H i intensity mapping: a single dish approach

Abstract

We discuss the detection of large scale HI intensity fluctuations using a single dish approach with the ultimate objective of measuring the Baryonic Acoustic Oscillations (BAO) and constraining the properties of dark energy. To characterise the signal we present 3D power spectra, 2D angular power spectra for individual redshift slices, and also individual line-of-sight spectra, computed using the S 3 simulated HI catalogue which is based on the Millennium Simulation. We consider optimal instrument design and survey strategies for a single dish observation at low and high redshift for a fixed sensitivity. For a survey corresponding to an instrument with T sys = 50 K, 50 feed horns and 1 year of observations, we find that at low redshift (z ≈ 0.3), a resolution of ∼ 40 arcmin and a survey of ∼ 5000 deg 2 is close to optimal, whereas at higher redshift (z ≈ 0.9) a resolution of ∼ 10 arcmin and ∼ 500 deg 2 would be necessarysomething which would be difficult to achieve cheaply using a single dish. Continuum foreground emission from the Galaxy and extragalactic radio sources are potentially a problem. In particular, we suggest that it could be that the dominant extragalactic foreground comes from the clustering of very weak sources. We assess its amplitude and discuss ways by which it might be mitigated. We then introduce our concept for a dedicated single dish telescope designed to detect BAO at low redshifts. It involves an under-illuminated static ∼ 40 m dish and a ∼ 60 element receiver array held ∼ 90 m above the under-illuminated dish. Correlation receivers will be used with each main science beam referenced against an antenna pointing at one of the Celestial Poles for stability and control of systematics. We make sensitivity estimates for our proposed system and projections for the uncertainties on the power spectrum after 1 year of observations. We find that it is possible to measure the acoustic scale at z ≈ 0.3 with an accuracy ∼ 2.4% and that w can be measured to an accuracy of 16%.

Extracting H i cosmological signal with generalized needlet internal linear combination

“…For each of the simulations, we consider the same bandwidth: 960 to 1260 MHz, which is the proposed range for the BINGO experiment (Battye et al 2013). This bandwidth corresponds to a redshift range of 0.13 to 0.48.…”

“…We consider circular Gaussian beams for the frequency channels of the experiment. For simplicity, independently of the number of frequency channels, we fix the full width at half minimum θFWHM of the beam for the first frequency channel to be equal to 40 arcmin, which is the angular resolution of the BINGO telescope at 1 GHz (Battye et al 2013). Considering that our HI intensity mapping is diffractionlimited, the full width at half minimum of the beam for the other frequency channels can be calculated through the following relation,…”

“…The brightness of each source is drawn from the differential source counts dN/dS, where N is the number of sources per steradian and S is the flux. In Battye et al (2013), the authors use data from multiple continuum surveys at 1.4 GHz (see the references in the cited paper) and fit a 5th order polynomial to these data, Figure 3. Power spectrum, ( + 1)C /2π, on a logarithmic scale, of the synchrotron with constant spectral index (black), point sources (pink), free-free (red), HI (blue), and thermal noise (green) at 1117.5 MHz.…”

THE SEARCH FOR Hi EMISSION AT z ≈ 0.4 IN GRAVITATIONALLY LENSED GALAXIES WITH THE GREEN BANK TELESCOPE

“…After successful pilot observations (Fernández et al 2013), the COSMOS HI Large Extragalactic Survey is currently using the recently upgraded Karl G. Jansky Very Large Array to search for 21 cm emission in individual galaxies in the well observed COSMOS field out to z = 0.45. Telescopes designed specifically to carry out intensity mapping surveys, like the Canadian Hydrogen Intensity Mapping Experiment (Battye et al 2013), Baryon Acoustic Oscillations in Neutral Gas Observations (Bandura et al 2014), and Tianlai (Chen 2015) will greatly improve measurements of Ω HI . Planned deep field surveys with telescopes such as ASKAP, MeerKAT, and the Square Kilometer Array (Meyer 2009;Holwerda et al 2012;Staveley-Smith & Oosterloo 2015) will have the sensitivity and frequency coverage required to directly detect HI emission in individual galaxies beyond z = 0.45.…”

Sky reconstruction for the Tianlai cylinder array

“…Large wide-field and wide band radio telescopes would be needed to achieve rapidly the observation of large volumes of the universe. Several dedicated experiments are aimed at such surveys, including our own experiment Tianlai 1 (Chen 2012), as well as CHIME (Bandura et al 2014), BINGO (Battye et al 2013), HIRAX 2 , and BAORadio 3 . In transit mode intensity mapping surveys, the antennas are fixed on the ground during observation, it observes the sky as the Earth rotates.…”