Publications
34 results found
Chen Z, Chapman E, Wolz L, et al., 2023, Detecting the H I power spectrum in the post-reionization Universe with SKA-Low, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 524, Pages: 3724-3740, ISSN: 0035-8711
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- Citations: 1
Chapman E, 2022, Between the frontier and the abyss, Physics World, Vol: 35, Pages: 42-43i, ISSN: 0953-8585
<jats:p>Emma Chapman reviews First Dawn: From the Big Bang to Our Future in Space by Roberto Battiston (translated by Bonnie McClellan-Broussard)</jats:p>
Chapman E, 2022, First light: switching on stars at the dawn of time, CONTEMPORARY PHYSICS, Vol: 63, Pages: 15-33, ISSN: 0010-7514
Mevius M, Mertens F, Koopmans LVE, et al., 2022, A numerical study of 21-cm signal suppression and noise increase in direction-dependent calibration of LOFAR data, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 509, Pages: 3693-3702, ISSN: 0035-8711
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- Citations: 10
Hothi I, Chapman E, Pritchard JR, et al., 2021, Comparing foreground removal techniques for recovery of the LOFAR-EoR 21 cm power spectrum, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 500, Pages: 2264-2277, ISSN: 0035-8711
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- Citations: 29
Ghara R, Giri SK, Mellema G, et al., 2020, Constraining the intergalactic medium at <i>z</i> ≈ 9.1 using LOFAR Epoch of Reionization observations, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 493, Pages: 4728-4747, ISSN: 0035-8711
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- Citations: 57
Mertens FG, Mevius M, Koopmans LVE, et al., 2020, Improved upper limits on the 21 cm signal power spectrum of neutral hydrogen at <i>z</i> ≈ 9.1 from LOFAR, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 493, Pages: 1662-1685, ISSN: 0035-8711
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- Citations: 150
Chapman E, Jelic V, 2020, Foregrounds and Their Mitigation, COSMIC 21-CM REVOLUTION: CHARTING THE FIRST BILLION YEARS OF OUR UNIVERSE, Editors: Mesinger, Publisher: IOP PUBLISHING LTD, ISBN: 978-0-7503-2234-8
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- Citations: 2
Bacon DJ, Battye RA, Bull P, et al., 2020, Cosmology with Phase 1 of the Square Kilometre Array Red Book 2018: Technical specifications and performance forecasts, PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF AUSTRALIA, Vol: 37, ISSN: 1323-3580
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- Citations: 99
Chapman E, Santos MG, 2019, A full treatment of peculiar velocities on the reionization light cone, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 490, Pages: 1255-1269, ISSN: 0035-8711
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- Citations: 5
Page T, Bull A, Chapman E, 2019, Making Power Visible: "Slow Activism" to Address Staff Sexual Misconduct in Higher Education, VIOLENCE AGAINST WOMEN, Vol: 25, Pages: 1309-1330, ISSN: 1077-8012
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- Citations: 19
Chapman E, 2019, Tuning in to the cosmic dawn, NATURE ASTRONOMY, Vol: 3, Pages: 298-299, ISSN: 2397-3366
Chapman E, 2018, Sexual misconduct in academia, PHYSICS TODAY, Vol: 71, Pages: 10-12, ISSN: 0031-9228
Chapman E, 2018, Breaking the silence, PHYSICS WORLD, Vol: 31, Pages: 17-18, ISSN: 0953-8585
Chapman E, 2018, Foreground Mitigation in the Epoch of Reionization, PEERING TOWARDS COSMIC DAWN, Vol: 12, Pages: 261-268, ISSN: 1743-9213
Patil AH, Yatawatta S, Koopmans LVE, et al., 2017, Upper limits on the 21 cm epoch of reionization power spectrum from one night with LOFAR, Astrophysical Journal, Vol: 838, ISSN: 1538-4357
We present the first limits on the Epoch of Reionization 21 cm H i power spectra, in the redshift range z = 7.9–10.6, using the Low-Frequency Array (LOFAR) High-Band Antenna (HBA). In total, 13.0 hr of data were used from observations centered on the North Celestial Pole. After subtraction of the sky model and the noise bias, we detect a non-zero ${{\rm{\Delta }}}_{{\rm{I}}}^{2}={(56\pm 13\mathrm{mK})}^{2}$ (1-σ) excess variance and a best 2-σ upper limit of ${{\rm{\Delta }}}_{21}^{2}\lt {(79.6\mathrm{mK})}^{2}$ at k = 0.053 h cMpc−1 in the range z = 9.6–10.6. The excess variance decreases when optimizing the smoothness of the direction- and frequency-dependent gain calibration, and with increasing the completeness of the sky model. It is likely caused by (i) residual side-lobe noise on calibration baselines, (ii) leverage due to nonlinear effects, (iii) noise and ionosphere-induced gain errors, or a combination thereof. Further analyses of the excess variance will be discussed in forthcoming publications.
Mevius M, van der Tol S, Pandey VN, et al., 2016, Probing ionospheric structures using the LOFAR radio telescope, RADIO SCIENCE, Vol: 51, Pages: 927-941, ISSN: 0048-6604
Chapman E, Zaroubi S, Abdalla FB, et al., 2016, The effect of foreground mitigation strategy on EoR window recovery, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 458, Pages: 2928-2939, ISSN: 0035-8711
Majumdar S, Jensen H, Mellema G, et al., 2016, Effects of the sources of reionization on 21-cm redshift-space distortions, \mnras, Vol: 456, Pages: 2080-2094
Jelic V, de Bruyn AG, Pandey VN, et al., 2015, Linear polarization structures in LOFAR observations of the interstellar medium in the 3C 196 field, ASTRONOMY & ASTROPHYSICS, Vol: 583, ISSN: 1432-0746
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- Citations: 64
Ciardi B, Inoue S, Abdalla FB, et al., 2015, Simulating the 21 cm forest detectable with LOFAR and SKA in the spectra of high-<i>z</i> GRBs, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 453, Pages: 101-105, ISSN: 0035-8711
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- Citations: 13
Ghosh A, Koopmans LVE, Chapman E, et al., 2015, A Bayesian analysis of redshifted 21-cm H I signal and foregrounds: simulations for LOFAR, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 452, Pages: 1587-1600, ISSN: 0035-8711
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- Citations: 16
Asad KMB, Koopmans LVE, Jelic V, et al., 2015, Polarization leakage in epoch of reionization windows - I. Low Frequency Array observations of the 3C196 field, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 451, Pages: 3709-3727, ISSN: 0035-8711
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- Citations: 58
Vedantham HK, Koopmans LVE, de Bruyn AG, et al., 2015, Lunar occultation of the diffuse radio sky: LOFAR measurements between 35 and 80 MHz, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 450, Pages: 2291-2305, ISSN: 0035-8711
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- Citations: 18
Koopmans LVE, Pritchard J, Mellema G, et al., 2015, The cosmic dawn and epoch of reionization with the square kilometre array, Proceedings of Sciencec
Concerted effort is currently ongoing to open up the Epoch of Reionization (EoR) (z∼15-6) for studies with IR and radio telescopes. Whereas IR detections have been made of sources (Lyman-α 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 EoR, 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 EoR, 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 (Abridged).
Patil AH, Zaroubi S, Chapman E, et al., 2014, Constraining the epoch of reionization with the variance statistic: simulations of the LOFAR case, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 443, Pages: 1113-1124, ISSN: 0035-8711
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- Citations: 52
Jelic V, de Bruyn AG, Mevius M, et al., 2014, Initial LOFAR observations of epoch of reionization windows II. Diffuse polarized emission in the ELAIS-N1 field, ASTRONOMY & ASTROPHYSICS, Vol: 568, ISSN: 0004-6361
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- Citations: 69
Wolz L, Abdalla FB, Blake C, et al., 2014, The effect of foreground subtraction on cosmological measurements from intensity mapping, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 441, Pages: 3271-3283, ISSN: 0035-8711
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- Citations: 78
Chapman E, Bonaldi A, Harker G, et al., 2014, Cosmic dawn and epoch of reionization foreground removal with the SKA
The exceptional sensitivity of the SKA will allow observations of the Cosmic Dawn and Epoch of Reionization (CD/EoR) in unprecedented detail, both spectrally and spatially. This wealth of information is buried under Galactic and extragalactic foregrounds, which must be removed accurately and precisely in order to reveal the cosmological signal. This problem has been addressed already for the previous generation of radio telescopes, but the application to SKA is different in many aspects. We summarise the contributions to the field of foreground removal in the context of high redshift and high sensitivity 21-cm measurements. We use a state-of-the-art simulation of the SKA Phase 1 observations complete with cosmological signal, foregrounds and frequencydependent instrumental effects to test both parametric and non-parametric foreground removal methods. We compare the recovered cosmological signal using several different statistics and explore one of the most exciting possibilities with the SKA - imaging of the ionized bubbles. We find that with current methods it is possible to remove the foregrounds with great accuracy and to get impressive power spectra and images of the cosmological signal. The frequency-dependent PSF of the instrument complicates this recovery, so we resort to splitting the observation bandwidth into smaller segments, each of a common resolution. If the foregrounds are allowed a random variation from the smooth power law along the line of sight, methods exploiting the smoothness of foregrounds or a parametrization of their behaviour are challenged much more than non-parametric ones. However, we show that correction techniques can be implemented to restore the performances of parametric approaches, as long as the first-order approximation of a power law stands.
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