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Global structure and kinematics of stellar haloes in cosmological hydrodynamic simulations

McCarthy, IG and Font, AS and Crain, RA and Deason, AJ and Schaye, J and Theuns, T (2012) Global structure and kinematics of stellar haloes in cosmological hydrodynamic simulations. Monthly Notices of the Royal Astronomical Society, 420 (3). pp. 2245-2262. ISSN 0035-8711

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We use the Galaxies–Intergalactic Medium Interaction Calculation (GIMIC) suite of cosmological hydrodynamical simulations to study the global structure and kinematics of stellar spheroids of Milky Way mass disc galaxies. Font et al. have recently demonstrated that these simulations are able to successfully reproduce the satellite luminosity functions and the metallicity and surface brightness profiles of the spheroids of the Milky Way and M31. A key to the success of the simulations is a significant contribution to the spheroid from stars that formed in situ. While the outer halo is dominated by accreted stars, stars formed in the main progenitor of the galaxy dominate at r≲ 30 kpc. In the present study, we show that this component was primarily formed in a protodisc at high redshift and was subsequently liberated from the disc by dynamical heating associated with mass accretion. As a consequence of its origin, the in situ component of the spheroid has different kinematics (namely net prograde rotation with respect to the disc) than that of the spheroid component built from the disruption of satellites. In addition, the in situ component has a flattened distribution, which is due in part to its rotation. We make comparisons with measurements of the shape and kinematics of local galaxies, including the Milky Way and M31, and stacked observations of more distant galaxies. We find that the simulated disc galaxies have spheroids of the correct shape (oblate with a median axial ratio of ∼0.6 at radii of ≲30 kpc, but note there is significant system-to-system scatter in this quantity) and that the kinematics show evidence for two components (due to in situ versus accreted), as observed. Our findings therefore add considerable weight to the importance of dissipative processes in the formation of stellar haloes and to the notion of a ‘dual stellar halo’.

Item Type: Article
Additional Information: This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astronomical Soceity following peer review. The version of record MNRAS (2012) 420 (3), pp 2245-2262 is available online at: http://dx.doi.org/10.1111/j.1365-2966.2011.20189.x
Uncontrolled Keywords: 0201 Astronomical And Space Sciences
Subjects: Q Science > QB Astronomy
Divisions: Astrophysics Research Institute
Publisher: Oxford University Press
Related URLs:
Date Deposited: 11 Feb 2015 15:28
Last Modified: 17 Apr 2015 13:31
DOI or Identification number: 10.1111/j.1365-2966.2011.20189.x
URI: http://researchonline.ljmu.ac.uk/id/eprint/445

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