Simultaneously constraining the astrophysics of reionisation and the epoch of heating with 21CMMC
Bradley Greig, Andrei Mesinger
备注：
20 pages, 10 figures, 4 tables. Accepted to MNRAS (matches online version). Movies showing the imprint of the astrophysical parameters on the 21cm signal can be found at http://homepage.sns.it/mesinger/21CMMC.html
The cosmic 21 cm signal is set to revolutionise our understanding of the early Universe, allowing us to probe the 3D temperature and ionisation structure of the intergalactic medium (IGM). It will open a window onto the unseen first galaxies, showing us how their UV and X-ray photons drove the cosmic milestones of the epoch of reionisation (EoR) and epoch of heating (EoH). To facilitate parameter inference from the 21 cm signal, we previously developed 21CMMC: a Monte Carlo Markov Chain sampler of 3D EoR simulations. Here we extend 21CMMC to include simultaneous modelling of the EoH, resulting in a complete Bayesian inference framework for the astrophysics dominating the observable epochs of the cosmic 21 cm signal. We demonstrate that second generation interferometers, the Hydrogen Epoch of Reionisation Array (HERA) and Square Kilometre Array (SKA) will be able to constrain ionising and X-ray source properties of the first galaxies with a fractional precision of order $\sim1$-10 per cent (1$σ$). The ionisation history of the Universe can be constrained to within a few percent. Using our extended framework, we quantify the bias in EoR parameter recovery incurred by the common simplification of a saturated spin temperature in the IGM. Depending on the extent of overlap between the EoR and EoH, the recovered astrophysical parameters can be biased by $\sim3-10σ$.
We extend 21CMMC, a Monte Carlo Markov Chain sampler of 3D reionisation simulations, to perform parameter estimation directly on 3D light-cones of the cosmic 21cm signal. This brings theoretical analysis closer to the tomographic 21-cm observations achievable with next generation interferometers like HERA and the SKA. Parameter recovery can therefore account for modes which evolve with redshift/frequency. Additionally, simulated data can be more easily corrupted to resemble real data. Using the light-cone version of 21CMMC, we quantify the biases in the recovered astrophysical parameters if we…
Interferometry of the cosmic 21-cm signal is set to revolutionise our understanding of the Epoch of Reionisation (EoR) and the Cosmic Dawn (CD). The culmination of ongoing efforts will be the upcoming Square Kilometre Array (SKA), which will provide tomography of the 21-cm signal from the first billion years of our Universe. Using a galaxy formation model informed by high-$z$ luminosity functions, here we forecast the accuracy with which the first phase of SKA-low (SKA1-low) can constrain the properties of the unseen galaxies driving the astrophysics of the EoR and CD. We consider three observ…
Intensity mapping enables us to test cosmology and fundamental physics during the Epoch of Reionisation, with power spectra of line fluctuations probing a large range of scales and redshifts. Cosmological volumes of 21cm line fluctuations in general modified gravity scenarios are presented, where additional parameters are the initial condition parameter $α$ of matter perturbations and the scale-dependent modified gravity parameter $Y$ that measures deviations from General Relativity in the Poisson equation. For upcoming surveys like the SKA we forecast, using the power spectra derived from our…
We use the latest multi-redshift ($z=6.5-8.7$) upper limits on the 21-cm signal from the Murchison Widefield Array (MWA) to explore astrophysical models which are inconsistent with the data. These upper limits are achieved using 298 h of carefully excised data over four observing seasons. To explore these upper limits in the context of reionisation astrophysics, we use 21CMMC. We then connect the disfavoured regions of parameter space to existing observational constraints on reionisation such as high-$z$ galaxy ultra-violet (UV) luminosity functions, background UV photoionisation rate, interga…
A Portrait of the Cosmic Reionisation History in the Context of the Early Dark Energy Model
National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；University of Chinese Academy of Sciences（中国科学院大学）；Peking University（北京大学）；Swinburne University of Technology（斯威本科技大学）；University of Arizona（亚利桑那大学）
Detecting the cosmic 21-cm signal during the Epoch of Reionisation and Cosmic Dawn will reveal insights into the properties of the first galaxies and advance cosmological parameter estimation. Until recently, the primary focus for astrophysical parameter inference from the 21-cm signal centred on the power spectrum (PS). However, the cosmic 21-cm signal is highly non-Gaussian rendering the PS sub-optimal for characterising the cosmic signal. In this work, we introduce a new technique to analyse the non-Gaussian information in images of the 21-cm signal called the Wavelet Scattering Transform (…
Using the latest upper limits on the 21-cm power spectrum at $z\approx9.1$ from the Low Frequency Array (LOFAR), we explore regions of parameter space which are inconsistent with the data. We use 21CMMC, a Monte Carlo Markov Chain sampler of 21cmFAST which directly forward models the 3D cosmic 21-cm signal in a fully Bayesian framework. We use the astrophysical parameterisation from 21cmFAST, which includes mass-dependent star formation rates and ionising escape fractions as well as soft-band X-ray luminosities to place limits on the properties of the high-$z$ galaxies. Further, we connect the…
Using a Bayesian framework, we quantify what current observations imply about the history of the epoch of reionisation (EoR). We use a popular, three-parameter EoR model, flexible enough to accommodate a wide range of physically-plausible reionisation 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 Ly$α$ emission (so-called "Ly$α$ fraction"); (iv) the clustering of Ly$α$ emitters; (v) the IGM damping wing imprint in the spectrum…
Detecting the 21-cm hyperfine transition from neutral hydrogen in the intergalactic medium is our best probe for understanding the astrophysical processes driving the Epoch of Reionisation (EoR). The primary means for a detection of this 21-cm signal is through a statistical measurement of the spatial fluctuations using the 21-cm power spectrum (PS). However, the 21-cm signal is non-Gaussian meaning the PS, which only measures the Gaussian fluctuations, is sub-optimal for characterising all of the available information. The upcoming Square Kilometre Array (SKA) will perform a deep, 1000 hr obs…
We discuss constraints on cosmic reionisation and their implications on a cosmic SFR density $ρ_\mathrm{SFR}$ model; we study the influence of key-parameters such as the clumping factor of ionised hydrogen in the intergalactic medium (IGM) $C_{H_{II}}$ and the fraction of ionising photons escaping star-forming galaxies to reionise the IGM $f_\mathrm{esc}$. Our analysis uses SFR history data coming from luminosity functions, assuming that star-forming galaxies were sufficient to lead the reionisation process at high redshift. We add two other sets of constraints: measurements of the IGM ionised…
Emulation of the Global (sky-averaged) 21-cm signal with neural networks has been shown to be an essential tool for physical signal modelling. In this paper we present globalemu, a Global 21-cm signal emulator that uses redshift as a character defining variable alongside a set of astrophysical parameters to estimate the signal brightness temperature. Combined with physically-motivated data pre-processing this makes for a reliable and fast emulator that is relatively insensitive to the network design. globalemu can emulate a high resolution signal in 1.3 ms in comparison to 133 ms, a factor of …
Higher-order methods of radiative transfer in simulations of the epoch of reionisation: Pn versus M1
Observatoire Astronomique de Strasbourg, Universite de Strasbourg, CNRS UMR 7550（斯特拉斯堡天文台，斯特拉斯堡大学）；Institut de Recherche Mathématique Avancée (IRMA), University of Strasbourg（斯特拉斯堡大学高等数学研究所）；Direction du Numérique - Pôle CESAR, University of Strasbourg（斯特拉斯堡大学数字事务处-CESAR中心）
Observations of high-redshift galaxies have provided us with a rich tool to study the physics at play during the epoch of reionisation. The luminosity function (LF) of these objects is an indirect tracer of the complex processes that govern galaxy formation, including those of the first dark-matter structures. In this work, we present an extensive analysis of the UV galaxy LF at high redshifts to extract cosmological and astrophysical parameters. We provide a number of phenomenological approaches in modelling the UV LF and take into account various sources of uncertainties and systematics in o…
21cm tomography opens a window to directly study astrophysics and fundamental physics of early epochs in our Universe's history, the Epoch of Reionisation (EoR) and Cosmic Dawn (CD). Summary statistics such as the power spectrum omit information encoded in this signal due to its highly non-Gaussian nature. Here we adopt a network-based approach for direct inference of CD and EoR astrophysics jointly with fundamental physics from 21cm tomography. We showcase a warm dark matter (WDM) universe, where dark matter density parameter $Ω_\mathrm{m}$ and WDM mass $m_\mathrm{WDM}$ strongly influence bot…
Creating a database of 21cm brightness temperature signals from the Epoch of Reionisation (EoR) for an array of reionisation histories is a complex and computationally expensive task, given the range of astrophysical processes involved and the possibly high-dimensional parameter space that is to be probed. We utilise a specific type of neural network, a Progressively Growing Generative Adversarial Network (PGGAN), to produce realistic tomography images of the 21cm brightness temperature during the EoR, covering a continuous three-dimensional parameter space that models varying X-ray emissivity…
The epochs of cosmic dawn and reionisation present promising avenues for understanding the role of dark matter (DM) in our cosmos. The first galaxies that populated the Universe during these eras resided in DM halos that were much less massive than their counterparts today. Consequently, observations of such galaxies can provide us with a handle on the clustering of DM in an otherwise currently inaccessible regime. In this work, we use high-redshift UV galaxy luminosity-function (UV LF) data from the Hubble Space Telescope to study the clustering properties of DM at small scales. In particular…
Prior to the epoch of reionisation, the 21-cm signal of the cosmic dawn is dominated by the Lyman-$α$ coupling and gas temperature fluctuations caused by the first sources of radiation. While early efforts to model this epoch relied on analytical techniques, the community quickly transitioned to more expensive semi-numerical models. Here, we re-assess the viability of simpler approaches that allow for rapid explorations of the vast astrophysical parameter space. We propose a new analytical method to calculate the 21-cm power spectrum based on the framework of the halo model. Both the Lyman-$α$…
Understanding the physics of star formation is one of the key problems facing modern astrophysics. The Cosmic Infrared Background (CIB), sourced by the emission from all dusty star-forming galaxies since the epoch of reionisation, is a complementary probe to study the star formation history, as well as an important extragalactic foreground for studies of the Cosmic Microwave Background (CMB). Understanding the physics of the CIB is therefore of high importance for both cosmology and galaxy formation studies. In this paper, we make high signal-to-noise measurements of the cross-correlation betw…
