Abstract
We study the stellar angular momentum of thousands of galaxies in the Illustris cosmological simulation, which captures gravitational and gas dynamics within galaxies, as well as feedback from stars and black holes. We find that the angular momentum of the simulated galaxies matches observations well, and in particular two distinct relations are found for late-type versus early-type galaxies. The relation for late-type galaxies corresponds to the value expected from full conservation of the specific angular momentum generated by cosmological tidal torques. The relation for early-type galaxies corresponds to retention of only ~30% of that, but we find that those early-type galaxies with low angular momentum at z=0 nevertheless reside at high redshift on the late-type relation. Some of them abruptly lose angular momentum during major mergers. To gain further insight, we explore the scaling relations in simulations where the galaxy formation physics is modified with respect to the fiducial model. We find that galactic winds with high mass-loading factors are essential for obtaining the high angular momentum relation typical for late-type galaxies, while AGN feedback largely operates in the opposite direction. Hence, feedback controls the stellar angular momentum of galaxies, and appears to be instrumental for establishing the Hubble sequence.
Highlights
The angular momentum content of a galaxy, which correlates with galaxy mass and type, is one of its primary properties
In this Letter, we study the angular momentum of thousands of galaxies in a set of cosmological hydrodynamical simulations
We study the angular momentum content of galaxies in the Illustris simulation
Summary
The angular momentum content of a galaxy, which correlates with galaxy mass and type, is one of its primary properties. Within the ΛCDM paradigm, the angular momentum J of dark matter halos, expressed using the “spin parameter” λ ≡ J E GM 5 3, with E representing energy and M mass, is robustly measured in N-body simulations, having a typical value of λ ≈ 0.034 (e.g., Bett et al 2007). In the “standard” theory of disk galaxy formation, baryons retain their specific angular momentum j ≡ J M as they collapse to halo centers (Fall & Efstathiou 1980; Mo et al 1998). There are, some reasons to question the generality of a simple relation between the angular momenta of galaxies and their dark halos (van den Bosch 2001; Vitvitska et al 2002; Bett et al 2010)
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