Zaki S. Ali

NEW LIMITS ON 21 cm EPOCH OF REIONIZATION FROM PAPER-32 CONSISTENT WITH AN X-RAY HEATED INTERGALACTIC MEDIUM AT z = 7.7

We present new constraints on the 21cm Epoch of Reionization (EoR) power spectrum derived from 3 months of observing with a 32-antenna, dual-polarization deployment of the Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER) in South Africa. In this paper, we demonstrate the efficacy of the delay-spectrum approach to avoiding foregrounds, achieving over 8 orders of magnitude of foreground suppression (in mK). Combining this approach with a procedure for removing off-diagonal covariances arising from instrumental systematics, we achieve a best 2σ upper limit of (41mK) for k = 0.27 h Mpc−1 at z = 7.7. This limit falls within an order of magnitude of the brighter predictions of the expected 21cm EoR signal level. Using the upper limits set by these measurements, we generate new constraints on the brightness temperature of 21cm emission in neutral regions for various reionization models. We show that for several ionization scenarios, our measurements are inconsistent with cold reionization. That is, heating of the neutral intergalactic medium (IGM) is necessary to remain consistent with the constraints we report. Hence, we have suggestive evidence that by z = 7.7, the HI has been warmed from its cold primordial state, probably by X-rays from high-mass X-ray binaries or mini-quasars. The strength of this evidence depends on the ionization state of the IGM, which we are not yet able to constrain. This result is consistent with standard predictions for how reionization might have proceeded.We present new constraints on the 21 cm Epoch of Reionization (EoR) power spectrum derived from three months of observing with a 32 antenna, dual-polarization deployment of the Donald C. Backer Precision Array for Probing the Epoch of Reionization in South Africa. In this paper, we demonstrate the efficacy of the delay-spectrum approach to avoiding foregrounds, achieving over eight orders of magnitude of foreground suppression (in mK2). Combining this approach with a procedure for removing off-diagonal covariances arising from instrumental systematics, we achieve a best 2σ upper limit of (41 mK)2 for k = 0.27 h Mpc–1 at z = 7.7. This limit falls within an order of magnitude of the brighter predictions of the expected 21 cm EoR signal level. Using the upper limits set by these measurements, we generate new constraints on the brightness temperature of 21 cm emission in neutral regions for various reionization models. We show that for several ionization scenarios, our measurements are inconsistent with cold reionization. That is, heating of the neutral intergalactic medium (IGM) is necessary to remain consistent with the constraints we report. Hence, we have suggestive evidence that by z = 7.7, the H I has been warmed from its cold primordial state, probably by X-rays from high-mass X-ray binaries or miniquasars. The strength of this evidence depends on the ionization state of the IGM, which we are not yet able to constrain. This result is consistent with standard predictions for how reionization might have proceeded.

PAPER-64 Constraints on Reionization: The 21 cm Power Spectrum at z = 8.4

© 2015. The American Astronomical Society. All rights reserved. In this paper, we report new limits on 21 cm emission from cosmic reionization based on a 135 day observing campaign with a 64-element deployment of the Donald C. Backer Precision Array for Probing the Epoch of Reionization in South Africa. This work extends the work presented in Parsons et al. with more collecting area, a longer observing period, improved redundancy-based calibration, improved fringe-rate filtering, and updated power-spectral analysis using optimal quadratic estimators. The result is a new 2σ upper limit on Δ2(k) of (22.4 mK)2 in the range < k < 0.5h Mpc-1 at z = 8.4. This represents a three-fold improvement over the previous best upper limit. As we discuss in more depth in a forthcoming paper, this upper limit supports and extends previous evidence against extremely cold reionization scenarios. We conclude with a discussion of implications for future 21 cm reionization experiments, including the newly funded Hydrogen Epoch of Reionization Array.

Hydrogen Epoch of Reionization Array (HERA)

The Hydrogen Epoch of Reionization Array (HERA http://reionization.org) is a staged experiment that uses the unique properties of the 21-cm line from neutral hydrogen to probe the Epoch of Reionization (EOR). During this epoch, roughly 0.3-1 billion years after the Big Bang, the first galaxies and black holes heated and reionized the early Universe. Direct observation of the large scale structure of reionization and its evolution with time will have a profound impact on our understanding of the birth of the first galaxies and black holes, their influence on the intergalactic medium (IGM), and cosmology. This paper will provide an overview of the project and describe the design of the HERA receiving element.

The Baryon Acoustic Oscillation Broadband and Broad-beam Array: Design Overview and Sensitivity Forecasts

This work describes a new instrument optimized for a detection of the neutral hydrogen 21 cm power spectrum between redshifts of 0.5 and 1.5: the Baryon Acoustic Oscillation Broadband and Broad-beam (BAOBAB) array. BAOBAB will build on the efforts of a first generation of 21 cm experiments that are targeting a detection of the signal from the Epoch of Reionization at z ~ 10. At z ~ 1, the emission from neutral hydrogen in self-shielded overdense halos also presents an accessible signal, since the dominant, synchrotron foreground emission is considerably fainter than at redshift 10. The principle science driver for these observations are baryon acoustic oscillations in the matter power spectrum which have the potential to act as a standard ruler and constrain the nature of dark energy. BAOBAB will fully correlate dual-polarization antenna tiles over the 600-900 MHz band with a frequency resolution of 300 kHz and a system temperature of 50 K. The number of antennas will grow in staged deployments, and reconfigurations of the array will allow for both traditional imaging and high power spectrum sensitivity operations. We present calculations of the power spectrum sensitivity for various array sizes, with a 35 element array measuring the cosmic neutral hydrogen fraction as a function of redshift, and a 132 element system detecting the BAO features in the power spectrum, yielding a 1.8% error on the z ~ 1 distance scale, and, in turn, significant improvements to constraints on the dark energy equation of state over an unprecedented range of redshifts from ~0.5 to 1.5.

Multiredshift limits on the 21 cm power spectrum from paper

The epoch of the reionization (EoR) power spectrum is expected to evolve strongly with redshift, and it is this variation with cosmic history that will allow us to begin to place constraints on the physics of reionization. The primary obstacle to the measurement of the EoR power spectrum is bright foreground emission. We present an analysis of observations from the Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER) telescope, which place new limits on the H i power spectrum over the redshift range of , extending previously published single-redshift results to cover the full range accessible to the instrument. To suppress foregrounds, we use filtering techniques that take advantage of the large instrumental bandwidth to isolate and suppress foreground leakage into the interesting regions of k-space. Our 500 hr integration is the longest such yet recorded and demonstrates this method to a dynamic range of 104. Power spectra at different points across the redshift range reveal the variable efficacy of the foreground isolation. Noise-limited measurements of Δ2 at k = 0.2 hr Mpc−1 and z = 7.55 reach as low as (48 mK)2 (1σ). We demonstrate that the size of the error bars in our power spectrum measurement as generated by a bootstrap method is consistent with the fluctuations due to thermal noise. Relative to this thermal noise, most spectra exhibit an excess of power at a few sigma. The likely sources of this excess include residual foreground leakage, particularly at the highest redshift, unflagged radio frequency interference, and calibration errors. We conclude by discussing data reduction improvements that promise to remove much of this excess.

PAPER-64 CONSTRAINTS on REIONIZATION. II. the TEMPERATURE of the z = 8.4 INTERGALACTIC MEDIUM

© 2015. The American Astronomical Society. All rights reserved. We present constraints on both the kinetic temperature of the intergalactic medium (IGM) at z = 8.4, and on models for heating the IGM at high-redshift with X-ray emission from the first collapsed objects. These constraints are derived using a semi-analytic method to explore the new measurements of the 21 cm power spectrum from the Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER), which were presented in a companion paper, Ali et al. Twenty-one cm power spectra with amplitudes of hundreds of mK2 can be generically produced if the kinetic temperature of the IGM is significantly below the temperature of the cosmic microwave background (CMB); as such, the new results from PAPER place lower limits on the IGM temperature at z = 8.4. Allowing for the unknown ionization state of the IGM, our measurements find the IGM temperature to be above ≈5 K for neutral fractions between 10% and 85%, above ≈7 K for neutral fractions between 15% and 80%, or above ≈10 K for neutral fractions between 30% and 70%. We also calculate the heating of the IGM that would be provided by the observed high redshift galaxy population, and find that for most models, these galaxies are sufficient to bring the IGM temperature above our lower limits. However, there are significant ranges of parameter space that could produce a signal ruled out by the PAPER measurements; models with a steep drop-off in the star formation rate density at high redshifts or with relatively low values for the X-ray to star formation rate efficiency of high redshift galaxies are generally disfavored. The PAPER measurements are consistent with (but do not constrain) a hydrogen spin temperature above the CMB temperature, a situation which we find to be generally predicted if galaxies fainter than the current detection limits of optical/NIR surveys are included in calculations of X-ray heating.

The Hydrogen Epoch of Reionization Array Dish. I. Beam Pattern Measurements and Science Implications

Author(s): Neben, Abraham R; Bradley, Richard F; Hewitt, Jacqueline N; DeBoer, David R; Parsons, Aaron R; Aguirre, James E; Ali, Zaki S; Cheng, Carina; Ewall-Wice, Aaron; Patra, Nipanjana; Thyagarajan, Nithyanandan; Bowman, Judd; Dickenson, Roger; Dillon, Joshua S; Doolittle, Phillip; Egan, Dennis; Hedrick, Mike; Jacobs, Daniel C; Kohn, Saul A; Klima, Patricia J; Moodley, Kavilan; Saliwanchik, Benjamin R. B; Schaffner, Patrick; Shelton, John; Taylor, H. A; Taylor, Rusty; Tegmark, Max; Wirt, Butch; Zheng, Haoxuan

NEW LIMITS ON POLARIZED POWER SPECTRA AT 126 AND 164 MHZ: RELEVANCE TO EPOCH OF REIONIZATION MEASUREMENTS

Polarized foreground emission is a potential contaminant of attempts to measure the fluctuation power spectrum of highly redshifted 21 cm Hi emission from the epoch of reionization, yet observational constraints on the level of polarized emission are poor. Using the Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER), we present the first limits on the power spectra of all four Stokes parameters in two frequency bands, centered at 126 MHz (z = 10.3) and 164 MHz (z = 7.66). This data comes from from a three-month observing campaign of a 32-antenna deployment, for which unpolarized power spectrum results have been reported at z = 7.7 (Parsons et al. 2014) and 7.5 < z < 10.5 (Jacobs et al. 2014). The power spectra in this paper are processed in the same way, and show no definitive detection of polarized power. The limits are sufficiently low that we are able to show that the excess unpolarized power reported in those works is not due to leakage of Faraday-rotated polarized emission. Building upon the Moore et al. (2013) simulations of polarized point sources, we further argue that our upper limits and previous observations imply that the mean polarization fraction of point sources at these frequencies is ∼ 2×10−3, roughly an order of magnitude lower than that observed for point sources at 1.4 GHz.Polarized foreground emission is a potential contaminant of attempts to measure the fluctuation power spectrum of highly redshifted 21 cm Hi emission from the epoch of reionization, yet observational constraints on the level of polarized emission are poor. Using the Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER), we present the first limits on the power spectra of all four Stokes parameters in two frequency bands, centered at 126 MHz (z = 10.3) and 164 MHz (z = 7.66). This data comes from from a three-month observing campaign of a 32-antenna deployment, for which unpolarized power spectrum results have been reported at z = 7.7 (Parsons et al. 2014) and 7.5 < z < 10.5 (Jacobs et al. 2014). The power spectra in this paper are processed in the same way, and show no definitive detection of polarized power. The limits are sufficiently low that we are able to show that the excess unpolarized power reported in those works is not due to leakage of Faraday-rotated polarized emission. Building upon the Moore et al. (2013) simulations of polarized point sources, we further argue that our upper limits and previous observations imply that the mean polarization fraction of point sources at these frequencies is ∼ 2×10 −3 , roughly an order of magnitude lower than that observed for point sources at 1.4 GHz.

CONSTRAINING POLARIZED FOREGROUNDS FOR EoR EXPERIMENTS. I. 2D POWER SPECTRA FROM THE PAPER-32 IMAGING ARRAY

Current-generation low frequency interferometers constructed with the objective of detecting the high-redshift 21 cm background, aim to generate power spectra of the brightness-temperature contrast of neutral hydrogen in primordial intergalactic medium. Two-dimensional power spectra (power in Fourier modes parallel and perpendicular to the line of sight) formed from interferometric visibilities have been shown to delineate a boundary between spectrally-smooth foregrounds (known as the wedge) and spectrally-structured 21 cm background emission (the EoR-window). However, polarized foregrounds are known to possess spectral structure due to Faraday rotation, which can leak into the EoR window. In this work, we create and analyze 2D power spectra from the PAPER-32 imaging array in Stokes I, Q, U and V. These allow us to observe and diagnose systematic effects in our calibration at high signal-to-noise within the Fourier space most relevant to EoR experiments. We observe well-defined windows in the Stokes visibilities, with Stokes Q, U and V power spectra sharing a similar wedge shape to that seen in Stokes I. With modest polarization calibration, we see no evidence that polarization calibration errors move power outside the wedge in any Stokes visibility, to the noise levels attained. Deeper integrations will be required to confirm that this behavior persists to the depth required for EoR detection.

Imaging on PAPER: Centaurus A at 148 MHz

We present observations taken with the Precision Array for Probing the Epoch of Reionization (PAPER) of the Centaurus A field in the frequency range 114 to 188 MHz. The resulting image has a 25 0 resolution, a dynamic range of 3500 and an r.m.s. of 0.5 Jy beam 1 (for a beam size of 25 0 23 0 ). A spectral index map of Cen A is produced across the full band. The spectral index distribution is qualitatively consistent with electron reacceleration in regions of excess turbulence in the radio lobes, as previously identified morphologically. Hence, there appears to be an association of ‘severe weather’ in radio lobes with energy input into the relativistic electron population. We compare the PAPER large scale radio image with the X-ray image from the ROSAT All Sky Survey. There is a tentative correlation between radio and X-ray features at the end of the southern lobe, some 200 kpc from the nucleus, as might be expected from inverse Compton scattering of the CMB by the relativistic electrons also responsible for the radio synchrotron emission. The magnetic fields derived from the (possible) IC and radio emission are of similar magnitude to fields derived under the minimum pressure assumptions, 1 mG. However, the X-ray field is complex, with large scale gradients and features possibly unrelated to Cen A. If these X-ray features are unrelated to Cen A, then these fields are lower limits.