NASA/IPAC EXTRAGALACTIC DATABASE
Date and Time of the Query: 2019-06-17 T07:18:24 PDT
Help | Comment | NED Home

For refcode 1995A&A...298...22M:
Retrieve 111 NED objects in this reference.
Please click here for ADS abstract

NED Abstract

Copyright by European Southern Observatory (ESO). Reproduced by permission
1995A&A...298...22M Multiwavelength analysis of active galaxies: implications on unified Seyfert models J. Miguel Mas-Hesse, Pedro M. Rodriguez-Pascual, Lourdes Sans Fernandez de Cordoba, I. Felix Mirabel, W. Wamsteker, F. MaKino, and C. Otani Laboratorio de Astrofisica Espacial y Fisica Fundamental, Apartado de Correos 50727, E-28080 Madrid, Spain ESA IUE Observatory, POB 50727, E-28080 Madrid, Spain Service d'Astrophysique, Centre d'Etudes de Saclay, F-9 1191 Gif-sur- Yvette, France ISAS, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229, Japan Received 7 February 19941 Accepted 20 October 1994 Abstract. We have analyzed the multiwavelength (radio to X-rays) observational properties of a sample of 111 galaxies covering a wide range of activity (QSO, Seyfert 1 and 2 and star forming galaxies), with the aim of looking for similarities and systematic differences between the different sub-classes, which could provide some clues about the nature of their dominant emission mechanism. Our sample of active galaxies can be divided into two major subgroups: those objects where the far infrared emission clearly dominates the spectral energy distribution (Seyfert 2 and star forming galaxies), and those where the high energy emission (UV to X-rays) is comparable to the far infrared (QSO and Seyfert 1 galaxies). The relative strength of the UV emission provides a further division between QSO and Seyfert 1 galaxies. On the other hand, while Seyfert 2 and star forming galaxies share many observational properties, the former are significantly brighter at X-rays than the latter. Seyfert 2 galaxies are found to show a large spread in properties, overlapping both with Seyfert 1 and star forming galaxies. We have tested the validity of the "unified Seyfert models", which assume that Seyfert 1 and 2 galaxies are intrinsically similar, but seen at different angles through a dense obscuring torus. Seyfert 1 galaxies are significantly brighter at UV and soft X-ray energies than Seyfert 2, as predicted by the unified models, but the measured L_softX_ /L_UV_ ratios in Seyfert 2 galaxies are in average lower than predicted by the "occultation reflection" picture. Furthermore, the hard X-ray emission is lower in Seyfert 2 than in Seyfert 1 galaxies. While the data are consistent with the presence of an obscuring torus around the nuclei of at least some Seyfert 2 galaxies (like NGC 1068), it seems that in any case the "active" component in Sy 2 represents a smaller contribution to the energy budget of the whole galaxy than it does in Sy 1 galaxies. A scheme becomes then evident in which the sequence QSO-Sy 1-Sy 2-star forming galaxies is determined mainly by the relative strength of some kind of "active" nucleus with respect to the global emission of stellar origin in the galaxy. Key words: galaxies: nuclei - galaxies: Seyfert - infrared: galaxies - ultraviolet: galaxies - x-rays: galaxies
Retrieve 111 NED objects in this reference.
Please click here for ADS abstract

Back to NED Home