Spatial Variation of Stellar Ages in GASP Galaxies Observed with MUSE.

The question of how and where galaxies build up their mass over time by converting their gas into stars is key to the understanding of galaxy evolution. In the hierarchical model of galaxy evolution, galaxies are thought to build their mass through inside-out growth (negative age gradients). This theoretical picture is widely supported for high-mass galaxies. However, in low-mass disk galaxies, star formation is seen to proceed through outside-in growth (positive age gradients) or equally at all radii (flat-gradients). The GASP program provides high-quality integral field spectroscopic data observed with MUSE, which can be used to investigate this issue. GASP is an ESO large program that was awarded 120 hours to observe 114 galaxies at z 0.04-0.1, with MUSE. This thesis probes 34 regular and undisturbed GASP galaxies, with the aim to study the spatially resolved star formation history (SFH) and the connection of the stellar mass growth to the global and spatially resolved galactic properties. It improves upon the current research in this field by quantifying the rate at which mass is being built from star formation by estimating the agegradients and thus being able to differentiate between the inside-out and outside-in scenarios. A transition of growth mechanism is witnessed from outside-in to inside-out as the stellar mass increases. A critical mass limit of M=1010:15 M⊙ is identified in agreement with previous studies beyond which only negative age-gradients are seen. These galaxies also comply with the downsizing argument indicating that more massive galaxies are also older. On disentangling the sample into galaxies with and without a bulge, both the luminosity-weighted and mass-weighted age gradients of galaxies with bulge are found to show a more negative correlation with respect to M, as compared to the entire sample. Contrary to this, the bulgeless galaxies show a positive correlation with respect to M. This work can be extended to the analysis of galaxies at different evolutionary phases which can thus help to form a complete picture of galaxy evolution.