Abstract
Based on data from the SAGES Legacy Unifying Globulars and GalaxieS (SLUGGS) survey, I present results on the assembly pathways, dark matter content and halo growth of massive early-type galaxies. Using galaxy starlight information we find that such galaxies had an early dissipative phase followed by a second phase of halo growth from largely minor mergers (and in rare cases major mergers). Thus our result fits in well with the two-phase scenario of galaxy formation. We also used globular cluster radial velocities to measure the enclosed mass within 5 effective radii. The resulting dark matter fractions reveal a few galaxies with very low dark matter fractions that are not captured in the latest cosmological models. Multiple solutions are possible, but none yet is convincing. Translating dark matter fractions into epochs of halo assembly, we show that low mass galaxies tend to grow via gas-rich accretion, while high mass galaxies grow via gas-poor mergers.
Highlights
Assembly PathwaysThe SAGES Legacy Unifying Globulars and GalaxieS (SLUGGS) survey (Brodie et al 2014) [1] is studying 25 nearby, massive (log stellar mass ∼11), early-type galaxies
Survey, I present results on the assembly pathways, dark matter content and halo growth of massive early-type galaxies
Translating dark matter fractions into epochs of halo assembly, we show that low mass galaxies tend to grow via gas-rich accretion, while high mass galaxies grow via gas-poor mergers
Summary
The SAGES Legacy Unifying Globulars and GalaxieS (SLUGGS) survey (Brodie et al 2014) [1] is studying 25 nearby, massive (log stellar mass ∼11), early-type galaxies. They are radial lambda (spin) profiles, 2D kinematic maps and higher order velocity moments h3 and h4 vs V/σ Using these 3 diagnostics (see Figure 2 for examples) we have classified each galaxy into a Nabb et al assembly class. Phase, at high redshift, is a dissipative one that results insimulations the in-situ formation of a compact, massive coreThe (redfirst nugget) redshift, is a and dissipative one that inphase, the in-situ formation of a compact, massive core Inresults he second after redshift z ∼2, growth is dominated by accretion from nugget) and minor or mergers phase, which leads to redshift the formation galaxy halo. Profiles, 2D kinematic maps and higher order velocity moments h3 and h4 vs V/σ
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