A GMRT Study of Seyfert Galaxies NGC4235 & NGC4594: Evidence of Episodic Activity ?
Autor: | V. Singh, Jack F. Gallimore, C. H. Ishwara-Chandra, S. Srivastava, Preeti Kharb, Hota Ananda |
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Jazyk: | angličtina |
Rok vydání: | 2016 |
Předmět: |
Physics
Luminous infrared galaxy 010308 nuclear & particles physics Radio galaxy Astrophysics::High Energy Astrophysical Phenomena Astronomy FOS: Physical sciences Astronomy and Astrophysics Type-cD galaxy Astrophysics Astrophysics::Cosmology and Extragalactic Astrophysics Disc galaxy 01 natural sciences Astrophysics - Astrophysics of Galaxies Galaxy Radio telescope X-shaped radio galaxy Space and Planetary Science Astrophysics of Galaxies (astro-ph.GA) 0103 physical sciences Spectral energy distribution Astrophysics::Solar and Stellar Astrophysics 010303 astronomy & astrophysics Astrophysics::Galaxy Astrophysics |
Popis: | Low frequency observations at 325 and 610 MHz have been carried out for two "radio-loud" Seyfert galaxies, NGC4235 and NGC4594 (Sombrero galaxy), using the Giant Meterwave Radio Telescope (GMRT). The 610 MHz total intensity and 325-610 MHz spectral index images of NGC4235 tentatively suggest the presence of a "relic" radio lobe, most likely from a previous episode of AGN activity. This makes NGC4235 only the second known Seyfert galaxy after Mrk6 to show signatures of episodic activity. Spitzer and Herschel infrared spectral energy distribution (SED) modelling using the clumpyDREAM code predicts star formation rates (SFR) that are an order of magnitude lower than those required to power the radio lobes in these Seyferts (~0.13-0.23 M_sun/yr compared to the required SFR of ~2.0-2.7 M_sun/yr in NGC4594 and NGC4235, respectively). This finding along with the detection of parsec and sub-kpc radio jets in both Seyfert galaxies, that are roughly along the same position angles as the radio lobes, strongly support the suggestion that Seyfert lobes are AGN-powered. SED modelling supports the "true" type 2 classification of NGC4594: this galaxy lacks significant dust obscuration as well as a prominent broad-line region. Between the two Seyfert galaxies, there is an inverse relation between their radio-loudness and Eddington ratio and a direct relation between their Eddington-scaled jet power and bolometric power. 22 pages, 11 figures, MNRAS, accepted |
Databáze: | OpenAIRE |
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