This present article is dedicated to thoroughly exploring the competency of the synergy of the upcoming Cosmic Microwave Background (CMB) missions and Square Kilometre Array (SKA) surveys in detecting features in the primordial power spectrum. Features are by definition specific scale-dependent modifications to the minimal power-law power spectrum. The functional form of the features depends on the inflationary scenarios taken into consideration. The identification of any conclusive deviation from the feature-less power-law power spectrum will allow us to largely fathom out the microphysics of the primordial universe. Here, we consider three vital theoretically motivated feature models, namely, Sharp feature signal, Resonance feature signal, and Bump feature. To investigate these features, we associate each feature model with a specific scale-dependent function called a template. Here we explore three distinct fiducial models for each feature model and for each fiducial model we compare the sensitivity of 36 different combinations of the cosmological surveys. We implement the Fisher matrix forecast method to obtain the possible constraints on the feature model parameters for the future CMB missions, namely, PICO, CORE-M5, LiteBIRD and CMB-S4 in synergy with upcoming SKA surveys, wherein we explore SKA-Cosmic Shear and SKA-Intensity Mapping surveys. Furthermore, the significance of combining EUCLID-Galaxy surveys with the SKA-Intensity Mapping survey is also explored. To consider the feasibility of propagating theoretical uncertainties of nonlinear scales in estimating the uncertainties on the feature parameters, we adopt redshift dependent upper limits of scales. To demonstrate the relative sensitivities of these future surveys towards the parameters of the feature models, we present a comparative analysis of all three feature models.
We describe a simulation for the distribution of galaxies focusing on the atomic Hydrogen content. We aim to make predictions for surveys of galaxies using the redshifted 21 cm line emission. We take the expected distribution of HI masses, circular velocities, sizes of galaxies and orientations into account for this simulation. We use the sensitivity of ASKAP and MeeKAT radio telescopes to estimate the number of detections of HI galaxies in upcoming surveys. We validate our simulation with earlier estimates carried out by using some of these considerations. We show that unlike earlier simulati…
The Square Kilometre Array (SKA) will produce spectroscopic surveys of tens to hundreds of millions of HI galaxies, eventually covering 30,000 sq. deg. and reaching out to redshift z~2. The huge volumes probed by the SKA will allow for some of the best constraints on primordial non-Gaussianity, based on measurements of the large-scale power spectrum. We investigate various observational set-ups for HI galaxy redshift surveys, compatible with the SKA Phase 1 and Phase 2 (full SKA) configurations. We use the corresponding number counts and bias for each survey from realistic simulations and deri…
Exploring Gravitational Wave Signatures Due to Primordial Non-gaussianity and Large Scale Structure Using SKAO
National Institute for Chemical Physics and Biophysics（国家化学物理与生物物理研究所）；Gran Sasso Science Institute（格兰萨索科学研究所）；Max Planck Institute for Gravitational Physics (Albert Einstein Institute)（马克斯·普朗克引力物理研究所（爱因斯坦研究所））
Hydroxyl ($\rm OH$) is known to form efficiently in cold gas ($T\sim 100$K) along with the molecule $\rm H_2$ and can be used as an efficient tracer of the diffuse molecular gas in the interstellar medium (ISM). Using a simple formalism describing the $\rm H\,I/H_2$ transition and a reduced network of major chemical reactions, we present a semi-analytical prescription to estimate the abundances of O-bearing molecules in the diffuse ISM. We show that predictions based on our prescription are in good agreement with the estimates obtained using the MEUDON PDR code which utilizes the full reaction…
It is usually assumed that we will need to wait until next-generation surveys like Euclid, LSST and SKA, in order to improve on the current best constraints on primordial non-Gaussianity from the Planck experiment. We show that two contemporary surveys, with the SKA precursor MeerKAT and the Dark Energy Survey (DES), can be combined using the multi-tracer technique to deliver an accuracy on measurement of $f_{\rm NL}$ that is up to three times better than Planck.
The Planck CMB experiment has delivered the best constraints so far on primordial non-Gaussianity, ruling out early-Universe models of inflation that generate large non-Gaussianity. Although small improvements in the CMB constraints are expected, the next frontier of precision will come from future large-scale surveys of the galaxy distribution. The advantage of such surveys is that they can measure many more modes than the CMB -- in particular, forthcoming radio surveys with the SKA will cover huge volumes. Radio continuum surveys deliver the largest volumes, but with the disadvantage of no r…
The primordial non-Gaussianity induces scale-dependent bias of the \hi with respect to the underlying dark matter, which exhibits features on the very large scales of the 21-cm power spectrum potentially observable with \hi intensity mapping observations. We forecast the prospective constraints on the four fundamental shapes of primordial non-Gaussianity (local, equilateral, orthogonal, and enfolded), with the current and future \hi intensity mapping experiments, BINGO, FAST, and SKA-I. With the current configuration of the experiments and assumed one-year observation time, we find that the SK…
It has been proposed recently that the SKA1-MID could be used to conduct an HI intensity mapping survey that could rival upcoming Stage IV dark energy surveys. However, measuring the weak HI signal is expected to be very challenging due to contaminations such as residual Galactic emission, RFI, and instrumental 1/f noise. Modelling the effects of these contaminants on the cosmological HI signal requires numerical end-to-end simulations. Here we present how 1/f noise within the receiver can double the effective uncertainty of an SKA-like survey to HI on large angular scales (l < 50).
The intergalactic medium (IGM) plays an important role in the formation and evolution of galaxies. Recent developments in upcoming radio telescopes are starting to open up the possibility of making a first direct detection of the 21 cm signal of neutral hydrogen (HI) from the warm gas of the IGM in large-scale filaments. The cosmological hydrodynamical EAGLE simulation is used to estimate the typical IGM filament signal. Assuming the same average signal for all filaments, a prediction is made for the detectability of such a signal with the upcoming mid-frequency array of the Square Kilometer A…
The early Universe is a precious probe of the birth of primordial objects, first star formation events and consequent production of photons and heavy elements. Higher-order corrections to the cosmological linear perturbation theory predicts the formation of coherent supersonic gaseous streaming motions at decoupling time. These bulk flows impact the gas cooling process and determine a cascade effect on the whole baryon evolution. By analytical estimates and N-body hydrodynamical chemistry numerical simulations including atomic and molecular evolution, gas cooling, star formation, feedback effe…
In the most distant reaches of the Universe, the 21-cm hyperfine transition in neutral hydrogen provides one of the only available tracers of large-scale structure. A number of instruments have been working and planned to measure the 21-cm line signals, and in particular, Experiment to Detect the Global EoR Signature (EDGES) recently has reported the first detection of an absorption signal, which corresponds to the 21-cm line global signal at the epoch of reionization (EoR). The future large radio telescope, Square Kilometre Array (SKA) will be able to deliver the high-precision measurement of…
We forecast future constraints on local-type primordial non-Gaussianity parameter $f_{\rm NL}$ with a photometric galaxy survey by Euclid, a continuum galaxy survey by Square Kilometre Array (SKA), and their combination. We derive a general expression for the covariance matrix of the power spectrum estimates of multiple tracers to show how the so-called multitracer technique improves constraints on $f_{\rm NL}$. In particular we clarify the role of the overlap fraction of multiple tracers and the division method of the tracers. Our Fisher matrix analysis indicates that stringent constraints of…
Studying the cosmic dawn and the epoch of reionization through the redshifted 21 cm line are among the major science goals of the SKA1. Their significance lies in the fact that they are closely related to the very first stars in the universe. Interpreting the upcoming data would require detailed modelling of the relevant physical processes. In this article, we focus on the theoretical models of reionization that have been worked out by various groups working in India with the upcoming SKA in mind. These models include purely analytical and semi-numerical calculations as well as fully numerical…
The Square Kilometre Array (SKA) is a planned radio interferometer of unprecedented scale that will revolutionize low-frequency radio astronomy when completed. In particular, one of its core science drivers is the systematic mapping of the Cosmic Dawn and Epoch of Reionization, which mark the birth of the first stars and galaxies in the Universe and their subsequent ionization of primordial intergalactic hydrogen, respectively. The SKA will offer the most sensitive view of these poorly understood epochs using the redshifted 21 cm hyperfine signal from intergalactic hydrogen. However, significa…
With a radio continuum galaxy survey by the Square Kilometre Array (SKA), a photometric galaxy survey by Euclid and their combination, we forecast future constraints on primordial non-Gaussianity. We focus on the potential impact of local-type higher-order nonlinear parameters on the parameter estimation and particularly the confirmation of the inflationary consistency inequality. Nonstandard inflationary models, such as multifield models, introduce the scale-dependent stochastic clustering of galaxies on large scales, which is a unique probe of mechanism for generating primordial density fluc…
We consider the possibility of the detection of $^3$HeII hyperfine line (rest frequency, $8.67 \, \rm GHz$) emission from ionized zones around accreting black holes (BHs) formed at high redshifts, $z=15\hbox{--}30$. We show that the brightness temperature in 8.67GHz line increases and reaches a peak value after the accretion onto the BH exhausts and HeIII recombines into HeII. This period of brightening last up to 40~million years. We find that during this period the maximum brightness temperature reaches $\simeq 0.2\hbox{--}0.5 μ$K, depending on the epoch when such a black hole starts growing…
The light-cone (LC) effect causes the mean as well as the statistical properties of the redshifted 21-cm signal $T_{\rm b}(\hat{\bf n},ν)$ to change with frequency $ν$ (or cosmic time). Consequently, the statistical homogeneity (ergodicity) of the signal along the line of sight (LoS) direction is broken. This is a severe problem particularly during the Epoch of Reionization (EoR) when the mean neutral hydrogen fraction ($\bar{x}_{\rm HI}$) changes rapidly as the universe evolves. This will also pose complications for large bandwidth observations. These effects imply that the 3D power spectrum …
Beyond ΛCDM with the SKA Observatory -- II: Unveiling the Secrets of the Early Universe
University of the Western Cape（西开普大学）；University of Portsmouth（朴茨茅斯大学）；The University of Manchester（曼彻斯特大学）；Van Swinderen Institute, University of Groningen（格罗宁根大学范斯温德伦研究所）
The statistical properties of the primordial perturbations contain clues about the origins of those fluctuations. Although the Planck collaboration has recently obtained tight constraints on primordial non-gaussianity from cosmic microwave background measurements, it is still worthwhile to mine upcoming data sets in effort to place independent or competitive limits. The ionized bubbles that formed at redshift z~6-20 during the Epoch of Reionization are seeded by primordial overdensities, and so the statistics of the ionization field at high redshift are related to the statistics of the primord…
We forecast constraints on primordial non-Gaussianity (PNG) and bias parameters from measurements of galaxy power spectrum and bispectrum in future radio continuum and optical surveys. In the galaxy bispectrum, we consider a comprehensive list of effects, including the bias expansion for non-Gaussian initial conditions up to second order, redshift space distortions, redshift uncertainties and theoretical errors. These effects are all combined in a single PNG forecast for the first time. Moreover, we improve the bispectrum modelling over previous forecasts, by accounting for trispectrum contrib…
Simulations of the 21cm emission line for upcoming large-scale HI galaxy surveys
ETH Zürich（苏黎世联邦理工学院）；Observatoire de la Côte d’Azur, Laboratoire J-L Lagrange（蔚蓝海岸天文台J-L拉格朗日实验室）；University of the Western Cape（西开普敦大学）；INAF - Astronomical Observatory of Trieste（意大利国家天体物理研究所的里雅斯特天文台）；IFPU - Institute for Fundamental Physics of the Universe（宇宙基础物理研究所）；Centre for Astrophysics Research, University of Hertfordshire（赫特福德大学天体物理学研究中心）；EPFL - Institute of Physics, Laboratory for Galaxy Evolution（洛桑联邦理工学院物理系星系演化实验室）；Tianjin Normal University（天津师范大学）
We give an overview of complementarity and synergy in cosmology between the Square Kilometre Array and future survey projects in other wavelengths. In the SKA era, precision cosmology will be limited by systematic errors and cosmic variance, rather than statistical errors. However, combining and/or cross-correlating multi-wavelength data, from the SKA to the cosmic microwave background, optical/infrared and X-ray, substantially reduce these limiting factors. In this chapter, we summarize future survey projects and show highlights of complementarity and synergy, which can be very powerful to pr…
In this article, we do a thorough investigation of the competency of the forthcoming Cosmic Microwave Background (CMB) and Galaxy surveys in probing the features in the primordial power spectrum. Primordial features are specific model-dependent corrections on top of the standard power-law inflationary power spectrum; the functional form being given by different inflationary scenarios. Signature of any significant departure from the feature-less power spectrum will enable us to decipher the intricacies of the inflationary Universe. Here, we delve into three major yet distinct features, namely, …
Current bounds from the polarization of the CMB predict the scale-invariant gravitational wave (GW) background of inflation to be out of reach for upcoming GW interferometers. This prospect dramatically changes if the inflaton is a pseudoscalar, in which case its generic coupling to any abelian gauge field provides a new source of GWs, directly related to the dynamics of inflation. This opens up new ways of probing the scalar potential responsible for cosmic inflation. Dividing inflation models into universality classes, we analyze the possible observational signatures. One of the most promisi…
It is broadly accepted that Supermassive Black Holes (SMBHs) are located in the centers of most massive galaxies, although there is still no convincing scenario for the origin of their massive seeds. It has been suggested that primordial black holes (PBHs) of masses $\gtrsim 10^{2} M_\odot$ may provide such seeds, which would grow to become SMBHs. We suggest an observational test to constrain this hypothesis: gas accretion around PBHs during the cosmic dark ages powers the emission of high energy photons which would modify the spin temperature as measured by 21cm Intensity Mapping (IM) observa…
Measuring the small primordial nonGaussianity (PNG) predicted by cosmic inflation theories may help diagnose them. The detectability of PNG by its imprint on the 21cm power spectrum from the epoch of reionization is reassessed here in terms of $f_{NL}$, the local nonlinearity parameter. We find that an optimum, multi-frequency observation by SKA can achieve $Δf_{NL} \sim 3$ (comparable to recent Planck CMB limits), while a cosmic-variance-limited array of this size like Omniscope can even detect $Δf_{NL} \sim 0.2$. This substantially revises the methods and results of previous work.
The scalar induced gravitational waves are produced from primordial curvature perturbations in the second order of perturbations. We constrain the fractional energy density of scalar induced gravitational waves from gravitational waves observations. If there is no detection of the scalar induced gravitational waves, the fractional energy density of scalar induced gravitational waves is constrained by some upper limits. Depends on these upper limits, we can obtain the constraints on the power spectrum of the primordial curvature perturbations. For a power-law scalar power spectrum, the constrai…
Primordial non-Gaussianity is a crucial test of inflationary cosmology. We consider the impact of non-Gaussianity on the ionization power spectrum from 21 cm emission during the epoch of reionization. We focus on the power spectrum on large scales at redshifts of 7 to 8 and explore the expected constraint on the local non-Gaussianity parameter f_NL for current and next-generation 21 cm experiments. We show that experiments such as SKA and MWA could measure f_NL values of order 10. This can be improved by an order of magnitude with a fast-Fourier transform telescope like Omniscope.
It is shown that small-scale magnetic fields present before recombination induce baryonic density inhomogeneities of appreciable magnitude. The presence of such inhomogeneities changes the ionization history of the Universe, which in turn decreases the angular scale of the Doppler peaks and increases Silk damping by photon diffusion. This unique signature could be used to (dis)prove the existence of primordial magnetic fields of strength as small as B~10^(-11) Gauss by upcoming cosmic microwave background observations.
Probing Primordial Black Holes with upcoming Radio Telescopes: a case study for LOFAR2.0, FAST Core Array and BINGO
Universidade Federal de Campina Grande（坎皮纳格兰德联邦大学）；Leibniz University Hannover（汉诺威莱布尼茨大学）；Ruprecht-Karls-Universität Heidelberg（海德堡大学）；Max Planck Institute for Gravitational Physics, Albert Einstein Institute（马克斯·普朗克引力物理研究所，爱因斯坦研究所）
We present a new probe of primordial non-Gaussianity via the 21cm radiation from minihalos at high redshifts. We calculate the fluctuations in the brightness temperature (measured against the cosmic microwave background) of the 21cm background from minihalos containing HI at redshift \sim 6-20, and find a significant enhancement due to small non-Gaussianity with amplitude f_NL \leq 1. This enhancement can be attributed to the nonlinear bias which is strongly increased in the presence of non-Gaussianity. We show that our results are robust against changes in the assumed mass function and some p…
Understanding properties of the first sources in the Universe using the redshifted \HI ~21-cm signal is one of the major aims of present and upcoming low-frequency experiments. We investigate the possibility of imaging the redshifted 21-cm pattern around the first sources during the cosmic dawn using the SKA1-low. We model the \HI ~21-cm image maps, appropriate for the SKA1-low, around the first sources consisting of stars and X-ray sources within galaxies. In addition to the system noise, we account also for the astrophysical foregrounds by adding them to the signal maps. We find that after s…
After reionisation, the 21cm emission line of neutral hydrogen within galaxies provides a tracer of dark matter. Next-generation intensity mapping surveys, with the SKA and other radio telescopes, will cover large sky areas and a wide range of redshifts, facilitating their use as probes of primordial non-Gaussianity. {Previous works have shown that the bispectrum can achieve tight constraints on primordial non-Gaussianity with future surveys that are purposely designed for intensity mapping in interferometer mode}. Here we investigate the constraints attainable from surveys operating in single…
The study of the Universe on ultra-large scales is one of the major science cases for the Square Kilometre Array (SKA). The SKA will be able to probe a vast volume of the cosmos, thus representing a unique instrument, amongst next-generation cosmological experiments, for scrutinising the Universe's properties on the largest cosmic scales. Probing cosmic structures on extremely large scales will have many advantages. For instance, the growth of perturbations is well understood for those modes, since it falls fully within the linear regime. Also, such scales are unaffected by the poorly understo…
HI intensity mapping (IM) is a novel technique capable of mapping the large-scale structure of the Universe in three dimensions and delivering exquisite constraints on cosmology, by using HI as a biased tracer of the dark matter density field. This is achieved by measuring the intensity of the redshifted 21cm line over the sky in a range of redshifts without the requirement to resolve individual galaxies. In this chapter, we investigate the potential of SKA1 to deliver HI intensity maps over a broad range of frequencies and a substantial fraction of the sky. By pinning down the baryon acoustic…
The dipole anisotropy seen in the {cosmic microwave background radiation} is interpreted as due to our peculiar motion. The Cosmological Principle implies that this cosmic dipole signal should also be present, with the same direction, in the large-scale distribution of matter. Measurement of the cosmic matter dipole constitutes a key test of the standard cosmological model. Current measurements of this dipole are barely above the expected noise and unable to provide a robust test. Upcoming radio continuum surveys with the SKA should be able to detect the dipole at high signal to noise. We simu…
We investigate the feasibility of measuring the effects of peculiar velocities in large-scale structure using the dipole of the redshift-space cross-correlation function. We combine number counts of galaxies with brightness-temperature fluctuations from 21cm intensity mapping, demonstrating that the dipole may be measured at modest significance ($\lesssim 2σ$) by combining the upcoming radio survey CHIME with the future redshift surveys of DESI and Euclid. More significant measurements ($\lesssim~10σ$) will be possible by combining intensity maps from the SKA with these of DESI or Euclid, and …
Current analyses of the Lyman-alpha forest assume that the primordial power spectrum of density perturbations obeys a simple power law, a strong theoretical assumption which should be tested. Employing a large suite of numerical simulations which drop this assumption, we reconstruct the shape of the primordial power spectrum using Lyman-alpha data from the Sloan Digital Sky Survey (SDSS). Our method combines a minimally parametric framework with cross-validation, a technique used to avoid over-fitting the data. Future work will involve predictions for the upcoming Baryon Oscillation Sky Survey…
We investigate future constraints on primordial local-type non-Gaussianity from 21 cm angular power spectrum from minihalos. We particularly focus on the trispectrum of primordial curvature perturbations which are characterized by the non-linearity parameters $τ_{\rm NL}$ and $g_{\rm NL}$. We show that future measurements of minihalo 21 cm angular power spectrum can probe these non-linearity parameters with an unprecedented precision of $τ_{\rm NL}\sim30$ and $g_{\rm NL}\sim2\times10^3$ for Square Kilometre Array (SKA) and $τ_{\rm NL}\sim0.6$ and $g_{\rm NL}\sim8\times10^2$ for Fast Fourier Tr…
We investigate the possibility of using future photometric and radio surveys to constrain the power spectrum of primordial fluctuations that is predicted by inflationary models with a violation of the slow-roll phase. We forecast constraints with a Fisher analysis on the amplitude of the parametrized features on ultra-large scales, in order to assess whether these could be distinguishable over the cosmic variance. We find that the next generation of photometric and radio surveys has the potential to test these models at a sensitivity better than current CMB experiments and that the synergy bet…
The 21cm emission of neutral hydrogen is a potential probe of the matter distribution in the Universe after reionisation. Cosmological surveys of this line intensity will be conducted in the coming years by the SKAO and HIRAX experiments, complementary to upcoming galaxy surveys. We present the first forecasts of the cosmological constraints from the combination of the 21cm power spectrum and bispectrum. Fisher forecasts are computed for the constraining power of these surveys on cosmological parameters, the BAO distance functions and the growth function. We also estimate the constraining powe…
We consider Cosmic Microwave Background constraints on inflation models for which the primordial power spectrum is a mixture of perturbations generated by inflaton fluctuations and fluctuations in a curvaton field. If future experiments do not detect isocurvature modes or large non-Gaussianity, it will not be possible to directly distinguish inflaton and curvaton contributions. We investigate whether current and future data can instead constrain the relative contributions of the two sources. We model the spectrum with a bimodal form consisting of a sum of two independent power laws, with diffe…
We explore possible non-Gaussian features of primordial gravitational waves by constructing model-independent templates for nonlinearity parameters of tensor bispectrum. Our analysis is based on Effective Field Theory of inflation that relies on no particular model as such and thus the results are quite generic. The analysis further reveals that chances of detecting squeezed limit tensor bispectrum are fairly higher than equilateral limit. We also discuss prospects of detectability in upcoming CMB missions.
The measurement of the large scale distribution of neutral hydrogen in the late Universe, obtained with radio telescopes through the hydrogen 21cm line emission, has the potential to become a key cosmological probe in the upcoming years. We explore the constraining power of 21cm intensity mapping observations on the full set of cosmological parameters that describe the $Λ$CDM model. We assume a single-dish survey for the SKA Observatory and simulate the 21cm linear power spectrum monopole and quadrupole within six redshift bins in the range $z=0.25-3$. Forecasted constraints are computed numer…
We explore the potential use of the Radio Continuum (RC) survey conducted by the Square Kilometre Array (SKA) to remove (delens) the lensing-induced B-mode polarization and thus enhance future cosmic microwave background (CMB) searches for inflationary gravitational waves. Measurements of large-scale B-modes of the CMB are considered to be the best method for probing gravitational waves from the cosmic inflation. Future CMB experiments will, however, suffer from contamination by non-primordial B-modes, one source of which is the lensing B-modes. Delensing, therefore, will be required for furth…
A claimed detection of cosmological tensor perturbations from inflation via B-mode polarization of the cosmic microwave background requires distinguishing other possible B-mode sources. One such potential source of confusion is primordial magnetic fields. For sufficiently low-amplitude B-mode signals, the microwave background temperature and polarization power spectra from power-law tensor perturbations and from a power-law primordial magnetic field are indistinguishable. However, we show that such a magnetic field will induce a small-scale Faraday rotation which is detectable using four-point…
Bursts of particle production during inflation provide a well-motivated mechanism for creating bump like features in the primordial power spectrum. Current data constrains these features to be less than about 5% the size of the featureless primordial power spectrum at wavenumbers of about 0.1 h Mpc^{-1}. We forecast that the Planck cosmic microwave background experiment will be able to strengthen this constraint to the 0.5% level. We also predict that adding data from a square kilometer array (SKA) galaxy redshift survey would improve the constraint to about the 0.1% level. For features at lar…
