recent observations strongly indicate that a substantial fraction of the energy emitted by an agn is absorbed by nearby optically thick material, which may be in a flattened distribution orbiting the central engine. this can account for a) the intrinsically bi-polar structure seen in many agns and b) the apparent differences between agn types (e.g. seyfert 1.s & 2.s), caused by variations in the viewing angle. detection of this obscuring gas and dust has been one of the highest priorities in the field, but huge extinction makes it invisible except in far-ir. only the very fine spectral resolution of lws and sws high-resolution fp spectroscopy can provide definitive evidence of dense, neutral and molecular gas in close orbit around the nucleus. the low resolution from the grating mode of lws is certainly inadequate. the r=1000 provided by sws at 33um is also insufficient to reliably separate weak high-velocity wings (or humps) from the stronger but narrower galactic pdr emission. only high snr fp line profiles can separate the higher- velocity gas in the torus from other components further out. the spacing of the red- and blue-shifted peaks will then give a direct dynamical measurement of the mass of the central engine. although the lws will obtain rather short-integration fp profiles of another oi and co line, there is no guarantee that these will detect decisively the rotating nuclear disk/torus, because of the very large uncertainties in its physical parameters (e.g. the wavelength at which it becomes optically thin). two of the most promising lines it is predicted to emit strongly, oi145um and co (j=81-->80), are not being observed at high resolution in the core program. given the great scientific importance of the result, more than one possible torus emission line should be studied in detail. if more than one is detected, additional torus physics can be determined. to search for the torus predicted in both seyfert 1 and 2 nuclei, we propose to observe these lines in by far the brightest example of each class: ngc4151 & ngc1068.
Instrument
LWS02 , LWS03
Temporal Coverage
1998-01-29T19:53:14Z/1998-02-12T21:38:24Z
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, MALKAN et al., 1999, 'HIGH RESOLUTION SPECTROSCOPY OF THE 2 BRIGHTEST SEYFERT NUCLEI SEARCHING FOR DENSE GAS ORBITING NEAR THE NUCLEUS', 1.0, European Space Agency, https://doi.org/10.5270/esa-pi5g4pk
