Journal Article

Hierarchical formation of bulgeless galaxies: why outflows have low angular momentum

C. B. Brook, F. Governato, R. Roškar, G. Stinson, A. M. Brooks, J. Wadsley, T. Quinn, B. K. Gibson, O. Snaith, K. Pilkington, E. House and A. Pontzen

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 415, issue 2, pages 1051-1060
Published in print August 2011 | ISSN: 0035-8711
Published online July 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.18545.x
Hierarchical formation of bulgeless galaxies: why outflows have low angular momentum

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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.

Keywords: galaxies: bulges; galaxies: evolution; galaxies: formation; galaxies: starburst

Journal Article.  8611 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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