With the first metal enrichment by Population III (Pop III) supernovae (SNe), the formation of the first metal-enriched, Pop II stars becomes possible. In turn, Pop III star formation and early metal ...enrichment are slowed by the high-energy radiation emitted by Pop II stars. Thus, through the SNe and radiation they produce, Pops II and III co-evolve in the early Universe, one regulated by the other. We present large (4 Mpc)3, high-resolution cosmological simulations in which we self-consistently model early metal enrichment and the stellar radiation responsible for the destruction of the coolants (H2 and HD) required for Pop III star formation. We find that the molecule-dissociating stellar radiation produced both locally and over cosmological distances reduces the Pop III star formation rate at z 10 by up to an order of magnitude, to a rate per comoving volume of 10− 4 M yr− 1 Mpc− 3, compared to the case in which this radiation is not included. However, we find that the effect of Lyman-Werner (LW) feedback is to enhance the amount of Pop II star formation. We attribute this to the reduced rate at which gas is blown out of dark matter haloes by SNe in the simulation with LW feedback, which results in larger reservoirs for metal-enriched star formation. Even accounting for metal enrichment, molecule-dissociating radiation and the strong suppression of low-mass galaxy formation due to reionization at z 10, we find that Pop III stars are still formed at a rate of ∼ 10− 5 M yr− 1 Mpc− 3 down to z ∼ 6. This suggests that the majority of primordial pair-instability SNe that may be uncovered in future surveys will be found at z 10. We also find that the molecule-dissociating radiation emitted from Pop II stars may destroy H2 molecules at a high enough rate to suppress gas cooling and allow for the formation of supermassive primordial stars which collapse to form ∼ 105 M black holes.
Protogalaxies forming in low-mass dark matter haloes are thought to provide the majority of ionizing photons needed to reionize the Universe, due to their high escape fractions of ionizing photons. ...We study how the escape fraction in high-redshift galaxies relates to the physical properties of the halo in which the galaxies form, by computing escape fractions in more than 75 000 haloes between redshifts 27 and 6 that were extracted from the First Billion Years project, high-resolution cosmological hydrodynamical simulations of galaxy formation. We find that the main constraint on the escape fraction is the gas column density in a radius of 10 pc around the stellar populations, causing a strong mass dependence of the escape fraction. The lower potential well in haloes with M
200 ≲ 108 M⊙ results in low column densities that can be penetrated by radiation from young stars (age <5 Myr). In haloes with M
200 ≳ 108 M⊙ supernova feedback is important, but only ∼30 per cent of the haloes in this mass range have an escape fraction higher than 1 per cent. We find a large range of escape fractions in haloes with similar properties, caused by different distributions of the dense gas in the halo. This makes it very hard to predict the escape fraction on the basis of halo properties and results in a highly anisotropic escape fraction. The strong mass dependence, the large spread and the large anisotropy of the escape fraction may strongly affect the topology of reionization and is something current models of cosmic reionization should strive to take into account.
When averaged over large scales, star formation in galaxies is observed to follow the empirical Kennicutt–Schmidt (KS) law for surface densities above a constant threshold. While the observed law ...involves surface densities, theoretical models and simulations generally work with volume density laws (i.e. Schmidt laws). We derive analytic relations between star formation laws expressed in terms of surface densities, volume densities, and pressures and we show how these relations depend on parameters such as the effective equation of state of the multiphase interstellar medium. Our analytic relations enable us to implement observed surface density laws into simulations. Because the parameters of our prescription for star formation are observables, we are not free to tune them to match the observations. We test our theoretical framework using high-resolution simulations of isolated disc galaxies that assume an effective equation of state for the multiphase interstellar medium. We are able to reproduce the star formation threshold and both the slope and the normalization of arbitrary input KS laws without tuning any parameters and with very little scatter, even for unstable galaxies and even if we use poor numerical resolution. Moreover, we can do so for arbitrary effective equations of state. Our prescription therefore enables simulations of galaxies to bypass our current inability to simulate the formation of stars. On the other hand, the fact that we can reproduce arbitrary input thresholds and KS laws, rather than just the particular ones picked out by nature, indicates that simulations that lack the physics and/or resolution to simulate the multiphase interstellar medium can only provide limited insight into the origin of the observed star formation laws.
We explore scenarios for reionizing the intergalactic medium with low galaxy ionizing photon escape fractions. We combine simulation-based halo mass-dependent escape fractions with an extrapolation ...of the observed galaxy rest-ultraviolet luminosity functions to solve for the reionization history from z = . We explore the posterior distributions for key unknown quantities, including the limiting halo mass for star formation, the ionizing photon production efficiency, and a potential contribution from active galactic nuclei (AGNs). We marginalize over the allowable parameter space using a Markov chain Monte Carlo method, finding a solution that satisfies the most model-independent constraints on reionization. Our fiducial model can match observational constraints with an average escape fraction of <5% throughout the bulk of the epoch of reionization if (i) galaxies form stars down to the atomic cooling limit before reionization and a photosuppression mass of log(Mh/M ) ∼ 9 during/after reionization (−13 < MUV,lim < −11), (ii) galaxies become more efficient producers of ionizing photons at higher redshifts and fainter magnitudes, and (iii) there is a significant but subdominant contribution by AGNs at z 7. In this model, the faintest galaxies (MUV > −15) dominate the ionizing emissivity, leading to an earlier start to reionization and a smoother evolution of the ionized volume-filling fraction than models that assume a single escape fraction at all redshifts and luminosities. The ionizing emissivity from this model is consistent with observations at z = 4-5 (and below, when extrapolated), in contrast to some models that assume a single escape fraction. Our predicted ionized volume-filling fraction at z = 7 of = 78% ( 8%) is in modest (∼1 -2 ) tension with observations of Ly emitters at z ∼ 7 and the damping-wing analyses of the two known z > 7 quasars, which prefer ∼ 40%-50%.
The contribution of stars in galaxies to cosmic reionization depends on the star formation history in the Universe, the abundance of galaxies during reionization, the escape fraction of ionizing ...photons and the clumping factor of the intergalactic medium. We compute the star formation rate and clumping factor during reionization in a cosmological volume using a high-resolution hydrodynamical simulation. We post-process the output with detailed radiative transfer simulations to compute the escape fraction of ionizing photons. Together, this gives us the opportunity to assess the contribution of galaxies to reionization self-consistently. The strong mass and redshift dependence of the escape fraction indicates that reionization occurred between z = 15 and 10 and was mainly driven by proto-galaxies forming in dark matter haloes with masses between 107 and 108 M. More massive galaxies that are rare at these redshifts and have significantly lower escape fractions contribute less photons to the reionization process than the more-abundant low-mass galaxies. Star formation in the low-mass haloes is suppressed by radiative feedback from reionization, therefore these proto-galaxies only contribute when the part of the Universe they live in is still neutral. After z ∼ 10, massive galaxies become more abundant and provide most of the ionizing photons. In addition, we find that Population III stars are too short-lived and not frequent enough to have a major contribution to reionization. Although the stellar component of the proto-galaxies that produce the bulk of ionizing photons during reionization is too faint to be detected by the James Webb Space Telescope (JWST), these sources are brightest in the Hα and Lyα recombination lines, which will likely be detected by JWST in deep surveys.
Measurements of the redshift-space galaxy clustering have been a prolific source of cosmological information in recent years. Accurate covariance estimates are an essential step for the validation of ...galaxy clustering models of the redshift-space two-point statistics. Usually, only a limited set of accurate N-body simulations is available. Thus, assessing the data covariance is not possible or only leads to a noisy estimate. Further, relying on simulated realizations of the survey data means that tests of the cosmology dependence of the covariance are expensive. With these points in mind, this work presents a simple theoretical model for the linear covariance of anisotropic galaxy clustering observations with synthetic catalogues. Considering the Legendre moments ('multipoles') of the two-point statistics and projections into wide bins of the line-of-sight parameter ('clustering wedges'), we describe the modelling of the covariance for these anisotropic clustering measurements for galaxy samples with a trivial geometry in the case of a Gaussian approximation of the clustering likelihood. As main result of this paper, we give the explicit formulae for Fourier and configuration space covariance matrices. To validate our model, we create synthetic halo occupation distribution galaxy catalogues by populating the haloes of an ensemble of large-volume N-body simulations. Using linear and non-linear input power spectra, we find very good agreement between the model predictions and the measurements on the synthetic catalogues in the quasi-linear regime.
ABSTRACT
We perform high-resolution cosmological hydrodynamic simulations to study the formation of the first galaxies that reach the masses of 108 − 9 h−1 M⊙ at z = 9. The resolution of the ...simulations is high enough to resolve minihaloes and allow us to successfully pursue the formation of multiple Population (Pop) III stars, their supernova (SN) explosions, resultant metal-enrichment of the inter-galactic medium (IGM) in the course of the build-up of the system. Metals are ejected into the IGM by multiple Pop III SNe, but some of the metal-enriched gas falls back on to the halo after $\gtrsim 100~\rm Myr$. The star formation history of the first galaxy depends sensitively on the initial mass function (IMF) of Pop III stars. The dominant stellar population transits from Pop III to Pop II at z ∼ 12−15 in the case of power-law Pop III IMF, dn/dM ∝ M−2.35 with the mass range 10−500 M⊙. At z ≲ 12, stars are stably formed in the first galaxies with a star formation rate of ∼10−3−10−1 M⊙ yr −1. In contrast, for the case with a flat IMF, gas-deprived first galaxies form due to frequent Pop III pair-instability SNe, resulting in the suppression of subsequent Pop II star formation. In addition, we calculate UV continuum, Lyα- and Hα-line fluxes from the first galaxies. We show that the James Webb Space Telescope will be able to detect both UV continuum, Lyα and Hα line emission from first galaxies with halo mass ≳ 109 M⊙ at z ≳ 10.
Feedback from star formation is thought to play a key role in the formation and evolution of galaxies, but its implementation in cosmological simulations is currently hampered by a lack of numerical ...resolution. We present and test a subgrid recipe to model feedback from massive stars in cosmological smoothed particle hydrodynamics simulations. The energy is distributed in kinetic form among the gas particles surrounding recently formed stars. The impact of the feedback is studied using a suite of high-resolution simulations of isolated disc galaxies embedded in dark haloes with total mass 1010 and 1012h−1M⊙. We focus, in particular, on the effect of pressure forces on wind particles within the disc, which we turn off temporarily in some of our runs to mimic a recipe that has been widely used in the literature. We find that this popular recipe gives dramatically different results because (ram) pressure forces on expanding superbubbles determine both the structure of the disc and the development of large-scale outflows. Pressure forces exerted by expanding superbubbles puff up the disc, giving the dwarf galaxy an irregular morphology and creating a galactic fountain in the massive galaxy. Hydrodynamic drag within the disc results in a strong increase in the effective mass loading of the wind for the dwarf galaxy, but quenches much of the outflow in the case of the high-mass galaxy.
ABSTRACT
We investigate the formation of infant globular cluster (GC) candidates in high-resolution cosmological simulations from the First Billion Years project. By analysing the evolution of the ...systems in the energy and angular momentum plane, we identify the redshift at which the infant GCs first became gravitationally bound, and we find evidence of radial infall of their gaseous and stellar components. The collapse appears to be driven by internal self-gravity; however, the initial trigger is sourced from the external environment. The phase space behaviour of the infant GCs also allows us to identify some characteristic groupings of objects. Such a classification based on internal properties appears to be reflected in the formation environment: GC candidates that belong to the same class are found in host galaxies of similar morphology, with the majority of the infant GCs located in clumpy, irregular proto-galaxies. Finally, through the inspection of two GC candidates that contain only stars by z = 6, we find that supernova feedback is the main physical mechanism behind their dearth of gas and that the systems subsequently respond with an approximately adiabatic expansion. Such infant GC candidates already resemble the GCs we currently observe in the local Universe.
ABSTRACT
By using deep observations of clusters of galaxies, it has been recently found that the projected stellar mass density closely follows the projected total (dark and baryonic) mass density ...within the innermost ∼140 kpc. In this work, we aim to test these observations using the Cluster-EAGLE simulations, comparing the projected densities inferred directly from the simulations. We compare the iso-density contours using the procedure of Montes & Trujillo, and find that the shape of the stellar mass distribution follows that of the total matter even more closely than observed, although their radial profiles differ substantially. The ratio between stellar and total matter density profiles in circular apertures shows a slope close to −1, with a small dependence on the cluster’s total mass. We propose an indirect method to calculate the halo mass and mass density profile from the radial profile of the intracluster stellar mass density.
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