35 research outputs found
Cosmological baryon transfer in the simba simulations
We present a framework for characterizing the large-scale movement of baryons relative to dark matter in cosmological simulations, requiring only the initial conditions and final state of the simulation. This is performed using the spread metric that quantifies the distance in the final conditions between initially neighbouring particles, and by analysing the baryonic content of final haloes relative to that of the initial Lagrangian regions (LRs) defined by their dark matter component. Applying this framework to the SIMBA cosmological simulations, we show that 40 per cent (10 per cent) of cosmological baryons have moved > 1 h−1 Mpc (3 h−1 Mpc) by z = 0, primarily due to entrainment of gas by jets powered by an active galactic nucleus, with baryons moving up to 12 h−1 Mpc away in extreme cases. Baryons decouple from the dynamics of the dark matter component due to hydrodynamic forces, radiative cooling, and feedback processes. As a result, only 60 per cent of the gas content in a given halo at z = 0 originates from its LR, roughly independent of halo mass. A typical halo in the mass range Mvir = 1012–1013 M only retains 20 per cent of the gas originally contained in its LR. We show that up to 20 per cent of the gas content in a typical Milky Way-mass halo may originate in the region defined by the dark matter of another halo. This inter-Lagrangian baryon transfer may have important implications for the origin of gas and metals in the circumgalactic medium of galaxies, as well as for semi-analytic models of galaxy formation and ‘zoom-in’ simulations
THESAN-HR: How does reionization impact early galaxy evolution?
Early galaxies were the radiation source for reionization, with the
photoheating feedback from the reionization process expected to reduce the
efficiency of star formation in low mass haloes. Hence, to fully understand
reionization and galaxy formation, we must study their impact on each other.
The THESAN project has so far aimed to study the impact of galaxy formation
physics on reionization, but here we present the new THESAN simulations with a
factor 50 higher resolution (~M) that aim to
self-consistently study the back-reaction of reionization on galaxies. By
resolving haloes with virial temperatures ~K, we are able
to demonstrate that simplistic, spatially-uniform, reionization models are not
sufficient to study early galaxy evolution. Comparing the self-consistent
THESAN model (employing fully coupled radiation hydrodynamics) to a uniform UV
background, we are able to show that galaxies in THESAN are predicted to be
larger in physical extent (by a factor ), less metal enriched (by ~dex), and less abundant (by a factor at ) by
. We show that differences in star formation and enrichment patterns lead
to significantly different predictions for star formation in low mass haloes,
low-metallicity star formation, and even the occupation fraction of haloes. We
posit that cosmological galaxy formation simulations aiming to study early
galaxy formation must employ a spatially inhomogeneous UV
background to accurately reproduce galaxy properties.Comment: Accepted for publication in MNRA
The THESAN project: Lyman-alpha emitter luminosity function calibration
The observability of Lyman-alpha emitting galaxies (LAEs) during the Epoch of
Reionization can provide a sensitive probe of the evolving neutral hydrogen gas
distribution, thus setting valuable constraints to distinguish different
reionization models. In this study, we utilize the new THESAN suite of
large-volume (95.5 cMpc) cosmological radiation-hydrodynamic simulations to
directly model the Ly emission from individual galaxies and the
subsequent transmission through the intergalactic medium. THESAN combines the
AREPO-RT radiation-hydrodynamic solver with the IllustrisTNG galaxy formation
model and includes high- and medium-resolution simulations designed to
investigate the impacts of halo-mass-dependent escape fractions, alternative
dark matter models, and numerical convergence. We find important differences in
the Ly transmission based on reionization history, bubble morphology,
frequency offset from line centre, and galaxy brightness. For a given global
neutral fraction, Ly transmission reduces when low mass haloes dominate
reionization over high mass haloes. Furthermore, the variation across
sightlines for a single galaxy is greater than the variation across all
galaxies. This collectively affects the visibility of LAEs, directly impacting
observed Ly luminosity functions (LFs). We employ Gaussian Process
Regression using SWIFTEmulator to rapidly constrain an empirical model for dust
escape fractions and emergent spectral line profiles to match observed LFs. We
find that dust strongly impacts the Ly transmission and covering
fractions of
haloes, such that the dominant mode of removing Ly photons in non-LAEs
changes from low IGM transmission to high dust absorption around .Comment: 20 pages, 18 figures, MNRAS, in press. Please visit
www.thesan-project.com for more detail
EAGLE-like simulation models do not solve the entropy core problem in groups and clusters of galaxies
Recent high-resolution cosmological hydrodynamic simulations run with a variety of codes systematically predict large amounts of entropy in the intra-cluster medium at low redshift, leading to flat entropy profiles and a suppressed cool-core population. This prediction is at odds with X-ray observations of groups and clusters. We use a new implementation of the EAGLE galaxy formation model to investigate the sensitivity of the central entropy and the shape of the profiles to changes in the sub-grid model applied to a suite of zoom-in cosmological simulations of a group of mass M500 = 8.8 × 1012 M⊙ and a cluster of mass 2.9 × 1014 M⊙. Using our reference model, calibrated to match the stellar mass function of field galaxies, we confirm that our simulated groups and clusters contain hot gas with too high entropy in their cores. Additional simulations run without artificial conduction, metal cooling or active galactic nuclei (AGN) feedback produce lower entropy levels but still fail to reproduce observed profiles. Conversely, the two objects run without supernova feedback show a significant entropy increase which can be attributed to excessive cooling and star formation. Varying the AGN heating temperature does not greatly affect the profile shape, but only the overall normalization. Finally, we compared runs with four AGN heating schemes and obtained similar profiles, with the exception of bipolar AGN heating, which produces a higher and more uniform entropy distribution. Our study leaves open the question of whether the entropy core problem in simulations, and particularly the lack of power-law cool-core profiles, arise from incorrect physical assumptions, missing physical processes, or insufficient numerical resolution
X-ray scaling relations of early-type galaxies in IllustrisTNG and a new way of identifying backsplash objects
We investigate how feedback and environment shapes the X-ray scaling
relations of early-type galaxies (ETGs), especially at the low-mass end. We
select central-ETGs from the IllustrisTNG-100 box that have stellar masses
. We derive mock X-ray
luminosity () and spectroscopic-like temperature
() of hot gas within of the ETG haloes using
the MOCK-X pipeline. The scaling between and the total
mass within 5 effective radii () agrees well with observed ETGs
from Chandra. IllustrisTNG reproduces the observed increase in scatter of
towards lower masses, and we find that ETGs with
with
above-average experienced systematically lower cumulative
kinetic AGN feedback energy historically (vice versa for below-average ETGs).
This leads to larger gas mass fractions and younger stellar populations with
stronger stellar feedback heating, concertedly resulting in the above-average
. The --
relation shows a similar slope to the observed ETGs but the simulation
systematically underestimates the gas temperature. Three outliers that lie far
below the -- relation all interacted with larger galaxy
clusters recently and demonstrate clear features of environmental heating. We
propose that the distinct location of these backsplash ETGs in the -- plane could provide a new way of identifying backsplash
galaxies in future X-ray surveys.Comment: 16 pages, 10 figures. Submitted to MNRA
The impact of stochastic modeling on the predictive power of galaxy formation simulations
All modern galaxy formation models employ stochastic elements in their
sub-grid prescriptions to discretise continuous equations across the time
domain. In this paper, we investigate how the stochastic nature of these
models, notably star formation, black hole accretion, and their associated
feedback, that act on small ( kpc) scales, can back-react on macroscopic
galaxy properties (e.g. stellar mass and size) across long ( Gyr)
timescales. We find that the scatter in scaling relations predicted by the
EAGLE model implemented in the SWIFT code can be significantly impacted by
random variability between re-simulations of the same object, even when
galaxies are resolved by tens of thousands of particles. We then illustrate how
re-simulations of the same object can be used to better understand the
underlying model, by showing how correlations between galaxy stellar mass and
black hole mass disappear at the highest black hole masses (
M), indicating that the feedback cycle may be interrupted by external
processes. We find that although properties that are collected cumulatively
over many objects are relatively robust against random variability (e.g. the
median of a scaling relation), the properties of individual galaxies (such as
galaxy stellar mass) can vary by up to 25\%, even far into the well-resolved
regime, driven by bursty physics (black hole feedback) and mergers between
galaxies. We suggest that studies of individual objects within cosmological
simulations be treated with caution, and that any studies aiming to closely
investigate such objects must account for random variability within their
results.Comment: Accepted for publication in MNRA