ABSTRACT
The recent detection of ULASJ1342+0928, a bright QSO at $z$ = 7.54, provides a powerful probe of the ionization state of the intervening intergalactic medium, potentially allowing us to set ...strong constraints on the epoch of reionization (EoR). Here we quantify the presence of Ly α damping wing absorption from the EoR in the spectrum of ULASJ1342+0928. Our Bayesian framework simultaneously accounts for uncertainties on (i) the intrinsic QSO emission (reconstructing the Ly α profile from a covariance matrix of emission lines) and (ii) the distribution of H ii regions during reionization (from three different 1.63 Gpc3 simulations spanning plausible EoR morphologies). Our analysis is complementary to the Banados et al. discovery and accompanying Davies et al. method paper as it focuses solely on the damping wing imprint redward of Ly α (1218 < λ < 1230 Å) and uses a different methodology for (i) and (ii). We recover weak evidence for damping wing absorption from our intermediate EoR model yielding a volume-weighted neutral hydrogen fraction at $z$ = 7.5: $\bar{x}_{\mathrm{H\, {\scriptscriptstyle I}}{}} = 0.21^{+0.17}_{-0.19}$ (68 per cent). These constraints depend weakly on the EoR morphology. Our limits are lower than those of the previous two analyses, though they are consistent at ∼ 1–1.5σ. We attribute differences to (i) a lower intrinsic amplitude for our recovered Ly α profile and (ii) only considering transmission redward of Ly α, reducing the available constraining power but making the results less model-dependent. Our results are consistent with previous estimates of the EoR history, supporting a moderately extended EoR.
We introduce the Evolution Of 21 cm Structure (EOS) project: providing periodic, public releases of the latest cosmological 21 cm simulations. 21 cm interferometry is set to revolutionize studies of ...the Cosmic Dawn (CD) and Epoch of Reionization (EoR). Progress will depend on sophisticated data analysis pipelines, initially tested on large-scale mock observations. Here we present the 2016 EOS release: 10243, 1.6 Gpc, 21 cm simulations of the CD and EoR, calibrated to the Planck 2015 measurements. We include calibrated, sub-grid prescriptions for inhomogeneous recombinations and photoheating suppression of star formation in small-mass galaxies. Leaving the efficiency of supernovae feedback as a free parameter, we present two runs which bracket the contribution from faint unseen galaxies. From these two extremes, we predict that the duration of reionization (defined as a change in the mean neutral fraction from 0.9 to 0.1) should be between 2.7 ≲ Δz
re ≲ 5.7. The large-scale 21 cm power during the advanced EoR stages can be different by up to a factor of ∼10, depending on the model. This difference has a comparable contribution from (i) the typical bias of sources and (ii) a more efficient negative feedback in models with an extended EoR driven by faint galaxies. We also present detectability forecasts. With a 1000 h integration, Hydrogen Epoch of Reionization Array and (Square Kilometre Array phase 1) SKA1 should achieve a signal-to-noise of ∼few to hundreds throughout the EoR/CD. We caution that our ability to clean foregrounds determines the relative performance of narrow/deep versus wide/shallow surveys expected with SKA1. Our 21-cm power spectra, simulation outputs and visualizations are publicly available.
An ionizing ultraviolet background (UVB) inhibits gas accretion and photoevaporates gas from the shallow potential wells of small, dwarf galaxies. During cosmological reionization, this effect can ...result in negative feedback: suppressing star formation inside H ii regions, thus impeding their continued growth. It is difficult to model this process, given the enormous range of scales involved. We tackle this problem using a tiered approach: combining parametrized results from single-halo collapse simulations with large-scale models of reionization. In the resulting reionization models, the ionizing emissivity of galaxies depends on the local values of the reionization redshift and the UVB intensity. We present a physically motivated analytic expression for the average minimum mass of star-forming galaxies, M
min, which can be readily used in modelling galaxy formation. We find that UVB feedback: (i) delays the end stages of reionization by Δz 0.5; (ii) results in a more uniform distribution of H ii regions, peaked on smaller scales (with large-scale ionization power suppressed by 10s of per cent) and (iii) suppresses the global photoionization rate per baryon by a factor of 2 towards the end of reionization. However, the impact is modest, since the hydrodynamic response of the gas to the UVB occurs on a time-scale comparable to reionization. In particular, the popular approach of modelling UVB feedback with an instantaneous transition in M
min, dramatically overestimates its importance. UVB feedback on galaxies does not significantly affect reionization unless: (i) molecularly cooled galaxies contribute significantly to reionization; or (ii) internal feedback processes strongly couple with UVB feedback in the early Universe. Since both are considered unlikely, we conclude that there is no significant self-regulation of reionization by UVB feedback.
ABSTRACT
Cross-correlating 21 cm with known cosmic signals will be invaluable proof of the cosmic origin of the first 21-cm detections. As some of the widest fields available, comprising thousands of ...sources with reasonably known redshifts, narrow-band Lyman-α emitter (LAE) surveys are an obvious choice for such cross-correlation. Here, we revisit the 21-cm–LAE cross-correlation, relaxing the common assumption of reionization occurring in a pre-heated intergalactic medium (IGM). Using specifications from the Square Kilometre Array and the Subaru Hyper Supreme-Cam, we present new forecasts of the 21-cm–LAE cross-correlation function at z ∼ 7. We sample a broad parameter space of the mean IGM neutral fraction and spin temperature, ($\bar{x}_{\rm H\,{\small I}}$, $\bar{T}_{\rm S}$). The sign of the cross-correlation roughly follows the sign of the 21-cm signal: Ionized regions that surround LAEs correspond to relative hot spots in the 21-cm signal when the neutral IGM is colder than the CMB, and relative cold spots when the neutral IGM is hotter than the CMB. The amplitude of the cross-correlation function generally increases with increasing $\bar{x}_{\rm H\,{\small I}}$, following the increasing bias of the cosmic H ii regions. As is the case for 21 cm, the strongest cross signal occurs when the IGM is colder than the CMB, providing a large contrast between the neutral regions and the ionized regions, which host LAEs. We also vary the topology of reionization and the epoch of X-ray heating. The cross-correlation during the first half of reionization is sensitive to these topologies, and could thus be used to constrain them.
The cosmological 21 cm signal is a physics-rich probe of the early Universe, encoding information about both the ionization and the thermal history of the intergalactic medium (IGM). The latter is ...likely governed by X-rays from star formation processes inside very high redshift (z ≳ 15) galaxies. Due to the strong dependence of the mean free path on the photon energy, the X-ray spectral energy distribution (SED) can have a significant impact on the interferometric signal from the cosmic dawn. Recent Chandra observations of nearby, star-forming galaxies show that their SEDs are more complicated than is usually assumed in 21 cm studies. In particular, these galaxies have ubiquitous, sub-keV thermal emission from the hot interstellar medium (ISM), which generally dominates the soft X-ray luminosity (with energies ≲1 keV, sufficiently low to significantly interact with the IGM). Using illustrative soft and hard SEDs, we show that the IGM temperature fluctuations in the early Universe would be substantially increased if the X-ray spectra of the first galaxies were dominated by the hot ISM, compared with X-ray binaries with harder spectra. The associated large-scale power of the 21 cm signal would be higher by a factor of ∼3. More generally, we show that the peak in the redshift evolution of the large-scale (k ∼ 0.2 Mpc−1) 21 cm power is a robust probe of the soft-band SED of the first galaxies, and importantly, is not degenerate with their bolometric luminosities. On the other hand, the redshift of the peak constrains the X-ray luminosity and halo masses which host the first galaxies.
The reionization of the intergalactic medium (IGM) was likely inhomogeneous and extended. By heating the IGM and photo-evaporating gas from the outskirts of galaxies, this process can have a dramatic ...impact on the growth of structures. Using a suite of spherically symetric collapse simulations spanning a large parameter space, we study the impact of an ultraviolet background (UVB) on the condensation of baryons onto dark matter haloes. We present an expression for the halo baryon fraction, f
b, which is an explicit function of (i) halo mass, (ii) UVB intensity, (iii) redshift and (iv) redshift at which the halo was exposed to a UVB. We also present a corresponding expression for the characteristic or critical mass, M
crit, defined as the halo mass which retains half of its baryons compared to the global value. Since our results are general and physically motivated, they can be broadly applied to inhomogeneous reionization models.
Detailed theoretical studies of the high-redshift universe, and especially reionization, are generally forced to rely on time-consuming N-body codes and/or radiative transfer algorithms. We present a ...method to construct seminumerical "simulations," which can efficiently generate realizations of halo distributions and lonization maps at high redshifts. Our procedure combines an excursion-set approach with first-order Lagrangian perturbation theory and operates directly on the linear density and velocity fields. As such, the achievable dynamic range with our algorithm surpasses the current practical limit of N-body codes by orders of magnitude. This is particularly significant in studies of reionization, where the dynamic range is the principal limiting factor, because ionized regions reach scales of tens of comoving Mpc. We test our halo-finding and ionization-mapping algorithms separately against /V-body simulations with radiative transfer and obtain excellent agreement. We compute the size distributions of ionized and neutral regions in our maps. We find even larger ionized bubbles than do purely analytic models at the same volume-weighted mean hydrogen neutral fraction, unk, especially early in reionization. We also generate maps and power spectra of 21 cm brightness temperature fluctuations, which for the first time include corrections due to gas bulk velocities. We find that velocities widen the tails of the temperature distributions and increase small-scale power, although these effects quickly diminish as reionization progresses. We also Include some preliminary results from a simulation run with the largest dynamic range to date: a 250 Mpc box that resolves halos with masses M greater than or equal to 2.2 x 10 super(8) M., we show that accurately modeling the late stages of reionization, unk unk 0-5, requires such large scales. The speed and dynamic range provided by our seminumerlcal approach will be extremely useful in the modeling of early structure formation and reionization.
PDF
