Exploring the Cosmic Dawn
Fig. 1: The PAPER configuration now òÀÓ the EoR array.
Cosmic reionization corresponds to the epoch in which the first starsˆàand black holes reionize the neutral intergalactic medium (IGM) thatˆàpervades the Universe following recombination, within a few hundredˆàmillion years of the Big Bang. The epoch of reionization, and theˆàpreceding ‘dark ages’ prior to the formation of the first stars,ˆàrepresent the last unexplored phases of cosmic evolution to be testedˆàand explored. Scientists at the Cavendish Astrophysics Group are involved in a majorˆàinternational program to explore this ‘last frontier’ in observationalˆàcosmology, using the unique properties of the 21cm emission line fromˆàneutral Hydrogen. Direct observation of the large scale structure ofˆàthe primordial IGM, and its evolution with time, via the HI 21cmˆàline will have a profound impact on our understanding of the birth ofˆàthe first galaxies and black holes, their influence on the surroundingˆàgas, and cosmology.
Fig.2: Power spectra at z = 7.7 derived from a 55-day PAPER observation. In both panels, solid cyan depicts upper limits derived from PAPER observations without the removal of off-diagonal covariance terms, and black indicates the final measured power spectrum with confidence intervals.
PAPER The Precision Array to Probe the Epoch of Reionization is anˆàarray of 128 dipole elements operating between 120MHz and 180MHz,ˆàcorresponding to HI redshifts between 11 and 7 (universal age betweenˆà0.4 Myr and 0.8Myr).ˆà The array is situated in the very lowˆàterrestrial interference environment of the SKA site in the Karoo regionˆàof South Africa. The array grid-design (Fig.1) exploits our new understandingˆàof the chromatic response of an interferometer to perform an optimalˆàstatistical (power spectrum) search for the HI 21cm signal, whileˆàavoiding the strong radio continuum foreground emission thatˆàwould otherwise overwhelm the cosmic HI signal. PAPER has currentlyˆàset the best limits to the HI signal from reionization (Fig.2). PAPER has alsoˆàproduced unprecedented wide field images of the radio sky at 120MHzˆàto 150MHz (Fig.3). In the next two years, we will obtain deep cosmological integrations with PAPER with the potential to make the first detectionˆàof the HI 21cm signal from cosmic reionization.
Fig.3: Image of the Centaurus A (Cen A) field obtained from PAPER data. The Cen A radio galaxy dominates the centre, while the Galactic plane crosses the lower half of the image.
Fig.4: Members of the Cambridge and SA teams reconfiguring the array.
PAPER is a collaboration between the Cavendish, Berkeley, NRAO,ˆàPennsylvania, the SKA-South Africa, and the University of KwaZulu-Natal, SA (Fig.4).
HERA
Fig.5: The configuration of HERAòÀÙs 500 antennas.
The Hydrogen Epoch of Reionization Array represents the nextˆàphase of our reionization experiments.ˆà Building on lessons learnedˆàwith PAPER and the Murchison Widefield Array, we have established aˆàbroader collaboration to construct a new array in South Africa with aˆàsensitivity close to two orders of magnitude greater than PAPER,ˆàoperating between 50MHz and 225MHz (Fig.5). HERA will move beyond simpleˆàstatistical detection of the HI signal, to a full characterization ofˆàthe HI 21cm power spectrum through reionization. HERA will also pushˆàpower spectral studies back to the end of the ‘Dark Ages’, when theˆàfirst sources of new light in the Universe warm the neutralˆàIGM. Ultimately, HERA-331 will have the sensitivity to perform directˆàimaging of the largest scale structures in the Cosmos duringˆàreionization (Fig.6). We expect first science observations with HERA in late 2017. HERA is a collaboration between the PAPER institutions above, withˆàthe U. of Washington, Arizona State Univ, and MIT.
Fig.6: Simulation by Dr. Daniel Jacobs of the imaging capabilities of HERA.
Cavendish Reionization Team
Prof. Chris Carilli: project lead at Cavendish
Irina Stefan: Imaging and calibration analysis
Dr. Nima Razavi-Ghods: Field engineering, deployment, testing
Dr. Jack Hickish: Digital design
Prof. Paul Alexander: oversight and science
Dr. Eloy de Lera Acedo: Array RF modeling
Lindley Lentati: Bayesian power spectral analysis
Peter Sims: 21cm and continuum sky simulations
Selected publications
- New Limits on 21cm EoR From PAPER-32 Consistent with an X-Ray Heated IGM at z=7.7,ˆàParsons et al., 2014,ˆàarXiv:1304.4991
- What Next-generation 21 cm Power Spectrum Measurements can Teach us About the Epoch of Reionization,ˆàPober et al. 2014, ApJ, 782, L66
- A Flux Scale for Southern Hemisphere 21 cm Epoch of Reionization Experiments,ˆàJacobs et al. 2013, ApJ, 776, 108
- Opening the 21 cm Epoch of Reionization Window: Measurements of Foreground Isolation with PAPER,ˆàPober et al. 2013, ApJ, 68, L36
- Imaging on PAPER: Centaurus A at 148 MHz,ˆàStefan et al. 2013, MNRAS, 432, 1205
- A Per-baseline, Delay-spectrum Technique for Accessing the 21 cm Cosmic Reionization Signature,ˆàParsons et al. 2012, ApJ, 756, 165
- Bright Source Subtraction Requirements for Redshifted 21 cm Measurements,ˆàDatta, Bowman, Carilli 2010, 724, 526