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Radial variation of the initial mass function and other stellar population parameters in early-type galaxies

Mensinga, G. (2016) Radial variation of the initial mass function and other stellar population parameters in early-type galaxies. Master's Thesis / Essay, Astronomy.

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We investigate the radial behaviour of the low-mass slope of the Initial Mass Function (IMF) and other stellar population parameters (metallicity, α-abundance, stellar age, and sodium abundance) in 17 Early-Type Galaxies (ETGs) provided by the CALIFA survey. For each system we construct four elliptical annuli with different apertures and distance from the centre, to determine radial gradients. The stellar population parameters are extracted by comparing several Lick/IDS indices with single stellar population models using χ2 statistics. Our main results are: 1) an IMF-σ relation and relations with σ in general are only loosely present or absent in our data. This is in disagreement with previously published results, most likely because we use spatially-resolved data and the σ relations are all reported in unresolved data; 2) a tight relation exists between IMF and metallicity, where to a higher metallicity corresponds a larger dwarf-to-giant ratio; 3) a tight relation exists between the gradients of the IMF and metallicity. The metallicity gradient is influenced by the merging history of ETGs, where shallower metallicity gradients imply a history of major merging events. The IMF slope is equally dependent on the merging history; 4) steep IMF slopes in the centres coincide with young stellar populations in the centre. These results fit in a two-phase IMF scenario. During the first star-forming phase a top-heavy IMF produces giant stars which die quickly and inject the interstellar medium with metals. The rise in metallicity causes later star-formation events to follow a more bottom-heavy IMF. Furthermore, we determine the mean radial trends of the stellar population parameters for the galaxies in our sample. We find that a) galaxies are more bottom-heavy in the centre and shallows to sub-Salpeter at 1 Reff , b) the metallicity declines radially with an average of -0.21 dex, and c) galaxies with young centres grow radially older whereas galaxies with old centres show no radial age gradients. We conclude that the IMF varies within ETGs and depends mainly on metallicity and the merging history of the system. Metallicity might be a promising new parameter by which we can infer the IMF of a galaxy.

Item Type: Thesis (Master's Thesis / Essay)
Degree programme: Astronomy
Thesis type: Master's Thesis / Essay
Language: English
Date Deposited: 15 Feb 2018 08:25
Last Modified: 15 Feb 2018 08:25

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