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Register a new userBINGO: a single dish approach to 21cm intensity mapping
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Added by
Alkistis Pourtsidou
Publication date
2012
fields
Physics
and research's language is
English
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BINGO is a concept for performing a 21cm intensity mapping survey using a single dish telescope. We briefly discuss the idea of intensity mapping and go on to define our single dish concept. This involves a sim 40 m dish with an array of sim 50 feed horns placed sim 90 m above the dish using a pseudo-correlation detection system based on room temperature LNAs and one of the celestial poles as references. We discuss how such an array operating between 960 and 1260 MHz could be used to measure the acoustic scale to 2.4% over the redshift range 0.13<z<0.48 in around 1 year of on-source integration time by performing a 10 deg times 200 deg drift scan survey with a resolution of sim 2/3 deg.
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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 and constraining the properties of dark energy. 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 approx 0.3), a resolution of 40 arc min and a survey of 5000 deg^2 is close to optimal, whereas at higher redshift (z approx 0.9) a resolution of 10 arcmin and 500 deg^2 would be necessary. Continuum foreground emission from the Galaxy and extragalactic radio sources are potentially a problem. 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 single dish telescope designed to detect BAO at low redshifts. It involves an under-illumintated 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 zapprox 0.3 with an accuracy 2.4% and that w can be measured to an accuracy of 16%.
21cm intensity mapping is a novel approach aimed at measuring the power spectrum of density fluctuations and deducing cosmological information, notably from the Baryonic Acoustic Oscillations (BAO). We give an update on the progress of BAO from Integrated Neutral Gas Observations (BINGO) which is a single dish intensity mapping project. First we explain the basic ideas behind intensity mapping concept before updating the instrument design for BINGO. We also outline the survey we plan to make and its projected science output including estimates of cosmological parameters.
HI intensity mapping is an emerging tool to probe dark energy. Observations of the redshifted HI signal will be contaminated by instrumental noise, atmospheric and Galactic foregrounds. The latter is expected to be four orders of magnitude brighter than the HI emission we wish to detect. We present a simulation of single-dish observations including an instrumental noise model with 1/f and white noise, and sky emission with a diffuse Galactic foreground and HI emission. We consider two foreground cleaning methods: spectral parametric fitting and principal component analysis. For a smooth frequency spectrum of the foreground and instrumental effects, we find that the parametric fitting method provides residuals that are still contaminated by foreground and 1/f noise, but the principal component analysis can remove this contamination down to the thermal noise level. This method is robust for a range of different models of foreground and noise, and so constitutes a promising way to recover the HI signal from the data. However, it induces a leakage of the cosmological signal into the subtracted foreground of around 5%. The efficiency of the component separation methods depends heavily on the smoothness of the frequency spectrum of the foreground and the 1/f noise. We find that as, long as the spectral variations over the band are slow compared to the channel width, the foreground cleaning method still works.
Line-intensity mapping, being an imperfect observation of the line-intensity field in a cosmological volume, will be subject to various anisotropies introduced in observation. Existing literature in the context of CO and [C II] line-intensity mapping often predicts only the real-space, spherically averaged line-intensity power spectrum, with some works considering anisotropies while examining projection of interloper emission. We explicitly consider a simplified picture of redshift-space distortions and instrumental effects due to limited resolution, and how these distort an isotropic line-intensity signal in real space and introduce strong apparent anisotropies. The results suggest that while signal loss due to limited instrumental resolution is unavoidable, measuring the quadrupole power spectrum in addition to the monopole would still break parameter degeneracies present in monopole-only constraints, even without a measurement of the full anisotropic power spectrum.
[Abridged] We study the abundance and clustering properties of HI at redshifts $zleqslant5$ using TNG100, a large state-of-the-art magneto-hydrodynamic simulation of a 75 Mpc/h box size. We show that most of the HI lies within dark matter halos and quantify the average HI mass hosted by halos of mass M at redshift z. We find that only halos with circular velocities larger than $simeq$ 30 km/s contain HI. While the density profiles of HI exhibit a large halo-to-halo scatter, the mean profiles are universal across mass and redshift. The HI in low-mass halos is mostly located in the central galaxy, while in massive halos is concentrated in the satellites. We show that the HI and matter density probability distribution functions differ significantly. Our results point out that for small halos the HI bulk velocity goes in the same direction and has the same magnitude as the halo peculiar velocity, while in large halos differences show up. We find that halo HI velocity dispersion follows a power-law with halo mass. We find a complicated HI bias, with HI becoming non-linear already at $k=0.3$ h/Mpc at $zgtrsim3$. Our simulation reproduces the DLAs bias value from observations. We find that the clustering of HI can be accurately reproduced by perturbative methods. We identify a new secondary bias, by showing that the clustering of halos depends not only on mass but also on HI content. We compute the amplitude of the HI shot-noise and find that it is small at all redshifts. We study the clustering of HI in redshift-space, and show that linear theory can explain the ratio between the monopoles in redshift- and real-space down to small scales at high redshift. We find that the amplitude of the Fingers-of-God effect is larger for HI than for matter. We point out that accurate 21 cm maps can be created from N-body or approximate simulations rather than full hydrodynamic simulations.
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