New near-infrared spectroscopic observations of several Active Galactic Nuclei (A G N)
are presented. In combination with existing data and X-ray, visible and far-infrared frequencies, these data are used to investigate the effects of interstellar extinction on then observed spectral energy distributions. The derived intrinsic properties of these sources
are compared in detail with those expected in terms of current ‘-unified schemes” of
AGN, which seek to relate the various observational classes through the parameters of
luminosity, viewing angle and obscurationAfter first presenting the methods of data reduction and analysis appropriate to
infrared spectra, I use observations of the Paschen ß hydrogen recombination line in
three so-called Narrow Line X-ray Galaxies to show that their intrinsic (extinction-corrected) broad-line and X-ray properties can be accounted for in terms of normal
Seyfert 1 nuclei obscured by moderate interstellar extinction along our line of sight.
Near-infrared spectroscopy of the luminous radio galaxy Cygnus Aᵥ at A≃2μm reveals strong narrow line emission from H₂ v=1-0 S(l), S(1), [Sivi] and H⁺, which I argue is
excited by a lightly-obscured quasar nucleus obscured by Av=37±7 mag. Wavelength independent electron scattering of this continuum plausibly accounts for the observed
optical and near-infrared non-stellar continuum. I also demonstrate that the quasar
nucleus is also able to power the observed far-infrared continuum through heating of
interstellar dust by the (unobserved) ultraviolet continuum.Similar observations of the infrared-luminous galaxy merger Markarian 463 are presented as part of a multiwavelength study to determine the origin of the high far-infrared
luminosities of such systems. In Markarian 463 this luminosity is provided almost wholly
by an optically-obscured Seyfert 1 nucleus, which I predict should be detectable as a hard
X-ray source. Using ultraviolet, optical and near-infrared line observations I am able
to quantify or set limits on the roles of various emission mechanisms and the roles of
interstellar dust and gas in shaping the appearance of Markarian 463(E) from hard X-ray
to sub-millimetre frequencies.These results demonstrate the utility of near-infrared spectroscopy in testing schemes
which seek to unify the observational classes of AGN, and in providing important links
between emission mechanisms over a wide range of frequency. I propose further observational tests for the AGN under study here, and for larger, unbiased samples of AGN
for which such observations should be possible in the near future
