Galaxies with Shells in the Illustris Simulation: Metallicity Signatures

Abstract

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 (${\mathrm{M}}_{200crit}>6\times 10^{12}{\mathrm{M}}_{\odot }$) 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 ${\mu }_{\mathrm{stars}}\gtrsim 1:10$). 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 $2$-$4{\mathrm{R}}_{\mathrm{eff}}$ 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.

15 pages, 5 figures. Article published in a special issue of MDPI Galaxies after the conference "On the Origin (and Evolution) of Baryonic Galaxy Halos", Galapagos Islands, 2017

References in corpus (13)

• Introducing the Illustris Project: Simulating the coevolution of dark and visible matter in the Universe
• Properties of galaxies reproduced by a hydrodynamic simulation
• Introducing the Illustris Project: the evolution of galaxy populations across cosmic time
• Tracing Galaxy Formation with Stellar Halos II: Relating Substructure in Phase- and Abundance-Space to Accretion Histories
• Spatially resolved spectroscopy of early-type galaxies over a range in mass
• The stellar accretion origin of stellar population gradients in massive galaxies at large radii
• P-MaNGA: Full spectral fitting and stellar population maps from prototype observations
• On feathers, bifurcations and shells: the dynamics of tidal streams across the mass scale
• The SLUGGS survey: Exploring the metallicity gradients of nearby early-type galaxies to large radii
• The build-up of the cD halo of M87 - evidence for accretion in the last Gyr
• Kinematics and simulations of the stellar stream in the halo of the Umbrella Galaxy
• The information content of stellar halos: Stellar population gradients and accretion histories in early-type Illustris galaxies
• Tracing the outer halo in a giant elliptical to 25 Reff

Cited by in corpus (3)

• Black hole mergers from dwarf to massive galaxies with the NewHorizon and Horizon-AGN simulations
• Remnants of recent mergers in nearby early-type galaxies and their classification
• NGC 474 as viewed with KCWI: diagnosing a shell galaxy