Alan Heavens
A5040378381- Galaxies: Formation, Evolution, Phenomena
- Cosmology and Gravitation Theories
- Astronomy and Astrophysical Research
- Stellar, planetary, and galactic studies
- Gamma-ray bursts and supernovae
- Scientific Research and Discoveries
- Astrophysics and Cosmic Phenomena
- Radio Astronomy Observations and Technology
- Adaptive optics and wavefront sensing
- Dark Matter and Cosmic Phenomena
- Gaussian Processes and Bayesian Inference
- Geophysics and Gravity Measurements
- Statistical and numerical algorithms
- Solar and Space Plasma Dynamics
- History and Developments in Astronomy
- Pulsars and Gravitational Waves Research
- Astronomical Observations and Instrumentation
- Blind Source Separation Techniques
- Relativity and Gravitational Theory
- Computational Physics and Python Applications
- Astrophysical Phenomena and Observations
- Astrophysics and Star Formation Studies
- Black Holes and Theoretical Physics
- Advanced Vision and Imaging
- Statistical Mechanics and Entropy
Imperial College London
2014-2023
Flatiron Institute
2022
Smithsonian Astrophysical Observatory
2022
University College London
2022
Sorbonne Université
2022
Centre National de la Recherche Scientifique
2022
Institut d'Astrophysique de Paris
2022
Flatiron Health (United States)
2022
University of Sussex
2022
The London College
2018
Pan-STARRS1 has carried out a set of distinct synoptic imaging sky surveys including the $3π$ Steradian Survey and Medium Deep in 5 bands ($grizy_{P1}$). The mean 5$σ$ point source limiting sensitivities stacked 3$π$ $grizy_{P1}$ are (23.3, 23.2, 23.1, 22.3, 21.4) respectively. upper bound on systematic uncertainty photometric calibration across is 7-12 millimag depending bandpass. astrometric using Gaia frame comes from comparison results with Gaia: standard deviation median residuals ($...
Since cosmology is no longer "the data-starved science," the problem of how to analyze large data sets best has recently received considerable attention, and Karhunen-Loève eigenvalue methods have been applied both galaxy redshift surveys cosmic microwave background (CMB) maps. We present a comprehensive discussion for estimating cosmological parameters from sets, which includes previously published techniques as special cases. show that several jointly not knowing priori can be readily...
We study the implications of Planck data for models dark energy (DE) and modified gravity (MG), beyond cosmological constant scenario. start with cases where DE only directly affects background evolution, considering Taylor expansions equation state, principal component analysis parameterizations related to potential a minimally coupled scalar field. When estimating density at early times, we significantly improve present constraints. then move general or MG perturbations that encompass both...
We present a finely-binned tomographic weak lensing analysis of the Canada-France-Hawaii Telescope Lensing Survey, CFHTLenS, mitigating contamination to signal from presence intrinsic galaxy alignments via simultaneous fit cosmological model and an alignment model. CFHTLenS spans 154 square degrees in five optical bands, with accurate shear photometric redshifts for sample median redshift zm =0.70. estimate 21 sets cosmic correlation functions associated six bins, each spanning angular range...
We compute the bispectrum of 2dF Galaxy Redshift Survey (2dFGRS) and use it to measure bias parameter galaxies. This quantifies strength clustering galaxies relative mass in Universe. By analysing 80 × 106 triangle configurations wavenumber range 0.1 < k 0.5 h Mpc−1 (i.e. on scales roughly between 5 30 h−1 Mpc) we find that linear is consistent with unity: b1= 1.04 ± 0.11, quadratic (non-linear) zero: b2=−0.054 0.08. Thus, at least large scales, optically selected do indeed trace underlying...
The Planck nominal mission cosmic microwave background (CMB) maps yield unprecedented constraints on primordial non-Gaussianity (NG). Using three optimal bispectrum estimators, separable template-fitting (KSW), binned, and modal, we obtain consistent values for the local, equilateral, orthogonal amplitudes, quoting as our final result fNL^local= 2.7+/-5.8, fNL^equil= -42+/-75, fNL^ortho= -25+\-39 (68% CL statistical). NG is detected in data; using skew-C_l statistics find a nonzero from...
The Planck full mission cosmic microwave background(CMB) temperature and E-mode polarization maps are analysed to obtain constraints on primordial non-Gaussianity(NG). Using three classes of optimal bispectrum estimators - separable template-fitting (KSW), binned, modal we consistent values for the local, equilateral, orthogonal amplitudes, quoting as our final result from alone fNL^local=2.5+\-5.7, fNL^equil=-16+\-70 fNL^ortho=-34+\-33(68%CL). Combining data fNL^local=0.8+\-5.0,...
We present an optimized variant of the halo model, designed to produce accurate matter power spectra well into non-linear regime for a wide range cosmological models. To do this, we introduce physically motivated free parameters halo-model formalism and fit these data from high-resolution N-body simulations. For variety Λ cold dark (ΛCDM) wCDM models, is ≃ 5 per cent k ≤ 10h Mpc−1 z 2. An advantage our new model that it can be adapted account effects baryonic feedback on spectrum....
When inferring parameters from a Gaussian-distributed data set by computing likelihood, covariance matrix is needed that describes the errors and their correlations. If not known priori, it may be estimated thereby becomes random object with some intrinsic uncertainty itself. We show how to infer in presence of such an matrix, marginalising over true conditioned on its value. This leads likelihood function no longer Gaussian, but rather adapted version multivariate t-distribution, which has...
Abstract Cosmological inference relies on compressed forms of the raw data for analysis, with traditional methods exploiting physics knowledge to define summary statistics, such as power spectra, that are known capture much information. An alternative approach is ask a neural network find set informative statistics from data, which can then be analysed either by likelihood- or simulation-based inference. This has advantage non-Gaussian fields, they may more information than two-point...
It has been proposed that the cosmological constant $\Lambda$ might be measured from geometric effects on large-scale structure. A positive vacuum density leads to correlation-function contours which are squashed in radial direction when calculated assuming a matter-dominated model. We show this effect will somewhat harder detect than previous calculations have suggested: squashing factor is likely $<1.3$, given realistic constraints matter contribution $\Omega$. Moreover, geometrical...
We present the results of a moped analysis ∼3 × 105 galaxy spectra from Sloan Digital Sky Survey Data Release 3 (SDSS DR3), with number improvements in data, modelling and compared our previous DR1. The include: galaxies theoretical models at higher spectral resolution Å, better calibrated an extended list excluded emission lines wider range dust models. new estimates cosmic star formation rate (SFR), evolution stellar mass density function fossil record. In contrast to earlier work show no...