Early-type galaxy density profiles from IllustrisTNG – III. Effects on outer kinematic structure. Issue 4 (19th May 2022)

• Record Type: Journal Article
• Authors: Wang, Yunchong; Mao, Shude; Vogelsberger, Mark; Springel, Volker; Hernquist, Lars; Wechsler, Risa H
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 513:Issue 4(2022)
• Page Start: 6134
• Page End: 6151
• Publication Date: 2022-05-19
• Subjects: galaxies: elliptical and lenticular, cD -- galaxies: evolution -- galaxies: kinematics and dynamics -- galaxies: structure -- methods: numerical; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stac1375
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: Early-type galaxies (ETGs) possess total density profiles close to isothermal, which can lead to non-Gaussian line-of-sight velocity dispersion (LOSVD) under anisotropic stellar orbits. However, recent observations of local ETGs in the MASSIVE Survey reveal outer kinematic structures at 1.5 R eff (effective radius) that are inconsistent with fixed isothermal density profiles; the authors proposed varying density profiles as an explanation. We aim to verify this conjecture and understand the influence of stellar assembly on these kinematic features through mock ETGs in IllustrisTNG. We create mock Integral-Field-Unit observations to extract projected stellar kinematic features for 207 ETGs with stellar mass $M_{\ast }\geqslant 10^{11} \, \mathrm{M_{\odot}}$ in TNG100-1. The mock observations reproduce the key outer (1.5 R eff ) kinematic structures in the MASSIVE ETGs, including the puzzling positive correlation between velocity dispersion profile outer slope γouter and the kurtosis h 4 's gradient. We find that h 4 is uncorrelated with stellar orbital anisotropy beyond R eff ; instead, we find that the variations in γouter and outer h 4 (a good proxy for h 4 gradient) are both driven by variations of the density profile at the outskirts across different ETGs. These findings corroborate the proposed conjecture and rule out velocity anisotropy as the origin of non-Gaussian outer kinematic structure in ETGs. We also find that the outer kurtosis and anisotropy correlate with different stellar assembly components, with the former related to minor mergers or flyby interactions while the latter is mainly driven by major mergers, suggesting distinct stellar assembly origins that decorrelates the two quantities.