A5006821432- Radio Astronomy Observations and Technology
- Astrophysics and Cosmic Phenomena
- Galaxies: Formation, Evolution, Phenomena
- Astronomy and Astrophysical Research
- Superconducting and THz Device Technology
- Cosmology and Gravitation Theories
- Antenna Design and Optimization
- Dark Matter and Cosmic Phenomena
- Radio Wave Propagation Studies
- Scientific Research and Discoveries
- Adaptive optics and wavefront sensing
- Astronomical Observations and Instrumentation
- Geophysics and Gravity Measurements
- Soil Moisture and Remote Sensing
- Neutrino Physics Research
- Pulsars and Gravitational Waves Research
- Millimeter-Wave Propagation and Modeling
- Solar and Space Plasma Dynamics
- Space Science and Extraterrestrial Life
- Stellar, planetary, and galactic studies
- Particle physics theoretical and experimental studies
- Terahertz technology and applications
- Black Holes and Theoretical Physics
- Gamma-ray bursts and supernovae
- History and Developments in Astronomy
Imperial College London
2015-2025
Imperial Valley College
2019
University of Groningen
2015
Raman Research Institute
2015
SKA Telescope, Australia
2015
Harvard University
2008-2012
Center for Astrophysics Harvard & Smithsonian
2008-2011
Ames Research Center
2011
Solar System Exploration Research Virtual Institute
2011
California Institute of Technology
2005-2008
Abstract We present a detailed overview of the cosmological surveys that we aim to carry out with Phase 1 Square Kilometre Array (SKA1) and science they will enable. highlight three main surveys: medium-deep continuum weak lensing low-redshift spectroscopic HI galaxy survey over 5 000 deg 2 ; wide deep intensity mapping (IM) 20 from $z = 0.35$ 3; deep, high-redshift IM 100 3$ 6. Taken together, these achieve an array important scientific goals: measuring equation state dark energy \sim...
Many models of early structure formation predict a period heating immediately preceding reionization, when X-rays raise the gas temperature above that cosmic microwave background.These are often assumed to heat intergalactic medium (IGM) uniformly, but in reality will more strongly closer sources.We develop framework for calculating fluctuations 21-cm brightness originate from this spatial variation rate.High-redshift sources highly clustered, leading significant (with fractional variations...
Context. It is well established that between 380 000 and 1 billion years after the Big Bang Inter Galactic Medium (IGM) underwent a "phase transformation" from cold fully neutral to warm (≈ 104 K) ionized. Whether this phase transformation was driven completed by photoionization young hot stars question of topical interest in cosmology.
The potential use of the redshifted 21 cm line from neutral hydrogen for probing epoch reionization is motivating construction several low-frequency interferometers. There also much interest in possibility constraining initial conditions inflation and nature dark matter energy by power spectrum density perturbations three dimensions on smaller scales than probed microwave background anisotropies. Theoretical understanding signal has been fragmented into different regimes physical interest....
Observations of the frequency dependence global brightness temperature redshifted 21 cm line neutral hydrogen may be possible with single dipole experiments. In this paper, we develop a Fisher matrix formalism for calculating sensitivity such instruments to signal from reionization and dark ages. We show that rapid histories duration $\ensuremath{\Delta}z\ensuremath{\lesssim}2$ can constrained, provided local foregrounds well modeled by low order polynomials. It is then shown observations in...
We consider the running of spectral index as a probe both inflation itself, and overall evolution very early universe. Surveying collection simple single field inflationary models, we confirm that magnitude is relatively consistent, unlike tensor amplitude, which varies by orders magnitude. Given this target, potentially detectable future large scale structure or 21 cm observations, but only most futuristic measurements can distinguish between these models on basis their running. For any...
Concerted effort is currently ongoing to open up the Epoch of Reionization (z ∼15-6) for studies with IR and radio telescopes.Whereas detections have been made sources (Lyman-α emitters, quasars drop-outs) in this redshift regime relatively small fields view, no direct detection neutral hydrogen, via redshifted 21-cm line, has yet established.Such a expected coming years, surveys, could entire universe from z ∼6-200 astrophysical cosmological studies, opening not only Reionization, but also...
Amongst standard model parameters that are constrained by cosmic microwave background (CMB) observations, the optical depth $τ$ stands out as a nuisance parameter. While provides some crude limits on reionization, it also degrades constraints other cosmological parameters. Here we explore how 21 cm cosmology---as direct probe of reionization---can be used to independently predict in an effort improve CMB parameter constraints. We develop two complementary schemes for doing so. The first uses...
The epoch of reionization (EoR) 21-cm signal is expected to be highly non-Gaussian in nature and this non-Gaussianity also evolve with the progressing state reionization. Therefore will correlated between different Fourier modes ($k$). power spectrum not able capture correlation signal. We use a higher-order estimator -- bispectrum quantify evolving non-Gaussianity. study using an ensemble simulated large variety $k$ triangles. observe two competing sources driving signal: fluctuations...
We examine the effect of Lyman-continuum photons on 21-cm background in high-redshift Universe. The brightness temperature this transition is determined by spin Ts, which describes relative populations singlet and triplet hyperfine states. Once first luminous sources appear, Ts set Wouthuysen–Field effect, Lyman-series mix levels. Here we consider coupling through n > 2 Lyman photons. show that (and heating) from scattering Lyn negligible, because they rapidly cascade to lower-energy These...
We quantify the prospects for using emission lines from rotational transitions of CO molecule to perform an `intensity mapping' observation at high redshift during Epoch Reionization (EoR). The aim intensity mapping is observe combined many unresolved galaxies, measure spatial fluctuations in this emission, and use as a tracer large scale structure very early times history our Universe. This measurement would help determine properties molecular clouds -- sites star formation galaxies that...
We measure several properties of the reionization process and corresponding low-frequency 21-cm signal associated with neutral hydrogen distribution, using a large volume, high resolution simulation cosmic reionization. The brightness temperature is derived by post-processing this numerical semi-analytical prescription. Our study extends to redshifts (z ~ 25) where, in addition collisional coupling, our post-processed simulations take into account inhomogeneities heating gas X-rays effect an...
Next generation radio experiments such as LOFAR, HERA, and SKA are expected to probe the Epoch of Reionization (EoR) claim a first direct detection cosmic 21cm signal within next decade. Data volumes will be enormous can thus potentially revolutionize our understanding early Universe galaxy formation. However, numerical modelling EoR prohibitively expensive for Bayesian parameter inference how optimally extract information from incoming data is currently unclear. Emulation techniques fast...
We present analysis of the normalised 21-cm bispectrum from fully-numerical simulations intergalactic-medium heating by stellar sources and high-mass X-ray binaries (HMXB) during cosmic dawn. Lyman-$\alpha$ coupling is assumed to be saturated, we therefore probe nature non-Gaussianities produced processes. find evolution very different that power spectrum. It exhibits a turnover whose peak moves large small scales with decreasing redshift, corresponds typical separation emission regions....
[Abridged] The spatially averaged global spectrum of the redshifted 21cm line has generated much experimental interest, for it is potentially a direct probe Epoch Reionization and Dark Ages. Since cosmological signal here purely spectral signature, most proposed experiments have little angular sensitivity. This worrisome because with only spectra, can be difficult to distinguish from foregrounds such as Galactic synchrotron radiation, both are spectrally smooth latter orders magnitude...
We explore the impact of reionization topology on 21-cm statistics. Four models are presented which emulate large ionized bubbles around over-dense regions (21CMFAST/ global-inside- out), small in (local-inside-out), under-dense (global-outside-in) and (local-outside-in). show that first-generation instruments might struggle to distinguish global using shape power spectrum alone. All considered capable breaking this degeneracy with variance, is higher outside-in models. Global can also be...
In this paper we establish the accuracy and robustness of a fast estimator for bispectrum - "FFT estimator". The implementation presented here offers speed simplicity benefits over direct sampling approach. We also generalise derivation so it may be easily applied to any order polyspectra, such as trispectrum, with cost only handful FFTs. All lower statistics can calculated simultaneously little extra cost. To test make use non-linear density field, more strongly non-Gaussian case toy-model...