The work presented in my thesis covers two aspects of modern astronomy: Observations and instrumentation. Part I of this thesis addresses the design, the development and the qualification of the Low Resolution Spectroscopy Double Prism Assembly (LRSDPA). From an instrumentational point of view, the purpose of the LRSDPA is to make an integration of two prisms, made of Germanium and Zincsulfide, into the imaging module of the mid infrared instrument of the James Webb Space Telescope possible. My design of the LRSDPA answers to several challenging specifications, joining together available envelope, mechanical, thermal, optical and alignment aspects. Both prisms are mounted separately onto a holder via a semi-kinematic interface. The Aluminium components of the demonstration, qualification and flight model all have been manufactured at the mechanical workshop of the 1st Institute of Physics. As it is demanded of all space equipment, the function and performance of the LRSDPA has to be thoroughly demonstrated. The qualification campaign that was conducted in collaboration with the Centre Spatial de Liège, has just been brought to a successful finish. A brief introduction to the James Webb Space Telescope and its mid infrared instrument are given in Chapters 1 and 2. Chapter 3 then describes in detail the scientific capabilities, the design and the qualification of the LRSDPA. The low resolution spectroscopy mode will provide prism slit spectroscopy at a resolution of R=100 and cover the wavelength range from 5µm-10µm. This mode is particularly aiming at spectroscopic analyses of very low surface brightness objects, such as the first light-emitting galaxies that re-ionized the universe shortly after the big bang. This scenario of re-ionization is supposed to happen shortly after the big bang, at redshifts of z=10-15. At these redshifts, the mid infrared wavelength domain gets in particular interesting, because it covers the rest-frame optical and near infrared wavelengths. Near infrared characteristics are also well suited to investigate key properties of host galaxies of active galactic nuclei (AGN), which constitute part II of my thesis. The study of host galaxies of quasi-stellar objects (QSO) is handicapped by the bright nucleus outshining its host, even with state-of-the-art telescopes. Untangling the host from the nucleus is easier for closer AGN, and in the near infrared wavelengths, the contrast in spectral energy distributions of active nucleus and host galaxy favor the detection of the host. For these reasons, we have created a nearby type I AGN sample optimized for near infrared studies, with a redshift limit of z<0.06. Chapter 4 gives a short introduction to the background motivating the selection of this sample. In Chapter 5, I present large scale, near infrared, seeing limited slit spectroscopy and imaging of nine of these AGN, carried out with ISAAC, mounted at the very large telescope (VLT) of the European Southern Observatory. Hydrogen recombination lines are observed in seven of the nine sources of which five show a broad component. In three sources, extended 1-0S(1) rotational-vibrational molecular hydrogen emission is detected. Stellar CO absorption is seen in four sources. In one of these objects, an upper limit of the central mass can be determined from the stellar velocity field. H- and Ks-band imaging allow me to determine the morphology class of the host galaxies. Colors (with supplementary J-band 2micron all sky survey images) show that the four galaxies with detected CO absorption are characterized by an overall strong stellar contribution. After removal of the nuclear point source, the host galaxies show colors typical for non-active spiral galaxies. In chapter 6, I analyze the central kiloparsec of another source included in this sample, HE 0036-5133, using adaptive optics and SINFONI, the integral field near infrared spectrograph of the VLT. This source is mostly famous for its extremely soft X-ray radiation and an X-ray outburst detected during the ROSAT all sky survey in 1990. With the help of different extinction maps and equivalent widths of various stellar absorption lines, the data reveals a deeply hidden nuclear bar and enhanced nuclear star formation, but no prominent sign of extreme QSO-like nuclear activity. In addition, the data supports that the origin of the soft X-ray core is caused by an absent hard X-ray source, rather than a deeply embedded hard X-ray source
