we propose to test the unified model. for active galactic nuclei (agn) by searching for broad emission lines in the spectrum of the most famous seyfert 2 galaxy, ngc1068. in the context of the unified model, it harbours a quasar-like nucleus which is obscured from direct view by dust. this model explains much of the diversity observed among agn simply by taking into account orientation effects, which result in different amounts of obscuring material to lie along the line of sight. in fact, polarimetric studies have shown that some seyfert 2 nuclei, and in particular ngc1068, have seyfert 1 characteristics, i.e. broad permitted lines and a non-stellar continuum when observed in polarized light (antonucci & miller 1985). nevertheless, the interpretation of the polarization data are not unique (see antonucci 1993) and hence independent tests for the unified model are required. one way to reduce the effect of the obscuring material is by observing at longer ir wavelengths where the extinction rapidly decreases. the detection of broad recombination lines in the near-ir would provide definite proof of the existence of the highly energetic processes linked to the central engine of a seyfert 1 or qso. although the obscuration decreases dramatically with increasing wavelength, the intrinsic strengths of the hydrogen lines also decrease, the best line for such observations is the pfund alpha line (7.46 microns) which will still be somewhat attenuated but intense enough to allow a good determination of its profile. the high signal to noise ratio required to clearly detect the broad wings means that such a project is unfeasible for the vast majority of seyfert 2s, and we have therefore chosen to observe the brightest. these observations will allow us to disentangle the controversy surrounding the amount of absorbing material required to explain its observed spectrum within the context of the unified model.
Instrument
CAM01 , CAM04 , PHT03 , PHT22
Temporal Coverage
1997-08-14T04:07:15Z/1998-04-10T07:25:17Z
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, BOISSON et al., 1999, 'TESTING THE UNIFYING SCHEME OF ACTIVE GALACTIC NUCLEI', 1.0, European Space Agency, https://doi.org/10.5270/esa-l19zqas
