Browsing by Author "Bernardi, Gianni"

Now showing 1 - 5 of 5
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    Antenna beam characterization for the global 21-cm experiment LEDA and its impact on signal model parameter reconstruction
    (Oxford University Press, 2022) Spinelli, Marta; Kyriakou, George A.; Bernardi, Gianni
    Cosmic dawn, the onset of star formation in the early universe, can in principle be studied via the 21-cm transition of neutral hydrogen, for which a sky-averaged absorption signal, redshifted to MHz frequencies, is predicted to be O(10-100) mK. Detection requires separation of the 21-cm signal from bright chromatic foreground emission due to Galactic structure, and the characterization of how it couples to instrumental response. In this work, we present characterization of antenna gain patterns for the Large-aperture Experiment to detect the Dark Ages (LEDA) via simulations, assessing the effects of the antenna ground-plane geometries used, and measured soil properties.
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    Cosmology with a SKA HI intensity mapping survey
    (Proceedings of Science, 2014) Santos, Mario G.; Bull, Philip; Alonso, David; Camera, Stefano; Ferreira, Pedro G.; Bernardi, Gianni; Maartens, Roy; Viel, Matteo; Villaescusa-Navarro, Francisco; Abdalla, Filipe B.; Jarvis, Matt; Metcalf, R. Benton; Pourtsidou, A.; Wolz, Laura
    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 oscillation and redshift space distortion features in the matter power spectrum – thus determining the expansion and growth history of the Universe – these surveys can provide powerful tests of dark energy models and modifications to General Relativity. They can also be used to probe physics on extremely large scales, where precise measurements of spatial curvature and primordial non-Gaussianity can be used to test inflation; on small scales, by measuring the sum of neutrino masses; and at high redshifts where non-standard evolution models can be probed. We discuss the impact of foregrounds as well as various instrumental and survey design parameters on the achievable constraints. In particular we analyse the feasibility of using the SKA1 autocorrelations to probe the large-scale signal.
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    Foreground modelling via Gaussian process regression: an application to HERA data
    (Oxford University Press, 2020) Ghosh, Abhik; Mertens, Florent; Bernardi, Gianni
    The key challenge in the observation of the redshifted 21-cm signal from cosmic reionization is its separation from the much brighter foreground emission. Such separation relies on the different spectral properties of the two components, although, in real life, the foreground intrinsic spectrum is often corrupted by the instrumental response, inducing systematic effects that can further jeopardize the measurement of the 21-cm signal. In this paper, we use Gaussian Process Regression to model both foreground emission and instrumental systematics in ∼2 h of data from the Hydrogen Epoch of Reionization Array.
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    HERA Phase I Limits on the Cosmic 21 cm Signal: Constraints on Astrophysics and Cosmology during the Epoch of Reionization
    (The American Astronomical Society., 2022) Abdurashidova, Zara; Aguirre, James E.; Alexander, Paul; Ali, Zaki S.; Balfour, Yanga; Barkana, Rennan; Beardsley, Adam P.; Bernardi, Gianni; Billings, Tashalee S.; Bowman, Judd D.; Bradley, Richard F.
    Recently, the Hydrogen Epoch of Reionization Array (HERA) has produced the experiment’s first upper limits on the power spectrum of 21 cm fluctuations at z ∼ 8 and 10. Here, we use several independent theoretical models to infer constraints on the intergalactic medium (IGM) and galaxies during the epoch of reionization from these limits. We find that the IGM must have been heated above the adiabatic-cooling threshold by z ∼ 8, independent of uncertainties about IGM ionization and the radio background. Combining HERA limits with complementary observations constrains the spin temperature of the z ∼ 8 neutral IGM to 27 KáTSñ 630 K (2.3 KáTSñ 640 K) at 68% (95%) confidence. They therefore also place a lower bound on X-ray heating, a previously unconstrained aspects of early galaxies. For example, if the cosmic microwave background dominates the z ∼ 8 radio background, the new HERA limits imply that the first galaxies produced X-rays more efficiently than local ones. The z ∼ 10 limits require even earlier heating if dark-matter interactions cool the hydrogen gas. If an extra radio background is produced by galaxies, we rule out (at 95% confidence) the combination of high radio and low X-ray luminosities of Lr,ν/SFR > 4 × 1024 W Hz−1 M-1  yr and LX/SFR < 7.6 × 1039 erg s−1 M-1  yr. The new HERA upper limits neither support nor disfavor a cosmological interpretation of the recent Experiment to Detect the Global EOR Signature (EDGES) measurement. The framework described here provides a foundation for the interpretation of future HERA results.
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    Probing reionization with LOFAR (Low Frequency Array) using 21-cm redshift space distortions
    (Oxford University Press, 2013) Jensen, Hannes; Datta, Kanan K.; Santos, Mario G.; Mellema, Garrelt; Chapman, Emma; Abdalla, Filipe B.; Iliev, Ilian T.; Mao, Yi; Shapiro, Paul R.; Zaroubi, Saleem; Bernardi, Gianni; Brentjens, M. A.; de Bruyn, A. G.; Ciardi, B.; Harker, G. J. A.; Jelić, V.; Kazemi, S.; Koopmans, L. V. E.; Labropoulos, P.; Martinez, O.; Offringa, A. R.; Pandey, V. N.; Schaye, J.; Thomas, R. M.; Veligatla, V.; Vedantham, H.; Yatawatta, S.
    One of the most promising ways to study the epoch of reionization (EoR) is through radio observations of the redshifted 21-cm line emission from neutral hydrogen. These observations are complicated by the fact that the mapping of redshifts to line-of-sight positions is distorted by the peculiar velocities of the gas. Such distortions can be a source of error if they are not properly understood, but they also encode information about cosmology and astrophysics. We study the effects of redshift space distortions on the power spectrum of 21-cm radiation from the EoR using large-scale N-body and radiative transfer simulations. We quantify the anisotropy introduced in the 21-cm power spectrum by redshift space distortions and show how it evolves as reionization progresses and how it relates to the underlying physics. We go on to study the effects of redshift space distortions on LOFAR observations, taking instrument noise and foreground subtraction into account.We find that LOFAR should be able to directly observe the power spectrum anisotropy due to redshift space distortions at spatial scales around k ∼ 0.1Mpc−1 after 1000 h of integration time. At larger scales, sample errors become a limiting factor, while at smaller scales detector noise and foregrounds make the extraction of the signal problematic. Finally, we show how the astrophysical information contained in the evolution of the anisotropy of the 21-cm power spectrum can be extracted from LOFAR observations, and how it can be used to distinguish between different reionization scenarios.