# Hierarchical formation of bulgeless galaxies: why outflows have low angular momentum - Zurich Open Repository and Archive

Brook, C B; Governato, F; Roskar, R; Stinson, G; Brooks, A M; Wadsley, J; Quinn, T; Gibson, B K; Snaith, O; Pilkington, K; House, E; Pontzen, A (2011). Hierarchical formation of bulgeless galaxies: why outflows have low angular momentum. Monthly Notices of the Royal Astronomical Society, 415(2):1051-1060.

## Abstract

Using high resolution, fully cosmological smoothed particle hydrodynamical simulations of dwarf galaxies in a Lambda cold dark matter Universe, we show how high redshift gas outflows can modify the baryon angular momentum distribution and allow pure disc galaxies to form. We outline how galactic outflows preferentially remove low angular momentum material due a combination of (a) star formation peaking at high redshift in shallow dark matter potentials, an epoch when accreted gas has relatively low angular momentum, (b) the existence of an extended reservoir of high angular momentum gas in the outer disc to provide material for prolonged SF at later times and (c) the tendency for outflows to follow the path of least resistance which is perpendicular to the disc. We also show that outflows are enhanced during mergers, thus expelling much of the gas which has lost its angular momentum during these events, and preventing the formation of ‘classical’, merger driven bulges in low-mass systems. Stars formed prior to such mergers form a diffuse, extended stellar halo component similar to those detected in nearby dwarfs.

## Abstract

Using high resolution, fully cosmological smoothed particle hydrodynamical simulations of dwarf galaxies in a Lambda cold dark matter Universe, we show how high redshift gas outflows can modify the baryon angular momentum distribution and allow pure disc galaxies to form. We outline how galactic outflows preferentially remove low angular momentum material due a combination of (a) star formation peaking at high redshift in shallow dark matter potentials, an epoch when accreted gas has relatively low angular momentum, (b) the existence of an extended reservoir of high angular momentum gas in the outer disc to provide material for prolonged SF at later times and (c) the tendency for outflows to follow the path of least resistance which is perpendicular to the disc. We also show that outflows are enhanced during mergers, thus expelling much of the gas which has lost its angular momentum during these events, and preventing the formation of ‘classical’, merger driven bulges in low-mass systems. Stars formed prior to such mergers form a diffuse, extended stellar halo component similar to those detected in nearby dwarfs.

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## Additional indexing

Item Type: Journal Article, refereed, original work 07 Faculty of Science > Institute for Computational Science 530 Physics English April 2011 18 Feb 2012 19:57 05 Apr 2016 14:55 Wiley-Blackwell 0035-8711 (P) 1365-2966 (E) The definitive version is available at www3.interscience.wiley.com https://doi.org/10.1111/j.1365-2966.2011.18545.x http://arxiv.org/abs/1010.1004

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