Experiment To Detect The Global Epoch Of Reionization Signature Research Articles

Tackling the Challenges in the 21 cm Global Spectrum Experiment: The Impact of Ionosphere and Beam Distortion

The H i 21 cm global signal from the Cosmic Dawn and the Epoch of Reionization (EoR) offers critical insights into the evolution of our Universe. Yet, its detection presents significant challenges, due to its extremely low signal-to-contamination ratio and complex instrumental systematics. In this paper, we examine the effects of the ionosphere and antenna beam on data analysis. The ionosphere, an ionized plasma layer in the Earth’s atmosphere, refracts, absorbs, and emits radio waves in the relevant frequency range. This interaction results in additional spectral distortion of the observed signal, complicating the process of foreground subtraction. Additionally, chromatic variations in the beam can also introduce further contamination into the global spectrum measurement. Notably, the ionospheric effect, being dependent on the direction of incoming light, interacts with the instrumental beam, adding another layer of complexity. To address this, we evaluate three different fitting templates of foreground: the logarithmic polynomial, the physically motivated Experiment to Detect the Global EoR Signature (EDGES) template, and a singular value decomposition (SVD)-based template. Our findings indicate that the EDGES and SVD templates generally surpass logarithmic polynomials in performance. Recognizing the significance of beam chromaticity, we further investigate specific beam distortion models and their impacts on the signal extraction process.

Probing the primordial Universe with 21 cm line from cosmic dawn/epoch of reionization

Abstract 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 or are planned to measure the 21 cm line signals, and in particular, the Experiment to Detect the Global EoR Signature (EDGES) has recently 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, the Square Kilometre Array (SKA) will be able to deliver the high-precision measurement of the 21 cm line emission/absorption signals. In this paper, we review the current status for the 21 cm line global and fluctuation signals from EoR to the dark ages, and then summarize the recent studies of how we probe the primordial Universe particularly motivated by the recent EDGES result and future observations by SKA. We focus on two applications for constraining cosmology with the EDGES result: constraints on the primordial magnetic fields and those on the primordial power spectrum. We also discuss the potential of future SKA for probing the inflationary Universe, by discussing expected constraints on the primordial power spectrum, its adiabaticity, and primordial non-Gaussianities from future observations of 21 cm fluctuations.

On the detection of a cosmic dawn signal in the radio background

The astrophysics of the cosmic dawn, when star formation commenced in the first collapsed objects, is predicted to be revealed by spectral and spatial signatures in the cosmic radio background at long wavelengths. The sky-averaged redshifted 21 cm absorption line of neutral hydrogen is a probe of the cosmic dawn. The line profile is determined by the evolving thermal state of the gas, radiation background, Lyman α radiation from stars scattering off cold primordial gas, and relative populations of the hyperfine spin levels in neutral hydrogen atoms. We report a radiometer measurement of the spectrum of the radio sky in the 55–85 MHz band, which shows that the profile found by Bowman et al. in data taken with the Experiment to Detect the Global Epoch of Reionization Signature (EDGES) low-band instrument is not of astrophysical origin; their best-fitting profile is rejected with 95.3% confidence. The profile was interpreted to be a signature of the cosmic dawn; however, its amplitude was substantially higher than that predicted by standard cosmological models. Our non-detection bears out earlier concerns and suggests that the profile found by Bowman et al. is not evidence for new astrophysics or non-standard cosmology.

Bounds on sterile neutrino lifetime and mixing angle with active neutrinos by global 21 cm signal

Sterile neutrinos can be a possible candidate for dark matter. Sterile neutrinos are radiatively unstable and can inject photon energy into the intergalactic medium (IGM). The injection of photon energy into IGM can modify the temperature and ionization history of IGM gas during cosmic dawn. Theoretical models based on the ΛCDM framework predict an absorption profile in the 21 cm line during the cosmic dawn era. Recently, the Experiment to Detect the Global Epoch of Reionization Signature (EDGES) collaboration confirmed such an adsorption signal. Injection of energy into IGM can modify the absorption amplitude in the 21 cm signal. Considering the 21 cm absorption signal at cosmic dawn, we constrain the lifetime of sterile neutrinos and the mixing angle of sterile neutrinos with active neutrinos. We also compare these bounds with other astrophysical observational bounds.

Kinetic theory of Jeans’ gravitational instability in millicharged dark matter system

The possibility of baryons cooled by a millicharged dark matter (mDM) via mDM-baryons scattering has recently been proposed to explain the observation discrepancy from the experiment to detect the global epoch of reionization signature (EDGES). In this sense, we analyze the Jeans instability of self-gravitational systems in the background of mDM under kinetic regime that the collisionless Boltzmann equation and Poisson equation have been combined to obtain the modified dispersion relation. It is shown that the effect of mDM is significant on the dynamics of gravitational collapse, i.e., the presence of mDM makes the self-gravitational systems more difficult to collapse relatively.

Validation of the EDGES Low-band Antenna Beam Model

Abstract The response of the antenna is a source of uncertainty in measurements with the Experiment to Detect the Global Epoch of Reionization Signature (EDGES). We aim to validate the electromagnetic beam model of the low-band (50–100 MHz) dipole antenna with comparisons between models and against data. We find that simulations of a simplified model of the antenna over an infinite perfectly conducting ground plane are, with one exception, robust to changes in the numerical electromagnetic solver code or algorithm. For simulations of the antenna with the actual finite ground plane and realistic soil properties, we find that two out of three numerical solvers agree well. Applying our analysis pipeline to a simulated drift-scan observation from an early EDGES low-band instrument that had a 10 m × 10 m ground plane, we find residual levels after fitting and removing a five-term foreground model from the simulated data binned in local sidereal time (LST) average about 250 mK with ±40 mK variation between numerical solvers. A similar analysis of the primary 30 m × 30 m sawtooth ground plane reduced the LST-averaged residuals to about 90 mK with ±10 mK between the two viable solvers. More broadly we show that larger ground planes generally perform better than smaller ground planes. Simulated data have a power that is within 4% of real observations, a limitation of net accuracy of the sky and beam models. We observe that residual spectral structures after foreground model fits match qualitatively between simulated data and observations, suggesting that the frequency dependence of the beam is reasonably represented by the models. We find that a soil conductivity of 0.02 S m−1 and relative permittivity of 3.5 yield good agreement between simulated spectra and observations. This is consistent with the soil properties reported by Sutinjo et al. for the Murchison Radio-astronomy Observatory, where EDGES is located.

Constraint on primordial magnetic fields in the light of ARCADE 2 and EDGES observations

We study the constraints on primordial magnetic fields (PMFs) in the light of the Experiment to Detect the Global Epoch of Reionization Signature (EDGES) low-band observation and Absolute Radiometer for Cosmology, Astrophysics and Diffuse Emission (ARCADE 2). ARCADE 2 observation detected extra-galactic excess radio radiation in the frequency range 3–90 GHz. The enhancement in the radio radiation is also supported by the first station of the Long Wavelength Array (LWA1) in the frequency range 40–80 MHz. The presence of early radiation excess over the cosmic microwave background can not be completely ruled out, and it may explain the EDGES anomaly. In the presence of decaying PMFs, 21 cm differential brightness temperature can modify due to the heating of the gas by decaying magnetic fields, and we can constraint the magnetic fields. For excess radiation fraction (A_r) to be LWA1 limit, we show that the upper bound on the present-day magnetic field strength, B_0, on the scale of 1 Mpc is lesssim 3.7 nG for spectral index n_B=-2.99. While for n_B=-1, we get B_0lesssim 1.1times 10^{-3} nG. We also discuss the effects of first stars on IGM gas evolution and the allowed value of B_0. For A_r to be LWA1 limit, we get the upper constraint on magnetic field to be B_0(n_B=-2.99)lesssim 4.9times 10^{-1} nG and B_0(n_B=-1)lesssim 3.7times 10^{-5} nG. By decreasing excess radiation fraction below the LWA1 limit, we get a more stringent bound on B_0.

Maxsmooth: rapid maximally smooth function fitting with applications in Global 21-cm cosmology

ABSTRACTMaximally Smooth Functions (MSFs) are a form of constrained functions in which there are no inflection points or zero crossings in high-order derivatives. Consequently, they have applications to signal recovery in experiments where signals of interest are expected to be non-smooth features masked by larger smooth signals or foregrounds. They can also act as a powerful tool for diagnosing the presence of systematics. The constrained nature of MSFs makes fitting these functions a non-trivial task. We introduce maxsmooth, an open-source package that uses quadratic programming to rapidly fit MSFs. We demonstrate the efficiency and reliability of maxsmooth by comparison to commonly used fitting routines and show that we can reduce the fitting time by approximately two orders of magnitude. We introduce and implement with maxsmooth Partially Smooth Functions, which are useful for describing elements of non-smooth structure in foregrounds. This work has been motivated by the problem of foreground modelling in 21-cm cosmology. We discuss applications of maxsmooth to 21-cm cosmology and highlight this with examples using data from the Experiment to Detect the Global Epoch of Reionization Signature (EDGES) and the Large-aperture Experiment to Detect the Dark Ages (LEDA) experiments. We demonstrate the presence of a sinusoidal systematic in the EDGES data with a log-evidence difference of 86.19 ± 0.12 when compared to a pure foreground fit. MSFs are applied to data from LEDA for the first time in this paper and we identify the presence of sinusoidal systematics. maxsmooth is pip installable and available for download at https://github.com/htjb/maxsmooth.

Formulating and Critically Examining the Assumptions of Global 21 cm Signal Analyses: How to Avoid the False Troughs That Can Appear in Single-spectrum Fits

Abstract The assumptions inherent to global 21 cm signal analyses are rarely delineated. In this paper, we formulate a general list of suppositions underlying a given claimed detection of the global 21 cm signal. Then, we specify the form of these assumptions for two different analyses: (1) the one performed by the team for the Experiment to Detect the Global Epoch-of-Reionization Signature (EDGES) showing an absorption trough in brightness temperature that they modeled separately from the sky foreground and (2) a new, so-called minimum assumption analysis (MAA) that makes the most conservative assumptions possible for the signal. We show fits using the EDGES analysis on various beam-weighted foreground simulations from the EDGES latitude with no signal added. Depending on the beam used, these simulations produce large false troughs because of the invalidity of the foreground model in describing the combination of beam chromaticity and the shape of the Galactic plane in the sky, the residuals of which are captured by the ad hoc flattened Gaussian signal model. On the other hand, the MAA provides robust fits by including many spectra at different time bins and allowing any possible 21 cm spectrum to be modeled exactly. We present uncertainty levels and example signal reconstructions found with the MAA for different numbers of time bins. With enough time bins, one can determine the true 21 cm signal with the MAA to <10 times the noise level.

Global 21 cm Signal Extraction from Foreground and Instrumental Effects. II. Efficient and Self-consistent Technique for Constraining Nonlinear Signal Models

Abstract We present the completion of a data analysis pipeline that self-consistently separates global 21 cm signals from large systematics using a pattern recognition technique. This pipeline will be used for both ground and space-based hydrogen cosmology instruments. In the first paper of this series, we obtain optimal basis vectors from signal and foreground training sets to linearly fit both components with the minimal number of terms that best extracts the signal given its overlap with the foreground. In this second paper, we utilize the spectral constraints derived in the first paper to calculate the full posterior probability distribution of any signal parameter space of choice. The spectral fit provides the starting point for a Markov Chain Monte Carlo (MCMC) engine that samples the signal without traversing the foreground parameter space. At each MCMC step, we marginalize over the weights of all linear foreground modes and suppress those with unimportant variations by applying priors gleaned from the training set. This method drastically reduces the number of MCMC parameters, augmenting the efficiency of exploration, circumvents the need for selecting a minimal number of foreground modes, and allows the complexity of the foreground model to be greatly increased to simultaneously describe many observed spectra without requiring extra MCMC parameters. Using two nonlinear signal models, one based on the Experiment to Detect the Global Epoch-of-Reionization Signature (EDGES) observations and the other on phenomenological frequencies and temperatures of theoretically expected extrema, we demonstrate the success of this methodology by recovering the input parameters from multiple randomly simulated signals at low radio frequencies (10–200 MHz), while rigorously accounting for realistically modeled beam-weighted foregrounds.

EDGES signal in the presence of magnetic fields

ABSTRACT We study the 21-cm differential brightness temperature in the presence of primordial helical magnetic fields for redshift z = 10–30. We argue that the α-effect that sets in at earlier time can be helpful in lowering the gas temperature to 3.2 K at z = 17. This effect can arise in the early Universe due to some parity-violating high-energy processes. Using the EDGES (Experiment to Detect the Global Epoch of Reionization Signature) results, we find the upper and lower limits on the primordial magnetic field to be 6 × 10−3 and 5 × 10−4 nG, respectively. We also discuss the effect of Ly α background on the bounds. Our results do not require any new physics in terms of dark matter.

Constraints on the Velocity Dispersion of Dark Matter from Cosmology and New Bounds on Scattering from the Cosmic Dawn

Abstract The observational value of the velocity dispersion, , is missing in the dark matter (DM) puzzle. Nonzero or nonthermal DM velocities can drastically influence large-scale structure and the 21 cm temperature at the epoch of the cosmic dawn, as well as the estimation of DM physical parameters, such as mass and interaction couplings. To study the phenomenology of , we model the evolution of DM in terms of a simplistic and generic Boltzmann-like momentum distribution. Using cosmological data from the cosmic microwave background, baryonic acoustic oscillations, and red luminous galaxies, we constrain the DM velocity dispersion for a broad range of masses, , finding (99% CL). Including the Experiment to Detect the Global Epoch of Reionization Signature (EDGES) T 21 measurements, we extend our study to constrain the baryon–DM interaction in the range of DM velocities allowed by our analysis. As a consequence, we present new bounds on two electromagnetic models of DM, namely minicharged particles (MCPs) and the electric dipole moment (EDM). For MCPs, the parameter region that is consistent with EDGES and independent bounds on cosmological and stellar physics is very small, pointing to the subelectronvolt mass regime of DM. A window in the MeV–GeV may still be compatible with these bounds for MCP models without a hidden photon. But the EDM parameter region consistent with EDGES is excluded by Big Bang nucleosynthesis and collider physics.

Constraining structure formation using EDGES

The experiment to detect the global epoch of reionization signature (EDGES) collaboration reported the detection of a line at 78 MHz in the sky-averaged spectrum due to neutral hydrogen (\\ion{H}{i}) 21-cm hyperfine absorption of cosmic microwave background (\\cmb) photons at redshift z∼ 17. This requires that the spin temperature of \\ion{H}{i} be coupled to the kinetic temperature of the gas at this redshift through the scattering of \\lya photons emitted by massive stars. To explain the experimental result, star formation needs to be sufficiently efficient at z∼ 17 and this can be used to constrain models in which small-scale structure formation is suppressed (\\dmf models), either due to dark matter free-streaming or non-standard inflationary dynamics. We combine simulations of structure formation with a simple recipe for star formation to investigate whether these models emit enough Lyman-α photons to reproduce the experimental signal for reasonable values of the star formation efficiency, f⋆. We find that a thermal warm dark matter (\\wdm) model with mass mWDM∼ 4.3 keV is consistent with the timing of the signal for f⋆ ≲ 2%. The exponential growth of structure around z∼ 17 in such a model naturally generates a sharp onset of the absorption. A warmer model with mWDM∼3 keV requires a higher star formation efficiency, f⋆∼ 6%, which is a factor of few above predictions of current star formation models and observations of satellites in the Milky Way. However, uncertainties in the process of star formation at these redshifts do not allow to derive strong constrains on such models using 21-cm absorption line. The onset of the 21-cm absorption is generally slower in \\dmf than observed in cold dark matter (\\cdm) models, unless some process significantly suppresses star formation in halos with masses below ~108h-1M⊙.

Implications of the possible 21-cm line excess at cosmic dawn on dynamics of interacting dark energy

In this Letter we study implications of the possible excess of 21-cm line global signal at the epoch of cosmic dawn on the evolutions of a class of dynamically interacting dark energy (IDE) models. We firstly summarize two dynamical mechanisms in which different background evolutions can exert considerable effects on the 21-cm line global signal. One of them is the change in decoupling time of Compton scattering heating, the other stems from the direct change of optical depth due to the different expansion rate of the Universe. After that, we investigate the influence of linear IDE models on 21-cm line signals and find that under the current observational constraints, it is difficult to yield a sufficiently strong 21-cm line signal to be consistent with the results of Experiment to Detect the Global Epoch of reionization Signature (EDGES) since only the optical depth could be effectively changed in these models. Accordingly, this implies us to construct a background evolution which could fulfill the reasonable change of optical depth and Compton heating decoupling time at the same moment by introducing an early dark energy dominated stage into the evolution governed by the IDE models. The comparison with astronomical observations indicate that this scenario could only alleviate, but not complete eliminate, the tension between EDGES and other cosmological surveys.

Constraining First Star Formation with 21 cm Cosmology

Abstract Within standard ΛCDM cosmology, Population III star formation in minihalos of mass M halo ≳ 5 × 105 M ⊙ provides the first stellar sources of Lyα photons. The Experiment to Detect the Global Epoch of Reionization Signature (EDGES) has measured a strong absorption signal of the redshifted 21 cm radiation from neutral hydrogen at z ≈ 17, requiring efficient formation of massive stars before then. In this Letter, we investigate whether star formation in minihalos plays a significant role in establishing the early Lyα background required to produce the EDGES absorption feature. We find that Population III stars are important in providing the necessary Lyα-flux at high redshifts, and derive a best-fitting average Population III stellar mass of ∼750 M ⊙ per minihalo, corresponding to a star formation efficiency of 0.1%. Furthermore, it is important to include baryon-dark matter streaming velocities in the calculation, to limit the efficiency of Population III star formation in minihalos. Without this effect, the cosmic dawn coupling between 21 cm spin temperature and that of the gas would occur at redshifts higher than what is implied by EDGES.

Analytic Formulation of 21 cm Signal from Cosmic Dawn: Lyα Fluctuations

Abstract We present an analytic formalism to compute the fluctuating component of the H i signal and extend it to take into account the effects of partial Lyα coupling during the era of cosmic dawn. We use excursion set formalism to calculate the size distribution of randomly distributed self-ionized regions. These ionization bubbles are surrounded by partially heated and Lyα coupled regions, which create spin temperature T S fluctuations. We use the ratio of number of Lyα to ionizing photons (f L ) and number of X-ray photons emitted per stellar baryon (N heat) as modeling parameters. Using our formalism, we compute the global H i signal, its autocorrelation, and its power spectrum in the redshift range 10 ≤ z ≤ 30 for the ΛCDM model. We check the validity of this formalism for various limits and simplified cases. Our results agree reasonably well with existing results from N-body simulations, in spite of following a different approach and requiring orders of magnitude less computation power and time. We further apply our formalism to study the fluctuating component corresponding to the recent observation by the Experiment to Detect the Global Epoch of reionization Signature (EDGES) that shows an unexpectedly deep absorption trough in the global H i signal in the redshift range 15 < z < 19. We show that, generically, the EDGES observation predicts a larger signal in this redshift range but a smaller signal at higher redshifts. We also explore the possibility of negative real-space autocorrelation of spin temperature and show that it can be achieved for partial Lyα coupling in many cases corresponding to simplified models and a complete model without density perturbations.

Constraining the Dark Matter Vacuum Energy Interaction Using the EDGES 21 cm Absorption Signal

Abstract The recent measurement of the global 21 cm absorption signal reported by the Experiment to Detect the Global Epoch of Reionization Signature (EDGES) Collaboration is in tension with the prediction of the ΛCDM model at a 3.8σ significance level. In this work, we report that this tension can be released by introducing an interaction between dark matter and vacuum energy. We perform a model parameter estimation using a combined data set including EDGES and other recent cosmological observations, and find that the EDGES measurement can marginally improve the constraint on parameters that quantify the interacting vacuum, and that the combined data set favors the ΛCDM at a 68% confidence level. This proof-of-concept study demonstrates the potential power of future 21 cm experiments to constrain the interacting dark energy models.

What does the first highly redshifted 21-cm detection tell us about early galaxies?

The Experiment to Detect the Global Epoch of Reionization Signature (EDGES) recently reported a strong 21-cm absorption signal relative to the cosmic microwave background at $z \sim 18$. While its anomalous amplitude may indicate new physics, in this work we focus on the timing of the signal, as it alone provides an important constraint on galaxy formation models. Whereas rest-frame ultraviolet luminosity functions (UVLFs) over a broad range of redshifts are well fit by simple models in which galaxy star formation histories track the assembly of dark matter halos, we find that these same models, with reasonable assumptions about X-ray production in star-forming galaxies, cannot generate a narrow absorption trough at $z \sim 18$. If verified, the EDGES signal therefore requires the fundamental inputs of galaxy formation models to evolve rapidly at $z \gtrsim 10$. Unless extremely faint sources residing in halos below the atomic cooling threshold are responsible for the EDGES signal, star formation in $\sim 10^8$-$10^{10} \ M_{\odot}$ halos must be more efficient than expected, implying that the faint-end of the UVLF at $M_{\mathrm{UV}} \lesssim -12$ must steepen at the highest redshifts. This steepening provides a concrete test for future galaxy surveys with the James Webb Space Telescope and ongoing efforts in lensed fields, and is required regardless of whether the amplitude of the EDGES signal is due to new cooling channels or a strong radio background in the early Universe. However, the radio background solution requires that galaxies at $z > 15$ emit 1-2 GHz photons with an efficiency $\sim 10^3$ times greater than local star-forming galaxies, posing a challenge for models of low-frequency photon production in the early Universe.

Constraining noncold dark matter models with the global 21-cm signal

Any particle dark matter (DM) scenario featuring a suppressed power spectrum of astrophysical relevance results in a delay of galaxy formation. As a consequence, such scenarios can be constrained using the global 21-cm absorption signal initiated by the UV radiation of the first stars. The Experiment to Detect the Global Epoch of Reionization Signature (EDGES) recently reported the first detection of such an absorption signal at redshift $\sim 17$. While its amplitude might indicate the need for new physics, we solely focus on the timing of the signal to test non-cold DM models. Assuming conservative limits for the stellar-to-baryon fraction ($f_{*}<0.03$) and for the minimum cooling temperature ($T_{\rm vir}>10^3$ Kelvin) motivated by radiation-hydrodynamic simulations, we are able to derive unprecedented constraints on a variety of non-cold DM models. For example, the mass of thermal warm DM is limited to $m_{\rm TH}>6.1$ keV, while mixed DM scenarios (featuring a cold and a hot component) are constrained to a hot DM fraction below 17 percent. The ultra-light axion DM model is limited to masses $m_{a}>8\times10^{-21}$ eV, a regime where its wave-like nature is pushed far below the kiloparsec scale. Finally, sterile neutrinos from resonant production can be fully disfavoured as a dominant DM candidate. The results of this paper show that the 21-cm absorption signal is a powerful discriminant of non-cold dark matter, allowing for significant improvements over to the strongest current limits. Confirming the result from EDGES is paramount in this context.

Implication of the Shape of the EDGES Signal for the 21 cm Power Spectrum

Abstract We revisit the 21 cm power spectrum from the epoch of cosmic dawn in light of the recent Experiment to Detect the Global Epoch of reionization Signature (EDGES) detection of the 21 cm global signal at frequencies corresponding to z ∼ 20. The shape of the signal suggests that the spin temperature of neutral hydrogen was coupled to the kinetic temperature of the gas relatively rapidly (19 ≲ z ≲ 21). We therefore consider models in which the ultraviolet photons were dominantly produced in the rarest and most massive halos (M ≳ 109 M ⊙), as their abundance grows fast enough at those redshifts to account for this feature of the signal. We show that these models predict large power spectrum amplitudes during the inhomogeneous coupling, and then inhomogeneous heating by cosmic microwave background and Lyα photons due to the large shot noise associated with the rare sources. The power spectrum is enhanced by more than an order of magnitude compared to previous models that did not include the shot-noise contribution, making it a promising target for upcoming radio interferometers that aim to detect high-redshift 21 cm fluctuations.