Search

We study the viability of using power spectrum clustering wedges as summary statistics of 21 cm surveys during the epoch of reionization (EoR). For observations in a wide redshift range |$z\sim 7{\!-\!}9$| corresponding to a line-of-sight scale of |$\sim 500\,$|  Mpc, the power spectrum is subject to anisotropic effects due to the evolution along the light of sight. Information on the physics of reionization can be extracted from the anisotropy using the power spectrum multipoles. Signals of the power spectrum monopole are highly correlated at scales smaller than the typical ionization bubble, which can be disentangled by including higher-order multipoles. By simulating observations of the low-frequency part of the Square Kilometre Array (SKA) Observatory, we find that the sampling of the cylindrical wavenumber |$\boldsymbol {k}$| -space is highly non-uniform due to the baseline distribution, i.e. the distribution of antenna pairs sampling different transverse |$\boldsymbol {k}_\perp$| scales. Measurements in clustering wedges partition the cylindrical |$\boldsymbol {k}$| -space into different radial |$k_\parallel$| scales, and can be used for isolating parts of |$\boldsymbol {k}$| -space with relatively uniform sampling, allowing for more precise parameter inference. Using Fisher Matrix forecasts, we find that the reionization model can be inferred with per cent level precision with |$\sim 120$|  h of integration time using SKA-Low. Compared to model inference using only the power spectrum monopole above the foreground wedge, model inference using multipole power spectra in clustering wedges yields a factor of |$\sim 3$| improvement on the marginalized 1D parameter constraints. [ABSTRACT FROM AUTHOR]

We report the tentative detection of the ring molecule cyclopropenylidene (c -C |$_3$| H |$_2$|⁠) in cometary comae. We observed three short-period comets: 73P/Schwassmann–Wachmann 3, 17P/Holmes, 103P Hartley 2, and two Oort Cloud comets: C/2007 N3 (Lulin) and C/2012 F6 (Lemmon) with the Arizona Radio Observatory Submillimeter Telescope (SMT) and the Atacama Large Millimeter/submillimeter Array (ALMA). We tentatively detected c -C |$_3$| H |$_2$| in three of the comets, with molecule production rates in the range of |$(0.2\!-\!3.8)\times 10^{25}$| molecules s |$^{-1}$|⁠ , and c -C |$_3$| H |$_2$| /H |$_2$| O mixing ratios of 0.01–0.19  per cent. Evidence from both the single-dish and interferometric data points to the presence of c -C |$_3$| H |$_2$| being of a discrete transient nature and exhibiting an extended spatial distribution, indicating production from the decomposition of organic dust particles in the coma. [ABSTRACT FROM AUTHOR]

Neutral hydrogen (H  i) serves as a competitive tracer of the large scale structures, especially with the advent of more intensity mapping H  i surveys. In this work, we present a simulation-based framework to forecast the H  i power spectrum on non-linear scales (⁠|$k\gtrsim 1\ {\rm Mpc^{-1}}$|⁠), as measured by interferometer arrays like MeerKAT in the low-redshift (⁠|$z\le 1.0$|⁠) Universe. Building on a galaxy-based H  i mock catalogue, we meticulously consider various factors, including the emission line profiles of H  i discs and some observational settings, and explore their impacts on the H  i power spectrum. We find that the H  i power spectrum is relatively insensitive to the profile shape of H  i emission line at these scales, while showing a strong correlation with the profile width. We propose an empirical model to simulate the emission line profile width for each H  i source. The resulting H  i power spectrum is consistent with the results from the IllustrisTNG hydrodynamical simulation and follows the trend of the measurements obtained by MeerKAT at |$z\approx 0.44$|⁠ , though with a significantly lower amplitude. We demonstrate how the H  i abundance |$\Omega _{\rm HI}$| and the amplitude parameter in our width model can be constrained with the MeerKAT measurements, though a strong degeneracy is uncovered. Our work shows the potential to constrain statistical properties of H  i emission line profiles with future H  i intensity mapping experiments. [ABSTRACT FROM AUTHOR]

One of the most promising probes to complement current standard cosmological surveys is the H  i intensity map, i.e. the distribution of temperature fluctuations in neutral hydrogen. In this paper we present calculations of the two-point function between HI (at redshift |$z\lt 1$|⁠) and lensing convergence (⁠|$\kappa$|⁠). We also construct HI intensity maps from N -body simulations, and measure two-point functions between HI and lensing convergence. HI intensity mapping requires stringent removal of bright foregrounds, including emission from our Galaxy. The removal of large-scale radial modes during this HI foreground removal will reduce the HI-lensing cross-power spectrum signal, as radial modes are integrated to find the convergence; here we wish to characterize this reduction in signal. We find that after a simple model of foreground removal, the cross-correlation signal is reduced by |$\sim$| 50–70  per cent; we present the angular and redshift dependence of the effect, which is a weak function of these variables. We then calculate S/N of |$\kappa$| HI detection, including cases with cut sky observations, and noise from radio and lensing measurements. We present Fisher forecasts based on the resulting two-point functions; these forecasts show that by measuring |$\kappa \Delta {T}_\mathrm{HI}$| correlation functions in a sufficient number of redshift bins, constraints on cosmology and HI bias will be possible. [ABSTRACT FROM AUTHOR]

A large arsenal of space-based and ground-based instruments is dedicated to the observation of radio emissions, whether they originate within our solar system or not. Radio photons interact with anisotropic density fluctuations in the heliosphere which can alter their trajectory and influence the properties that are deduced from observations. This is particularly evident in solar radio observations, where anisotropic scattering leads to highly directional radio emissions. Consequently, observers at varying locations will measure different properties, including different source sizes, source positions, and intensities. However, it is not known whether the measurements of the decay time of solar radio bursts are also affected by the observer's position. Decay times are dominated by scattering effects, and so are frequently used as proxies of the level of density fluctuations in the heliosphere, making the identification of any location-related dependence crucial. We combine multi-vantage observations of interplanetary Type III bursts from four non-collinear, angularly separated spacecraft with simulations to investigate the dependence of the decay- and rise-time measurements on the separation of the observer from the source. We propose a function to characterise the entire time profile of radio signals, allowing for the simultaneous estimation of the peak flux, decay time, and rise time, while demonstrating that the rise phase of radio bursts is non-exponential, having a non-constant growth rate. We determine that the decay and rise times are independent of the observer's position, identifying them as the only properties that remain unaffected and thus do not require corrections for the observer's location. Moreover, we examine the ratio between the rise and decay times and find that it does not depend on the frequency. Therefore, we provide the first evidence that the rise phase is also significantly impacted by scattering effects, adding to our understanding of the plasma emission process. [ABSTRACT FROM AUTHOR]

The optical depth parameterization is typically used to study the 21-cm signals associated with the properties of the neutral hydrogen (H  i) gas and the ionization morphology during the Epoch of Reionization (EoR), without solving the radiative transfer equation. To assess the uncertainties resulting from this simplification, we conduct explicit radiative transfer calculations using the cosmological 21-cm line radiative transfer (C21LRT) code and examine the imprints of ionization structures on the 21-cm spectrum. We consider a globally averaged reionization history and implement fully ionized cavities (H  ii bubbles) of diameters d ranging from 0.01 to 10 Mpc at epochs within the emission and the absorption regimes of the 21-cm global signal. The single-ray C21LRT calculations show that the shape of the imprinted spectral features are primarily determined by d and the 21-cm line profile, which is parametrized by the turbulent velocity of the H  i gas. It reveals the spectral features tied to the transition from ionized to neutral regions that calculations based on the optical depth parametrization were unable to capture. We also present analytical approximations of the calculated spectral features of the H  ii bubbles. The multiple-ray calculations show that the apparent shape of an H  ii bubble (of d  = 5 Mpc at z  = 8), because of the finite speed of light, differs depending on whether the bubble's ionization front is stationary or expanding. Our study shows the necessity of properly accounting for the effects of line-continuum interaction, line broadening, and cosmological expansion to correctly predict the EoR 21-cm signals. [ABSTRACT FROM AUTHOR]

The 21-cm hyperfine line of neutral hydrogen is a useful tool to probe the conditions of the Universe during the Dark Ages, Cosmic Dawn, and the Epoch of Reionization. In most of the current calculations, the 21-cm line signals at given frequencies are computed, using an integrated line-of-sight line opacity, with the correction for cosmological expansion. These calculations have not fully captured the line and continuum interactions in the radiative transfer, in response to evolution of the radiation field and the variations of thermal and dynamic properties of the line-of-sight medium. We construct a covariant formulation for the radiative transfer of the 21-cm line and derive the cosmological 21-cm line radiative transfer (C21LRT) equation. The formulation properly accounts for local emission and absorption processes and the interaction between the line and continuum when the radiation propagates across the expanding Universe to the present observer. Our C21LRT calculations show that methods simply summing the line optical depth could lead to error of 5  per cent in the 21-cm signals for redshift z ∼ 12–35 and of |$\gt 10~{{\ \rm per\ cent}}$| for redshift z ≲ 8. Proper covariant radiative transfer is therefore necessary for producing correct theoretical templates for extracting information of the structural evolution of the Universe through the Epoch of Reionization from the 21-cm tomographic data. [ABSTRACT FROM AUTHOR]

We present a comprehensive set of forecasts for the cross-correlation signal between 21 cm intensity mapping and galaxy redshift surveys. We focus on the data sets that will be provided by the SKAO for the 21 cm signal, DESI and Euclid for galaxy clustering. We build a likelihood which takes into account the effect of the beam for the radio observations, the Alcock–Paczynski effect, a simple parametrization of astrophysical nuisances, and fully exploit the tomographic power of such observations in the range z  = 0.7–1.8 at linear and mildly non-linear scales (k < 0.25 h  Mpc−1). The forecasted constraints, obtained with Monte Carlo Markov Chains techniques in a Bayesian framework, in terms of the six base parameters of the standard ΛCDM model, are promising. The predicted signal-to-noise ratio for the cross-correlation can reach ∼50 for z ∼ 1 and k ∼ 0.1 h  Mpc−1. When the cross-correlation signal is combined with current Cosmic Microwave Background (CMB) data from Planck, the error bar on |$\Omega _{\rm c}\, h^2$| and H 0 is reduced by factors 3 and 6, respectively, compared to CMB only data, due to the measurement of matter clustering provided by the two observables. The cross-correlation signal has a constraining power that is comparable to the autocorrelation one and combining all the clustering measurements a sub-per cent error bar of 0.33 per cent on H 0 can be achieved, which is about a factor 2 better than CMB only measurements. Finally, as a proof of concept, we test the full pipeline on the real data measured by the MeerKat collaboration (Cunnington et al. 2022) presenting some (weak) constraints on cosmological parameters. [ABSTRACT FROM AUTHOR]

Estimators for n -point clustering statistics in Fourier-space demand that modern surveys of large-scale structure be transformed to Cartesian coordinates to perform Fast Fourier Transforms (FFTs). In this work, we explore this transformation in the context of pixelized line intensity maps (LIM), highlighting potential biasing effects on power-spectrum measurements. Current analyses often avoid a complete resampling of the data by approximating survey geometry as rectangular in Cartesian space, an increasingly inaccurate assumption for modern wide-sky surveys. Our simulations of a |$20\, {\times }\, 20\, \text{deg}^2$| 21 cm LIM survey at |$0.34\, {\lt }\, z\, {\lt }\, 0.54$| show this assumption biases power-spectrum measurements by |${\gt }\, 20~{{\ \rm per\ cent}}$| across all scales. We therefore present a more robust framework for regridding the voxel intensities on to a 3D FFT field by coordinate transforming large numbers of Monte-Carlo sampling particles. Whilst this unbiases power-spectrum measurements on large scales, smaller scale discrepancies remain, caused by structure smoothing and aliasing from separations unresolved by the grid. To correct these effects, we introduce modelling techniques, higher order particle assignments, and interlaced FFT grids to suppress the aliased power. Using a piecewise cubic spline (PCS) particle assignment and an interlaced FFT field, we achieve sub-per cent accuracy up to 80 per cent of the Nyquist frequency for our 21 cm LIM simulations. We find a more subtle hierarchical improvement in results for higher order assignment schemes, relative to the gains made for galaxy surveys, which we attribute to the extra complexity in LIM from additional discretizing steps. python code accompanying this paper is available at github.com/stevecunnington/gridimp. [ABSTRACT FROM AUTHOR]

We probe the neutral circumgalactic medium (CGM) along the major axes of NGC 891 and NGC 4565 in 21-cm emission out to ≳100 kpc using the Green Bank Telescope (GBT), extending our previous minor axes observations. We achieve an unprecedented 5σ sensitivity of 6.1 × 1016 cm−2 per 20 km s−1 velocity channel. We detect H  i with diverse spectral shapes, velocity widths, and column densities. We compare our detections to the interferometric maps from the Westerbork Synthesis Radio Telescope (WSRT) obtained as part of the HALOGAS survey. At small impact parameters, |$\gt 31\!-\!43~{{\ \rm per\ cent}}$| of the emission detected by the GBT cannot be explained by emission seen in the WSRT maps, and it increases to |$\gt 64\!-\!73~{{\ \rm per\ cent}}$| at large impact parameters. This implies the presence of diffuse circumgalactic H  i. The mass ratio between H  i in the CGM and H  i in the disc is an order of magnitude larger than previous estimates based on shallow GBT mapping. The diffuse H  i along the major axes pointings is corotating with the H  i disc. The velocity along the minor axes pointings is consistent with an inflow and/or fountain in NGC 891 and an inflow/outflow in NGC 4565. Including the circumgalactic H  i , the depletion time and the accretion rate of NGC 4565 are sufficient to sustain its star formation. In NGC 891, most of the required accreting material is still missing. [ABSTRACT FROM AUTHOR]

The circum-galactic medium (CGM) can feasibly be mapped by multiwavelength surveys covering broad swaths of the sky. With multiple large data sets becoming available in the near future, we develop a likelihood-free Deep Learning technique using convolutional neural networks (CNNs) to infer broad-scale physical properties of a galaxy's CGM and its halo mass for the first time. Using CAMELS (Cosmology and Astrophysics with MachinE Learning Simulations) data, including IllustrisTNG, SIMBA, and Astrid models, we train CNNs on Soft X-ray and 21-cm (H  i) radio two-dimensional maps to trace hot and cool gas, respectively, around galaxies, groups, and clusters. Our CNNs offer the unique ability to train and test on 'multifield' data sets comprised of both H  i and X-ray maps, providing complementary information about physical CGM properties and improved inferences. Applying eRASS:4 survey limits shows that X-ray is not powerful enough to infer individual haloes with masses log (M halo/M⊙) < 12.5. The multifield improves the inference for all halo masses. Generally, the CNN trained and tested on Astrid (SIMBA) can most (least) accurately infer CGM properties. Cross-simulation analysis – training on one galaxy formation model and testing on another – highlights the challenges of developing CNNs trained on a single model to marginalize over astrophysical uncertainties and perform robust inferences on real data. The next crucial step in improving the resulting inferences on the physical properties of CGM depends on our ability to interpret these deep-learning models. [ABSTRACT FROM AUTHOR]

Context. The Baryon Acoustic Oscillations (BAO) from Integrated Neutral Gas Observations (BINGO) radio telescope will use the neutral hydrogen emission line to map the Universe in the redshift range 0.127 ≤ z ≤ 0.449, with the main goal of probing BAO. In addition, the instrument's optical design and hardware configuration support the search for fast radio bursts (FRBs). Aims. In this work, we propose the use of a BINGO Interferometry System (BIS) including new auxiliary, smaller radio telescopes (hereafter outriggers). The interferometric approach makes it possible to pinpoint the FRB sources in the sky. We present the results of several BIS configurations combining BINGO horns with and without mirrors (4 m, 5 m, and 6 m) and five, seven, nine, or ten for single horns. Methods. We developed a new Python package, the FRBlip, which generates mock catalogs of synthetic FRB and computes, based on a telescope model, the observed signal-to-noise ratio, which we use to numerically compute the detection rates of the telescopes and how many interferometry pairs of telescopes (baselines) can observe an FRB. The FRBs observed by more than one baseline are the ones whose location can be determined. We thus evaluated the performance of BIS regarding FRB localization. Results. We found that BIS would be able to localize 23 FRBs yearly with single horn outriggers in the best configuration (using ten outriggers of 6-m mirrors), with redshift z ≤ 0.96. The full localization capability depends on the number and type of the outriggers. Wider beams are best for pinpointing FRB sources because potential candidates will be observed by more baselines, while narrow beams search deep in redshift. Conclusions. The BIS can be a powerful extension of the BINGO telescope, dedicated to observe hundreds of FRBs during Phase 1. Many of FRBs will be well localized with a single horn and a 6-m dish as outriggers. [ABSTRACT FROM AUTHOR]

We present a survey strategy to detect the neutral hydrogen (H  i) power spectrum at 5 < z < 6 using the SKA-Low radio telescope in presence of foregrounds and instrumental effects. We simulate observations of the inherently weak H  i signal post-reionization with varying levels of noise and contamination with foreground amplitudes equivalent to residuals after sky model subtraction. We find that blind signal separation methods on imaged data are required in order to recover the H  i signal at large cosmological scales. Comparing different methods of foreground cleaning, we find that Gaussian Process Regression (GPR) performs better than Principle Component Analysis (PCA), with the key difference being that GPR uses smooth kernels for the total data covariance. The integration time of one field needs to be larger than ∼250 h to provide large enough signal-to-noise ratio (SNR) to accurately model the data covariance for foreground cleaning. Images within the primary beam field-of-view give measurements of the H  i power spectrum at scales |$k\sim 0.02\, {\rm Mpc^{-1}}-0.3\, {\rm Mpc^{-1} }$| with SNR ∼2–5 in Δ[log(k /Mpc−1)] = 0.25 bins assuming an integration time of 600 h. Systematic effects, which introduce small-scale fluctuations across frequency channels, need to be ≲ 5 × 10−5 to enable unbiased measurements outside the foreground wedge. Our results provide an important validation towards using the SKA-Low array for measuring the H  i power spectrum in the post-reionization Universe. [ABSTRACT FROM AUTHOR]

Neutral hydrogen (H  i) intensity-mapping (IM) surveys are considered a promising tool for investigating the expansion history of the Universe. In this work, we explore the potential of MeerKAT H  i IM observations in interferometer mode to estimate the power spectrum and constrain cosmological parameters within typical dark-energy models. We employ an approach called the 'delay spectrum', which allows us to separate the weak H  i signal from foreground contamination in the frequency domain. Our findings indicate that the choice of survey fields significantly impacts the fractional errors on the power spectrum (Δ P / P) within a limited observational time of 10 h. As the integration time increases from 10–10 000 h, Δ P / P progressively decreases until cosmic variance begins to dominate. For a total observation time of 10 000 h, the lowest Δ P / P at low k can be achieved by tracking 100 points for the MeerKAT L band (900–1200 MHz) and 10 points for the MeerKAT UHF band (580–1000 MHz). Next, we assess the performance of H  i IM in constraining typical dark-energy models. We find that the MeerKAT H  i IM survey in interferometer mode demonstrates limited capability in constraining the dark-energy equation of state, even when combined with Planck data. Our analysis serves as a valuable guide for future MeerKAT observations in H  i IM surveys. [ABSTRACT FROM AUTHOR]

Context. A lower-than-solar elemental nitrogen content has been demonstrated for several comets, including 1P/Halley and 67P/Churyumov-Gerasimenko (67P/C-G) with independent in situ measurements of volatile and refractory budgets. The recently discovered semi-refractory ammonium salts in 67P/C-G are thought to be the missing nitrogen reservoir in comets. Aims. The thermal desorption of ammonium salts from cometary dust particles leads to their decomposition into ammonia (NH3) and a corresponding acid. The NH3/H2O ratio is expected to increase with decreasing heliocentric distance with evidence for this in near-infrared observations. NH3 has been claimed to be more extended than expected for a nuclear source. Here, the aim is to constrain the NH3/H2O ratio in comet C/2020 F3 (NEOWISE) during its July 2020 passage. Methods. OH emission from comet C/2020 F3 (NEOWISE) was monitored for 2 months with the Nançay Radio Telescope (NRT) and observed from the Green Bank Telescope (GBT) on 24 July and 11 August 2020. Contemporaneously with the 24 July 2020 OH observations, the NH3 hyperfine lines were targeted with GBT. From the data, the OH and NH3 production rates were derived directly, and the H2O production rate was derived indirectly from the OH. Results. The concurrent GBT and NRT observations allowed the OH quenching radius to be determined at (5.96 ± 0.10) × 104 km on 24 July 2020, which is important for accurately deriving Q(OH). C/2020 F3 (NEOWISE) was a highly active comet with Q(H2O) ≈ 2 × 1030 mol s−1 one day before perihelion. The 3σ upper limit for QNH3 / QH2O is < 0.29% at 0.7 au from the Sun. Conclusions. The obtained NH3/H2O ratio is a factor of a few lower than measurements for other comets at such heliocentric distances. The abundance of NH3 may vary strongly with time depending on the amount of water-poor dust in the coma. Lifted dust can be heated, fragmented, and super-heated; whereby, ammonium salts, if present, can rapidly thermally disintegrate and modify the NH3/H2O ratio. [ABSTRACT FROM AUTHOR]

We determine the atomic hydrogen (H  i) to halo mass relation (HIHM) using Arecibo Legacy Fast ALFA survey H  i data at the location of optically selected groups from the Galaxy And Mass Assembly (GAMA) survey. We make direct H  i detections for 37 GAMA groups. Using H  i group spectral stacking of 345 groups, we study the group H  i content as a function of halo mass across a halo mass range of 1011–1014.7 M⊙. We also correct our results for Eddington bias. We find that the group H  i mass generally rises as a function of halo mass from 1.3% of the halo mass at |$10^{11.6} \, \text{M}_\odot$| to 0.4% at |$10^{13.7} \, \text{M}_\odot$| with some indication of flattening towards the high-mass end. Despite the differences in optical survey limits, group catalogues, and halo mass estimation methods, our results are consistent with previous group H  i -stacking studies. Our results are also consistent with mock observations from shark and IllustrisTNG. [ABSTRACT FROM AUTHOR]

Blind cleaning methods are currently the preferred strategy for handling foreground contamination in single-dish H  i intensity mapping surveys. Despite the increasing sophistication of blind techniques, some signal loss will be inevitable across all scales. Constructing a corrective transfer function using mock signal injection into the contaminated data has been a practice relied on for H  i intensity mapping experiments. However, assessing whether this approach is viable for future intensity mapping surveys, where precision cosmology is the aim, remains unexplored. In this work, using simulations, we validate for the first time the use of a foreground transfer function to reconstruct power spectra of foreground-cleaned low-redshift intensity maps and look to expose any limitations. We reveal that even when aggressive foreground cleaning is required, which causes |${\gt }\, 50~{{\ \rm per\ cent}}$| negative bias on the largest scales, the power spectrum can be reconstructed using a transfer function to within sub-per cent accuracy. We specifically outline the recipe for constructing an unbiased transfer function, highlighting the pitfalls if one deviates from this recipe, and also correctly identify how a transfer function should be applied in an autocorrelation power spectrum. We validate a method that utilizes the transfer function variance for error estimation in foreground-cleaned power spectra. Finally, we demonstrate how incorrect fiducial parameter assumptions (up to |${\pm }100~{{\ \rm per\ cent}}$| bias) in the generation of mocks, used in the construction of the transfer function, do not significantly bias signal reconstruction or parameter inference (inducing |${\lt }\, 5~{{\ \rm per\ cent}}$| bias in recovered values). [ABSTRACT FROM AUTHOR]

The application of very long baseline interferometry (VLBI) to the search for extraterrestrial intelligence (SETI) has been limited to date, despite the technique offering many advantages over traditional single-dish SETI observations. In order to further develop interferometry for SETI, we used the European VLBI network (EVN) at 21 cm to observe potential secondary phase calibrators in the Kepler field. Unfortunately, no secondary calibrators were detected. However, a VLBA primary calibrator in the field, J1926+4441, offset only ∼1.88 arcmin from a nearby exoplanet Kepler-111 b, was correlated with high temporal |$\left(0.25 \, \rm {s}\right)$| and spectral |$\left(16384 \times 488\, \rm {Hz \ channels}\right)$| resolution. During the analysis of the high-resolution data, we identified a spectral feature that was present in both the auto and cross-correlation data with a central frequency of 1420.424 ± 0.0002 MHz and a width of 0.25 MHz. We demonstrate that the feature in the cross-correlations is an artefact in the data, associated with a significant increase in each telescope's noise figure due to the presence of H  i in the beam. This would typically go unnoticed in data correlated with standard spectral resolution. We flag (excluded from the subsequent analysis) these channels and phase rotate the data to the location of Kepler-111 b aided by the Gaia catalogue and search for signals with |$\rm {SNR}\gt 7$|. At the time of our observations, we detect no transmitters with an equivalent isotropically radiated power ≳4 × 1015 W. [ABSTRACT FROM AUTHOR]

Breakthrough Listen is the most comprehensive and sensitive search for extraterrestrial intelligence (SETI) to date, employing a collection of international observational facilities including both radio and optical telescopes. During the first three years of the Listen program, thousands of targets have been observed with the Green Bank Telescope (GBT), Parkes Telescope and Automated Planet Finder. At GBT and Parkes, observations have been performed ranging from 700 MHz to 26 GHz, with raw data volumes averaging over 1 PB day−1. A pseudo-real time software spectroscopy suite is used to produce multi-resolution spectrograms amounting to approximately 400 GB h−1 GHz−1 beam−1. For certain targets, raw baseband voltage data is also preserved. Observations with the Automated Planet Finder produce both two-dimensional and one-dimensional high-resolution (R ∼ 105) echelle spectral data. Although the primary purpose of Listen data acquisition is for SETI, a range of secondary science has also been performed with these data, including studies of fast radio bursts. Other current and potential research topics include spectral line studies, searches for certain kinds of dark matter, probes of interstellar scattering, pulsar searches, radio transient searches and investigations of stellar activity. Listen data are also being used in the development of algorithms, including machine-learning approaches to modulation scheme classification and outlier detection, that have wide applicability not just for astronomical research but for a broad range of science and engineering. In this paper, we describe the hardware and software pipeline used for collection, reduction, archival, and public dissemination of Listen data. We describe the data formats and tools, and present Breakthrough Listen Data Release 1.0 (BLDR 1.0), a defined set of publicly available raw and reduced data totaling 1 PB.

The measurement of the large-scale distribution of neutral hydrogen in the late Universe, obtained with radio telescopes through the hydrogen 21 cm line emission, has the potential to become a key cosmological probe in the upcoming years. We explore the constraining power of 21 cm intensity mapping observations on the full set of cosmological parameters that describe the ΛCDM model. We assume a single-dish survey for the SKA Observatory and simulate the 21 cm linear power spectrum monopole and quadrupole within six redshift bins in the range |$z$|  = 0.25–3. Forecasted constraints are computed numerically through Markov Chain Monte Carlo techniques. We extend the sampler CosmoMC by implementing the likelihood function for the 21 cm power spectrum multipoles. We assess the constraining power of the mock data set alone and combined with Planck 2018 CMB observations. We find that 21 cm multipoles observations alone are enough to obtain constraints on the cosmological parameters comparable with other probes. Combining the 21 cm data set with CMB observations results in significantly reduced errors on all the cosmological parameters. The strongest effect is on Ω c h 2 and H 0, for which the error is reduced by almost a factor four. The percentage errors we estimate are |$\sigma _{\Omega _ch^2} = 0.25~{{\ \rm per\ cent}}$| and |$\sigma _{H_0} = 0.16~{{\ \rm per\ cent}}$|⁠ , to be compared with the Planck only results |$\sigma _{\Omega _ch^2} = 0.99~{{\ \rm per\ cent}}$| and |$\sigma _{H_0} = 0.79~{{\ \rm per\ cent}}$|⁠. We conclude that 21 cm SKAO observations will provide a competitive cosmological probe, complementary to CMB and, thus, pivotal for gaining statistical significance on the cosmological parameters constraints, allowing a stress test for the current cosmological model. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The recent radioastronomical detection of magnesium dicarbide (MgC2) towards the carbon-rich star IRC+10216 leads to questions about whether this molecule can be observed in other wavelengths, especially with the wealth of IR data being produced by JWST. This present, theoretical spectral characterization, unfortunately, implies that mid-IR observations of MgC2 are unlikely due to small IR transition intensities, overlap with polycyclic aromatic hydrocarbon IR features, low frequencies/long wavelengths, or the relatively small column densities. In spite of this, the full set of fundamental anharmonic vibrational frequencies are provided for each of the 24Mg, 25Mg, and 26Mg isotopologues as are the complete rotational constants for the same set for additional laboratory characterization. Most notably and with regards to 24MgC2, the B 0 and C 0 (11452.7 and 9362.7 MHz) rotational constants are uniquely provided for the first time. The experimentally derived A 0, (B + C)/2, and (B − C)/4 values are within 0.7 % of the presently computed anharmonic results implying similar accuracy for the remaining spectroscopic constants. [ABSTRACT FROM AUTHOR]

We present a detection of correlated clustering between MeerKAT radio intensity maps and galaxies from the WiggleZ Dark Energy Survey. We find a 7.7σ detection of the cross-correlation power spectrum, the amplitude of which is proportional to the product of the |${\rm H}\, {\small I}$| density fraction (⁠|$\Omega _{{\rm H}\, {\small I}}$|⁠), |${\rm H}\, {\small I}$| bias (⁠|$b_{{\rm H}\, {\small I}}$|⁠), and the cross-correlation coefficient (r). We therefore obtain the constraint |$\Omega _{{\rm H}\, {\small I}}b_{{\rm H}\, {\small I}}r\, {=}\, [0.86\, {\pm }\, 0.10\, ({\rm stat})\, {\pm }\, 0.12\, ({\rm sys})]\, {\times }\, 10^{-3}$|⁠ , at an effective scale of |$k_{\rm eff}\ {\sim }\ 0.13\, h\, \text{Mpc}^{-1}$|⁠. The intensity maps were obtained from a pilot survey with the MeerKAT telescope, a 64-dish pathfinder array to the SKA Observatory (SKAO). The data were collected from 10.5 h of observations using MeerKAT 's L -band receivers over six nights covering the 11 h field of WiggleZ, in the frequency range 1015–973 MHz (0.400 |$\, {\lt }\, z\, {\lt }\,$| 0.459 in redshift). This detection is the first practical demonstration of the multidish autocorrelation intensity mapping technique for cosmology. This marks an important milestone in the roadmap for the cosmology science case with the full SKAO. [ABSTRACT FROM AUTHOR]

The cross-correlation between 21-cm intensity mapping (IM) experiments and photometric surveys of galaxies (or any other cosmological tracer with a broad radial kernel) is severely degraded by the loss of long-wavelength radial modes due to Galactic foreground contamination. Higher-order correlators are able to restore some of these modes due to the non-linear coupling between them and the local small-scale clustering induced by gravitational collapse. We explore the possibility of recovering information from the bispectrum between a photometric galaxy sample and an IM experiment, in the context of the clustering-redshifts technique. We demonstrate that the bispectrum is able to calibrate the redshift distribution of the photometric sample to the required accuracy of future experiments such as the Rubin Observatory, using future single-dish and interferometric 21-cm observations, in situations where the two-point function is not able to do so due to foreground contamination. We also show how this calibration is affected by the photometric redshift width σ z ,0 and maximum scale k max. We find that it is important to reach scales |$k \gtrsim 0.3\, h\, {\rm Mpc}^{-1}$|⁠ , with the constraints saturating at around |$k\sim 1\, h\, {\rm Mpc}^{-1}$| for next-generation experiments. [ABSTRACT FROM AUTHOR]

We briefly discuss the history of pumping schemes for the common 22-GHz maser transition in o-H2O, and note that radiative mechanisms have been considered in the past, as well as the better known collisional pumping mechanisms associated with shock waves. Substantial IR irradiation is indeed destructive to inversion at 22-GHz under a wide range of physical conditions. We identify a small number of transitions, including 22 GHz, that can be pumped by both collisional and radiative schemes, and, through radiative transfer modelling over a grid of values in kinetic temperature, number density, and dust temperature, identify loci in density-kinetic temperature space where these schemes lead to strong inversions. The radiative pumping scheme generally operates at higher dust temperature, and lower kinetic temperature, than the collisional scheme. We identify a small network of transitions that form a radiative pumping scheme for the 22-GHz maser, involving radiative transitions of wavelength approximately 6  |$\mu$| m. This network is capable of supplying more than 50 per cent of the 22-GHz inversion under typical radiative pumping conditions, and it is consistent with the need for high dust and low kinetic temperatures determined from the modelling. We identify a probable case of radiative pumping in a massive star-forming region from the observation of a positive correlation between the flux densities of 22-GHz H2O masers and 6.7-GHz methanol masers. We discuss possibilities for finding radiatively pumped H2O maser lines in other source types. [ABSTRACT FROM AUTHOR]

A goal for pathfinder intensity mapping (IM) surveys will be detecting features in the neutral hydrogen (⁠|${{\rm H}\, \small {\rm I}}$|⁠) power spectrum, which serve as conclusive evidence of cosmological signals. Observing such features at the expected scales in |${{\rm H}\, \small {\rm I}}$| IM autocorrelations, where contribution from systematics is uncertain, will provide a more convincing cosmological detection. We demonstrate how the turnover, i.e. the peak of the power spectrum at ultra-large scales, can be detected with |${{\rm H}\, \small {\rm I}}$| IM. We find that a MeerKAT 4000 |$\, \text{deg}^2$| survey using the UHF band is capable of a 3.1σ detection of the turnover, relative to a null model power spectrum with no turnover. This should exceed what is capable by current galaxy surveys in optical and near-infrared. The detection significance falls to ∼1σ in MeerKAT's L band but can reach ∼13σ with the Square Kilometre Array Observatory (SKAO), which should easily surpass the constraintsno from future Stage-IV-like spectroscopic galaxy surveys. We also propose a new model-independent methodology for constraining the precise turnover scale (k 0) and our tests on UHF -band simulated data achieved a precision of 10 per cent. This improved to 2.4 per cent when using the full SKAO. We demonstrate how the results are robust to foreground contamination by using transfer functions, even when an incorrect cosmology has been assumed in their construction. Given that the turnover is related to the horizon scale at matter–radiation equality, a sufficiently precise constraint of k 0 presents the possibility for a novel probe of cosmology. We therefore present a potential methodology for constructing a standard-ruler-based distance measurement, independent of the sound horizon, using the turnover location in the |${{\rm H}\, \small {\rm I}}$| power spectrum. [ABSTRACT FROM AUTHOR]

Context. Observations of molecular clouds, prestellar cores, and protoplanetary disks have established that the HNC/HCN ratio may be a potent diagnostic of molecular gas physical conditions. The processes that govern the relative abundances of these molecules nevertheless remain poorly understood. Aims. We seek to exploit the wide range of UV irradiation strengths within the ∼pc diameter Helix planetary nebula to explore the potential role of UV radiation in driving HNC/HCN. Methods. We performed IRAM 30 m and APEX 12 m radio line observations across six positions within the Helix Nebula, making use of radiative transfer and photodissociation modeling codes to interpret the results for line intensities and line ratios in terms of the molecular gas properties. Results. We have obtained the first detections of the plasma-embedded Helix molecular knots (globules) in HCN, HNC, HCO+, and other trace molecules. Analysis of the HNC/HCN integrated line intensity ratio reveals an increase with radial distance from the Helix central star. In the context of molecular line ratios of other planetary nebulae from the literature, the HNC/HCN ratio appears to be anticorrelated with UV emission over four orders of magnitude in incident flux. Models of the photodissociation regions within the Helix using the RADEX and Meudon codes reveal strong constraints on the column density (1.5–2.5 × 1012 cm−2) of the molecular gas, as well as pressure and temperature. Analysis of the molecular ion HCO+ across the Helix indicates that X-ray irradiation is likely driving HCO+ production in the outer regions of planetary nebulae, where photodissociation is limited but cold gas and ionized molecules are abundant. Conclusions. Although the observational results clearly indicate that UV irradiation is important in determining the HNC/HCN ratio, our photodissociation region modeling indicates that the UV flux gradient alone cannot reproduce the observed variation in HNC/HCN across the Helix Nebula. Instead, HNC/HCN appears to be dependent on both UV irradiation and gas pressure and density. [ABSTRACT FROM AUTHOR]

The 64-dish MeerKAT telescope was inaugurated in 2018 and has been conducting regular science operations since then. In the meantime, new observation modes have been under development. Spectral line modes are available, as well as L-, UHF- and S-band receivers. MeerKAT's excellent sensitivity over a wide range of angular scales makes it an excellent choice for studies of HII regions, supernova remnants and planetary nebulae. In addition, an OH megamaser has been detected at z > 0.5 for the first time. [ABSTRACT FROM AUTHOR]

Intensity mapping of 21-cm line by several radio telescope experiments will probe the large-scale structure of the Universe in the post-reionization epoch. It requires a theoretical framework of neutral hydrogen (H i) clustering, such as modelling of H i power spectrum for baryon acoustic oscillations (BAO) analysis. We propose a new method for reconstructing the H i map from dark matter distribution using N -body simulations. Several studies attempt to compute the H i power spectrum with N -body simulations by pasting H i gas at the dark matter halo centre, assuming the relation between the halo and H i masses. On the other hand, the method proposed in this paper reproduces the H i power spectrum from simulated dark matter distribution truncated at specific scales from the halo centre. With this method, the slope of H i power spectrum is reproduced well at the BAO scales, k < 1 h/Mpc. Furthermore, we find the fluctuation of spin temperature, which is often ignored at the post-reionization epoch, alters the power spectrum of brightness temperature by at most 8 per cent in the power spectrum. Finally, we discuss how our method works by comparing the density profiles of H i and dark matter around the dark matter haloes. [ABSTRACT FROM AUTHOR]

The bispectrum is a three-point statistic with the potential to provide additional information beyond power spectra analyses of survey data sets. Radio telescopes that broadly survey the 21-cm emission from neutral hydrogen (H  i) are a promising way to probe LSS and in this work we present an investigation into the H  i intensity mapping (IM) bispectrum using simulations. We present a model of the redshift space H  i IM bispectrum including observational effects from the radio telescope beam and 21-cm foreground contamination. We validate our modelling prescriptions with measurements from robust IM simulations, inclusive of these observational effects. Our foreground simulations include polarization leakage, on which we use a principal component analysis cleaning method. We also investigate the effects from a non-Gaussian beam including side-lobes. For a MeerKAT-like single-dish IM survey at z  = 0.39, we find that foreground removal causes an |$8{{\ \rm per\ cent}}$| reduction in the equilateral bispectrum's signal-to-noise ratio, whereas the beam reduces it by |$62{{\ \rm per\ cent}}$|⁠. We find our models perform well, generally providing |$\chi ^2_\text{dof}\sim 1$|⁠ , indicating a good fit to the data. Whilst our focus is on post-reionization, single-dish IM, our modelling of observational effects, especially foreground removal, can also be relevant to interferometers and reionization studies. [ABSTRACT FROM AUTHOR]

The mean and the scatter of the H i content of a dark matter halo as a function of the halo mass are useful statistics that can be used to test models of structure and galaxy formation. We investigate the possibility of constraining this H i –halo mass relation (HIHMR) from intensity maps of the redshifted 21-cm line. In particular, we use the geometry and topology of the brightness-temperature isocontours in a single frequency channel as quantified by the Minkowski functionals. First, we generate mock maps from a large N -body simulation considering the impact of thermal noise and foreground removal. We then use the Fisher information formalism to forecast constraints on a parametric model for the HIHMR. We consider a 20  000 deg2 survey (originally proposed for dark energy science) conducted with the Square Kilometre Array Phase 1 (SKA-1) MID observatory operating in single-dish mode. For a channel bandwidth of 2 MHz, we show that an integration time of a few |$\, \times \, 10^4$| s per pointing is sufficient to image the smoothed H i distribution at redshift z ≃ 1 and to measure the HIHMR in a nearly optimal way from the Minkowski functionals. Tighter constraints on some of the parameters can be obtained by using also an independent measurement of the mean H i density. Combining the results from different frequency channels provides exquisite constraints on the evolution of the HIHMR, especially in the central frequency range of the data cube. [ABSTRACT FROM AUTHOR]

The success of H  i intensity mapping is largely dependent on how well 21-cm foreground contamination can be controlled. In order to progress our understanding further, we present a range of simulated foreground data from two different ∼3000 deg2 sky regions, with varying effects from polarization leakage. Combining these with cosmological H  i simulations creates a range of intensity mapping test cases that require different foreground treatments. This allows us to conduct the most generalized study to date into 21-cm foregrounds and their cleaning techniques for the post-reionization era. We first provide a pedagogical review of the most commonly used blind foreground removal techniques [principal component analysis (PCA)/singular value decomposition (SVD), fast independent component analysis (FASTICA), and generalized morphological component analysis (GMCA)]. We also trial a non-blind parametric fitting technique and discuss potential hybridization of methods. We highlight the similarities and differences in these techniques finding that the blind methods produce near equivalent results, and we explain the fundamental reasons for this. Our results demonstrate that polarized foreground residuals should be generally subdominant to H  i on small scales (⁠|$k\gtrsim 0.1\, h\, \text{Mpc}^{-1}$|⁠). However, on larger scales, results are more case dependent. In some cases, aggressive cleans severely damp H  i power but still leave dominant foreground residuals. We find a changing polarization fraction has little impact on results within a realistic range (0.5–2 per cent); however, a higher level of Faraday rotation does require more aggressive cleaning. We also demonstrate the gain from cross-correlations with optical galaxy surveys, where extreme levels of residual foregrounds can be circumvented. However, these residuals still contribute to errors and we discuss the optimal balance between overcleaning and undercleaning. [ABSTRACT FROM AUTHOR]

We consider a primordial black hole of very high mass, |$10^9\!-\!10^{10}\, \mathrm{M}_\odot$|⁠ , surrounded by the dark matter and bayonic halo at redshifts z ∼ 20 without any local sources of energy release. Such heavy and concentrated objects in the early Universe were previously called 'cosmological dinosaurs'. Spectral distribution and spatial variation of the brightness in the 21-cm line of atomic hydrogen are calculated with the theory of radiation transfer. It is shown that a narrow and deep absorption arises in the form of the spherical shell around the primordial black hole at the certain radius. The parameters of this shell depend almost exclusively on the mass of the black hole. The angular diameter 18 arcsec of the absorption ring at z ∼ 20 is well within the current technical possibilities of the Square Kilometre Array type telescopes. But the observation of the ring width itself requires an order of magnitude better resolution. [ABSTRACT FROM AUTHOR]

We present a new halo model of neutral hydrogen (H  i) calibrated to galaxy formation simulations at redshifts z ∼ 0.1 and z ∼ 1.0 that we employ to investigate the constraining power of interferometric H  i intensity mapping on H  i astrophysics. We demonstrate that constraints on the small-scale H  i power spectrum can break the degeneracy between the H  i density |$\Omega _{\rm H\, \small {I}}$| and the H  i bias |$b_{\rm H\, \small {I}}$|⁠. For z ∼ 0.1, we forecast that an accurate measurement of |$\Omega _{\rm H\, \small {I}}$| up to 6 per cent level precision and the large-scale H  i bias |$b_{\rm H\, \small {I}}^0$| up to 1 per cent level precision can be achieved using Square Kilometre Array (SKA) pathfinder data from MeerKAT and Australian SKA Pathfinder (ASKAP). We also propose a new description of the H  i shot noise in the halo model framework in which a scatter of the relation between the H  i mass of galaxies and their host halo mass is taken into account. Furthermore, given the number density of H  i galaxies above a certain H  i mass threshold, future surveys will also be able to constrain the H  i mass function using only the H  i shot noise. This will lead to constraints at the 10 per cent level using the standard Schechter function. This technique will potentially provide a new way of measuring the H  i mass function, independent from existing methods. We predict that the SKA will be able to further improve the low-redshift constraints by a factor of 3, as well as pioneering measurements of H  i astrophysics at higher redshifts. [ABSTRACT FROM AUTHOR]

We assess the performance of the multipole expansion formalism in the case of single-dish H  i intensity mapping, including instrumental and foreground removal effects. This formalism is used to provide Markov chain Monte Carlo forecasts for a range of H  i and cosmological parameters, including redshift space distortions and the Alcock–Paczynski effect. We first determine the range of validity of our power spectrum modelling by fitting to simulation data, concentrating on the monopole, quadrupole, and hexadecapole contributions. We then show that foreground subtraction effects can lead to severe biases in the determination of cosmological parameters, in particular the parameters relating to the transverse Baryon Acoustic Oscillations (BAO) rescaling, the growth rate, and the H  i bias (α⊥, |$\overline{T}_\rm{H{\small I}}f\sigma _8$|⁠ , and |$\overline{T}_{\mathrm {H}\,{\small I}}b_{\mathrm {H}\,{\small I}}\sigma _8$|⁠ , respectively). We attempt to account for these biases by constructing a two-parameter foreground modelling prescription, and find that our prescription leads to unbiased parameter estimation at the expense of increasing the estimated uncertainties on cosmological parameters. In addition, we confirm that instrumental and foreground removal effects significantly impact the theoretical covariance matrix, and cause the covariance between different multipoles to become non-negligible. Finally, we show the effect of including higher order multipoles in our analysis, and how these can be used to investigate the presence of instrumental and systematic effects in H  i intensity mapping data. [ABSTRACT FROM AUTHOR]

Allowing for enhanced Lyα photon line emission from Population III dominated stellar systems in the first forming galaxies, we show the 21-cm cosmic dawn signal at 10 < |$z$| < 30 may substantially differ from standard scenarios. Energy transfer by Lyα photons emerging from galaxies may heat intergalactic gas if H  ii regions within galaxies are recombination bound, or cool the gas faster than by adiabatic expansion if reddened by winds internal to the haloes. In some extreme cases, differential 21-cm antenna temperatures near −500 mK may be achieved at 15 < |$z$| < 25, similar to the signature detected by the EDGES 21-cm cosmic dawn experiment. [ABSTRACT FROM AUTHOR]

Aims. Radio observing efficiency can be improved by calibrating and reducing the observations in total power mode rather than in frequency, beam, or position-switching modes. Methods. We selected a sample of spectra obtained from the Institut de Radio-Astronomie Millimétrique (IRAM) 30-m telescope and the Green Bank Telescope (GBT) to test the feasibility of the method. Given that modern front-end amplifiers for the GBT and direct Local Oscillator injection for the 30 m telescope provide smooth pass bands that are a few tens of megahertz in width, the spectra from standard observations can be cleaned (baseline removal) separately and then co-added directly when the lines are narrow enough (a few km s−1), instead of performing the traditional ON minus OFF data reduction. This technique works for frequency-switched observations as well as for position- and beam-switched observations when the ON and OFF data are saved separately. Results. The method works best when the lines are narrow enough and not too numerous so that a secure baseline removal can be achieved. A signal-to-noise ratio improvement of a factor of √2 2 $ \sqrt{2} $ is found in most cases, consistent with theoretical expectations. Conclusions. By keeping the traditional observing mode, the fallback solution of the standard reduction technique is still available in cases of suboptimal baseline behavior, sky instability, or wide lines, and to confirm the line intensities. These techniques of total-power-mode reduction can be applied to any radio telescope with stable baselines as long as they record and deliver the ONs and OFFs separately, as is the case for the GBT. [ABSTRACT FROM AUTHOR]

Probing statistical distribution of the neutral hydrogen (H  i) using the redshifted 21-cm hyperfine-transition spectral line holds the key to understand the formation and evolution of the matter density in the Universe. The two-point statistics of the H  i distribution can be estimated by measuring the power spectrum of the redshifted 21-cm signal using visibility correlation. A major challenge in this regard is that the expected signal is weak compared to the foreground contribution from the Galactic synchrotron emission and extragalactic point sources in the observing frequencies. In this work, we investigate the possibility of detecting the power spectrum of the redshifted 21-cm signal by using strong gravitational lensing of the galaxy clusters. This method has the advantage that it only enhances the H  i signal and not the diffuse Galactic foreground. Based on four simple models of the cluster potentials, we show that the strong lenses at relatively lower redshifts with more than one dark matter halo significantly enhance the 21-cm signal from the post-reionization era. We discuss the merits and demerits of the method and the future studies required for further investigations. [ABSTRACT FROM AUTHOR]

A 3D maser model has been used to perform an inverse problem on the light curves from three high-amplitude maser flares, selected on the basis of contemporaneous infrared observations. Plots derived from the model recover the size of the maser cloud, and two parameters linked to saturation, from three observational properties of the light curve. Recovered sizes are consistent with independent interferometric measurements. Maser objects transition between weak and moderate saturation during a flare. [ABSTRACT FROM AUTHOR]

We present a framework and an open-source python toolkit to analyse the two-point statistics of 3D fluctuations in the context of H  i intensity maps using the multipole expansion formalism. We include simulations of the cosmological H  i signal using N -body and lognormal methods, foregrounds and their removal, as well as instrumental effects. Using these simulations and analytical modelling, we investigate the impact of foreground cleaning and the instrumental beam on the power spectrum multipoles as well as on the Fourier space clustering wedges. We find that both the instrumental beam and the foreground removal can produce a quadrupole (and a hexadecapole) signal, and demonstrate the importance of controlling and accurately modelling these effects for precision radio cosmology. We conclude that these effects can be modelled with reasonable accuracy using our multipole expansion technique. We also perform a Markov Chain Monte Carlo (MCMC) analysis to showcase the effect of foreground cleaning on the estimation of the H  i abundance and bias parameters. The accompanying python toolkit is available at https://github.com/IntensityTools/MultipoleExpansion , and includes an interactive suite of examples to aid new users. [ABSTRACT FROM AUTHOR]

In this work, we propose a new method of computing the Karhunen–Loève Transform (KLT) applied to complex voltage data for the detection and noise level reduction in astronomical signals. We compared this method with the standard KLT techniques based on the Toeplitz correlation matrix and we conducted a performance analysis for the detection and extraction of astrophysical and artificial signals via Monte Carlo (MC) simulations. We applied our novel method to a real data study-case: the Voyager 1 telemetry signal. We evaluated the KLT performance in an astrophysical context: our technique provides a remarkable improvement in computation time and MC simulations show significant reconstruction results for signal-to-noise ratio (SNR) down to −10 dB and comparable results with standard signal detection techniques. The application to artificial signals, such as the Voyager 1 data, shows a notable gain in SNR after the KLT. [ABSTRACT FROM AUTHOR]

We simulate maser flares by varying either the pump rate or the background level of radiation in a 3D model of a maser cloud. We investigate the effect of different cloud shapes, saturation levels, and viewpoints. Results are considered for clouds with both uniform and internally variable unsaturated inversion. Pumping and background variations are represented by several different driving functions, some of which are light curves drawn from observations. We summarize the pumping variability results in terms of three observable parameters: the maximum flux density achieved, a variability index, and duty cycle. We demonstrate typical ranges of the flux density that may result from viewing an aspherical object from random viewpoints. The best object for a flare is a prolate cloud, viewed close to its long axis and driven from unsaturated conditions to at least modest saturation. Results for variation of the background level are qualitatively different from the variable pumping results in that they tend to produce short intervals of low flux density under conditions of moderate saturation and sufficient variability to be consistent with strong flaring. Variable background models typically have a significantly higher duty cycle than those with variable pumping. [ABSTRACT FROM AUTHOR]

This manuscript summarizes the contributions presented and discussed during the conference “A new window on radio galaxies, clusters and cosmic web: current status and new challenges”. The meeting was held online in March 2021. The works presented during the conference have been published in this associated Special Issue. Here, we outline the scientific context of the published results.

We consider the possibility of the detection of 3He  ii hyperfine line (rest frequency, |$8.67 \, \rm GHz$|⁠) emission from ionized zones around accreting black holes (BHs) formed at high redshifts, |$z$|  = 15–30. We show that the brightness temperature in 8.67GHz line increases and reaches a peak value after the accretion on to the BH exhausts and He  iii recombines into He  ii. This period of brightening last up to 40 Myr. We find that during this period the maximum brightness temperature reaches |$\simeq\! 0.2{\!-\!}0.5 \, \mu$| K, depending on the epoch when such a BH starts growing. The maximum angular size of the region emitting in the hyperfine line is around 0.5 arcmin. The flux from such a region (⁠|$\simeq\! 0.3 \, \rm nJy$|⁠) is too small to be detected by Square Kilometre Array1-MID (SKA1-MID). The rms of the collective flux from many emitting regions from a volume bounded by the synthesized beam and the bandwidth of SKA1-MID might reach 100 nJy, which is potentially detectable by SKA1-MID. [ABSTRACT FROM AUTHOR]

Observations of the redshifted 21-cm hyperfine line of neutral hydrogen from early phases of the Universe such as Cosmic Dawn and the Epoch of Reionization promise to open a new window onto the early formation of stars and galaxies. We present the first upper limits on the power spectrum of redshifted 21-cm brightness temperature fluctuations in the redshift range z  = 19.8–25.2 (54–68 MHz frequency range) using 14 h of data obtained with the LOFAR-Low Band Antenna (LBA) array. We also demonstrate the application of a multiple pointing calibration technique to calibrate the LOFAR-LBA dual-pointing observations centred on the North Celestial Pole and the radio galaxy 3C220.3. We observe an unexplained excess of |$\sim 30\!-\!50{{\ \rm per\ cent}}$| in Stokes / noise compared to Stokes V for the two observed fields, which decorrelates on ≳12 s and might have a physical origin. We show that enforcing smoothness of gain errors along frequency direction during calibration reduces the additional variance in Stokes I compared Stokes V introduced by the calibration on sub-band level. After subtraction of smooth foregrounds, we achieve a 2σ upper limit on the 21-cm power spectrum of |$\Delta _{21}^2 \lt (14561\, \text{mK})^2$| at |$k\sim 0.038\, h\, \text{cMpc}^{-1}$| and |$\Delta _{21}^2 \lt (14886\, \text{mK})^2$| at |$k\sim 0.038 \, h\, \text{cMpc}^{-1}$| for the 3C220 and NCP fields respectively and both upper limits are consistent with each other. The upper limits for the two fields are still dominated by systematics on most k modes. [ABSTRACT FROM AUTHOR]

We investigated, through numerical models, the flaring variability that may arise from the rotation of maser clouds of approximately spheroidal geometry, ranging from strongly oblate to strongly prolate examples. Inversion solutions were obtained for each of these examples over a range of saturation levels from unsaturated to highly saturated. Formal solutions were computed for rotating clouds with many randomly chosen rotation axes, and corresponding averaged maser light curves plotted with statistical information. The dependence of results on the level of saturation and on the degree of deformation from the spherical case was investigated in terms of a variability index and duty cycle. It may be possible to distinguish observationally between flares from oblate and prolate objects. Maser flares from rotation are limited to long time-scales (at least a few years) and modest values of the variability index (≲100), and can be aperiodic or quasi-periodic. Rotation is therefore not a good model for H2O variability on time-scales of weeks to months, or of truly periodic flares. [ABSTRACT FROM AUTHOR]

At intermediate to high densities, electron (de-)excitation collisions are the dominant process for populating or depopulating high Rydberg states. In particular, the accurate knowledge of the energy changing (n -changing) collisional rates is determinant for predicting the radio recombination spectra of gaseous nebula. The different data sets present in the literature come either from impact parameter calculations or semi-empirical fits and the rate coefficients agree within a factor of 2. We show in this paper that these uncertainties cause errors lower than 5 per cent in the emission of radio recombination lines of most ionized plasmas of typical nebulae. However, in special circumstances where the transitions between Rydberg levels are amplified by maser effects, the errors can increase up to 20 per cent. We present simulations of the optical depth and H n α line emission of active galactic nuclei broad-line regions and the Orion Nebula Blister to showcase our findings. [ABSTRACT FROM AUTHOR]

We use full sky simulations, including the effects of foreground contamination and removal, to explore multitracer synergies between a SKA-like 21cm intensity mapping survey and an LSST-like photometric galaxy redshift survey. In particular we study ratios of auto and cross-correlations between the two tracers as estimators of the ratio of their biases, a quantity that should benefit considerably from the cosmic variance (CV) cancellation of the multitracer approach. We show how well we should be able to measure the bias ratio on very large scales (down to ℓ ∼ 3), which is crucial to measure primordial non-Gaussianity and general relativistic effects on large-scale structure. We find that, in the absence of foregrounds but with realistic noise levels of such surveys, the multitracer estimators are able to improve on the sensitivity of a cosmic variance contaminated measurement by a factor of 2–4. When foregrounds are included, estimators using the 21cm autocorrelation become biased. However, we show that cross-correlation estimators are immune to this and do not incur in any significant penalty in terms of sensitivity from discarding the autocorrelation data. However, the loss of long-wavelength radial modes caused by foreground removal in combination with the low-redshift resolution of photometric surveys, reduces the sensitivity of the multitracer estimator, albeit still better than the cosmic variance contaminated scenario even in the noise free case. Finally we explore different alternative avenues to avoid this problem. [ABSTRACT FROM AUTHOR]

We measure the scale dependence and redshift dependence of 21 cm line emitted from the neutral hydrogen gas at redshift 1 < |$z$| < 5 using full cosmological hydrodynamic simulations by taking the ratios between the power spectra of H  i –dark matter (DM) cross-correlation and DM autocorrelation. The neutral hydrogen distribution is computed in full cosmological hydrodynamic simulations including star formation and supernova feedback under a uniform ultraviolet background radiation. We find a significant scale dependence of H  i bias at |$z$| > 3 on scales of k ≳ 1 h  Mpc−1, but it is roughly constant at lower redshift |$z$| < 3. The redshift evolution of H  i bias is relatively slow compared to that of QSOs at similar redshift range. We also measure a redshift space distortion (RSD) of H  i gas to explore the properties of H  i clustering. Fitting to a widely applied theoretical prediction, we find that the constant bias is consistent with that measured directly from the real space power spectra, and the velocity dispersion is marginally consistent with the linear perturbation prediction. Finally, we compare the results obtained from our simulation and the Illustris simulation, and conclude that the detailed astrophysical effects do not affect the scale dependence of H  i bias very much, which implies that the cosmological analysis using 21 cm line of H  i will be robust against the uncertainties arising from small-scale astrophysical processes such as star formation and supernova feedback. [ABSTRACT FROM AUTHOR]