Journal Article

An <i>N</i>-body/SPH study of isolated galaxy mass density profiles

Kelly Foyle, Stéphane Courteau and Robert J. Thacker

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 386, issue 4, pages 1821-1844
Published in print June 2008 | ISSN: 0035-8711
Published online April 2008 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2008.13201.x
An N-body/SPH study of isolated galaxy mass density profiles

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We investigate the evolution of mass density profiles in secular disc galaxy models, paying special attention to the development of a two-component profile from a single initial exponential disc free of cosmological evolution (i.e. no accretion or interactions). As the source of density profile variations, we examine the parameter space of the spin parameter, halo concentration, virial mass, disc mass and bulge mass, for a total of 162 simulations in the context of a plausible model of star formation and feedback. The isolated galaxy models are based on the method of Springel & White and were evolved using the N-body/SPH code gadget-2. The initially pure exponential discs have a minimum of 1.4 million particles and most models were evolved over a period of 10 Gyr. We find that the slope of the outer density profile is in close agreement with that of the initial profile and remains stable over time, whereas the inner density profile slope evolves considerably as a result of angular momentum redistribution. The evolution of the galaxy mass density profile, including the development of a two-component profile with an inner and outer segment, is controlled by the ratio of the disc mass fraction, md, to the halo spin parameter, λ. The location of the break between the two components and speed at which it develops is directly proportional to md/λ; the amplitude of the transition between the inner and outer regions is however controlled by the ratio of halo concentration to virial velocity. The location of the divide between the inner and outer profile does not change with time. The condition for a two-component profile is roughly md/λ≥ 1. While the development of a two-component density profile is coupled to bar formation, not all barred galaxies develop a two-component profile. A galaxy model showing a clear minimum Toomre Q, normally linked to a double exponential in the stellar profile, may never exhibit any two-component feature thus yielding a fully evolved pure exponential disc.

Keywords: methods: numerical; galaxies: kinematics and dynamics; galaxies: spiral

Journal Article.  14909 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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