220 research outputs found
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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 hâ1 Mpc (3 hâ1 Mpc) by z = 0, primarily due to entrainment of gas by jets powered by an active galactic nucleus, with baryons moving up to 12 hâ1 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 = 1012â1013 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 âzoom-inâ simulations
Torque-Limited Growth of Massive Black Holes in Galaxies Across Cosmic Time
We combine cosmological hydrodynamic simulations with analytic models to
evaluate the role of galaxy-scale gravitational torques on the evolution of
massive black holes at the centers of star-forming galaxies. We confirm and
extend our earlier results to show that torque-limited growth yields black
holes and host galaxies evolving on average along the Mbh-Mbulge relation from
early times down to z = 0 and that convergence onto the scaling relation occurs
independent of the initial conditions and with no need for mass averaging
through mergers or additional self-regulation processes. Smooth accretion
dominates the long-term evolution, with black hole mergers with mass ratios
>1:5 representing typically a small fraction of the total growth. Winds from
the accretion disk are required to eject significant mass to suppress black
hole growth, but there is no need for coupling this wind to galactic-scale gas
to regulate black holes in a non-linear feedback loop. Torque-limited growth
yields a close-to-linear relation for the star formation rate and the black
hole accretion rate averaged over galaxy evolution time scales. However, the
SFR-AGN connection has significant scatter owing to strong variability of black
hole accretion at all resolved time scales. Eddington ratios can be described
by a broad lognormal distribution with median value evolving roughly as (1 +
z)^1.9, suggesting a main sequence for black hole growth similar to the cosmic
evolution of specific SFRs. Our results offer an attractive scenario consistent
with available observations in which cosmological gas infall and transport of
angular momentum in the galaxy by gravitational instabilities regulate the
long-term co-evolution of black holes and star-forming galaxies.Comment: 26 pages, 15 figures, replaced by published versio
Jet Feedback and the Photon Underproduction Crisis in Simba
We examine the impact of black hole jet feedback on the properties of the
low-redshift intergalactic medium (IGM) in the SIMBA simulation, with a focus
on the Ly forest mean flux decrement . Without jet feedback, we
confirm the Photon Underproduction Crisis (PUC) in which at
must be increased by over the Haardt & Madau value in order to
match the observed . Turning on jet feedback lowers this discrepancy to
, and additionally using the recent Faucher-Gigu\`ere
background mostly resolves the PUC, along with producing a flux probability
distribution function in accord with observations. The PUC becomes apparent at
late epochs () where the jet and no-jet simulations diverge; at
higher redshifts SIMBA reproduces the observed with no adjustment, with
or without jets. The main impact of jet feedback is to lower the cosmic baryon
fraction in the diffuse IGM from 39% to 16% at , while increasing the
warm-hot intergalactic medium (WHIM) baryon fraction from 30% to 70%; the
lowering of the diffuse IGM content directly translates into a lowering of
by a similar factor. Comparing to the older MUFASA simulation that
employs different quenching feedback but is otherwise similar to SIMBA, MUFASA
matches less well than SIMBA, suggesting that low-redshift measurements
of and could provide constraints on feedback
mechanisms. Our results suggest that widespread IGM heating at late times is a
plausible solution to the PUC, and that SIMBA's jet AGN feedback model,
included to quench massive galaxies, approximately yields this required
heating.Comment: 19 pages, 11 Figures, accepted to MNRA
Disappearing galaxies: the orientation dependence of JWST-bright, HST-dark, star-forming galaxy selection
Galaxies that are invisible in deep optical-NIR imaging but detected at
longer wavelengths have been the focus of several recent observational studies,
with speculation that they could constitute a substantial missing population
and even dominate the cosmic star formation rate density at . The
depths now achievable with JWST at the longest wavelengths probed by HST,
coupled with the transformative resolution at longer wavelengths, are already
enabling detailed, spatially-resolved characterisation of sources that were
invisible to HST, often known as `HST-dark' galaxies. However, until now, there
has been little theoretical work to compare against. We present the first
simulation-based study of this population, using highly-resolved galaxies from
the Feedback in Realistic Environments (FIRE) project, with multi-wavelength
images along several lines of sight forward-modelled using radiative transfer.
We naturally recover a population of modelled sources that meet commonly-used
selection criteria ( and
). These simulated HST-dark galaxies lie at high
redshifts (), have high levels of dust attenuation (), and
display compact recent star formation
(). Orientation is very
important: for all but one of the 17 simulated galaxy snapshots with HST-dark
sightlines, there exist other sightlines that do not meet the criteria. This
result has important implications for comparisons between observations and
models that do not resolve the detailed star-dust geometry, such as
semi-analytic models or coarsely-resolved hydrodynamical simulations.
Critically, we demonstrate that HST-dark sources are not an unexpected or
exotic population, but a subset of high-redshift, highly-dust-attenuated
sources viewed along certain lines of sight.Comment: 12 pages, 8 figures. Accepted for publication in Ap
Simba:The average properties of the circumgalactic medium of 2 †z †3 quasars are determined primarily by stellar feedback
We use the Simba cosmological hydrodynamic simulation suite to explore the
impact of feedback on the circumgalactic medium (CGM) and intergalactic medium
(IGM) around quasars. We identify quasars in Simba as the
most rapidly-accreting black holes, and show that they are well-matched in
bolometric luminosity and correlation strength to real quasars. We extract
Lyman-alpha (Ly-a) absorption in spectra passing at different transverse
distances (10 kpc 10 Mpc) around those quasars, and
compare to observations of the mean Ly-a absorption profile. The observations
are well reproduced, except within 100 kpc from the foreground quasar, where
Simba overproduces absorption; this could potentially be mitigated by including
ionisation from the quasar itself. By comparing runs with different feedback
modules activated, we find that (mechanical) AGN feedback has little impact on
the surrounding CGM even around these most highly luminous black holes, while
stellar feedback has a significant impact. By further investigating
thermodynamic and kinematic properties of CGM gas, we find that stellar
feedback, and not AGN feedback, is the primary physical driver in determining
the average properties of the CGM around quasars. We also compare
our results with previous works, and find that Simba predicts much more
absorption within 100 kpc than the Nyx and Illustris simulations, showing that
the Ly-a absorption profile can be a powerful constraint on simulations.
Instruments such as VLT-MUSE and upcoming surveys (e.g., WEAVE and DESI)
promise to further improve such constraints.Comment: Published in MNRAS. This is a pre-copyedited, author-produced PDF of
an article accepted for publication in MNRAS following peer review. The
version of record (Volume 499, Issue 2, December 2020, Pages 2760-2784) is
available online at:
https://academic.oup.com/mnras/article/499/2/2760/591800
Measuring dynamical masses from gas kinematics in simulated high-redshift galaxies
Advances in instrumentation have recently extended detailed measurements of gas kinematics to large samples of high-redshift galaxies. Relative to most nearby, thin disc galaxies, in which gas rotation accurately traces the gravitational potential, the interstellar medium (ISM) of z âł 1 galaxies is typically more dynamic and exhibits elevated turbulence. If not properly modelled, these effects can strongly bias dynamical mass measurements. We use high-resolution FIRE-2 cosmological zoom-in simulations to analyse the physical effects that must be considered to correctly infer dynamical masses from gas kinematics. Our analysis covers a range of galaxy properties from low-redshift Milky-Way-mass galaxies to massive high-redshift galaxies (Mâ > 10ÂčÂč Mâ at z = 1). Selecting only snapshots where a disc is present, we calculate the rotational profile v_Ï(r) of the cool (â 10^(3.5) < T <10^(4.5) Kâ ) gas and compare it to the circular velocity v_c = âGM_(enc)/râ . In the simulated galaxies, the gas rotation traces the circular velocity at intermediate radii, but the two quantities diverge significantly in the centre and in the outer disc. Our simulations appear to over-predict observed rotational velocities in the centres of massive galaxies (likely from a lack of black hole feedback), so we focus on larger radii. Gradients in the turbulent pressure at these radii can provide additional radial support and bias dynamical mass measurements low by up to 40 per cent. In both the interior and exterior, the gasâ motion can be significantly non-circular due to e.g. bars, satellites, and inflows/outflows. We discuss the accuracy of commonly used analytic models for pressure gradients (or âasymmetric driftâ) in the ISM of high-redshift galaxies
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