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 observing strategies: (i) deep (1000h on a single field); (ii) medium-deep (100hr on 10 independent fields); and (iii) shallow (10hr on 100 independent fields). Using the 21-cm power spectrum as a summary statistic, and conservatively only using the 21-cm signal above the foreground wedge, we predict that all three observing strategies should recover astrophysical parameters to a fractional precision of $\sim 0.1$ -- 10 per cent. The reionisation history is recovered to an uncertainty of $Δz \lesssim 0.1$ (1$σ$) for the bulk of its duration. The medium-deep strategy, balancing thermal noise against cosmic variance, results in the tightest constraints, slightly outperforming the deep strategy. The shallow observational strategy performs the worst, with up to a $\sim 10$ -- 60 per cent increase in the recovered uncertainty. We note, however, that non-Gaussian summary statistics, tomography, as well as unbiased foreground removal would likely favour the deep strategy.
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…
Revealing the cosmic reionisation history is at the frontier of extragalactic astronomy. The power spectrum of the cosmic microwave background (CMB) polarisation can be used to constrain the reionisation history. Here we propose a CMB-independent method using fast radio bursts (FRBs) to directly measure the ionisation fraction of the intergalactic medium (IGM) as a function of redshift. FRBs are new astronomical transients with millisecond timescales. Their dispersion measure (DM$_{\rm IGM}$) is an indicator of the amount of ionised material in the IGM. Since the differential of DM$_{\rm IGM}$…
The Square Kilometre Array (SKA) will have a low frequency component (SKA-low) which has as one of its main science goals the study of the redshifted 21cm line from the earliest phases of star and galaxy formation in the Universe. This 21cm signal provides a new and unique window on both the formation of the first stars and accreting black holes and the later period of substantial ionization of the intergalactic medium. The signal will teach us fundamental new things about the earliest phases of structure formation, cosmology and even has the potential to lead to the discovery of new physical …
SKA-Low simulations for a cosmic dawn/epoch of reionisation deep field
SKA Observatory（SKA天文台）；Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester（曼彻斯特大学物理与天文学学院乔德雷尔银行天体物理学中心）；Department of Physics and Astronomy, University of Pennsylvania（宾夕法尼亚大学物理与天文学系）；LUX, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université（巴黎天文台卢克斯实验室，PSL研究大学，法国国家科学研究中心，索邦大学）；Kapteyn Astronomical Institute, University of Groningen（格罗宁根大学卡普坦天文研究所）；INAF – Osservatorio Astrofisico di Arcetri（意大利国家天体物理研究所阿切特里天文台）；Laboratoire de Physique de l’Ecole Normale Supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université de Paris（巴黎高等师范学校物理实验室，PSL大学，法国国家科学研究中心，索邦大学，巴黎大学）；International Centre for Radio Astronomy Research, Curtin University（科廷大学国际射电天文研究中心）；ARC Centre of Excellence for All-Sky Astrophysics in 3D（ARC三维全天体物理学卓越中心）
Cosmic reionization is known to be a major phase transition of the gas in the Universe. Since astronomical objects formed in the early Universe, such as the first stars, galaxies and black holes, are expected to have caused cosmic reionization, the formation history and properties of such objects are closely related to the reionization process. In spite of the importance of exploring reionization, our understandings regarding reionization is not sufficient yet. Square Kilometre Array (SKA) is a next-generation large telescope that will be operated in the next decade. Although several programs …
Concerted effort is currently ongoing to open up the Epoch of Reionization (EoR) ($z\sim$15-6) for studies with IR and radio telescopes. Whereas IR detections have been made of sources (Lyman-$α$ emitters, quasars and drop-outs) in this redshift regime in relatively small fields of view, no direct detection of neutral hydrogen, via the redshifted 21-cm line, has yet been established. Such a direct detection is expected in the coming years, with ongoing surveys, and could open up the entire universe from $z\sim$6-200 for astrophysical and cosmological studies, opening not only the EoR, but also…
In this review article, we briefly outline our current understanding of the physics associated with the HI 21-cm signal from cosmic dawn. We discuss different phases of cosmic dawn as the ambient gas and the background radiations evolve with the redshift. We address the consequences of several possible heating sources and radiation background on the global 21-cm signal. We further review our present perspective of other important aspects of the HI 21-cm signal such as the power spectrum and imaging. Finally, we highlight the future key measurements of the Square Kilometre Array and other ongoi…
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 …
The Square Kilometre Array (SKA) will offer an unprecedented view onto the early Universe, using interferometric observations of the redshifted 21cm line. The 21cm line probes the thermal and ionization state of the cosmic gas, which is governed by the birth and evolution of the first structures in our Universe. Here we show how the evolution of the 21cm signal will allow us to study when the first generations of galaxies appeared, what were their properties, and what was the structure of the intergalactic medium. We highlight qualitative trends which will offer robust insights into the early …
Dark matter annihilation or decay could have a significant impact on the ionisation and thermal history of the universe. In this paper, we study the potential contribution of dark matter annihilation (s-wave- or p-wave-dominated) or decay to cosmic reionisation, via the production of electrons, positrons and photons. We map out the possible perturbations to the ionisation and thermal histories of the universe due to dark matter processes, over a broad range of velocity-averaged annihilation cross-sections/decay lifetimes and dark matter masses. We have employed recent numerical studies of the …
Intensity mapping of the 21cm signal of neutral hydrogen will yield exciting insights into the Epoch of Reionisation and the nature of the first galaxies. However, the large amount of data that will be generated by the next generation of radio telescopes, such as the Square Kilometre Array (SKA), as well as the numerous observational obstacles to overcome, require analysis techniques tuned to extract the reionisation history and morphology. In this context, we introduce a one-point statistic, to which we refer as the local variance, $σ_\mathrm{loc}$, that describes the distribution of the mean…
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…
The upcoming radio interferometer Square Kilometre Array is expected to directly detect the redshifted 21-cm signal from the Cosmic Dawn for the first time. In this era temperature fluctuations from X-ray heating of the neutral intergalactic medium can impact this signal dramatically. Previously, in (Ross et al, 2017), we presented the first large-volume, 244 $h^{-1}$Mpc = 349 Mpc a side, fully numerical radiative transfer simulations of X-ray heating. This work is a follow-up where we now also consider QSO-like sources in addition to high mass X-ray binaries. Images of the two cases are clear…
We investigate the contribution of extended radio sources such as Centaurus A, and Galactic supernova remnants (SNRs) to our ability to detect the statistical $21\,\rm{cm}$ signal from the Epoch of Reionisation (EoR) with the Murchison Widefield Array (MWA). These sources are typically ignored because they are in highly attenuated parts of the MWA primary beam, however in aggregate these sources have apparent flux densities of $10\,\rm{Jy}$ on angular scales we expect to detect the $21\,\rm{cm}$ signal. We create bespoke multi-component 2D Gaussian models for Galactic SNRs and for Centaurus A,…
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 (…
The 21-cm signal from the epoch of cosmic dawn prior to reionization consists of a promising observable to gain new insights into the dark matter (DM) sector. In this paper, we investigate its potential to constrain mixed (cold + non-cold) dark matter scenarios that are characterised by the non-cold DM fraction ($f_{\rm nCDM}$) and particle mass ($m_{\rm nCDM}$). As non-cold DM species, we investigate both a fermionic (sterile neutrino) and a bosonic (ultra-light axion) particle. We show how these scenarios affect the global signal and the power spectrum using a halo-model implementation of th…
The Cosmic Dawn and Epoch of Reionisation, during which collapsed structures produce the first ionising photons and proceed to reionise the intergalactic medium, span a large range in redshift (z~30-6) and time (t_{age} ~ 0.1-1.0~Gyr). Exploration of these epochs using the redshifted 21~cm emission line from neutral hydrogen is currently limited to statistical detection and estimation metrics (e.g., the power spectrum) due to the weakness of the signal. Brightness temperature fluctuations in the line-of-sight (LOS) dimension are probed by observing the emission line at different frequencies, a…
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…
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-$α$…
The upcoming radio interferometer Square Kilometre Array (SKA) is expected to directly detect the redshifted 21-cm signal from the neutral hydrogen present during the Cosmic Dawn. Temperature fluctuations from X-ray heating of the neutral intergalactic medium can dominate the fluctuations in the 21-cm signal from this time. This heating depends on the abundance, clustering, and properties of the X-ray sources present, which remain highly uncertain. We present a suite of three new large-volume, 349\,Mpc a side, fully numerical radiative transfer simulations including QSO-like sources, extending…
The effect of photon re-scattering due to cosmic reionization on 21-cm images and power spectra
School of Physics and Astronomy, Tel-Aviv University（特拉维夫大学物理与天文学院）；Institute of Astronomy, University of Cambridge（剑桥大学天体研究所）；Kavli Institute for Cosmology（卡弗里宇宙学研究所）
Spectral features introduced by instrumental chromaticity of radio interferometers have the potential to negatively impact the ability to perform Epoch of Reionisation (EoR) and Cosmic Dawn (CD) science using the redshifted neutral hydrogen emission line from the early Universe. We describe instrument calibration choices that influence the spectral characteristics of the science data, and assess their impact on EoR statistical and tomographic experiments. Principally, we consider the intrinsic spectral response of the receiving antennas, embedded within a complete frequency-dependent primary b…
The redshifted 21cm line of neutral hydrogen (Hi), potentially observable at low radio frequencies (~50-200 MHz), is a promising probe of the physical conditions of the inter-galactic medium during Cosmic Dawn and the Epoch of Reionisation (EoR). The sky-averaged Hi signal is expected to be extremely weak (~100 mK) in comparison to the Galactic foreground emission (~$10^4$ K). Moreover, the sky-averaged spectra measured by ground-based instruments are affected by chromatic propagation effects (of the order of tens of Kelvins) originating in the ionosphere. We analyze data collected with the up…
Direct detection of regions of ionized hydrogen (HII) has been suggested as a promising probe of cosmic reionization. Observing the redshifted 21-cm signal of hydrogen from the epoch of reionization (EoR) is a key scientific driver behind new-generation, low-frequency radio interferometers. We investigate the feasibility of combining low-frequency observations with the Square Kilometre Array and near infra-red survey data of the Wide-Field Infrared Survey Telescope to detect cosmic reionization by imaging HII bubbles surrounding massive galaxies during the cosmic dawn. While individual bubbles…
The 21-cm signal from the Cosmic Dawn (CD) is likely to contain large fluctuations, with the most extreme astrophysical models on the verge of being ruled out by observations from radio interferometers. It is therefore vital that we understand not only the astrophysical processes governing this signal, but also other inherent processes impacting the signal itself, and in particular line-of-sight effects. Using our suite of fully numerical radiative transfer simulations, we investigate the impact on the redshifted 21-cm from the CD from one of these processes, namely the redshift-space distorti…
The Square Kilometre Array (SKA) is a planned large radio interferometer designed to operate over a wide range of frequencies, and with an order of magnitude greater sensitivity and survey speed than any current radio telescope. The SKA will address many important topics in astronomy, ranging from planet formation to distant galaxies. However, in this work, we consider the perspective of the SKA as a facility for studying physics. We review four areas in which the SKA is expected to make major contributions to our understanding of fundamental physics: cosmic dawn and reionisation; gravity and …
Detection of the redshifted 21-cm signal of neutral hydrogen from the Cosmic Dawn and the Epoch of Reionization is one of the final frontiers of modern observational cosmology. The inherently faint signal makes it susceptible to contamination by several sources like astrophysical foregrounds and instrumental systematics. Nevertheless, developments achieved in the recent times will combine to make signal detection possible with the upcoming Square Kilometer Array (SKA), both statistically and via tomography. This review describes an indigenously developed end-to-end pipeline that simulates sens…
We test the bandpass smoothness performance of two prototype Square Kilometre Array (SKA) SKA1-Low log-periodic dipole antennas, the SKALA2 and SKALA3 (`SKA Log-periodic Antenna'), and the current dipole from the Murchison Widefield Array (MWA) precursor telescope. Throughout this paper, we refer to the output complex-valued voltage response of an antenna when connected to a low noise amplifier (LNA), as the dipole bandpass. In Paper I (de Lera Acedo et al. 2017), the bandpass spectral response of the log-periodic antenna being developed for the SKA1-Low was estimated using numerical electroma…
In the most distant reaches of the Universe, the 21-cm hyperfine transition in neutral hydrogen provides one of the only available tracers of large-scale structure. A number of instruments have been working and planned to measure the 21-cm line signals, and in particular, Experiment to Detect the Global EoR Signature (EDGES) recently has reported the first detection of an absorption signal, which corresponds to the 21-cm line global signal at the epoch of reionization (EoR). The future large radio telescope, Square Kilometre Array (SKA) will be able to deliver the high-precision measurement of…
Exploring the Cosmic Dawn through the 21 cm Forest and High-redshift Radio Sources with the SKA
Max Planck Institute for Astrophysics（马克斯·普朗克天体物理学研究所）；Gifu Shotoku Gakuen University（岐阜女子大学）；Kobayashi Maskawa Institute, Nagoya University（名古屋大学小林益川研究所）；Northeastern University（东北大学）；Liaoning Normal University（辽宁师范大学）；University of Nevada, Las Vegas（内华达大学拉斯维加斯分校）；Yunnan University（云南大学）；Nagoya University（名古屋大学）；Institute for Fundamental Physics of the Universe（宇宙基础物理研究所）；The Institute of Statistical Mathematics（统计数学研究所）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；University of Tsukuba（筑波大学）
The shape of the faint-end of the high-z galaxy luminosity function (LF) informs early star formation and reionization physics during the Cosmic Dawn and Epoch of Reionization. Until recently, based on the strong gravitational lensing cluster deep surveys, the Hubble Frontier Fields (HFF) has found a potential turnover in the ultraviolet (UV) LF at z$\sim$6. In this paper, we analyze the contribution of extremely faint galaxies with the magnitude larger than the turnover magnitude in LF to cosmic reionization. We apply the measurement from HFF to our suppressed star formation efficiency model,…
The 21cm line brightness temperature brings rich information about Epoch of Reionizaton (EoR) and high-$z$ universe (Cosmic Dawn and Dark Age). While the power spectrum is a useful tool to investigate the EoR signal statistically, higher-order statistics such as bispectrum are also valuable because the EoR signal is expected to be highly non-Gaussian. In this paper, we develop a formalism to calculate the bispectrum contributed from the thermal noise taking array configularion of telescopes into account, by extending a formalism for the power spectrum \cite{2006ApJ...653..815M}. We apply our f…
Impact of Primordial Black Hole population on 21 cm observables at high redshift
Kapteyn Astronomical Institute, University of Groningen（格罗宁根大学卡普坦天文研究所）；International Centre for Space and Cosmology, School of Arts and Sciences, Ahmedabad University（艾哈迈达巴德大学文理学院国际空间与宇宙学中心）；Max-Planck-Institut für Astronomie（马克斯·普朗克天文学研究所）
Stations of dipole antennas for SKA1-Low will comprise 256 elements spread over an area with a diameter of 38~m. We consider the effect of residual unsubtracted sources well outside of the main beam for differing numbers of unique station configurations, in the Epoch of Reionisation (EoR) and the Cosmic Dawn (CD), both in simulation and with theoretical considerations. We find that beam sidelobes imprint power that renders the cosmological signal unobservable over a range of scales unless compact sources are subtracted beyond θ_Z=30 degrees from zenith, and that station apodization will likely…
The process of wide-field synthesis imaging is explored, with the aim of understanding the implications of variable, polarised primary beams for forthcoming Epoch of Reionisation experiments. These experiments seek to detect weak signatures from redshifted 21cm emission in deep residual datasets, after suppression and subtraction of foreground emission. Many subtraction algorithms benefit from low side-lobes and polarisation leakage at the outset, and both of these are intimately linked to how the polarised primary beams are handled. Building on previous contributions from a number of authors,…
Global 21cm experiments aim to measure the sky averaged HI absorption signal from cosmic dawn and the epoch of reionisation. However, antenna chromaticity coupling to bright foregrounds can introduce distortions into the observational data of such experiments. We demonstrate a method for guiding the antenna design of a global experiment through data analysis simulations. This is done by performing simulated observations for a range of inserted 21cm signals, then attempting to identify the signals with a data analysis pipeline. We demonstrate this method on five antennae that were considered as…
Aiming to fill a crucial gap in our observational knowledge of the early Universe, experiments around the world continue to attempt to verify the claimed detection of the redshifted 21-cm signal from Cosmic Dawn by the EDGES experiment. This sky-averaged or 'global' signal from neutral hydrogen should be detectable at low radio frequencies (50-200 MHz), but is difficult to measure due to bright foreground emission and difficulties in reaching the required levels of instrumental-calibration precision. In this paper we outline our progress toward using a novel new method to measure the global re…
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…
Significant new opportunities for astrophysics and cosmology have been identified at low radio frequencies. The Murchison Widefield Array is the first telescope in the Southern Hemisphere designed specifically to explore the low-frequency astronomical sky between 80 and 300 MHz with arcminute angular resolution and high survey efficiency. The telescope will enable new advances along four key science themes, including searching for redshifted 21 cm emission from the epoch of reionisation in the early Universe; Galactic and extragalactic all-sky southern hemisphere surveys; time-domain astrophys…
