Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.mrao.cam.ac.uk/research/exploring-the-cosmic-dawn/
Äàòà èçìåíåíèÿ: Unknown
Äàòà èíäåêñèðîâàíèÿ: Sun Apr 10 03:07:07 2016
Êîäèðîâêà: IBM-866
Ïîèñêîâûå ñëîâà: ï ï ï ï ï ï ï ï ï ï ï ï ð ï ð ï ð ï ð ï ð ï ð ï ð ï ð ï ð ï ð ï ð ï ð ï ð ï ð ï ð ï ð ï ð ð ï ï ð ï ï ð ï ï ð ï ï ð ï ï ð ï ï ð ï ï ð ï ï ð ï ï ð ï
Astrophysics Group » Exploring the Cosmic Dawn

Astrophysics Group

Cavendish Laboratory

Exploring the Cosmic Dawn

PAPER_grid_array

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.

PAPER_CenA

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.

moving_antenna

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

Hera_array

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.

Hera_HI

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