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

Abstract

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 2 ). Combining this approach with a procedure for removing off-diagonal covariances arising from instrumental systematics, we achieve a best 2σ upper limit of (41mK) 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 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.

Optimized Beam Sculpting With Generalized Fringe-Rate Filters

“…the maximum-redundancy array configuration it uses for power spectral measurements (Parsons et al 2012a(Parsons et al , 2014Ali et al 2015). As such, our simulations demonstrate the performance of fringe-rate filtering in the context of the specific instrument configuration that has recently been used to place the current best upper limits on 21 cm emission from cosmic reionization (Parsons et al 2014;Jacobs et al 2014;Ali et al 2015).…”

“…These differences have led to the design, construction, and usage of new interferometers that only have moderate angular resolution, but are comprised of a large number of receiving elements with wide fields of view operating over a wide bandwidth. Examples of new interferometers that broadly fit some or all of this description include the Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER; Parsons et al 2010), the Murchison Widefield Array (MWA; Tingay et al 2013;Bowman et al 2013), the LOw Frequency ARray (LOFAR; van Haarlem et al 2013), the Canadian Hydrogen Intensity Mapping Experiment (CHIME; Bandura et al 2014), the MIT Epoch of Reionization experiment (MITEoR; Zheng et al 2014), the Large Aperture Experiment to Detect the Dark Ages (LEDA; Greenhill & Bernardi 2012), and the Hydrogen Epoch of Reionization Array (HERA; Pober et al 2014). Further deviating from conventional array designs, the PAPER, MITEoR, CHIME, HERA projects have also maximized sensitivity by choosing to place their antenna elements in regular, redundant grids (Parsons 1 Astronomy Dept., U. California, Berkeley, CA 2 Radio Astronomy Lab., U. California, Berkeley, CA 3 Berkeley Center for Cosmological Physics, Berkeley, CA et al 2012a).…”

Cross-correlation of the cosmic 21-cm signal and Lyman α emitters during reionization

“…where X 2 Y is a cosmological conversion factor between observing bandwidth, frequency and comoving distance units, Ω is a beamdependent factor derived in Parsons et al (2014), t is the total time spent by all baselines within a particular k mode and Tsys is the system temperature, the sum of the receiver temperature, Trec, and the sky temperature, T sky . For all telescope configurations considered in this work we assume tracked scanning with a total synthesis time of 6 h per night.…”

Reionizing the universe

“…According to their models, if the hydrogen gas just before reionization had been cold, the signal should already be visible to current radio telescopes. The fact that it isn't means that the neutral hydrogen was heated up slightly before reionization, probably by the first generation of stars (5).…”