the zoo of active galaxy classifications is now very extensive. adding to this list may not be helpful in furthering our basic understanding of the agn phenomena. however, it does appear that a sub-set of seyfert 1s, known as the narrow line seyfert 1s (nls1s), share interesting properties which make them worthy of further study, particularly at infrared wavelengths. the velocity widths of their permitted lines are less than 2,500 km/s (fwhm), they have exceptionally strong high ionization line species, and dramatic euv/soft x-ray excesses, many times more than normal unreddened seyfert 1s, when normalized by the optical continuum. within the framework of the unified schemes involving a dusty torus, this extra continuum component can be predicted to manifest itself via re-radiation at infrared wavelengths. although many of our sample of nls1s are detected by iras (demonstrating the feasibility of the project) these data are insufficient to define the multiple components which make up their infrared spectral energy distributions (seds). recent models of agn seds suggest the mid ir continuum is mostly from dust heated by the agn, whilst the far ir originates from cooler dust further out in the host galaxy. this is supported by recent isophot observations of seyferts (astron. and astro. special iso issue). based only on iras data there is evidence that the average ratio of ir to optical continua for the nls1s is several times higher than is typical for seyfert 1s. the iso data are essential to properly model the infrared sed, and to determine the temperatures and contributions of the various ir components, and thereby test the hypothesis that the extra euv/soft x-ray component is influencing the nature of the torus. note: only 2 examples of the nls1 class are currently in the isophot observation programme. this is a continuation project in the sense that it studies re-radiating dust in agn, but the importance of the narrow line seyfert 1s was not fully realised at the time of cycle 1 submissions.
Instrument
PHT03 , PHT22
Temporal Coverage
1997-03-30T20:59:09Z/1997-08-09T00:02:27Z
Version
1.0
Mission Description
The Infrared Space Observatory (ISO) was the worlds first true orbiting infrared observatory. Equipped with four highly-sophisticated and versatile scientific instruments, it was launched by Ariane in November 1995 and provided astronomers world-wide with a facility of unprecedented sensitivity and capabilities for a detailed exploration of the Universe at infrared wavelengths.
European Space Agency, WARD et al., 1999, 'NARROW-LINE SEYFERT 1S: THE INFRARED CONNECTION', 1.0, European Space Agency, https://doi.org/10.5270/esa-augu6q0
