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

By S. Wellons, P. Torrey, Chung-Pei Ma, V. Rodriguez-Gomez, M. Vogelsberger, M. Kriek, P. V. van Dokkum, E. Nelson, Shy Genel, A. Pillepich and 6 more. 2014

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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.

Subfields: Astronomy and Astrophysics, Instrumentation, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/eabd3807a25c76da4705d43c83d05d1e74e0f20b

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Citations in the corpus

The Horizon-AGN Simulation: Morphological Diversity of Galaxies ,Promoted by AGN Feedback (2016, background): “…the mergers to be efficient enough to turn the remnant into an elliptical galaxy and increase its size, it needs to be dissipation-less, i.e. contain a low amount of cold star-forming gas, or, otherwise will decrease the galaxy size (Khochfar & Silk 2006; Wellons et al. 2015; Welker et al. 2015a).”
Size evolution of normal and compact galaxies in the EAGLE simulation (2015, methodology): “Recently, the theoretical study of Wellons et al. (2015a) considered the evolution of compact galaxies identified in the ILLUSTRIS simulation, using the Barro et al. (2013) criterion for compactness (transformed to a 3D radius), R50/(M∗/1011 M )0.75 < 4.5.”
MOSFIRE Spectroscopy of Quiescent Galaxies at 1.5 < z < 2.5. II. Star Formation Histories and Galaxy Quenching (2018, background): “The alternative possibility is that these systems formed at very high redshift, when star-forming disks were significantly smaller, and then evolved passively retaining their compact structures (Wellons et al. 2015).”
The size evolution of star-forming and quenched galaxies in the IllustrisTNG simulation (2017, methodology): “Although galaxy size evolution was studied using that simulation in certain regimes (Wellons et al. 2015, 2016), this offset precluded a reliable study of the size evolution of galaxies as a whole.”
FORMING COMPACT MASSIVE GALAXIES (2015, background): “5 of Wellons et al. (2015).”
Near infrared spectroscopy and star-formation histories of 3 ≤ z ≤ 4 quiescent galaxies (2018, background): “Given the box size of Illustris, this translates into an average number density at 3 z 4 of 2.1 × 10−6 Mpc−3, an order of magnitude too low.”