The shape of the ionised gas abundance distribution in spiral galaxies

Abstract

The study of the gas-phase chemical composition of spiral galaxies has proven to be a powerful tool to improve our knowledge on the evolution of these complex systems. In particular, the analysis of Hii regions (regions of ionised gas associated with star formation) is of great importance, as it is through the birth and death of stars that the galaxies chemically evolve. In this thesis we use two sets of high-quality integral field spectroscopic (IFS) data from two different surveys, CALIFA and AMUSING, to characterise the oxygen abundance distribution of the ionised gas in star-forming (SF) regions of spiral galaxies. The first survey provides a sample of 122 disc galaxies extracted from a well-defined, statistically significant mother sample, representative of galaxies in the Local Universe. The latter provides a sample of 102 galaxies that allows us to complement the study based on CALIFA data using a higher spatial resolution dataset. The abundance distribution of the analysed galaxies is determined based on the O3N2 strong-line indicator (although others are also tested). To measure the emission lines involved we apply FIT3D, an extensively tested code designed to deal with spatially resolved IFS data. The study of the 2-dimensional (2D) ionised gas abundance distribution is addressed by analysing separately the radial and azimuthal trends. The large number of SF regions provided by both analysed samples, together with the good coverage of the galaxy discs with high spatial resolution, allow us to undertake this study as never done before. To sum up, this thesis comprises the most complete 2D characterisation of the oxygen abundance distribution of the ionised gas in a large and statistically significant sample of spiral galaxies up to date. We show that this distribution display a wide range of features such as inner drops, outer flattenings, and azimuthal variations, as opposed to the simplistic view of a single radial decline. These features display clear trends with galaxy properties such as spiral structure, mass, or bar presence. These results provide strong constraints to chemical evolution models aimed at explaining the formation and evolution of spiral galaxies, trying to do our bit in the comprehension of the Universe around us.