36 research outputs found
Firefly: a browser-based interactive 3D data visualization tool for millions of data points
We present Firefly, a new browser-based interactive tool for visualizing 3D
particle data sets. On a typical personal computer, Firefly can simultaneously
render and enable real-time interactions with > ~10 million particles, and can
interactively explore datasets with billions of particles using the included
custom-built octree render engine. Once created, viewing a Firefly
visualization requires no installation and is immediately usable in most modern
internet browsers simply by visiting a URL. As a result, a Firefly
visualization works out-of-the-box on most devices including smartphones and
tablets. Firefly is primarily developed for researchers to explore their own
data, but can also be useful to communicate results to
researchers/collaborators and as an effective public outreach tool. Every
element of the user interface can be customized and disabled, enabling easy
adaptation of the same visualization for different audiences with little
additional effort. Creating a new Firefly visualization is simple with the
provided Python data pre-processor (PDPP) that translates input data to a
Firefly-compatible format and provides helpful methods for hosting instances of
Firefly both locally and on the internet. In addition to visualizing the
positions of particles, users can visualize vector fields (e.g., velocities)
and also filter and color points by scalar fields. We share three examples of
Firefly applied to astronomical datasets: 1) the FIRE cosmological zoom-in
simulations, 2) the SDSS galaxy catalog, and 3) Gaia DR3. A gallery of
additional interactive demos is available at https://alexbgurvi.ch/Firefly.Comment: 25 pages, 8 figures. Submitting to ApjS, comments welcome
The low redshift Lyman- Forest as a constraint for models of AGN feedback
We study the low redshift Lyman- Forest in the Illustris and
IllustrisTNG (TNG) cosmological simulations to demonstrate their utility in
constraining aspects of sub-grid models of feedback from active galactic nuclei
(AGN). The two simulations share an identical Ultraviolet Background
prescription and similar cosmological parameters, but TNG features an entirely
reworked AGN feedback model. Therefore a comparison of these simulations is
useful to assess the effects of an altered AGN sub-grid model on the low
redshift Lyman- Forest. We find significant differences in the IGM
temperature-density relation between the two simulations due to changes in the
gas heating rate due to AGN. We investigate Lyman- Forest observables
such as the column density distribution function, flux PDF, and Doppler width
(-parameter) distribution. Due to the AGN radio mode model, the original
Illustris simulations have a factor of 2-3 fewer absorbers than TNG at column
densities cm. We show that TNG is in much better
agreement with the observed flux power spectrum than Illustris. The
differences in the amplitude and shape of the flux PDF and power spectrum
between Illustris and TNG cannot be attributed to simple changes in the
photoheating rate. We also compare the simulated Forest statistics to UV data
from the Cosmic Origins Spectrograph (COS) and find that neither simulation can
reproduce the slope of the absorber distribution. Both Illustris and TNG also
produce significantly smaller -parameter distributions than observed in the
COS data, possibly due to unresolved or missing sources of turbulence.Comment: Submitted to ApJL, comments welcom
Born this way: thin disc, thick disc, and isotropic spheroid formation in FIRE-2 Milky-Way-mass galaxy simulations
We investigate the formation of Milky-Way-mass galaxies using FIRE-2 LCDM
cosmological zoom-in simulations by studying the orbital evolution of stars
formed in the main progenitor of the galaxy, from birth to the present day. We
classify in situ stars as isotropic spheroid, thick-disc, and thin-disc
according to their orbital circularities and show that these components are
assembled in a time-ordered sequence from early to late times, respectively.
All simulated galaxies experience an early phase of bursty star formation that
transitions to a late-time steady phase. This transition coincides with the
time that the inner CGM virializes. During the early bursty phase, galaxies
have irregular morphologies and new stars are born on radial orbits; these
stars evolve into an isotropic spheroidal population today. The bulk of
thick-disc stars form at intermediate times, during a clumpy-disc ``spin-up''
phase, slightly later than the peak of spheroid formation. At late times, once
the CGM virializes and star formation ``cools down," stars are born on circular
orbits within a narrow plane. Those stars mostly inhabit thin discs today.
Broadly speaking, stars with disc-like or spheroid-like orbits today were born
that way. Mergers onto discs and secular processes do affect kinematics in our
simulations, but play only secondary roles in populating thick-disc and in situ
spheroid populations at z=0. The age distributions of spheroid, thick disc, and
thin disc populations scale self-similarly with the steady-phase transition
time, which suggests that morphological age dating can be linked to the CGM
virialization time in galaxies.Comment: 16 pages, 10 figures, submitted to MNRA
Swirls of FIRE: spatially resolved gas velocity dispersions and star formation rates in FIRE-2 disc environments
We study the spatially resolved (sub-kpc) gas velocity dispersion (Ï)âstar formation rate (SFR) relation in the FIRE-2 (Feedback in Realistic Environments) cosmological simulations. We specifically focus on Milky Way-mass disc galaxies at late times (z â 0). In agreement with observations, we find a relatively flat relationship, with Ï â 15â30 kmâsâ»Âč in neutral gas across 3 dex in SFRs. We show that higher dense gas fractions (ratios of dense gas to neutral gas) and SFRs are correlated at constant Ï. Similarly, lower gas fractions (ratios of gas to stellar mass) are correlated with higher Ï at constant SFR. The limits of the ÏâÎŁ_(SFR) relation correspond to the onset of strong outflows. We see evidence of âon-offâ cycles of star formation in the simulations, corresponding to feedback injection time-scales of 10â100 Myr, where SFRs oscillate about equilibrium SFR predictions. Finally, SFRs and velocity dispersions in the simulations agree well with feedback-regulated and marginally stable gas disc (Toomreâs Q = 1) model predictions, and the simulation data effectively rule out models assuming that gas turns into stars at (low) constant efficiency (i.e. 1 perâcent per free-fall time). And although the simulation data do not entirely exclude gas accretion/gravitationally powered turbulence as a driver of Ï, it appears to be subdominant to stellar feedback in the simulated galaxy discs at z â 0
Pressure balance in the multiphase ISM of cosmologically simulated disc galaxies
Pressure balance plays a central role in models of the interstellar medium (ISM), but whether and how pressure balance is realized in a realistic multiphase ISM is not yet well understood. We address this question by using a set of FIRE-2 cosmological zoom-in simulations of Milky Way-mass disc galaxies, in which a multiphase ISM is self-consistently shaped by gravity, cooling, and stellar feedback. We analyse how gravity determines the vertical pressure profile as well as how the total ISM pressure is partitioned between different phases and components (thermal, dispersion/turbulence, and bulk flows). We show that, on average and consistent with previous more idealized simulations, the total ISM pressure balances the weight of the overlying gas. Deviations from vertical pressure balance increase with increasing galactocentric radius and with decreasing averaging scale. The different phases are in rough total pressure equilibrium with one another, but with large deviations from thermal pressure equilibrium owing to kinetic support in the cold and warm phases, which dominate the total pressure near the mid-plane. Bulk flows (e.g. inflows and fountains) are important at a few disc scale heights, while thermal pressure from hot gas dominates at larger heights. Overall, the total mid-plane pressure is well-predicted by the weight of the disc gas and we show that it also scales linearly with the star formation rate surface density (ÎŁSFR). These results support the notion that the Kennicutt-Schmidt relation arises because ÎŁSFR and the gas surface density (ÎŁg) are connected via the ISM mid-plane pressure
Pressure balance in the multiphase ISM of cosmologically simulated disc galaxies
Pressure balance plays a central role in models of the interstellar medium (ISM), but whether and how pressure balance is realized in a realistic multiphase ISM is not yet well understood. We address this question by using a set of FIRE-2 cosmological zoom-in simulations of Milky Way-mass disc galaxies, in which a multiphase ISM is self-consistently shaped by gravity, cooling, and stellar feedback. We analyse how gravity determines the vertical pressure profile as well as how the total ISM pressure is partitioned between different phases and components (thermal, dispersion/turbulence, and bulk flows). We show that, on average and consistent with previous more idealized simulations, the total ISM pressure balances the weight of the overlying gas. Deviations from vertical pressure balance increase with increasing galactocentric radius and with decreasing averaging scale. The different phases are in rough total pressure equilibrium with one another, but with large deviations from thermal pressure equilibrium owing to kinetic support in the cold and warm phases, which dominate the total pressure near the mid-plane. Bulk flows (e.g. inflows and fountains) are important at a few disc scale heights, while thermal pressure from hot gas dominates at larger heights. Overall, the total mid-plane pressure is well-predicted by the weight of the disc gas and we show that it also scales linearly with the star formation rate surface density (ÎŁ_(SFR)). These results support the notion that the KennicuttâSchmidt relation arises because ÎŁ_(SFR) and the gas surface density (ÎŁ_g) are connected via the ISM mid-plane pressure
The time-scales probed by star formation rate indicators for realistic, bursty star formation histories from the FIRE simulations
Understanding the rate at which stars form is central to studies of galaxy
formation. Observationally, the star formation rates (SFRs) of galaxies are
measured using the luminosity in different frequency bands, often under the
assumption of a time-steady SFR in the recent past. We use star formation
histories (SFHs) extracted from cosmological simulations of star-forming
galaxies from the FIRE project to analyze the time-scales to which the
H and far-ultraviolet (FUV) continuum SFR indicators are sensitive.
In these simulations, the SFRs are highly time variable for all galaxies at
high redshift, and continue to be bursty to z=0 in dwarf galaxies. When FIRE
SFHs are partitioned into their bursty and time-steady phases, the best-fitting
FUV time-scale fluctuates from its ~10 Myr value when the SFR is time-steady to
>~100 Myr immediately following particularly extreme bursts of star formation
during the bursty phase. On the other hand, the best-fitting averaging
time-scale for H is generally insensitive to the SFR variability in
the FIRE simulations and remains ~5 Myr at all times. These time-scales are
shorter than the 100 Myr and 10 Myr time-scales sometimes assumed in the
literature for FUV and H, respectively, because while the FUV
emission persists for stellar populations older than 100 Myr, the
time-dependent luminosities are strongly dominated by younger stars. Our
results confirm that the ratio of SFRs inferred using H vs. FUV can
be used to probe the burstiness of star formation in galaxies.Comment: 14 pages, 10 figures, accepted to MNRA
Hot-mode accretion and the physics of thin-disc galaxy formation
We use FIRE simulations to study disc formation in z ⌠0, Milky Way-mass galaxies, and conclude that a key ingredient for the formation of thin stellar discs is the ability for accreting gas to develop an aligned angular momentum distribution via internal cancellation prior to joining the galaxy. Among galaxies with a high fraction (â >70 per centâ ) of their young stars in a thin disc (h/R ⌠0.1), we find that: (i) hot, virial-temperature gas dominates the inflowing gas mass on halo scales (âł20 kpc), with radiative losses offset by compression heating; (ii) this hot accretion proceeds until angular momentum support slows inward motion, at which point the gas cools to âČ104Kâ ; (iii) prior to cooling, the accreting gas develops an angular momentum distribution that is aligned with the galaxy disc, and while cooling transitions from a quasi-spherical spatial configuration to a more-flattened, disc-like configuration. We show that the existence of this ârotating cooling flowâ accretion mode is strongly correlated with the fraction of stars forming in a thin disc, using a sample of 17 z ⌠0 galaxies spanning a halo mass range of 1010.5 Mâ âČ Mh âČ 1012 Mâ and stellar mass range of 108 Mâ âČ Mâ âČ 1011 Mâ. Notably, galaxies with a thick disc or irregular morphology do not undergo significant angular momentum alignment of gas prior to accretion and show no correspondence between halo gas cooling and flattening. Our results suggest that rotating cooling flows (or, more generally, rotating subsonic flows) that become coherent and angular momentum-supported prior to accretion on to the galaxy are likely a necessary condition for the formation of thin, star-forming disc galaxies in a ÎCDM universe
What Causes The Formation of Disks and End of Bursty Star Formation?
As they grow, galaxies can transition from irregular/spheroidal with 'bursty'
star formation histories (SFHs), to disky with smooth SFHs. But even in
simulations, the direct physical cause of such transitions remains unclear. We
therefore explore this in a large suite of numerical experiments re-running
portions of cosmological simulations with widely varied physics, further
validated with existing FIRE simulations. We show that gas supply,
cooling/thermodynamics, star formation model, Toomre scale, galaxy dynamical
times, and feedback properties do not have a direct causal effect on these
transitions. Rather, both the formation of disks and cessation of bursty star
formation are driven by the gravitational potential, but in different ways.
Disk formation is promoted when the mass profile becomes sufficiently
centrally-concentrated in shape (relative to circularization radii): we show
that this provides a well-defined dynamical center, ceases to support the
global 'breathing modes' which can persist indefinitely in less-concentrated
profiles and efficiently destroy disks, promotes orbit mixing to form a
coherent angular momentum, and stabilizes the disk. Smooth SF is promoted by
the potential or escape velocity (not circular velocity) becoming sufficiently
large at the radii of star formation that cool, mass-loaded
(momentum-conserving) outflows are trapped/confined near the galaxy, as opposed
to escaping after bursts. We discuss the detailed physics, how these conditions
arise in cosmological contexts, their relation to other correlated phenomena
(e.g. inner halo virialization, vertical disk 'settling'), and observations.Comment: Submitted to MNRAS. 44 pages, 32 figures. Comments welcome. (Minor
text corrections from previous version
Galaxies lacking dark matter produced by close encounters in a cosmological simulation
The standard cold dark matter plus cosmological constant model predicts that galaxies form within dark-matter haloes, and that low-mass galaxies are more dark-matter dominated than massive ones. The unexpected discovery of two low-mass galaxies lacking dark matter immediately provoked concerns about the standard cosmology and ignited explorations of alternatives, including self-interacting dark matter and modified gravity. Apprehension grew after several cosmological simulations using the conventional model failed to form adequate numerical analogues with comparable internal characteristics (stellar masses, sizes, velocity dispersions and morphologies). Here we show that the standard paradigm naturally produces galaxies lacking dark matter with internal characteristics in agreement with observations. Using a state-of-the-art cosmological simulation and a meticulous galaxy-identification technique, we find that extreme close encounters with massive neighbours can be responsible for this. We predict that ~30% of massive central galaxies (with at least 1011 solar masses in stars) harbour at least one dark-matter-deficient satellite (with 108â109 solar masses in stars). This distinctive class of galaxies provides an additional layer in our understanding of the role of interactions in shaping galactic properties. Future observations surveying galaxies in the aforementioned regime will provide a crucial test of this scenario