Early-type galaxy density profiles from IllustrisTNG – III. Effects on outer kinematic structure

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 1.5Reff (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* ≥ 1011 M⊙ in TNG100-1. The mock observations reproduce the key outer (1.5Reff) kinematic structures in the MASSIVE ETGs, including the puzzling positive correlation between velocity dispersion profile outer slope γouter and the kurtosis h4’s gradient. We find that h4 is uncorrelated with stellar orbital anisotropy beyond Reff; instead we find that the variations in γouter and outer h4 (a good proxy for h4 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.

Kinematics of the diffuse intragroup and intracluster light in groups and clusters of galaxies in the local universe within 100 Mpc distance

“…On the other hand, kinematic studies of the most luminous ETGs (M K < −25.7; Veale et al, 2017) measuring h3 and h4 values out to two effective radii with extended IFS (the MASSIVE survey, Veale et al, 2017) or deep long-slit (Bender et al, 2015) data, found high mean values <h4 >≈ 0.05 at 2 Re while values at the centers are near-zero (e.g., van de Sande et al, 2017). The high h4 values correlate with increasing projected velocity profiles and both are likely caused by mass distributions increasing outwards faster than isothermal (Veale et al, 2018;Wang et al, 2022). We use this to interpret some of the IGL kinematic data below.…”

“…They also find that most slow rotators are radially anisotropic, whereas simulated fast rotator galaxies have both radially andtangentially biased anisotropy profiles. Wang et al (2022) studied the distribution of β values around 1.5 effective radii in ETGs from the TNG simulation (Springel et al, 2018). They find that galaxies with flat or rising outer velocity dispersion profiles are generally radially anisotropic, whereas galaxies with falling outer dispersion profiles can have a wide range of anisotropies at this fiducial radius.…”

X-ray scaling relations of early-type galaxies in IllustrisTNG and a new way of identifying backsplash objects

“…These improvements lead to more realistic predictions in terms of observed galaxy properties and demonstrates the capacity of IllustrisTNG to shed light on the underlying physical processes shaping these properties. Some of the comparison works with observations include the galaxy mass-metallicity relation (Torrey et al 2018(Torrey et al , 2019, the galaxy-color bimodality in the Sloan Digital Sky Survey (Nelson et al 2018), the intra-cluster metal distribution (Vogelsberger et al 2018), early-type galaxy total density profiles (Wang et al 2020), gas-phase metallicity gradients in star-forming galaxies (Hemler et al 2021), stellar orbital fraction and outer kinematic structure (Xu et al 2019;Wang et al 2022), optical morphologies of galaxies (Rodriguez-Gomez et al 2019), the size evolution of galaxies (Genel et al 2018), star formation activities and quenched fractions (Donnari et al 2019), spatially-resolved star formation in galaxies (Nelson et al 2021), the fraction of cool-core clusters (Barnes et al 2018), as well as AGN galaxy occupation and X-ray luminosities (Weinberger et al 2018;Habouzit et al 2019;Terrazas et al 2020), and predictions of high redshift galaxy luminosity functions for JWST (Vogelsberger et al 2020b). Although certain aspects of these predictions are still discrepant with observations, the broad agreement in many properties related to gas cycle, star formation, and feedback lends us generous predicative power to gain insights on the key factors that shape the X-ray scaling relations in ETGs.…”

“…Vogelsberger et al 2020a for a review). To further elucidate the origin of these ETG X-ray scaling relations, we use a legacy ETGs sample (Wang et al 2020) from the cosmological hydrodynamic simulation IllustrisTNG, which is an updated version of the Illustris Project (Vogelsberger et al 2014a,b;Genel et al 2014;Sijacki et al 2015;Nelson et al 2015), and that has well-studied density profile, stellar properties, and dark matter fractions (Lovell et al 2018;Wang et al 2019Wang et al , 2020Wang et al , 2022. Our work further extends the previous X-ray scaling relation studies using IllustrisTNG (e.g., X-ray scaling relations for star-forming and quenched galaxies: Truong et al 2020; the relation of black hole growth to CGM properties: Oppenheimer et al 2020;Truong et al 2021; X-ray scaling relations in galaxy groups and clusters: Pop et al 2022) by especially focusing on the formation mechanisms leading to the scatter at the low-mass-end.…”

On the Origin of the Variety of Velocity Dispersion Profiles of Galaxies

“…Advances in computational resources and simulation codes have enabled the emergence of large, high-resolution cosmological simulations with sophisticated subgrid prescriptions (e.g., Pillepich et al 2019;Tremmel et al 2019;Dubois et al 2021). Recent numerical simulations have successfully reproduced various observed trends in velocity dispersion profiles (e.g., Lu et al 2020;Pulsoni et al 2020;Wang et al 2022;Cannarozzo et al 2023). However, the full understanding of the physical processes that shape galaxy velocity dispersion remains limited.…”