21 Centimeter Fluctuations from Cosmic Gas at High Redshifts

By M. Zaldarriaga, S. Furlanetto, L. Hernquist. 2003

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The relatively large Thomson optical depth, τes, inferred recently from the WMAP observations suggests that the universe was reionized in a more complex manner than previously believed. However, the value of τes provides only an integral constraint on the history of reionization and, by itself, cannot be used to determine the nature of the sources responsible for this transition. Here we show that the evolution of the ionization state of the intergalactic medium (IGM) at high redshifts can be measured statistically using fluctuations in 21 cm radiation from neutral hydrogen. By analogy with the mathematical description of anisotropies in the cosmic microwave background, we develop a formalism to quantify the variations in 21 cm emission as a function of both frequency and angular scale. Prior to and following reionization, fluctuations in the 21 cm signal are mediated by density perturbations in the distribution of matter. Between these epochs, pockets of gas surrounding luminous objects become ionized, producing large H II regions. These "bubbles" of ionized material imprint features into the 21 cm power spectrum that make it possible to distinguish them from fluctuations produced by the density perturbations. The variation of the power spectrum with frequency can be used to infer the evolution of this process. As has been emphasized previously by others, the absolute 21 cm signal from neutral gas at high redshifts is difficult to detect as a result of contamination by foreground sources. However, we argue that this source of noise can be suppressed by comparing maps closely spaced in frequency, i.e., redshift, so that 21 cm fluctuations from the IGM can be measured against a much brighter, but smoothly varying (in frequency), background.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/00f553c41a5a8d5d1832503f832b3ec92bbfff6f

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Citations in the corpus

FOUR FUNDAMENTAL FOREGROUND POWER SPECTRUM SHAPES FOR 21 cm COSMOLOGY OBSERVATIONS (2012, background): “Conceptually, purely angular modes are dominated by the foregrounds, but the EoR signal can be observed in the line-of-sight (frequency) modes (Zaldarriaga et al. 2004; Morales & Hewitt 2004; Jelić et al. 2008; Wang et al. 2006; Harker et al. 2009).”
Detecting the Earliest Galaxies through Two New Sources of 21 Centimeter Fluctuations (2004, background): “Consequently, the prospects for extraction of the 21cm signal are promising (Gnedin & Shaver 2004; Zaldarriaga et al. 2004; Morales & Hewitt 2004; Morales 2004; Santos et al. 2004).”
Cosmological Parameter Estimation Using 21 cm Radiation from the Epoch of Reionization (2005, background): “White et al. (1999) and Zaldarriaga et al. (2004) do a similar interferometric detector noise calculation, but for the angular power spectrum.”
A Method for Separating the Physics from the Astrophysics of High-Redshift 21 Centimeter Fluctuations (2004, background): “The ionized bubbles imprinted a knee in the power spectrum of 21 cm fluctuations (Zaldarriaga et al. 2004), which traces the Hi topology until the process of reionization was completed (Furlanetto et al. 2004).”
21-cm fluctuations from inhomogeneous X-ray heating before reionization (2006, methodology): “Once the ionization fraction becomes large (xi 0.1), the 21-cm signal becomes dominated by the imprint of H II regions (Furlanetto et al. 2004; Zaldarriaga et al. 2004).”
Reionization and the Cosmic Dawn with the Square Kilometre Array (2012, background): “…HI gas density field, which contribute to the 21cm signal, should trace those of the underlying CDM, and thus, of the fundamental cosmological parameters that define the power spectrum of the linear density field (Tozzi et al. 2000; Zaldarriaga et al. 2004; Bowman et al. 2007; McQuinn et al. 2006).”
Multifrequency Analysis of 21 Centimeter Fluctuations from the Era of Reionization (2004, methodology): “If Cl is dominated by clustering and d lnCl/d lnα = 0 then ξ = σα/∆α 2 where, following Zaldarriaga et al. (2004), we assume that correlations between sources with α1 and α2 fall off as exp [−(α1 − α2)2/(2σ2α)].”
New Limits on 21cm EoR From PAPER-32 Consistent with an X-Ray Heated IGM at z=7.7 (2013, background): “The pre-factor is then T0(z) = 23 mK ( Ωbh 2 0.02 )[( 0.15 Ωmh2 )( 1 + z 10 )]1/2 = 25 mK ( 1 + z 10 )1/2 (7) (see, e.g., Zaldarriaga et al. 2004; Furlanetto et al. 2006), 20 The constraint in Paciga et al. (2011) on the brightness temperature of 21cm emission for a single-bubble reionization model…”
21 cm Tomography with Foregrounds (2005, background): “The key to doing 21 cm cosmology is, therefore, removing foregrounds using multifrequency information, as emphasized by, for example, Zaldarriaga et al. (2004), and we now turn to this subject.”
INTENSITY MAPPING WITH CARBON MONOXIDE EMISSION LINES AND THE REDSHIFTED 21 cm LINE (2011, methodology): “…Pasadena, CA 91125 7 Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA Electronic address: alidz@sas.upenn.edu line, which may ultimately provide full three-dimensional maps of the reionization process (e.g. Madau et al. 1997, Zaldarriaga et al. 2004, Furlanetto et al. 2006a).”
BRIGHT SOURCE SUBTRACTION REQUIREMENTS FOR REDSHIFTED 21 cm MEASUREMENTS (2010, methodology): “Detailed formulation has been developed in the literature by Morales & Hewitt (2004) and Zaldarriaga et al. (2004).”