable and it is characterised by a broken power law that agrees well with the expected values given the size of the black hole and its accretion rate. The X-ray spectrum also features a FeKα line. The emission is similar to that of radio quiet Seyfert galaxies, indicating that the X-rays are emitted by the accetion disk and its corona and not from the jet.{{cite journal |last1=Rani |first1=Priyanka |last2=Stalin |first2=C. S. |title=Coronal Proerties [sic] of the Seyfert 1 Galaxy 3C 120 with NuSTAR |journal=The Astrophysical Journal |date=30 March 2018 |volume=856 |issue=2 |pages=120 |doi=10.3847/1538-4357/aab356|arxiv=1802.09724 |bibcode=2018ApJ...856..120R |s2cid=55775276 |doi-access=free }} The column density is estimated to be logNH= 20.67 ± 0.05 cm−2. Soft X-rays are emitted from hot gas that could originate from outflows or a superbubble.{{cite journal |last1=Tombesi |first1=F. |last2=Mushotzky |first2=R. F. |last3=Reynolds |first3=C. S. |last4=Kallman |first4=T. |last5=Reeves |first5=J. N. |last6=Braito |first6=V. |last7=Ueda |first7=Y. |last8=Leutenegger |first8=M. A. |last9=Williams |first9=B. J. |last10=Stawarz |first10=ł. |last11=Cappi |first11=M. |title=Feeding and Feedback in the Powerful Radio Galaxy 3C 120 |journal=The Astrophysical Journal |date=20 March 2017 |volume=838 |issue=1 |pages=16 |doi=10.3847/1538-4357/aa6342|arxiv=1703.00516 |bibcode=2017ApJ...838...16T |doi-access=free }}

The variations observed in X-Rays are also observed in optical wavelengths after 28 days.{{cite journal |last1=Marshall |first1=Kevin |last2=Ryle |first2=Wesley T. |last3=Miller |first3=H. Richard |last4=Marscher |first4=Alan P. |last5=Jorstad |first5=Svetlana G. |last6=Chicka |first6=Benjamin |last7=McHardy |first7=Ian M. |title=Multiwavelength Variability of the Broad Line Radio Galaxy 3C 120 |journal=The Astrophysical Journal |date=1 May 2009 |volume=696 |issue=1 |pages=601–607 |doi=10.1088/0004-637X/696/1/601|arxiv=0902.2927 |bibcode=2009ApJ...696..601M |s2cid=14198709 }} The variations are also observed at 37 GHz with a 20-day delay after the optical/UV ones.{{cite journal |last1=Marscher |first1=Alan P. |last2=Jorstad |first2=Svetlana G. |last3=Williamson |first3=Karen E. |last4=Lähteenmäki |first4=Anne |last5=Tornikoski |first5=Merja |last6=Hunter |first6=John M. |last7=Leidig |first7=Katya A. |last8=Mobeen |first8=Muhammad Zain |last9=Vera |first9=Rafael J. C. |last10=Chamani |first10=Wara |title=X-Ray, UV, and Radio Timing Observations of the Radio Galaxy 3C 120 |journal=The Astrophysical Journal |date=7 November 2018 |volume=867 |issue=2 |pages=128 |doi=10.3847/1538-4357/aae4de|arxiv=1809.09721 |bibcode=2018ApJ...867..128M |s2cid=119222564 |doi-access=free }} It has been suggested that 3C 120 exhibits quasi-periodic oscillation, with a period of about 1.65 days.{{cite journal |last1=Agarwal |first1=Aditi |last2=Rani |first2=Priyanka |last3=Prince |first3=Raj |last4=Stalin |first4=C. S. |last5=Anupama |first5=G. C. |last6=Agrawal |first6=Vipul |title=A Possible Quasi-Periodic Oscillation in the X-ray Emission of 3C 120 |journal=Galaxies |date=25 March 2021 |volume=9 |issue=2 |pages=20 |doi=10.3390/galaxies9020020|bibcode=2021Galax...9...20A |doi-access=free }}

Gamma rays emission up to 10 GeV was detected by Fermi-LAT, which appears to variate in luminosity, with the flux doubling within a year, indicating a sustained rise in luminosity and not a flare as those observed in blazars.{{cite journal |last1=Sahakyan |first1=N. |last2=Zargaryan |first2=D. |last3=Baghmanyan |first3=V. |title=On the gamma-ray emission from 3C 120 |journal=Astronomy & Astrophysics |date=February 2015 |volume=574 |pages=A88 |doi=10.1051/0004-6361/201425114|arxiv=1412.3559 |bibcode=2015A&A...574A..88S |s2cid=119231414 }}

3C 120 has been found when observed in radio waves to have a jet. The jet is one sided and its brightness decreases as it gets farther from the core in accordance with a simple power law. A bright knot is seen in the jet 4 arcseconds west of the core. After the knot the jet bends toward the northwest and one more knot is seen 20 arcseconds further west. X-ray emission has been associated with a radio knot about 25 arcseconds from the core.{{cite journal |last1=Harris |first1=D. E. |last2=Hjorth |first2=J. |last3=Sadun |first3=A. C. |last4=Silverman |first4=J. D. |last5=Vestergaard |first5=M. |title=X-Ray Emission from the Radio Jet in 3C 120 |journal=The Astrophysical Journal |date=10 June 1999 |volume=518 |issue=1 |pages=213–218 |doi=10.1086/307284|arxiv=astro-ph/9901132 |bibcode=1999ApJ...518..213H |s2cid=12937193 }} Another knot is seen 1.3 arcminutes from the core. After 3 arcminutes the jet appears broken and diffuse. A diffuse radio lobe without hot spots is visible southeast of the core. Radio emission from 3C 120 extends up to 14 arcminutes from the core.{{cite journal |last1=Walker |first1=R. C. |last2=Benson |first2=J. M. |last3=Unwin |first3=S. C. |title=The radio morphology of 3C 120 on scales from 0.5 parsecs to 400 kiloparsecs |journal=The Astrophysical Journal |date=May 1987 |volume=316 |pages=546 |doi=10.1086/165225|bibcode=1987ApJ...316..546W }}

Inside the jet there are knots that appear to move 4.1 to 5 times faster than the speed of light. The appearance of new bright knots in the jet has been found to happen after a decrease in X-ray emission, which indicates that the source of the radio jet is material from the inner part of the accretion disk falling into the black hole, with some passing through the event horizon while the rest is ejected into the jet. 3C 120 was the first AGN where this relation, previously only observed in microquasars, was established.{{cite journal |last1=Marscher |first1=Alan P. |last2=Jorstad |first2=Svetlana G. |last3=Gómez |first3=José-Luis |last4=Aller |first4=Margo F. |last5=Teräsranta |first5=Harri |last6=Lister |first6=Matthew L. |last7=Stirling |first7=Alastair M. |title=Observational evidence for the accretion-disk origin for a radio jet in an active galaxy |journal=Nature |date=June 2002 |volume=417 |issue=6889 |pages=625–627 |doi=10.1038/nature00772|pmid=12050658 |bibcode=2002Natur.417..625M |hdl=2027.42/62888 |s2cid=4382324 |hdl-access=free }} The knots appear to fluctuate in brightness and polarisation changes direction, maybe due to the presence of a cloud about 8 parsec from the nucleus.{{cite journal |last1=Gómez |first1=José-Luis |last2=Marscher |first2=Alan P. |last3=Alberdi |first3=Antonio |last4=Jorstad |first4=Svetlana G. |last5=Garcı́a-Miró |first5=Cristina |title=Flashing Superluminal Components in the Jet of the Radio Galaxy 3C120 |journal=Science |date=29 September 2000 |volume=289 |issue=5488 |pages=2317–2320 |doi=10.1126/science.289.5488.2317|pmid=11009410 |bibcode=2000Sci...289.2317G }} A stationary feature has been observed at a distance of 1.3 parsecs from the source of the jet, and it has been found that when the knot passes from that point, an optical flare is observed.{{cite journal |last1=León-Tavares |first1=J. |last2=Lobanov |first2=A. P. |last3=Chavushyan |first3=V. H. |last4=Arshakian |first4=T. G. |last5=Doroshenko |first5=V. T. |last6=Sergeev |first6=S. G. |last7=Efimov |first7=Y. S. |last8=Nazarov |first8=S. V. |title=Relativistic Plasma as the Dominant Source of the Optical Continuum Emission in the Broad-Line Radio Galaxy 3C 120 |journal=The Astrophysical Journal |date=20 May 2010 |volume=715 |issue=1 |pages=355–361 |doi=10.1088/0004-637X/715/1/355|arxiv=0910.1320 |bibcode=2010ApJ...715..355L |s2cid=119238963 }} The angle between the line of sight and the axis of the jet is estimated to be between 10° and 20°.{{cite journal |last1=Zdziarski |first1=Andrzej A. |last2=Phuravhathu |first2=Dakalo G. |last3=Sikora |first3=Marek |last4=Böttcher |first4=Markus |last5=Chibueze |first5=James O. |title=The Composition and Power of the Jet of the Broad-line Radio Galaxy 3C 120 |journal=The Astrophysical Journal Letters |date=1 March 2022 |volume=928 |issue=1 |pages=L9 |doi=10.3847/2041-8213/ac5b70|arxiv=2202.11174 |bibcode=2022ApJ...928L...9Z |s2cid=247058726 |doi-access=free }}

A faint optical jet that is 15 arcseconds long has been observed which coincides with the radio jet. There appears to be a visual counterpart for the bright radio knot 4 arcseconds west of the nucleus but there is no clear visual counterpart of the other knots.{{cite journal |last1=Hjorth |first1=Jens |last2=Vestergaard |first2=Marianne |last3=Sørensen |first3=Anton N. |last4=Grundahl |first4=Frank |title=Detection of a Faint Optical Jet in 3C 120 |journal=The Astrophysical Journal |date=10 October 1995 |volume=452 |issue=1 |doi=10.1086/309701|arxiv=astro-ph/9506117 |bibcode=1995ApJ...452L..17H |s2cid=1225824 }}

• 3C 390.3 - a similar radio galaxy

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• [http://simbad.u-strasbg.fr/simbad/sim-id?Ident=3C%20120 3C 120 on SIMBAD]

{{Taurus (constellation)}}

Category:Radio galaxies

Category:Seyfert galaxies

Category:Lenticular galaxies

Category:Taurus (constellation)

120

03087

Markarian 1506

+05.20

15504

Tauri, BW