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BINGO - Baryon acoustic oscillations In Neutral Gas Observations

The BINGO experiment is a project to build a special purpose radio telescope to map redshifted neutral hydrogen emission between z = 0.13 and 0.48. It is an international project with collaborators in Brazil, Saudi Arabia, Switzerland, United Kingdom and Uruguay. It is the only radio telescope which aims at mapping neutral gas, as traced by the 21cm line, on large angular scales and at redshift z~0.3. We call this method HI intensity mapping. Using the Baryon Acoustic Oscillations (BAOs) as a standard ruler allows to measure the expansion of the universe as a function of redshift and so, to constrain the properties of dark energy. The telescope will have no moving parts and consist of a primary mirror of about 40 m diameter and a secondary a bit smaller. It will have around 50 "pixels". With this design, the accuracy on the measurement on the acoustic scale will be 2.4% for one year of integration time, by performing a drift scan survey of 15 deg x 200 deg, with a resolution of 40 arcmin at 1 GHz. The plan is to build the telescope in a disused open-caste gold mine in Uruguay.

The BINGO concept is discussed in the paper Battye et al., 2013 MNRAS, 434, 1239 at (http://arxiv.org/abs/1209.0343).

Expected measurements

Context

One of the main challenge of the today cosmology is to explain the late-time acceleration of the expansion of the Universe. This acceleration, which has been measured by two independant collaborations studying Supernovae Ia (Perlmutter et al. 1998, Riess et al. 1998), could be explained by a negative pressure from a new component, known as dark energy. There are different ways of trying to determine the properties of the dark energy as Baryonic Acoustic Oscillations (BAO), weak and strong gravitational lensing, cluster counts and supernova. But, BAO measurements appear to be the most powerful tool in order to contrain the properties of Dark Energy (Eisenstein et al. 1998, Eisenstein 2003). The BAOs arise because the coupling of baryons and photons by Thomson scattering in the early universe allows acoustic oscillations at early times, which leads to a feature in the distribution of matter and the anisotropies of the cosmic microwave background radiation. The distance that acoustic waves can propagate in the first million years of the universe becomes a characteristic comoving scale. This acoustic signature has been detected in different optical galaxy surveys (Cole et al. 2005, Percival et al. 2009, Blake et al. 2011, Anderson et al. 2012). HI intensity mapping is an efficient alternative to measure a large number of galaxies individually. It allows to measure the fluctuations of the HI signal and to obtain the power spectrum of these fluctuations as a function of frequency. This method is complementary to optical galaxy surveys (BOSS, WiggleZ, SDSS-II, 6dFGS) in terms of systematics. The figure on the right shows the predicted sensitivity of BINGO to the BAOs for 1-year observation for 70 horns and 15 degree FOV. The experiment will allow to measure the acoustic scale at z~0.3 with an accuracy ~2.4% and the equation of state of the dark energy with 16%, which is a level comparable with the current state-of-the-art large optical surveys. We use the Fisher Matrix code of (Bull et al. 2014) to compute the likelihoods for cosmological parameters given various cosmological data. These figures show the joint constraints for the equation-of-state of the dark energy with w0 and wa (1st time derivative of w0) given for various datasets (BINGO, CHIME and BINGO). It shows the improvement obtained with the combination of different intensity mapping experiments BINGO compared to the current constraints given by Planck + WMAP (polarisations) + highL (SPT, ACT) + BAO (BOSS, WiggleZ, 6dF).

BINGO concept

Design

The guiding principle in the design of BINGO has been for all components to be as simple as possible to minimize the cost, and also to allow repetitive observations so that they are simple to model and the redundancy is optimized. The design of BINGO instrument is a 40 m transit telescope with an offset focus. To minimise the cost, the telescope will have no moving parts. The instrument will realise a drift scan on the sky during two years in order to have one year of full integration time. The telescope is designed for having a good detection of the BAO at low resolution. The angular resolution of the instrument will be 40 arcmin at 1000 MHz. The instrument will operate in the frequency range between 960 to 1260 MHz which is relatively RFI free band and corresponds to a redshift range between 0.13 and 0.48. The frequency resolution will be about 1 MHz over a bandwidth of about 300 MHz. To reach the required sky coverage, the focal plane will contain 50 dual polarisation feeds, each horn will have an aperture diameter of 2 m and a length of 6 m. With this configuation, the focal plane will be 16 m x 15 m and the instantaneous field of view will be 10 deg x 10 deg. The volume survey will be 10 deg x 200 deg. The design and the fabrication of these large feeds represent a key technical challenge for the project and differents methods are explored. The receiver modules will need to present a high stability. We will use the experience of the CMB experience (WMAP, Planck) and choose the same approach in using correlation receivers. Each receiver module will produce a spectrum of the difference between the observed region of the sky and a reference signal. The reference feed will have to present the same spectrum of the science beam and no variations. It will point at a Celestial Pole.

A 3D view of the BINGO telescope

Quarry Castrillon

Site

We will build the BINGO telescope in Uruguay because of its favourable latitude and topography. Our two reflector systems have to be positioned in a quarry which has two parallel walls and the local topography has to support the dish and feed structure. The chosen site is the Quarry Castrillon located in Minas Corrales in the north of Uruguay. This site also presents good results according to RFI measurements.

Collaboration and Timing

Manchester will lead the horn design and testing and the production of a prototype receiver-unit. Brazil and Uruguay will lead the telescope construction, receiver integration and site operations while Switzerland will design and construct the digital backend. The calibration and data analysis be a joint effort. Early receiver prototypes are already being tested and working on simulations and analysis software is well underway. The project is able to start as soon as fundings are available. The construction phase is expected to start in the beginning of 2015 and last 1.25 yr. Operations will last for a further 4 years.

Meeting

A RAS Specialist Discussion Meeting was organised by Professor Ian Browne (University of Manchester) and Dr Filipe Abdalla (UCL) on the 9th of May, 2014. Programme and talks: (RAS Discussion Meeting on Intensity Mapping).

News

News of the BINGO telescope.

Documents

Publications, presentations, technical documents of the BINGO experiment are available on Documents.

Here are a list of people that are currently involved with the project