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Galaxies with Shells in the Illustris Simulation: Metallicity Signatures

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Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA
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Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
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Max Planck Institute for Astrophysics, Karl-Schwarzschild-Strasse 1, D-85740 Garching, Germany
*
Author to whom correspondence should be addressed.
Academic Editors: Duncan A. Forbes and Ericson D. Lopez
Galaxies 2017, 5(3), 34; https://doi.org/10.3390/galaxies5030034
Received: 1 July 2017 / Revised: 28 July 2017 / Accepted: 1 August 2017 / Published: 4 August 2017
(This article belongs to the Special Issue On the Origin (and Evolution) of Baryonic Galaxy Halos)
Stellar shells are low surface brightness arcs of overdense stellar regions, extending to large galactocentric distances. In a companion study, we identified 39 shell galaxies in a sample of 220 massive ellipticals ( M 200 crit > 6 × 10 12 M ) from the Illustris cosmological simulation. We used stellar history catalogs to trace the history of each individual star particle inside the shell substructures, and we found that shells in high-mass galaxies form through mergers with massive satellites (stellar mass ratios μ stars 1 : 10 ). Using the same sample of shell galaxies, the current study extends the stellar history catalogs in order to investigate the metallicity of stellar shells around massive galaxies. Our results indicate that outer shells are often times more metal-rich than the surrounding stellar material in a galaxy’s halo. For a galaxy with two different satellites forming z = 0 shells, we find a significant difference in the metallicity of the shells produced by each progenitor. We also find that shell galaxies have higher mass-weighted logarithmic metallicities ([Z/H]) at 2– 4 R eff compared to galaxies without shells. Our results indicate that observations comparing the metallicities of stars in tidal features, such as shells, to the average metallicities in the stellar halo can provide information about the assembly histories of galaxies. View Full-Text
Keywords: cosmology: theory; galaxies: evolution; galaxies: interactions; galaxies: kinematics and dynamics; galaxies: structure; methods: numerical; stellar shells; stellar metallicities cosmology: theory; galaxies: evolution; galaxies: interactions; galaxies: kinematics and dynamics; galaxies: structure; methods: numerical; stellar shells; stellar metallicities
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Pop, A.-R.; Pillepich, A.; Amorisco, N.C.; Hernquist, L. Galaxies with Shells in the Illustris Simulation: Metallicity Signatures. Galaxies 2017, 5, 34.

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