1,721,136 research outputs found
Reionization and Cosmic Dawn: Theory and simulations
Full text linkWe highlight recent progress in the sophistication and diversification of the simulations of cosmic dawn and reionization. The application of these modeling tools to recent observations has allowed us narrow down the timing of reionization. The midpoint of reionization is constrained to z = 7.6-0.7+0.8(1 σ), with the strongest constraints coming from the optical depth to the CMB measured with the Planck satellite and the first detection of ongoing reionization from the spectra of the z = 7.1 QSOs ULASJ1120+0641. However, we still know virtually nothing about the astrophysical sources during the first billion years. The revolution in our understanding will be led by upcoming interferometric observations of the cosmic 21-cm signal. The properties of the sources and sinks of UV and X-ray photons are encoded in the 3D patterns of the signal. The development of Bayesian parameter recovery techniques, which tap into the wealth of the 21-cm signal, will soon usher in an era of precision astrophysical cosmology
The clustering of Lyman α emitters atz≈ 7: implications for reionization and host halo masses
No full textThe global history of reionization
Full text linkUsing a Bayesian framework, we quantify what current observations imply about the history of the epoch of reionization (EoR). We use a popular, three-parameter EoR model, flexible enough to accommodate a wide range of physically plausible reionization histories. We study the impact of various EoR observations: (i) the optical depth to the CMB measured by Planck 2016; (ii) the dark fraction in the Lyman α and β forests; (iii) the redshift evolution of galactic Lyα emission (so-called ‘Lyα fraction’); (iv) the clustering of Lyα emitters; (v) the IGM damping wing imprint in the spectrum of QSO ULASJ1120+0641; (vi) and the patchy kinetic Sunyaev–Zel'dovich signal. Combined, (i) and (ii) already place interesting constraints on the reionization history, with the epochs corresponding to an average neutral fraction of (75, 50, 25) per cent, constrained at 1σ to z=(9.21+1.22−1.15,8.14+1.08−1.00,7.26+1.13−0.96). Folding-in more model-dependent EoR observations [(iii)–(vi)], strengthens these constraints by tens of per cent, at the cost of a decrease in the likelihood of the best-fitting model, driven mostly by (iii). The tightest constraints come from (v). Unfortunately, no current observational set is sufficient to break degeneracies and constrain the astrophysical EoR parameters. However, model-dependent priors on the EoR parameters themselves can be used to set tight limits by excluding regions of parameter space with strong degeneracies. Motivated by recent observations of z ∼ 7 faint, lensed galaxies, we show how a conservative upper limit on the virial temperature of haloes which host reionizing galaxies can constrain the escape fraction of ionizing photons to fesc=0.14+0.26−0.09
21CMMC: an MCMC analysis tool enabling astrophysical parameter studies of the cosmic 21 cm signal
Full text linkWeintroduce 21CMMC: a parallelized, Monte Carlo Markov Chain analysis tool, incorporating the epoch of reionization (EoR) seminumerical simulation 21CMFAST. 21CMMC estimates astrophysical parameter constraints from 21 cm EoR experiments, accommodating a variety of EoR models, as well as priors on model parameters and the reionization history. To illustrate its utility, we consider two different EoR scenarios, one with a single population of galaxies (with a mass-independent ionizing efficiency) and a second, more general model with two different, feedback-regulated populations (each with mass-dependent ionizing efficiencies). As an example, combining three observations (z = 8, 9 and 10) of the 21 cm power spectrum with a conservative noise estimate and uniform model priors, we find that interferometers with specifications like the Low Frequency Array/Hydrogen Epoch of Reionization Array (HERA)/Square Kilometre Array 1 (SKA1) can constrain common reionization parameters: the ionizing efficiency (or similarly the escape fraction), the mean free path of ionizing photons and the log of the minimumvirial temperature of star-forming haloes to within 45.3/22.0/16.7, 33.5/18.4/17.8 and 6.3/3.3/2.4 per cent, ∼1σ fractional uncertainty, respectively. Instead, if we optimistically assume that we can perfectly characterize the EoR modelling uncertainties, we can improve on these constraints by up to a factor of ∼few. Similarly, the fractional uncertainty on the average neutral fraction can be constrained to within ≲ 10percent for HERA and SKA1. By studying the resulting impact on astrophysical constraints, 21CMMC can be used to optimize (i) interferometer designs; (ii) foreground cleaning algorithms; (iii) observing strategies; (iv) alternative statistics characterizing the 21 cm signal; and (v) synergies with other observational programs
Probing reionization with the cosmological proximity effect and high-redshift supernovae rates
No full textWe develop and assess the potential of several powerful techniques, designed to investigate the details of reionization. First, we present a procedure to probe the neutral fraction, xHI, using the Lyman α transmission statistics of high-redshift (z ≳ 6) sources. We find that only tens of bright quasar spectra could distinguish between xHI ∼ 1 and xHI ≲ 10-2. A rudimentary application of such a technique on quasar SDSS J1030+0524 has yielded compelling evidence of a large neutral fraction (xHI ≳ 0.2) at z ∼ 6. We also generate the observable, high-z supernovae (SNe) rates and quantify the prospects of detecting the suppression of star-formation in low-mass galaxies at reionization from such SNe rates, specifically from those obtainable from the James Webb Space Telescope (JWST). Our analysis suggests that searches for SNe could yield thousands of SNe per unit redshift at z ∼ 6, and be a valuable tool at studying reionization features and feedback effects out to z ≲ 13. © 2005 Elsevier B.V. All rights reserved
Lyα damping wing constraints on inhomogeneous reionization
No full textOne well-known way to constrain the hydrogen neutral fraction, of the high-redshift intergalactic medium (IGM) is through the shape of the red damping wing of the Lyα absorption line. We examine this method's effectiveness in light of recent models showing that the IGM neutral fraction is highly inhomogeneous on large scales during reionization. Using both analytic models and 'seminumeric' simulations, we show that the 'picket-fence' absorption typical in reionization models introduces both scatter and a systematic bias to the measurement of. In particular, we show that simple fits to the damping wing tend to overestimate the true neutral fraction in a partially ionized universe, with a fractional error of ∼30 per cent near the middle of reionization. This bias is generic to any inhomogeneous model. However, the bias is reduced and can even underestimate if the observational sample only probes a subset of the entire halo population, such as quasars with large H ii regions. We also find that the damping wing absorption profile is generally steeper than one would naively expect in a homogeneously ionized universe. The profile steepens and the sightline-to-sightline scatter increases as reionization progresses. Of course, the bias and scatter also depend on and so can, at least in principle, be used to constrain it. Damping wing constraints must therefore be interpreted by comparison to theoretical models of inhomogeneous reionization. © 2008 RAS
Evidence of a Cosmological Strömgren Surface and of Significant Neutral Hydrogen Surrounding the Quasar SDSS J1030+0524
No full textA bright quasar residing in a dense and largely neutral intergalactic medium at high redshifts (z ≳ 6) will be surrounded by a large cosmological Strömgren sphere. The quasar's spectrum will then show a sharp increase in resonant Lyman line absorption at wavelengths approaching and shorter than that corresponding to the Strömgren sphere's boundary along the line of sight. We show here that simultaneously considering the measured absorption in two or more hydrogen Lyman lines can provide the dynamical range required to detect this feature. We model broad and robust features of the Lyα and Lyβ regions of the spectrum of the z = 6.28 quasar SDSS J1030+0524, using a hydrodynamical simulation. From the steep wavelength dependence of the inferred absorption opacity, we detect the boundary of the Strömgren sphere at a proper distance of 6.0 ± 0.2 Mpc away from the source redshift. From the spectrum alone, we also find that beyond this distance, cosmic hydrogen turns nearly neutral, with a neutral fraction of xH1 ≳ 0.2, and that the ionizing luminosity of this quasar is in the range of (5.2 ± 2.5) × 1056 photons s-1. The method presented here, when applied to future quasars, can probe the complex topology of overlapping ionized regions and can be used to study the details of the reionization process
Lyα emitters during the early stages of reionization
No full textWe investigate the potential of exploiting Lyα emitters (LAEs) to constrain the volume-weighted mean neutral hydrogen fraction of the intergalactic medium, at high redshifts (specifically z ∼ 9). We use 'seminumerical' simulations to efficiently generate density, velocity and halo fields at z = 9 in a 250-Mpc box, resolving haloes with masses M ≥ 2.2 × 108 M⊙. We construct ionization fields corresponding to various values of. With these, we generate LAE luminosity functions and 'counts-in-cell' statistics. As in previous studies, we find that LAEs begin to disappear rapidly when. Constraining with luminosity functions is difficult due to the many uncertainties inherent in the host halo mass ↔ Lyα luminosity mapping. However, using a very conservative mapping, we show that the number densities derived using the six z ∼ 9 LAEs recently discovered by Stark et al. (2007a) imply. On a more fundamental level, these LAE number densities, if genuine, require substantial star formation in haloes with M ≲ 109 M⊙, making them unique among the current sample of observed high-z objects. Furthermore, reionization increases the apparent clustering of the observed LAEs. We show that a 'counts-in-cell' statistic is a powerful probe of this effect, especially in the early stages of reionization. Specifically, we show that a field of view (typical of upcoming infrared instruments) containing LAEs has ≳10 per cent higher probability of containing more than one LAE in a universe than a universe with the same overall number density. With this statistic, an ionized universe can be robustly distinguished from one with using a survey containing only ∼20-100 galaxies. © 2008 RAS
The inhomogeneous ionizing background following reionization
No full textWe study the spatial fluctuations in the hydrogen-ionizing background in the epoch following reionization (z ∼ 5-6). The rapid decrease with redshift in the photon mean free path (mfp), combined with the clustering of increasingly rare ionizing sources, can result in a very inhomogenous ionizing background during this epoch. We systematically investigate the probability density functions (PDFs) and power spectra of ionizing flux, by varying several parameters such as the mfp, minimum halo mass capable of hosting stars and halo duty cycle. In order to be versatile, we make use of analytic, seminumeric and numeric approaches. Our models show that the ionizing background indeed has sizable fluctuations during this epoch, with the PDFs being a factor of few wide at half of the maximum likelihood. The clustering of sources dominates the width of the PDFs, so analytic models must take large-scale clustering into account. The distributions also show marked asymmetries, with a high-value tail set by clustering on small scales, and a shorter low-value tail which is set by the mfp. The power spectrum of the ionizing background is much more sensitive to source properties than the PDF and can be well understood analytically with a framework similar to the halo model (usually used to describe dark matter clustering). Nevertheless, we find that Lyα forest spectra are extremely insensitive to the details of the ultraviolet background, despite marked differences in the PDFs and power spectra of our various ionizing backgrounds. Assuming a uniform ionizing background only underestimates the value of the mean ionization rate, 〈Γ12〉, inferred from the Lyα forest by a few per cent. Instead, analysis of the Lyα forest is dominated by the uncertainties in the density field. Thus, our results justify the common assumption of a uniform ionizing background in Lyα forest analysis even during this epoch. © 2009 RAS
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