Abstract Details

Name: Savithri H Ezhikode
Affiliation: St. Thomas College, Kozhencherry, Kerala
Conference ID: ASI2017_469
Title : Torus covering factors of type 1 AGN: A study based on a sample of 51 sources in the nearby universe
Authors and Co-Authors : Poshak Gandhi(1), Chris Done(2), Martin Ward(2), Gulab C. Dewangan(3), Ranjeev Misra(3), Ninan Sajeeth Philip(4): (1) School of Physics & Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ, UK (2) Centre for Extragalactic Astronomy, Department of Physics, Durham University, South Road, Durham DH1 3LE, UK (3) Inter-University Centre for Astronomy & Astrophysics, Post Bag 4, Ganeshkhind, Pune, India (4) Department Of Physics, St. Thomas College, Kozhencherry, Kerala 689641, India
Abstract Type : Poster
Abstract Category : Extragalactic astronomy
Abstract : The unification scheme of active galactic nuclei (AGN) proposes the presence of an obscuring torus around the central source, which is responsible for the observed differences in the AGN spectral energy distributions (SEDs). It is assumed that a fraction of the AGN luminosity is absorbed by the dusty torus and re-radiated in the infrared (IR) band. Then the fraction of the sky covered by the torus, known as the covering factor fc, can be indirectly obtained from the ratio of the IR to the bolometric luminosities of AGN. However, it is difficult to determine the bolometric luminosities of AGN since SEDs peak in the unobservable ultraviolet region. In this work, we estimated the bolometric luminosities of a sample of 51 type 1 AGN using a self-consistent, energy-conserving model. The IR and bolometric luminosities are computed by analyzing the broadband SEDs of the sample using multi-wavelength data from XMM-Newton, SDSS, WISE and 2MASS/UKIDSS. The obtained torus covering factor is found to be in the range of ~0.02-0.88 with a mean value of ~0.3 and a dispersion of about 0.17. We also find that fc is anti-correlated with both the bolometric luminosity and the Eddington ratio. A simulation using random samples of these parameters suggest that, rather than the bolometric luminosity, the Eddington ratio is the underlying driver of the torus covering factor. This points to a changing geometry of the accretion flow connected to Eddington ratio rather than a receding torus driven solely by illumination.