The SLUGGS Survey: The Assembly Histories of Individual Early-type Galaxies

Abstract

Early-type (E and S0) galaxies may have assembled via a variety of different evolutionary pathways. Here we investigate these pathways by comparing the stellar kinematic properties of 24 early-type galaxies from the SLUGGS survey with the hydrodynamical simulations of Naab et al. (2014). In particular, we use the kinematics of starlight up to 4 effective radii (R${}_e$) as diagnostics of galaxy inner and outer regions, and assign each galaxy to one of six Naab et al. assembly classes. The majority of our galaxies (14/24) have kinematic characteristics that indicate an assembly history dominated by gradual gas dissipation and accretion of many gas-rich minor mergers. Three galaxies, all S0s, indicate that they have experienced gas-rich major mergers in their more recent past. One additional elliptical galaxy is tentatively associated with a gas-rich merger which results in a remnant galaxy with low angular momentum. Pathways dominated by gas-poor (major or minor) mergers dominate the mass growth of six galaxies. Most SLUGGS galaxies appear to have grown in mass (and size) via the accretion of stars and gas from minor mergers, with late major mergers playing a much smaller role. We find that the fraction of accreted stars correlates with the stellar mean age and metallicity gradient, but not with the slope of the total mass density profile. We briefly mention future observational and modelling approaches that will enhance our ability to accurately reconstruct the assembly histories of individual present day galaxies.

17 pages, 10 figures, MNRAS in press

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Cited by in corpus (20)

• The SAMI Galaxy Survey: Revisiting Galaxy Classification Through High-Order Stellar Kinematics
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• The SLUGGS Survey: Dark matter fractions at large radii and assembly epochs of early-type galaxies from globular cluster kinematics
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• Mass of the dynamically hot inner stellar halo predicts the ancient accreted stellar mass
• Galaxy Zoo: major galaxy mergers are not a significant quenching pathway
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• The SLUGGS survey: Using extended stellar kinematics to disentangle the formation histories of low mass S0 galaxies
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