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Published May 1, 2015 | Published + Submitted
Journal Article Open

The formation of massive, compact galaxies at z = 2 in the Illustris simulation

Abstract

Massive, quiescent galaxies at high redshift have been found to be considerably more compact than galaxies of similar mass in the local universe. How these compact galaxies formed has yet to be determined, though several progenitor populations have been proposed. Here we investigate the formation processes and quantify the assembly histories of such galaxies in Illustris, a suite of hydrodynamical cosmological simulations encompassing a sufficiently large volume to include rare objects, while simultaneously resolving the internal structure of galaxies. We select massive (∼10^(11) M_⊙) and compact (stellar half-mass radius <2 kpc) galaxies from the simulation at z = 2. Within the Illustris suite, we find that these quantities are not perfectly converged, but are reasonably reliable for our purposes. The resulting population is composed primarily of quiescent galaxies, but we also find several star-forming compact galaxies. The simulated compact galaxies are similar to observed galaxies in star formation activity and appearance. We follow their evolution at high redshift in the simulation and find that there are multiple pathways to form these compact galaxies, dominated by two mechanisms: (i) intense, centrally concentrated starbursts generally triggered by gas-rich major mergers between z ∼ 2–4, reducing the galaxies' half-mass radii by a factor of a few to below 2 kpc, and (ii) assembly at very early times when the universe was much denser; the galaxies formed compact and remained so until z ∼ 2.

Additional Information

© 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2015 February 11. Received 2015 January 20; in original form 2014 October 31. First published online March 17, 2015. SW is supported by the National Science Foundation Graduate Research Fellowship under grant number DGE1144152. LH acknowledges support from NASA grant NNX12AC67G and NSF grant AST-1312095. We thank Pascal Oesch for helpful discussions and guidance on generating the mock observations presented in this paper.

Attached Files

Published - MNRAS-2015-Wellons-361-72.pdf

Submitted - 1411.0667v3.pdf

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