ABSTRACT
Using cosmological, radiation-hydrodynamic simulations targeting a rare ${\approx}2 \times 10^{12} \, \rm {\rm M}_{\odot }$ halo at $z = 6$, we show that the number counts and internal ...properties of satellite galaxies within the massive halo are sensitively regulated by a combination of local stellar radiative feedback and strong tidal forces. Radiative feedback operates before the first supernova explosions erupt and results in less tightly bound galaxies. Satellites are therefore more vulnerable to tidal stripping when they accrete on to the main progenitor and are tidally disrupted on a significantly shorter time-scale. Consequently, the number of satellites with $M_{\rm \star } \gt 10^{7} \, \rm {\rm M}_{\odot }$ within the parent system’s virial radius drops by up to $60 \, {\rm per\, cent}$ with respect to an identical simulation performed without stellar radiative feedback. Radiative feedback also impacts the central galaxy, whose effective radius increases by a factor ≲3 due to the presence of a more extended and diffuse stellar component. We suggest that the number of satellites in the vicinity of massive high-redshift galaxies is an indication of the strength of stellar radiative feedback and can be anomalously low in the extreme cosmic environments of high-redshift quasars.
ABSTRACT
The physical origin of low escape fractions of ionizing radiation derived from massive star-forming galaxies at z ∼ 3–4 is not well understood. We perform idealized disc galaxy simulations ...to understand how galactic properties such as metallicity and gas mass affect the escape of Lyman continuum (LyC) photons using radiation-hydrodynamic simulations with strong stellar feedback. We find that the luminosity-weighted escape fraction from a metal-poor (Z = 0.002) galaxy embedded in a halo of mass $M_{\rm h}\simeq 10^{11}\, \mathrm{M}_\odot$ is $\left\langle {f_{\rm esc}^{\rm 3D}}\right\rangle \simeq 10\, {{\ \rm per\ cent}}$. Roughly half of the LyC photons are absorbed within scales of 100 pc, and the other half is absorbed in the ISM ($\lesssim 2\, {\rm kpc}$). When the metallicity of the gas is increased to Z = 0.02, the escape fraction is significantly reduced to $\left\langle {f_{\rm esc}^{\rm 3D}}\right\rangle \simeq 1{{\ \rm per\ cent}}$ because young stars are enshrouded by their birth clouds for a longer time. In contrast, increasing the gas mass by a factor of 5 leads to $\left\langle {f_{\rm esc}^{\rm 3D}}\right\rangle \simeq 5\, {{\ \rm per\ cent}}$ because LyC photons are only moderately absorbed by the thicker disc. Our experiments suggest that high metallicity is likely more responsible for the low escape fractions observed in massive star-forming galaxies, supporting the scenario in which the escape fraction is decreasing with increasing halo mass. Finally, negligible correlation is observed between the escape fraction and surface density of star formation or galactic outflow rates.
We investigate the impact of ram pressure stripping due to the intracluster medium (ICM) on star-forming disk galaxies with a multiphase interstellar medium maintained by strong stellar feedback. We ...carry out radiation-hydrodynamic simulations of an isolated disk galaxy embedded in a 1011 M dark matter halo with various ICM winds mimicking the cluster outskirts (moderate) and the central environment (strong). We find that both star formation quenching and triggering occur in ram pressure-stripped galaxies, depending on the strength of the winds. H i and H2 in the outer galactic disk are significantly stripped in the presence of moderate winds, whereas turbulent pressure provides support against ram pressure in the central region, where star formation is active. Moderate ICM winds facilitate gas collapse, increasing the total star formation rates by ∼40% when the wind is oriented face-on or by ∼80% when it is edge-on. In contrast, strong winds rapidly blow away neutral and molecular hydrogen gas from the galaxy, suppressing star formation by a factor of 2 within ∼200 Myr. Dense gas clumps with nH 10 M pc−2 are easily identified in extraplanar regions, but no significant young stellar populations are found in such clumps. In our attempts to enhance radiative cooling by adopting a colder ICM of T = 106 K, only a few additional stars are formed in the tail region, even if the amount of newly cooled gas increases by an order of magnitude.
ABSTRACT
Infrared and nebular lines provide some of our best probes of the physics regulating the properties of the interstellar medium (ISM) at high redshift. However, interpreting the physical ...conditions of high-redshift galaxies directly from emission lines remains complicated due to inhomogeneities in temperature, density, metallicity, ionization parameter, and spectral hardness. We present a new suite of cosmological, radiation-hydrodynamics simulations, each centred on a massive Lyman-break galaxy that resolves such properties in an inhomogeneous ISM. Many of the simulated systems exhibit transient but well-defined gaseous discs that appear as velocity gradients in C ii 157.6 $\mu$m emission. Spatial and spectral offsets between C ii 157.6 $\mu$m and O iii 88.33 $\mu$m are common, but not ubiquitous, as each line probes a different phase of the ISM. These systems fall on the local C ii–SFR relation, consistent with newer observations that question previously observed C ii 157.6 $\mu$m deficits. Our galaxies are consistent with the nebular line properties of observed z ∼ 2–3 galaxies and reproduce offsets on the BPT and mass-excitation diagrams compared to local galaxies due to higher star formation rate (SFR), excitation, and specific-SFR, as well as harder spectra from young, metal-poor binaries. We predict that local calibrations between H α and O ii 3727$\, \mathring{\rm A}$ luminosity and galaxy SFR apply up to z > 10, as do the local relations between certain strong line diagnostics (R23 and O iii 5007$\, \mathring{\rm A}$/H β) and galaxy metallicity. Our new simulations are well suited to interpret the observations of line emission from current (ALMA and HST) and upcoming facilities (JWST and ngVLA).
Analysis is performed on ultra-high-resolution large-scale cosmological radiation-hydrodynamic simulations to quantify, for the first time, the physical environment of long-duration gamma-ray bursts ...(GRBs) at the epoch of re ionization. We find that, on parsec scales, 13% of GRBs remain in high-density (> or =, slanted10 super(4) cm super(-3)) low-temperature star-forming regions, whereas 87% of GRBs occur in low-density (~10 super(-2.5) cm super(-3)) high-temperature regions heated by supernovae. More importantly, the spectral properties of GRB afterglows, such as the neutral hydrogen column density, total hydrogen column density, dust column density, gas temperature, and metallicity of intervening absorbers, vary strongly from sight line to sight line. Although our model explains extant limited observationally inferred values with respect to circumburst density, metallicity, column density, and dust properties, a substantially larger sample of high-z GRB afterglows would be required to facilitate a statistically solid test of the model. Our findings indicate that any attempt to infer the physical properties (such as metallicity) of the interstellar medium (ISM) of the host galaxy based on a very small number (usually one) of sight lines would be precarious. Utilizing high-z GRBs to probe the ISM and intergalactic medium should be undertaken properly, taking into consideration the physical diversities of the ISM.
ABSTRACT
The recent launch of JWST has enabled the exciting prospect of detecting the first generation of metal-free, Population III (Pop. III) stars. Determining characteristics that robustly ...signify Pop. III stars against other possible contaminants represents a key challenge. To this end, we run high-resolution (sub-pc) cosmological radiation hydrodynamics simulations of the region around a dwarf galaxy at z ≥ 10 to predict the emission line signatures of the Pop. III/Pop. II transition. We show that the absence of metal emission lines is a poor diagnostic of Pop. III stars because metal-enriched galaxies can maintain low O iii 5007 Å that may be undetectable due to sensitivity limits. Combining spectral hardness probes (e.g. He ii 1640 Å/H α) with metallicity diagnostics is more likely to probe metal-free stars, although contamination from Wolf−Rayet stars, X-ray binaries, or black holes may be important. The hard emission from Pop. III galaxies fades fast due to the short stellar lifetimes of massive stars, which could further inhibit detection. Pop. III stars may be identifiable after they evolve off the main sequence due to the cooling radiation from nebular gas or a supernova remnant; however, these signatures are also short-lived (i.e. few Myr). Contaminants including flickering black holes might confuse this diagnostic. While JWST will provide a unique opportunity to spectroscopically probe the nature of the earliest galaxies, both the short time-scales associated with pristine systems and ambiguities in interpreting emission lines may hinder progress. Special care will be needed before claiming the discovery of systems with pure Pop. III stars.
Hydrodynamical cosmological simulations are increasing their level of realism by considering more physical processes and having greater resolution or larger statistics. However, usually either the ...statistical power of such simulations or the resolution reached within galaxies are sacrificed. Here, we introduce the N
EW
H
ORIZON
project in which we simulate at high resolution a zoom-in region of ∼(16 Mpc)
3
that is larger than a standard zoom-in region around a single halo and is embedded in a larger box. A resolution of up to 34 pc, which is typical of individual zoom-in, up-to-date resimulated halos, is reached within galaxies; this allows the simulation to capture the multi-phase nature of the interstellar medium and the clumpy nature of the star formation process in galaxies. In this introductory paper, we present several key fundamental properties of galaxies and their black holes, including the galaxy mass function, cosmic star formation rate, galactic metallicities, the Kennicutt–Schmidt relation, the stellar-to-halo mass relation, galaxy sizes, stellar kinematics and morphology, gas content within galaxies and its kinematics, and the black hole mass and spin properties over time. The various scaling relations are broadly reproduced by N
EW
H
ORIZON
with some differences with the standard observables. Owing to its exquisite spatial resolution, N
EW
H
ORIZON
captures the inefficient process of star formation in galaxies, which evolve over time from being more turbulent, gas rich, and star bursting at high redshift. These high-redshift galaxies are also more compact, and they are more elliptical and clumpier until the level of internal gas turbulence decays enough to allow for the formation of discs. The N
EW
H
ORIZON
simulation gives access to a broad range of galaxy formation and evolution physics at low-to-intermediate stellar masses, which is a regime that will become accessible in the near future through surveys such as the LSST.
ABSTRACT
The Ly α emission line is one of the most promising probes of cosmic reionization but isolating the signature of a change in the ionization state of the intergalactic medium (IGM) is ...challenging because of intrinsic evolution and internal radiation transfer effects. We present the first study of the evolution of Ly α emitters (LAE) during the epoch of reionization based on a full radiation-hydrodynamics cosmological simulation that is able to capture both the large-scale process of reionization and the small-scale properties of galaxies. We predict the Ly α emission of galaxies in the 103 cMpc3sphinx simulation at 6 ≤ z ≤ 9 by computing the full Ly α radiation transfer from interstellar medium (ISM) to IGM scales. sphinx is able to reproduce many observational constraints such as the UV/Ly α luminosity functions and stellar mass functions at z ≳ 6 for the dynamical range probed by our simulation (M1500 ≳ −18, LLy α ≲ 1042 erg s−1, M⋆ ≲ 109 M⊙). As intrinsic Ly α emission and internal Ly α escape fractions barely evolve from z = 6–9, the observed suppression of Ly α luminosities with increasing redshift is fully attributed to IGM absorption. For most observable galaxies (M1500 ≲ −16), the Ly α line profiles are slightly shifted to the red due to internal radiative transfer effects that mitigates the effect of IGM absorption. Overall, the enhanced Ly α suppression during reionization traces the IGM neutral fraction $x_{{\rm H\, {i}}}$ well, but the predicted amplitude of this reduction is a strong function of the Ly α peak shift, which is set at ISM/circumgalactic medium scales. We find that a large number of LAEs could be detectable in very deep surveys during reionization when $x_{{\rm H\, {i}}}$ is still $\approx 50{{\ \rm per\ cent}}$.
We use cosmological hydrodynamical simulations to show that a significant fraction of the gas in high redshift rare massive haloes falls nearly radially to their very centre on extremely short ...time-scales. This process results in the formation of very compact bulges with specific angular momentum a factor of 5-30 smaller than the average angular momentum of the baryons in the whole halo. Such low angular momentum originates from both segregation and effective cancellation when the gas flows to the centre of the halo along well-defined cold filamentary streams. These filaments penetrate deep inside the halo and connect to the bulge from multiple rapidly changing directions. Structures falling in along the filaments (satellite galaxies) or formed by gravitational instabilities triggered by the inflow (star clusters) further reduce the angular momentum of the gas in the bulge. Finally, the fraction of gas radially falling to the centre appears to increase with the mass of the halo; we argue that this is most likely due to an enhanced cancellation of angular momentum in rarer haloes which are fed by more isotropically distributed cold streams. Such an increasingly efficient funnelling of low angular momentum gas to the centre of very massive haloes at high redshift may account for the rapid pace at which the most massive supermassive black holes grow to reach observed masses around 109 M⊙ at an epoch when the Universe is barely 1 Gyr old.
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