NGC 4278 is an elliptical galaxy. Its nucleus has been found to beactive (AGN) and based on itsspectrum has been identified as aLINER.[5] The most accepted theory for the power source of active galactic nuclei is the presence of anaccretion disk around asupermassive black hole. In the centre of NGC 4278 lies a supermassive black hole with an estimated mass(3.09±0.54)×108M☉ based on stellarvelocity dispersion.[6] The X-ray emission of the nucleus is consistent with one of a black hole fed by a low radiative efficiency accretion flow.[7]
The nucleus is asource of radio waves and two small symmetric S-shapedradio jets have been observed spanning for 20 mas each, which corresponds to 1.4 parsec at the distance of NGC 4278, emanating from the central source.[8] The nucleus also hosts a compactultraviolet source, which features strong variability in the form of flares. One such flare was observed between June 1994 and January 1995, when the nuclear source became 1.6 times brighter in six months. Similar flares have also being observed in other low luminosity AGN.[9]
The central region of NGC 4278, with the dust features, by Hubble Space Telescope
Variability has also being observed inX-rays. The galaxy has been found to brighten 5 times within three years, while fluctuations have been observed in shorter time periods, even within an hour, with the flux increasing by a factor of 10% in one observation byXMM-Newton. The spectrum obtained by XMM-Newton can be accounted for by an absorbed power-law, withcolumn density of the order of 1020 cm-2. TheFeKα emission line has not been detected, as is typical for LINERs. Thespectral energy distribution of NGC 4278 resembles a LINER at lower fluxes while at higher fluxes it resembles a low luminositySeyfert galaxy.[10]
Dust features have been observed in the central part of the galaxy[11] and the area that appears northwest of the nucleus. The dust forms knots and filaments that spiral down to the nucleus.[12] Moreover, the galaxy, contrary to most elliptical galaxies which lack neutral hydrogen emission, has been found to possess a massiveHI disk, probably formed after theaccretion of a dwarf satellite galaxy.[13] The total mass of the HI disk is estimated to be6.9×108M☉. The disk rotates at the same sense as the stars, but is misaligned by 20° to 70°.[14]Molecular clouds, as pointed byCO emission, have also been detected in the galaxy.[15]
The galaxy has been observed with the InfraRedSpectrograph (IRS) onboardSpitzer Space Telescope, examining the dust features of NGC 4278. Multiphase gas and dust have been observed in the same elongated features. Another uncommon finding for an elliptical galaxy is the detection of emission bypolycyclic aromatic hydrocarbons (PAHs) and of strong [Si II] 34.8-μm emission. PAHs in other elliptical galaxies are believed to be destroyed by the hot interstellar medium. Emission by molecular hydrogen andionised gas has also been reported. The observed emission of the gas in the nuclear region has been suggested to be the result of the accretion of cold gas by the HI disk.[16]
NGC 4278 is home to a larger than average number ofglobular clusters compared with galaxies of similar luminosity, with an estimated total number of1378+32 −194. As it has been found in other galaxies, the colour distribution of the globular clusters in the galaxy features bimodiality, with the clusters forming a red and a blue subpopulation. The blue clusters have been found to be larger than the red ones at the same galactocentric distance, while the size of the clusters increases with galactocentric radius.[17]
NGC 4283 lies 3.5 arcminutes to the northeast andNGC 4286 9 arcminutes northeast of NGC 4278 in the sky.[22] NGC 4274 lies about 20 arcminutes north of NGC 4278.[4]
^Ho, Luis C.; Filippenko, Alexei V.; Sargent, Wallace L. W. (October 1997). "A Search for "Dwarf" Seyfert Nuclei. III. Spectroscopic Parameters and Properties of the Host Galaxies".The Astrophysical Journal Supplement Series.112 (2):315–390.arXiv:astro-ph/9704107.Bibcode:1997ApJS..112..315H.doi:10.1086/313041.S2CID17086638.
^Pellegrini, Silvia; Wang, Junfeng; Fabbiano, Giuseppina; Kim, Dong-Woo; Brassington, Nicola J.; Gallagher, John S.; Trinchieri, Ginevra; Zezas, Andreas (20 October 2012). "Agn Activity and the Misaligned Hot Ism in the Compact Radio Elliptical NGC 4278".The Astrophysical Journal.758 (2): 94.arXiv:1206.2533.Bibcode:2012ApJ...758...94P.doi:10.1088/0004-637X/758/2/94.S2CID17608488.
^Cardullo, A.; Corsini, E. M.; Beifiori, A.; Buson, L. M.; Dalla Bontà, E.; Morelli, L.; Pizzella, A.; Bertola, F. (4 November 2009). "The ultraviolet flare at the center of the elliptical galaxy NGC 4278".Astronomy & Astrophysics.508 (2):641–644.arXiv:0909.4048.Bibcode:2009A&A...508..641C.doi:10.1051/0004-6361/200913046.S2CID17543152.
^Lauer, Tod R.; Faber, S. M.; Gebhardt, Karl; Richstone, Douglas; Tremaine, Scott; Ajhar, Edward A.; Aller, M. C.; Bender, Ralf; Dressler, Alan; Filippenko, Alexei V.; Green, Richard; Grillmair, Carl J.; Ho, Luis C.; Kormendy, John; Magorrian, John; Pinkney, Jason; Siopis, Christos (May 2005). "The Centers of Early-Type Galaxies with Hubble Space Telescopes. V. New WFPC2 Photometry".The Astronomical Journal.129 (5):2138–2185.arXiv:astro-ph/0412040.Bibcode:2005AJ....129.2138L.doi:10.1086/429565.S2CID15473461.
^Raimond, E.; Faber, S. M.; Gallagher, J. S. III; Knapp, G. R. (June 1981). "H I synthesis observations of the elliptical galaxy NGC 4278".The Astrophysical Journal.246: 708.Bibcode:1981ApJ...246..708R.doi:10.1086/158967.
