Galáxias Anãs com Linhas de Emissão Largas

Abstract

In this work, we present the results of a kinematic study of two metal poor HII galaxies which show a broad component in their emission lines(SDSS J1047+0739 and MRK996), using the Near Infrared Integral Field Spectrograph (NIFS) from the Gemini North. The presence of broad componentes in their permitted emission lines is uncommon for typical HII galaxies. The main objective of this work is to analyse the origin of the broad line emission, and to investigate whether they arise from a thermal process or not. Specifically, we investigated if the line emission from both galaxies is related to star formation, or if they are active galaxies. Active galaxies are usually thought to be metal rich, with the metallicity ranging from solar to super solar. Consequently, another point investigated is whether there exist active galaxies with low metallicity. There is very little literature on this subject. Our kinematic study of these galaxies consists of analysing the phenomelogy observed in their radial velocity and velocity dispersion maps, derived from our integral field spectroscopy (IFU). Besides that, we also used PCA tomography, a technique that is not common-place yet. This technique explores the data cubes in an alternative statistical way to finding uncorrelated efficient information, not detected directly with classical imaging or spectroscopic analysis. Both galaxies present unresolved nuclei in the scale of hundreds of parsecs. Besides that, the permitted emission line wings come from this unresolved nuclear region. From the analysis of the maps, we can distinguish two regions, one with broad lines in the nuclear region, and region of smaller density around the nuclear region. These two regions present different kinematic properties. The two galaxies are similar in the fact that both present an unresolved nucleus, and also because their broad broad line emission exist only in the nucleus. There seems to be indication of nuclear outflows that can be originated from either the presence of an AGN or due to massive stars in a Wolf-Rayet phase. Our results favor the interpretation of the motions being due to WR stars in the case of Mrk 996, but cannot rule out the AGN interpretation, particularly in the case of J1047+0739 where no other evidence of the presence of WR stars is seen. This type of galaxies where broad permitted lines are seen in their optical spectra, and in some case high ionization lines are observed, but a low mass and metal content is derived, deserves more attention. Further searches for active nuclei in dwarf galaxies can provide unique constraints on the demographics of black holes in the mass range below 10^6 M(sun).