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.