# Galactic angular momentum in cosmological zoom-in simulations. I. disk and bulge components and the galaxy–halo connection

Sokołowska, Aleksandra; Capelo, Pedro R; Fall, S. Michael; Mayer, Lucio; Shen, Sijing; Bonoli, Silvia (2017). Galactic angular momentum in cosmological zoom-in simulations. I. disk and bulge components and the galaxy–halo connection. The Astrophysical Journal, 835(2):289.

## Abstract

We investigate the angular momentum evolution of four disk galaxies residing in Milky-Way–sized halos formed in cosmological zoom-in simulations with various sub-grid physics and merging histories. We decompose these galaxies, kinematically and photometrically, into their disk and bulge components. The simulated galaxies and their components lie on the observed sequences in the j *–M * diagram, relating the specific angular momentum and mass of the stellar component. We find that galaxies in low-density environments follow the relation ${j}_{* }\,\propto \,{M}_{* }^{\alpha }$ past major mergers, with $\alpha \sim 0.6$ in the case of strong feedback, when bulge-to-disk ratios are relatively constant, and $\alpha \sim 1.4$ in the other cases, when secular processes operate on shorter timescales. We compute the retention factors (i.e., the ratio of the specific angular momenta of stars and dark matter) for both disks and bulges and show that they vary relatively slowly after averaging over numerous but brief fluctuations. For disks, the retention factors are usually close to unity, while for bulges, they are a few times smaller. Our simulations therefore indicate that galaxies and their halos grow in a quasi-homologous way.

## Abstract

We investigate the angular momentum evolution of four disk galaxies residing in Milky-Way–sized halos formed in cosmological zoom-in simulations with various sub-grid physics and merging histories. We decompose these galaxies, kinematically and photometrically, into their disk and bulge components. The simulated galaxies and their components lie on the observed sequences in the j *–M * diagram, relating the specific angular momentum and mass of the stellar component. We find that galaxies in low-density environments follow the relation ${j}_{* }\,\propto \,{M}_{* }^{\alpha }$ past major mergers, with $\alpha \sim 0.6$ in the case of strong feedback, when bulge-to-disk ratios are relatively constant, and $\alpha \sim 1.4$ in the other cases, when secular processes operate on shorter timescales. We compute the retention factors (i.e., the ratio of the specific angular momenta of stars and dark matter) for both disks and bulges and show that they vary relatively slowly after averaging over numerous but brief fluctuations. For disks, the retention factors are usually close to unity, while for bulges, they are a few times smaller. Our simulations therefore indicate that galaxies and their halos grow in a quasi-homologous way.

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## Additional indexing

Item Type: Journal Article, refereed, original work 07 Faculty of Science > Institute for Computational Science 530 Physics English 2 February 2017 09 Jan 2018 21:48 19 Feb 2018 09:32 IOP Publishing 1538-4357 Green Publisher DOI. An embargo period may apply. https://doi.org/10.3847/1538-4357/835/2/289

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