This PhD thesis is dedicated to the analysis of Herbig-Haro objects (HHs) in the central region of the Orion Nebula and their impact on the surrounding ionised gas. HHs are collimated gas jets ejected from protostars. Although their physical properties and excitation mechanism have been extensively studied in neutral gas clouds, those HHs immersed in HII regions have been less explored. The study of these latter HHs require the use of high spectral resolution spectroscopy in order to separate their emission from the strong nebular background, using their Doppler shift. In this work, we mainly use high spectral resolution spectra from the Ultraviolet and Visual Echelle Spectrograph (UVES) of the Very Large Telescope (VLT) and high spatial resolution Hubble Space Telescope (HST) imaging. We focus on HH529II, HH529III, HH204 and HH514, located at different distances from the main ionising star of the Orion Nebula, theta1 Ori C, and showing different apparent propagation velocities. Our theoretical and observational analysis confirms that photoionisation is the main excitation mechanism of these HHs, in contrast with their counterparts immersed in neutral gas clouds, which are excited by shock heating. This fact allowed us to analyse the selected sample of HHs as small-scale HII regions. Therefore, we were able to determine their physical properties, kinematics and chemical abundances with an unprecedented detail. With the HST imaging and kinematic data, we determined the three-dimensional trajectories of these HHs, locating their possible origin within the star-forming areas of the Orion Nebula. The local impact of HHs on the photoionised gas is important, since they strongly increase the local density and decrease the degree of ionisation. These phenomena have an important impact on the chemical abundances obtained in limited regions of the Orion Nebula when intermediate or low spectral resolution spectra are used and the different kinematic components can not be resolved. The results of this thesis have been published in a series of three articles in the peer-reviewed scientific journals Monthly Notices of the Royal Astronomical Society and The Astrophysical Journal. These papers are presented as separate sections of this PhD Thesis.
José Eduardo Méndez Delgado