Imperial College London

Dr Jonathan R. Pritchard

Faculty of Natural SciencesDepartment of Physics

Senior Lecturer
 
 
 
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Contact

 

+44 (0)20 7594 7557j.pritchard Website CV

 
 
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Location

 

1018CBlackett LaboratorySouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

54 results found

Majumdar S, Pritchard JR, Mondal R, Watkinson CA, Bharadwaj S, Mellema Get al., 2018, Quantifying the non-Gaussianity in the EoR 21-cm signal through bispectrum, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 476, Pages: 4007-4024, ISSN: 0035-8711

JOURNAL ARTICLE

Schmit CJ, Pritchard JR, 2018, Emulation of reionization simulations for Bayesian inference of astrophysics parameters using neural networks, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 475, Pages: 1213-1223, ISSN: 0035-8711

JOURNAL ARTICLE

Burns JO, Bradley R, Tauscher K, Furlanetto S, Mirocha J, Monsalve R, Rapetti D, Purcell W, Newell D, Draper D, MacDowall R, Bowman J, Nhan B, Wollack EJ, Fialkov A, Jones D, Kasper JC, Loeb A, Datta A, Pritchard J, Switzer E, Bicay Met al., 2017, A Space-based Observational Strategy for Characterizing the First Stars and Galaxies Using the Redshifted 21cm Global Spectrum, ASTROPHYSICAL JOURNAL, Vol: 844, ISSN: 0004-637X

JOURNAL ARTICLE

Schmit CJ, Pritchard JR, 2017, Neural Network Emulation of Reionization Simulations, Proceedings of the International Astronomical Union, Vol: 12, Pages: 43-46, ISSN: 1743-9213

© 2018 International Astronomical Union. Next generation radio experiments such as LOFAR, HERA and SKA are expected to probe the Epoch of Reionization and claim a first direct detection of the cosmic 21cm signal within the next decade. One of the major challenges for these experiments will be dealing with enormous incoming data volumes. Machine learning is key to increasing our data analysis efficiency. We consider the use of an artificial neural network to emulate 21cmFAST simulations and use it in a Bayesian parameter inference study. We then compare the network predictions to a direct evaluation of the EoR simulations and analyse the dependence of the results on the training set size. We find that the use of a training set of size 100 samples can recover the error contours of a full scale MCMC analysis which evaluates the model at each step.

JOURNAL ARTICLE

Watkinson CA, Majumdar S, Pritchard JR, Mondal Ret al., 2017, A fast estimator for the bispectrum and beyond - a practical method for measuring non-Gaussianity in 21-cm maps, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 472, Pages: 2436-2446, ISSN: 0035-8711

JOURNAL ARTICLE

Harker GJA, Mirocha J, Burns JO, Pritchard JRet al., 2016, Parametrizations of the 21-cm global signal and parameter estimation from single-dipole experiments, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 455, Pages: 3829-3840, ISSN: 0035-8711

JOURNAL ARTICLE

Liu A, Pritchard JR, Allison R, Parsons AR, Seljak U, Sherwin BDet al., 2016, Eliminating the optical depth nuisance from the CMB with 21 cm cosmology, PHYSICAL REVIEW D, Vol: 93, ISSN: 2470-0010

JOURNAL ARTICLE

Pritchard J, 2015, Reionization and the SKA, ASTRONOMY & GEOPHYSICS, Vol: 56, ISSN: 1366-8781

JOURNAL ARTICLE

Watkinson CA, Mesinger A, Pritchard JR, Sobacchi Eet al., 2015, 21-cm signatures of residual H I inside cosmic H II regions during reionization, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 449, Pages: 3202-3211, ISSN: 0035-8711

JOURNAL ARTICLE

Watkinson CA, Pritchard JR, 2015, The impact of spin-temperature fluctuations on the 21-cm moments, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 454, Pages: 1416-1431, ISSN: 0035-8711

JOURNAL ARTICLE

Watkinson CA, Pritchard JR, Mesinger A, Sobacchi Eet al., 2015, The impact of small absorbers, galactic neutral hydrogen & X-rays on 1-point statistics of the 21-cm line., Proceedings of the International Astronomical Union, Vol: 10, Pages: 189-191, ISSN: 1743-9213

© International Astronomical Union 2015. We discuss a selection of semi-numerical simulations of reionization whose analysis investigates the effect of small absorbing systems, neutral hydrogen within galaxies and the efficiency with which galaxies produce X-rays. We focus on the consequences for both observing the 21-cm 1-point statistics and their interpretation.

JOURNAL ARTICLE

Chang TC, Gong Y, Santos M, Silva M, Aguirre J, Doré O, Pritchard Jet al., 2014, Synergy of CO/[CII]/Lya line intensity mapping with the SKA, Proceedings of Science, Vol: 9-13-June-2014

© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. This subchapter describes the science enabled by cross-correlations of the SKA1-LOW 21-cm EoR surveys with other line mapping programs. In particular, we identify and investigate potential synergies with planned programs, such as the line intensity mapping of redshifted CO rotational lines, [CII] and Ly-a emissions during reionization. We briefly describe how these tracers of the star-formation rate at z ∼ 8 can be modeled jointly before forecasting their autoand cross-power spectra measurements with the nominal 21cm EoR survey. After discussing the measurement prospect, we discuss how reionization parameters can be better constrained using these new measurements.

JOURNAL ARTICLE

Glover SCO, Chluba J, Furlanetto SR, Pritchard JR, Savin DWet al., 2014, Atomic, Molecular, and Optical Physics in the Early Universe: From Recombination to Reionization, Editors: Arimondo, Berman, Lin, Publisher: ELSEVIER ACADEMIC PRESS INC, Pages: 135-270, ISBN: 978-0-12-800129-5

BOOK CHAPTER

Koopmans LVE, Pritchard J, Mellema G, Abdalla F, Aguirre J, Ahn K, Barkana R, Van Bemmel I, Bernardi G, Bonaldi A, Briggs F, De Bruyn AG, Chang TC, Chapman E, Chen X, Ciardi B, Datta KK, Dayal P, Ferrara A, Fialkov A, Fiore F, Ichiki K, Illiev IT, Inoue S, Jelić V, Jones M, Lazio J, Maio U, Majumdar S, Mack KJ, Mesinger A, Morales MF, Parsons A, Pen UL, Santos M, Schneider R, Semelin B, De Souza RS, Subrahmanyan R, Takeuchi T, Trott C, Vedantham H, Wagg J, Webster R, Wyithe Set al., 2014, The cosmic dawn and epoch of reionization with the square kilometre array

© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. Concerted effort is currently ongoing to open up the Epoch of Reionization (z ∼15-6) for studies with IR and radio telescopes. Whereas IR detections have been made of sources (Lyman-a emitters, quasars and drop-outs) in this redshift regime in relatively small fields of view, no direct detection of neutral hydrogen, via the redshifted 21-cm line, has yet been established. Such a direct detection is expected in the coming years, with ongoing surveys, and could open up the entire universe from z ∼6-200 for astrophysical and cosmological studies, opening not only the Epoch of Reionization, but also its preceding Cosmic Dawn (z ∼30-15) and possibly even the later phases of the Dark Ages (z ∼200-30). All currently ongoing experiments attempt statistical detections of the 21-cm signal during the Epoch of Reionization, with limited signal-to-noise. Direct imaging, except maybe on the largest (degree) scales at lower redshifts, as well as higher redshifts will remain out of reach. The Square Kilometre Array (SKA) will revolutionize the field, allowing direct imaging of neutral hydrogen from scales of arc-minutes to degrees over most of the redshift range z ∼6-28 with SKA1-LOW, and possibly even higher redshifts with the SKA2-LOW. In this SKA will be unique, and in parallel provide enormous potential of synergy with other upcoming facilities (e.g. JWST). In this chapter we summarize the physics of 21-cm emission, the different phases the universe is thought to go through, and the observables that the SKA can probe, referring where needed to detailed chapters in this volume. This is done within the framework of the current SKA1 baseline design and a nominal CD/EoR straw-man survey, consisting of a shallow, medium-deep and deep survey, the latter probing down to ∼1mK brightness temperature on arc-minute scales at the end of reion

CONFERENCE PAPER

Mesinger A, Ferrara A, Greig B, Iliev I, Mellema G, Pritchard J, Santos MGet al., 2014, Constraining the astrophysics of the cosmic dawn and the epoch of reionization with the SKA, Proceedings of Science, Vol: 9-13-June-2014

© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. The Square Kilometre Array (SKA) will offer an unprecedented view onto the early Universe, using interferometric observations of the redshifted 21cm line. The 21cm line probes the thermal and ionization state of the cosmic gas, which is governed by the birth and evolution of the first structures in our Universe. Here we show how the evolution of the 21cm signal will allow us to study when the first generations of galaxies appeared, what were their properties, and what was the structure of the intergalactic medium. We highlight qualitative trends which will offer robust insights into the early Universe. Advancing.

JOURNAL ARTICLE

Pritchard J, Masters K, Allen J, Contenta F, Huckvale L, Wilkins S, Zocchi Aet al., 2014, Asking gender questions, Astronomy and Geophysics, Vol: 55, Pages: 6.8-6.12, ISSN: 1366-8781

JOURNAL ARTICLE

Pritchard J, Masters K, Allen J, Contenta F, Huckvale L, Wilkins S, Zocchi Aet al., 2014, Asking gender questions, ASTRONOMY & GEOPHYSICS, Vol: 55, Pages: 8-12, ISSN: 1366-8781

JOURNAL ARTICLE

Subrahmanyan R, Shankar NU, Pritchard J, Vedantham HKet al., 2014, All-sky signals from recombination to reionization with the SKA, Proceedings of Science, Vol: 9-13-June-2014

© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. Cosmic evolution in the hydrogen content of the Universe through recombination and up to the end of reionization is expected to be revealed as subtle spectral features in the uniform extragalactic cosmic radio background. The redshift evolution in the excitation temperature of the 21-cm spin flip transition of neutral hydrogen appears as redshifted emission and absorption against the cosmic microwave background. The precise signature of the spectral trace from cosmic dawn and the epoch of reionization are dependent on the spectral radiance, abundance and distribution of the first bound systems of stars and early galaxies, which govern the evolution in the spin-flip level populations. Redshifted 21 cm from these epochs when the spin temperature deviates from the temperature of the ambient relic cosmic microwave background results in an all-sky spectral structure in the 40-200 MHz range, almost wholly within the band of SKA-Low. Another spectral structure from gas evolution is redshifted recombination lines from epoch of recombination of hydrogen and helium; the weak all-sky spectral structure arising from this event is best detected at the upper end of the 350-3050 MHz band of SKA-mid. Total power spectra of SKA interferometer elements form the measurement set for these faint signals from recombination and reionization; the inter-element interferometer visibilities form a calibration set. The challenge is in precision polarimetric calibration of the element spectral response and solving for additives and unwanted confusing leakages of sky angular structure modes into spectral modes. Herein we discuss observing methods and design requirements that make possible these all-sky SKA measurements of the cosmic evolution of hydrogen.

JOURNAL ARTICLE

Watkinson CA, Pritchard JR, 2014, Distinguishing models of reionization using future radio observations of 21-cm 1-point statistics, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 443, Pages: 3090-3106, ISSN: 0035-8711

JOURNAL ARTICLE

Liu A, Pritchard JR, Tegmark M, Loeb Aet al., 2013, Global 21 cm signal experiments: A designer's guide, PHYSICAL REVIEW D, Vol: 87, ISSN: 1550-7998

JOURNAL ARTICLE

Mellema G, Koopmans LVE, Abdalla FA, Bernardi G, Ciardi B, Daiboo S, de Bruyn AG, Datta KK, Falcke H, Ferrara A, Iliev IT, Iocco F, Jelic V, Jensen H, Joseph R, Labroupoulos P, Meiksin A, Mesinger A, Offringa AR, Pandey VN, Pritchard JR, Santos MG, Schwarz DJ, Semelin B, Vedantham H, Yatawatta S, Zaroubi Set al., 2013, Reionization and the Cosmic Dawn with the Square Kilometre Array, EXPERIMENTAL ASTRONOMY, Vol: 36, Pages: 235-318, ISSN: 0922-6435

JOURNAL ARTICLE

Pritchard JR, Loeb A, 2013, Evolution of the 21cm signal throughout cosmic history, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 78, ISSN: 1089-4918

The potential use of the redshifted 21 cm line from neutral hydrogen for probing the epoch of reionization is motivating the construction of several low-frequency interferometers. There is also much interest in the possibility of constraining the initial conditions from inflation and the nature of the dark matter and dark energy by probing the power spectrum of density perturbations in three dimensions and on smaller scales than probed by the microwave background anisotropies. Theoretical understanding of the 21 cm signal has been fragmented into different regimes of physical interest. In this paper, we make the first attempt to describe the full redshift evolution of the 21 cm signal between 0<z<300. We include contributions to the 21 cm signal from fluctuations in the gas density, temperature, and neutral fraction, as well as the Lyα flux, and allow for a post-reionization signal from damped Lyα systems. Our comprehensive analysis provides a useful foundation for optimizing the design of future arrays whose goal is to separate the particle physics from the astrophysics, either by probing the peculiar velocity distortion of the 21 cm power spectrum, or by extending the 21 cm horizon to z≳25 before the first galaxies had formed, or to z≲6 when the residual pockets of hydrogen trace large-scale structure.

JOURNAL ARTICLE

Burns JO, Lazio J, Bale S, Bowman J, Bradley R, Carilli C, Furlanetto S, Harker G, Loeb A, Pritchard Jet al., 2012, Probing the first stars and black holes in the early Universe with the Dark Ages Radio Explorer (DARE), ADVANCES IN SPACE RESEARCH, Vol: 49, Pages: 433-450, ISSN: 0273-1177

JOURNAL ARTICLE

Harker GJA, Pritchard JR, Burns JO, Bowman JDet al., 2012, An MCMC approach to extracting the global 21-cm signal during the cosmic dawn from sky-averaged radio observations, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 419, Pages: 1070-1084, ISSN: 0035-8711

JOURNAL ARTICLE

Loeb A, Pritchard J, 2012, The missing reel, NEW SCIENTIST, Vol: 216, Pages: 30-33, ISSN: 0262-4079

JOURNAL ARTICLE

Pritchard JR, Loeb A, 2012, 21 cm cosmology in the 21st century, REPORTS ON PROGRESS IN PHYSICS, Vol: 75, ISSN: 0034-4885

JOURNAL ARTICLE

Silva MB, Santos MG, Pritchard JR, Cen R, Cooray Aet al., 2012, Probing the very first galaxies with the SKA, Pages: 101-116, ISSN: 1570-6591

We describe the use of the high redshift 21 cm signal to probe the very first galaxies to appear in the Universe. Using fast large volume simulations of the pre-Reionization epoch we have shown that the Lyman alpha radiation emitted from these young galaxies makes a strong contribution to the 21cm signal on large scales at z∼20. With the current setup the Square Kilometre Array (SKA) should be able to measure this signal, therefore making it probably the only telescope capable of giving us detailed information about the radiation emitted by the first stars and characterizing their host galaxies. SKA-pathfinders with ∼10%of the full collecting area should be capable of making a statistical detection of the 21cm power spectrum at redshifts z<20.We then discuss the use of the redshift space distortions as a way to further constrain the Lyman alpha signal and demonstrate that they can be used as a model independent way to extract this signature with the SKA. © Springer-Verlag Berlin Heidelberg 2012.

CONFERENCE PAPER

Silva MB, Santos MG, Pritchard JR, Cen R, Cooray Aet al., 2012, Probing the Very First Galaxies with the SKA, Joint European and National Astronomy Meeting (JENAM)/18th Annual Meeting of the European-Astronomical-Society/20th Annual Portuguese Meeting of Astronomy and Astrophysics/Symposium 7 - Square Kilometre Array (SKA), Publisher: SPRINGER, Pages: 101-116, ISSN: 1570-6591

CONFERENCE PAPER

Abazajian KN, Calabrese E, Cooray A, De Bernardis F, Dodelson S, Friedland A, Fuller GM, Hannestad S, Keating BG, Linder EV, Lunardini C, Melchiorri A, Miquel R, Pierpaoli E, Pritchard J, Serra P, Takada M, Wong YYYet al., 2011, Cosmological and astrophysical neutrino mass measurements, ASTROPARTICLE PHYSICS, Vol: 35, Pages: 177-184, ISSN: 0927-6505

JOURNAL ARTICLE

Adshead P, Easther R, Pritchard J, Loeb Aet al., 2011, Inflation and the scale dependent spectral index: prospects and strategies, JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, ISSN: 1475-7516

JOURNAL ARTICLE

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