194 research outputs found
The Carbon Content of Intergalactic Gas at z=4.25 and its Evolution Toward z=2.4
This paper presents ionization-corrected measurements of the carbon abundance
in intergalactic gas at 4.0 < z < 4.5, using spectra of three bright quasars
obtained with the MIKE spectrograph on Magellan. By measuring the CIV strength
in a sample of 131 discrete HI-selected quasar absorbers with
\rho/\bar{\rho}>1.6, we derive a median carbon abundance of [C/H]=-3.55, with
lognormal scatter of approximately ~0.8 dex. This median value is a factor of
two to three lower than similar measurements made at z~2.4 using CIV and OVI.
The strength of evolution is modestly dependent on the choice of UV background
spectrum used to make ionization corrections, although our detection of an
abundance evolution is generally robust with respect to this model uncertainty.
We present a framework for analyzing the effects of spatial fluctuations in the
UV ionizing background at frequencies relevant for CIV production. We also
explore the effects of reduced flux between 3-4 Rydbergs (as from HeII Lyman
series absorption) on our abundance estimates. At HeII line absorption levels
similar to published estimates the effects are very small, although a larger
optical depth could reduce the strength of the abundance evolution. Our results
imply that ~50% of the heavy elements seen in the IGM at z~2.4 were deposited
in the 1.3 Gyr between z~4.3 and z~2.4. The total implied mass flux of carbon
into the Lyman alpha forest would constitute ~30% of the IMF-weighted carbon
yield from known star forming populations over this period.Comment: Accepted for publication in the Astrophysical Journal. 23 pages, 24
figures, 2 table
Black Holes on FIRE: Stellar Feedback Limits Early Feeding of Galactic Nuclei
We introduce massive black holes (BHs) in the Feedback In Realistic
Environments project and perform high-resolution cosmological hydrodynamic
simulations of quasar-mass halos () down to . These simulations model stellar
feedback by supernovae, stellar winds, and radiation, and BH growth using a
gravitational torque-based prescription tied to resolved properties of galactic
nuclei. We do not include BH feedback. We show that early BH growth occurs
through short (Myr) accretion episodes that can reach or even
exceed the Eddington rate. In this regime, BH growth is limited by bursty
stellar feedback continuously evacuating gas from galactic nuclei, and BHs
remain under-massive relative to the local -
relation. BH growth is more efficient at later times, when the nuclear stellar
potential retains a significant gas reservoir, star formation becomes less
bursty, and galaxies settle into a more ordered state, with BHs rapidly
converging onto the scaling relation when the host reaches . Our results are not sensitive to the details of the
accretion model so long as BH growth is tied to the gas content within pc of the BH. Our simulations imply that bursty stellar feedback has
strong implications for BH and AGN demographics, especially in the early
Universe and for low-mass galaxies.Comment: 5 pages, 3 figures, submitted to MNRA
Testing the Recovery of Intrinsic Galaxy Sizes and Masses of z~2 Massive Galaxies Using Cosmological Simulations
Accurate measurements of galaxy masses and sizes are key to tracing galaxy
evolution over time. Cosmological zoom-in simulations provide an ideal test bed
for assessing the recovery of galaxy properties from observations. Here, we
utilize galaxies with at z~1.7-2 from the
MassiveFIRE cosmological simulation suite, part of the Feedback in Realistic
Environments (FIRE) project. Using mock multi-band images, we compare intrinsic
galaxy masses and sizes to observational estimates. We find that observations
accurately recover stellar masses, with a slight average underestimate of ~0.06
dex and a ~0.15 dex scatter. Recovered half-light radii agree well with
intrinsic half-mass radii when averaged over all viewing angles, with a
systematic offset of ~0.1 dex (with the half-light radii being larger) and a
scatter of ~0.2 dex. When using color gradients to account for mass-to-light
variations, recovered half-mass radii also exceed the intrinsic half-mass radii
by ~0.1 dex. However, if not properly accounted for, aperture effects can bias
size estimates by ~0.1 dex. No differences are found between the mass and size
offsets for star-forming and quiescent galaxies. Variations in viewing angle
are responsible for ~25% of the scatter in the recovered masses and sizes. Our
results thus suggest that the intrinsic scatter in the mass-size relation may
have previously been overestimated by ~25%. Moreover, orientation-driven
scatter causes the number density of very massive galaxies to be overestimated
by ~0.5 dex at .Comment: Published in the Astrophysical Journal Letters (7 pages, 5 figures;
updated to match published version
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 ≳ 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 (M⋆ > 10¹¹ M⊙ at z = 1). Selecting only snapshots where a disc is present, we calculate the rotational profile v_ϕ(r) of the cool (10^(3.5) < T <10^(4.5) K) gas and compare it to the circular velocity v_c = √GM_(enc)/r. 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 gas’ 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 ‘asymmetric drift’) in the ISM of high-redshift galaxies
The HI covering fraction of Lyman Limit Systems in FIRE haloes
Atomic hydrogen (HI) serves a crucial role in connecting galactic-scale
properties such as star formation with the large-scale structure of the
Universe. While recent numerical simulations have successfully matched the
observed covering fraction of HI near Lyman Break Galaxies (LBGs) and in the
foreground of luminous quasars at redshifts , the low-mass end
remains as-of-yet unexplored in observational and computational surveys. We
employ a cosmological, hydrodynamical simulation (FIREbox) supplemented with
zoom-in simulations (MassiveFIRE) from the Feedback In Realistic Environments
(FIRE) project to investigate the HI covering fraction of Lyman Limit Systems
( cm) across a wide range of
redshifts () and halo masses ( at ,
at ) in the absence of feedback from active
galactic nuclei (AGN). We find that the covering fraction inside haloes
exhibits a strong increase with redshift, with only a weak dependence on halo
mass for higher-mass haloes. For massive haloes (), the radial profiles showcase scale-invariance and
remain independent of mass. The radial dependence is well-captured by a fitting
function. The covering fractions in our simulations are in good agreement with
measurements of the covering fraction in LBGs. Our comprehensive analysis
unveils a complex dependence with redshift and halo mass for haloes with
that future observations aim to
constrain, providing key insights into the physics of structure formation and
gas assembly
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
On the dust temperatures of high redshift galaxies
Dust temperature is an important property of the interstellar medium (ISM) of
galaxies. It is required when converting (sub)millimeter broadband flux to
total infrared luminosity (L_IR), and hence star formation rate, in high-z
galaxies. However, different definitions of dust temperatures have been used in
the literature, leading to different physical interpretations of how ISM
conditions change with, e.g., redshift and star formation rate. In this paper,
we analyse the dust temperatures of massive (M* > 10^10 Msun) z=2-6 galaxies
with the help of high-resolution cosmological simulations from the Feedback in
Realistic Environments (FIRE) project. At z~2, our simulations successfully
predict dust temperatures in good agreement with observations. We find that
dust temperatures based on the peak emission wavelength increase with redshift,
in line with the higher star formation activity at higher redshift, and are
strongly correlated with the specific star formation rate. In contrast, the
mass-weighted dust temperature does not strongly evolve with redshift over
z=2-6 at fixed IR luminosity but is tightly correlated with L_IR at fixed z.
The mass-weighted temperature is important for accurately estimating the total
dust mass. We also analyse an 'equivalent' dust temperature for converting
(sub)millimeter flux density to total IR luminosity, and provide a fitting
formula as a function of redshift and dust-to-metal ratio. We find that
galaxies of higher equivalent (or higher peak) dust temperature ('warmer dust')
do not necessarily have higher mass-weighted temperatures. A 'two-phase'
picture for interstellar dust can explain the different scaling relations of
the various dust temperatures.Comment: 26 pages, 15 figures, accepted for publication in MNRA
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