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Title: Elucidating dark energy with future 21 cm observations at the epoch of reionization

Abstract

We investigate how precisely we can determine the nature of dark energy such as the equation of state (EoS) and its time dependence by using future observations of 21 cm fluctuations at the epoch of reionization (06.8∼< z ∼<1) such as Square Kilometre Array (SKA) and Omniscope in combination with those from cosmic microwave background, baryon acoustic oscillation, type Ia supernovae and direct measurement of the Hubble constant. We consider several parametrizations for the EoS and find that future 21 cm observations will be powerful in constraining models of dark energy, especially when its EoS varies at high redshifts.

Authors:
 [1];  [2];  [3];  [4]
  1. The Graduate University for Advanced Studies (SOKENDAI), 1-1 Oho, Tsukuba 305-0801 (Japan)
  2. Institute for Cosmic Ray Research, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8582 (Japan)
  3. Center for Theoretical Physics of the Universe, Institute for Basic Science (IBS), 193, Munjiro, Yuseoung-gu, Daejeon 34051 (Korea, Republic of)
  4. Department of Physics, Saga University, 1 Honjo, Saga 840-8502 (Japan)
Publication Date:
OSTI Identifier:
22680030
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Cosmology and Astroparticle Physics; Journal Volume: 2017; Journal Issue: 02; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BARYONS; EQUATIONS OF STATE; FLUCTUATIONS; NONLUMINOUS MATTER; OSCILLATIONS; RED SHIFT; RELICT RADIATION; SUPERNOVAE; TIME DEPENDENCE

Citation Formats

Kohri, Kazunori, Oyama, Yoshihiko, Sekiguchi, Toyokazu, and Takahashi, Tomo, E-mail: kohri@post.kek.jp, E-mail: oyamayo@icrr.u-tokyo.ac.jp, E-mail: sekiguti@ibs.re.kr, E-mail: tomot@cc.saga-u.ac.jp. Elucidating dark energy with future 21 cm observations at the epoch of reionization. United States: N. p., 2017. Web. doi:10.1088/1475-7516/2017/02/024.
Kohri, Kazunori, Oyama, Yoshihiko, Sekiguchi, Toyokazu, & Takahashi, Tomo, E-mail: kohri@post.kek.jp, E-mail: oyamayo@icrr.u-tokyo.ac.jp, E-mail: sekiguti@ibs.re.kr, E-mail: tomot@cc.saga-u.ac.jp. Elucidating dark energy with future 21 cm observations at the epoch of reionization. United States. doi:10.1088/1475-7516/2017/02/024.
Kohri, Kazunori, Oyama, Yoshihiko, Sekiguchi, Toyokazu, and Takahashi, Tomo, E-mail: kohri@post.kek.jp, E-mail: oyamayo@icrr.u-tokyo.ac.jp, E-mail: sekiguti@ibs.re.kr, E-mail: tomot@cc.saga-u.ac.jp. Wed . "Elucidating dark energy with future 21 cm observations at the epoch of reionization". United States. doi:10.1088/1475-7516/2017/02/024.
@article{osti_22680030,
title = {Elucidating dark energy with future 21 cm observations at the epoch of reionization},
author = {Kohri, Kazunori and Oyama, Yoshihiko and Sekiguchi, Toyokazu and Takahashi, Tomo, E-mail: kohri@post.kek.jp, E-mail: oyamayo@icrr.u-tokyo.ac.jp, E-mail: sekiguti@ibs.re.kr, E-mail: tomot@cc.saga-u.ac.jp},
abstractNote = {We investigate how precisely we can determine the nature of dark energy such as the equation of state (EoS) and its time dependence by using future observations of 21 cm fluctuations at the epoch of reionization (06.8∼< z ∼<1) such as Square Kilometre Array (SKA) and Omniscope in combination with those from cosmic microwave background, baryon acoustic oscillation, type Ia supernovae and direct measurement of the Hubble constant. We consider several parametrizations for the EoS and find that future 21 cm observations will be powerful in constraining models of dark energy, especially when its EoS varies at high redshifts.},
doi = {10.1088/1475-7516/2017/02/024},
journal = {Journal of Cosmology and Astroparticle Physics},
number = 02,
volume = 2017,
place = {United States},
year = {Wed Feb 01 00:00:00 EST 2017},
month = {Wed Feb 01 00:00:00 EST 2017}
}
  • The primary challenge for experiments measuring the neutral hydrogen power spectrum from the epoch of reionization (EoR) is mode-mixing effects, where foregrounds from very bright astrophysical sources interact with the instrument to contaminate the EoR signal. In this paper, we identify a new type of mode mixing that occurs when measurements from non-identical baselines are combined for increased power spectrum sensitivity. This multi-baseline effect dominates the mode-mixing power in our simulations and can contaminate the EoR window, an area in Fourier space previously identified to be relatively free of foreground power.
  • In this paper we present observations, simulations, and analysis demonstrating the direct connection between the location of foreground emission on the sky and its location in cosmological power spectra from interferometric redshifted 21 cm experiments. We begin with a heuristic formalism for understanding the mapping of sky coordinates into the cylindrically averaged power spectra measurements used by 21 cm experiments, with a focus on the effects of the instrument beam response and the associated sidelobes. We then demonstrate this mapping by analyzing power spectra with both simulated and observed data from the Murchison Widefield Array. We find that removing amore » foreground model that includes sources in both the main field of view and the first sidelobes reduces the contamination in high k{sub ∥} modes by several per cent relative to a model that only includes sources in the main field of view, with the completeness of the foreground model setting the principal limitation on the amount of power removed. While small, a percent-level amount of foreground power is in itself more than enough to prevent recovery of any Epoch of Reionization signal from these modes. This result demonstrates that foreground subtraction for redshifted 21 cm experiments is truly a wide-field problem, and algorithms and simulations must extend beyond the instrument’s main field of view to potentially recover the full 21 cm power spectrum.« less
  • Observations of the frequency dependence of the global brightness temperature of the redshifted 21 cm line of neutral hydrogen may be possible with single dipole experiments. In this paper, we develop a Fisher matrix formalism for calculating the sensitivity of such instruments to the 21 cm signal from reionization and the dark ages. We show that rapid reionization histories with duration {Delta}z < or approx. 2 can be constrained, provided that local foregrounds can be well modeled by low order polynomials. It is then shown that observations in the range {nu}=50-100 MHz can feasibly constrain the Ly{alpha} and x-ray emissivitymore » of the first stars forming at z{approx}15-25, provided that systematic temperature residuals can be controlled to less than 1 mK. Finally, we demonstrate the difficulty of detecting the 21 cm signal from the dark ages before star formation.« less
  • Precise subtraction of foreground sources is crucial for detecting and estimating 21 cm H I signals from the Epoch of Reionization (EoR). We quantify how imperfect point-source subtraction due to limitations of the measurement data set yields structured residual signal in the data set. We use the Cramer-Rao lower bound, as a metric for quantifying the precision with which a parameter may be measured, to estimate the residual signal in a visibility data set due to imperfect point-source subtraction. We then propagate these residuals into two metrics of interest for 21 cm EoR experiments-the angular power spectrum and two-dimensional powermore » spectrum-using a combination of full analytic covariant derivation, analytic variant derivation, and covariant Monte Carlo simulations. This methodology differs from previous work in two ways: (1) it uses information theory to set the point-source position error, rather than assuming a global rms error, and (2) it describes a method for propagating the errors analytically, thereby obtaining the full correlation structure of the power spectra. The methods are applied to two upcoming low-frequency instruments that are proposing to perform statistical EoR experiments: the Murchison Widefield Array and the Precision Array for Probing the Epoch of Reionization. In addition to the actual antenna configurations, we apply the methods to minimally redundant and maximally redundant configurations. We find that for peeling sources above 1 Jy, the amplitude of the residual signal, and its variance, will be smaller than the contribution from thermal noise for the observing parameters proposed for upcoming EoR experiments, and that optimal subtraction of bright point sources will not be a limiting factor for EoR parameter estimation. We then use the formalism to provide an ab initio analytic derivation motivating the 'wedge' feature in the two-dimensional power spectrum, complementing previous discussion in the literature.« less
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