59 research outputs found
On the deuterium abundance and the importance of stellar mass loss in the interstellar and intergalactic medium
We quantify the gas-phase abundance of deuterium and fractional contribution
of stellar mass loss to the gas in cosmological zoom-in simulations from the
Feedback In Realistic Environments project. At low metallicity, our simulations
confirm that the deuterium abundance is very close to the primordial value. The
chemical evolution of the deuterium abundance that we derive here agrees
quantitatively with analytical chemical evolution models. We furthermore find
that the relation between the deuterium and oxygen abundance exhibits very
little scatter. We compare our simulations to existing high-redshift
observations in order to determine a primordial deuterium fraction of 2.549 +/-
0.033 x 10^-5 and stress that future observations at higher metallicity can
also be used to constrain this value. At fixed metallicity, the deuterium
fraction decreases slightly with decreasing redshift, due to the increased
importance of mass loss from intermediate-mass stars. We find that the
evolution of the average deuterium fraction in a galaxy correlates with its
star formation history. Our simulations are consistent with observations of the
Milky Way's interstellar medium: the deuterium fraction at the solar circle is
85-92 per cent of the primordial deuterium fraction. We use our simulations to
make predictions for future observations. In particular, the deuterium
abundance is lower at smaller galactocentric radii and in higher mass galaxies,
showing that stellar mass loss is more important for fuelling star formation in
these regimes (and can even dominate). Gas accreting onto galaxies has a
deuterium fraction above that of the galaxies' interstellar medium, but below
the primordial fraction, because it is a mix of gas accreting from the
intergalactic medium and gas previously ejected or stripped from galaxies.Comment: Accepted for publication in MNRAS. Revised version: expanded
discussion and added Figure 2 (residual dependence on iron abundance
Great Balls of FIRE III: Modeling Black Hole Mergers from Massive Star Clusters in Simulations of Galaxies
After the nearly hundred gravitational-wave detections reported by the
LIGO-Virgo-KAGRA Collaboration, the question of the cosmological origin of
merging binary black holes (BBHs) remains open. The two main formation channels
generally considered are from isolated field binaries or via dynamical assembly
in dense star clusters. Here, we focus on understanding the dynamical formation
of merging BBHs within massive clusters in galaxies of different masses. To
this end, we apply a new framework to consistently model the formation and
evolution of massive star clusters in zoom-in cosmological simulations of
galaxies. Each simulation, taken from the FIRE project, provides a realistic
star formation environment with a unique star formation history and hosts
realistic giant molecular clouds that constitute the birthplace of star
clusters. Combined with the code for star cluster evolution CMC, we are able to
produce populations of dynamically formed merging BBHs across cosmic time in
different environments. As the most massive star clusters preferentially form
in dense massive clouds of gas, we find that, despite their low metallicities
favourable to the creation of black holes, low-mass galaxies contain few
massive clusters and therefore have a limited contribution to the global
production of dynamically formed merging BBHs. Furthermore, we find that
massive clusters can host hierarchical BBH mergers with clear identifiable
physical properties. Looking at the evolution of the BBH merger rate in
different galaxies, we find strong correlations between BBH mergers and the
most extreme episodes of star formation. Finally, we discuss the implications
for future LIGO-Virgo-KAGRA gravitational wave observations.Comment: 14 pages, 9 figures, 3 table
Accretion onto disk galaxies via hot and rotating CGM inflows
Observed accretion rates onto the Milky-Way and other local spirals fall
short of that required to sustain star formation for cosmological timescales. A
potential avenue for this unseen accretion is an inflow in the volume-filling
hot phase ( K) of the circumgalactic medium (CGM), as suggested by
some cosmological simulations. We derive an approximate axisymmetric analytic
solution of such hot CGM accretion flows, and validate it with hydrodynamic
simulations. We show that a hot inflow spins up as it approaches the galaxy,
while remaining hot, subsonic and quasi-spherical. At the radius of angular
momentum support ( kpc for the Milky-Way) the hot flow flattens into
a disk geometry and then cools from K to K at the
disk-halo interface. Cooling affects all hot gas, rather than just a subset of
individual gas clouds, implying that accretion via hot inflows does not rely on
local thermal instability in contrast with 'precipitation' models for galaxy
accretion. Prior to cooling and accretion the inflow completes radians of rotation, where is the
cooling time to free-fall time ratio in hot gas immediately outside the galaxy.
The ratio may thus govern the development of
turbulence and enhancement of magnetic fields in gas accreting onto
low-redshift spirals. We argue that accretion via hot inflows can explain the
observed truncation of nearby thin stellar disks at disk radii. We
also show that if rotating hot inflows are common in Milky-Way size disk
galaxies, as predicted, then signatures should be observable with X-ray
telescopes, kinetic SZ measurements, and FRB surveys.Comment: 19 pages, 11 figures, submitted to MNRA
The impact of stellar feedback on hot gas in galaxy haloes: the Sunyaev–Zel'dovich effect and soft X-ray emission
The thermal Sunyaev–Zel'dovich (SZ) effect and soft X-ray emission are routinely observed around massive galaxies and in galaxy groups and clusters. We study these observational diagnostics of galaxy haloes for a suite of cosmological ‘zoom-in’ simulations from the ‘Feedback In Realistic Environments’ project, which spans a large range in halo mass (10^(10–13) M_⊙). We explore the effect of stellar feedback on the hot gas observables. The properties of our simulated groups, such as baryon fractions, SZ flux, and X-ray luminosities (LX), are broadly consistent with existing observations, even though feedback from active galactic nuclei is not included. We make predictions for future observations of lower mass objects for both SZ and diffuse X-ray measurements, finding that they are not just scaled-down versions of massive galaxies, but more strongly affected by galactic winds driven by star formation. Low-mass haloes (≲ 10^(11) M_⊙) retain a low fraction of their baryons, which results in a strong suppression of the SZ signal. Our simulations therefore predict a scaling with halo mass that is steeper than self-similar for haloes less massive than 10^(13) M_⊙. For halo masses ≲ 10^(12) M_⊙, LX is time variable and correlated primarily with the star formation rate (SFR). For these objects, the diffuse X-ray emission is powered mostly by galactic winds and the gas dominating the X-ray emission is flowing out with radial velocities close to the halo's circular velocity. For halo masses ≳ 10^(13) M_⊙, on the other hand, LX is much less variable and not correlated with the SFR, because the emission originates from the quasi-hydrostatic, virialized halo gas
Probing the CGM of low-redshift dwarf galaxies using FIRE simulations
Observations of ultraviolet (UV) metal absorption lines have provided insight into the structure and composition of the circumgalactic medium (CGM) around galaxies. We compare these observations with the low-redshift (z ≤ 0.3) CGM around dwarf galaxies in high-resolution cosmological zoom-in runs in the FIRE-2 (Feedback In Realistic Environments) simulation suite. We select simulated galaxies that match the halo mass, stellar mass, and redshift of the observed samples. We produce absorption measurements using TRIDENT for UV transitions of C IV, O VI, Mg II, and Si III. The FIRE equivalent width (EW) distributions and covering fractions for the C IV ion are broadly consistent with observations inside 0.5R_(vir), but are underpredicted for O VI, Mg II, and Si III. The absorption strengths of the ions in the CGM are moderately correlated with the masses and star formation activity of the galaxies. The correlation strengths increase with the ionization potential of the ions. The structure and composition of the gas from the simulations exhibit three zones around dwarf galaxies characterized by distinct ion column densities: the discy interstellar medium, the inner CGM (the wind-dominated regime), and the outer CGM (the IGM accretion-dominated regime). We find that the outer CGM in the simulations is nearly but not quite supported by thermal pressure, so it is not in hydrostatic equilibrium, resulting in halo-scale bulk inflow and outflow motions. The net gas inflow rates are comparable to the star formation rate of the galaxy, but the bulk inflow and outflow rates are greater by an order of magnitude, with velocities comparable to the virial velocity of the halo. These roughly virial velocities (∼100 km s⁻¹) produce large EWs in the simulations. This supports a picture for dwarf galaxies in which the dynamics of the CGM at large scales are coupled to the small-scale star formation activity near the centre of their haloes
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
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