HI intensity mapping is a new observational technique to map fluctuations in the large-scale structure of matter using the 21 cm emission line of atomic hydrogen (HI). Sensitive HI intensity mapping experiments have the potential to detect Baryon Acoustic Oscillations (BAO) at low redshifts (z 1) in order to constrain the properties of dark energy. Observations of the HI signal will be contaminated by instrumental noise and, more significantly, by astrophysical foregrounds, such as Galactic synchrotron emission, which is at least four orders of magnitude brighter than the HI signal. Foreground cleaning is recognised as one of the key challenges for future radio astronomy surveys. We study the ability of the Generalized Needlet Internal Linear Combination (GNILC) method to subtract radio foregrounds and to recover the cosmological HI signal for a general HI intensity mapping experiment. The GNILC method is a new technique that uses both frequency and spatial information to separate the components of the observed data. Our results show that the method is robust to the complexity of the foregrounds. For simulated radio observations including HI emission, Galactic synchrotron, Galactic free-free, radio sources and 0.05 mK thermal noise, we find that the GNILC method can reconstruct the HI power spectrum for multipoles 30 < < 150 with 6% accuracy on 50% of the sky for a redshift z ∼ 0.25.

We consider a quintessence model for dark energy interacting with dark matter via a Yukawa interaction. To put constraints on this model we use the CMB measurements from the Planck satellite together with BAO, SNIa and H0 data. We conclude that this is a viable model and an appropriate scalar potential can favor the interacting scenario.PACS numbers: 98.80. Es, 98.80.Jk, 95.30.Sf

Cosmology has entered an era where the experimental limitations are not due to instrumental sensitivity but instead due to inherent systematic uncertainties in the instrumentation and data analysis methods. The field of HI intensity mapping (IM) is still maturing, however early attempts are already systematics limited. One such systematic limitation is 1/ f noise, which largely originates within the instrumentation and manifests as multiplicative gain fluctuations.To date there has been little discussion about the possible impact of 1/ f noise on upcoming single-dish HI IM experiments such as BINGO, FAST or SKA. Presented in this work are Monte-Carlo end-to-end simulations of a 30 day HI IM survey using the SKA-MID array covering a bandwidth of 950 and 1410 MHz. These simulations extend 1/ f noise models to include not just temporal fluctuations but also correlated gain fluctuations across the receiver bandpass. The power spectral density of the spectral gain fluctuations are modelled as a power-law, and characterised by a parameter β. It is found that the degree of 1/ f noise frequency correlation will be critical to the success of HI IM experiments. Small values of β (β < 0.25) or high correlation is preferred as this is more easily removed using current component separation techniques. Spectral index of temporal fluctuations (α) is also found to have a large impact on signal-to-noise. Telescope slew speed has a smaller impact, and a scan speed of 1 deg s −1 should be sufficient for a HI IM survey with the SKA.

HI intensity mapping is a new observational technique to survey the large-scale structure of matter using the 21 cm emission line of atomic hydrogen (HI). In this work, we simulate BINGO (BAO from Integrated Neutral Gas Observations) and SKA (Square Kilometre Array) phase-1 dish array operating in auto-correlation mode. For the optimal case of BINGO with no foregrounds, the combination of the HI angular power spectra with Planck results allows w to be measured with a precision of 4%, while the combination of the BAO acoustic scale with Planck gives a precision of 7%. We consider a number of potentially complicating effects, including foregrounds and redshift dependent bias, which increase the uncertainty on w but not dramatically; in all cases the final uncertainty is found to be ∆w < 8% for BINGO. For the combination of SKA-MID in auto-correlation mode with Planck, we find that, in ideal conditions, w can be measured with a precision of 4% for the redshift range 0.35 < z < 3 (i.e., for the bandwidth of ∆ν = [350, 1050] MHz) and 2% for 0 < z < 0.49 (i.e., ∆ν = [950, 1421] MHz). Extending the model to include the sum of neutrino masses yields a 95% upper limit of m ν < 0.24 eV for BINGO and m ν < 0.08 eV for SKA phase 1, competitive with the current best constraints in the case of BINGO and significantly better than them in the case of SKA.

We discuss the detectability of large-scale HI intensity fluctuations using the FAST telescope. We present forecasts for the accuracy of measuring the Baryonic Acoustic Oscillations and constraining the properties of dark energy. The FAST 19beam L-band receivers (1.05-1.45 GHz) can provide constraints on the matter power spectrum and dark energy equation of state parameters (w 0 , w a ) that are comparable to the BINGO and CHIME experiments. For one year of integration time we find that the optimal survey area is 6000 deg 2 . However, observing with larger frequency coverage at higher redshift (0.95-1.35 GHz) improves the projected errorbars on the HI power spectrum by more than 2 σ confidence level. The combined constraints from FAST, CHIME, BINGO and Planck CMB observations can provide reliable, stringent constraints on the dark energy equation of state.