The Square Kilometre Array (SKA) will conduct the biggest spectroscopic galaxy survey ever, by detecting the 21cm emission line of neutral hydrogen (HI) from around a billion galaxies over 3 /4 of the sky, out to a redshift of z ∼ 2. This will allow the redshift-space matter power spectrum, and corresponding dark energy observables, to be measured with unprecedented precision. In this paper, we present an improved model of the HI galaxy number counts and bias from semi-analytic simulations, and use it to calculate the expected yield of HI galaxies from surveys with a variety of Phase 1 and 2 SKA configurations. We illustrate the relative performance of the different surveys by forecasting errors on the radial and transverse scales of the baryon acoustic oscillation (BAO) feature, finding that the full "billion galaxy survey" with SKA2 will deliver the largest dark energy figure of merit of any current or future large-scale structure survey.

Context. Type Ia Supernovae (SNe Ia) have been used as standardizable candles in the optical wavelengths to measure distances with an accuracy of ∼ 7% out to redshift z ∼ 1.5. There is evidence that in the near-infrared (NIR) wavelengths SNe Ia are even better standard candles, however, NIR observations are much more time-consuming. Aims. We aim to test whether the NIR peak magnitudes could be accurately estimated with only a single observation obtained close to maximum light, provided that the time of B band maximum, the B − V color at maximum and the optical stretch parameter are known. Methods. We present multi-epoch U BVRI and single-epoch J and H photometric observations of 16 SNe Ia in the redshift range z = 0.037 − 0.183, doubling the leverage of the current SN Ia NIR Hubble diagram and the number of SNe beyond redshift 0.04. This sample was analyzed together with 102 NIR and 458 optical light curves (LCs) of normal SNe Ia from the literature. Results. The analysis of 45 NIR LCs with well-sampled first maximum shows that a single template accurately describes the LCs if its time axis is stretched with the optical stretch parameter. This allows us to estimate the peak NIR magnitudes of SNe with only few observations obtained within ten days from B-band maximum. The NIR Hubble residuals show weak correlation with ∆M 15 and the color excess E(B − V), and for the first time we report a potential dependence on the J max − H max color. With these corrections, the intrinsic NIR luminosity scatter of SNe Ia is estimated to be ∼ 0.10 mag, which is smaller than what can be derived for a similarly heterogeneous sample at optical wavelengths. Analysis of both NIR and optical data shows that the dust extinction in the host galaxies corresponds to a low R V 1.8 − 1.9. Conclusions. We conclude that SNe Ia are at least as good standard candles in the NIR as in the optical and are potentially less affected by systematic uncertainties. We extended the NIR SN Ia Hubble diagram to its nonlinear part at z ∼ 0.2 and confirmed that it is feasible to accomplish this result with very modest sampling of the NIR LCs, if complemented by well-sampled optical LCs. With future facilities it will be possible to extend the NIR Hubble diagram beyond redshift z 1, and our results suggest that the most efficient way to achieve this would be to obtain a single observation close to the NIR maximum.Send offprint requests to: vallery.stanishev@gmail.comPartly based on observations made with ESO telescopes at the Paranal Observatory under program IDs 079.A-0192 and 081.A-0734.The tables with the near-infrared J and H K-corrections are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via (21) 9.962 (0.004) 9.963 (0.002) Var Notes. (a)See text for the references for the NIR photometry. (b) The two numbers are the uncertainties of the peak magnitude and the K-corrections. (c) Estimated from our s opt − ∆M 15 relation. The ∆M 15 relation. (c) See text for the references for the NIR photometry. ...

Distance measurement provide no constraints on curvature independent of assumptions about the dark energy, raising the question, how flat is our Universe if we make no such assumptions? Allowing for general evolution of the dark energy equation of state with 20 free parameters that are allowed to cross the phantom divide, w(z) = −1, we show that while it is indeed possible to match the first peak in the Cosmic Microwave Background with non-flat models and arbitrary Hubble constant, H0, the full WMAP7 and supernova data alone imply −0.12 < Ω k < 0.01(2σ). If we add an H0 prior, this tightens significantly to Ω k = 0.002 ± 0.009. These constitute the most conservative and model-independent constraints on curvature available today, and illustrate that the curvaturedynamics degeneracy is broken by current data, with a key role played by the Integrated Sachs Wolfe effect rather than the distance to the surface of last scattering. If one imposes a quintessence prior on the dark energy (−1 ≤ w(z) ≤ 1) then just the WMAP7 and supernova data alone force the Universe to near flatness: Ω k = 0.013 ± 0.012. Finally, allowing for curvature, we find that all datasets are consistent with a Harrison-Zel'dovich spectral index, ns = 1, at 2σ, illustrating the interplay between early and late-universe constraints.Introduction -The sign and magnitude of the cosmic curvature, Ω k , is one of the most fundamental characteristics of our cosmos. The sign controls the default topology of the universe while the magnitude has real importance in testing theories: eternal inflation would be seriously tested if |Ω k | > 10 −4 [1, 2] while anthropic considerations suggest that |Ω k | might be large enough to be detectable [3]. Assuming ΛCDM is correct, we are not far from reaching this interesting regime with the latest curvature constraints around the σ Ω k ≃ 10 −3 level [4,5]. Although there is significant prior dependence in these constraints [6] as we will discuss in detail below, they represent a huge improvement over the major breakthrough from the BOOMERANG mission a decade ago which gave |Ω k | ≤ 0.2 [7], itself an order of magnitude improvement over earlier constraints [8].The key step forward in measuring curvature was the realisation that the position of the first acoustic peak in the Cosmic Microwave Background (CMB) provides a standard ruler, and hence the angular diameter distance to the surface of last scattering [9]. However, this alone does not constrain Ω k because of the well-known geometric degeneracy between Ω k and the Hubble parameter

We highlight the unexpected impact of nucleosynthesis and other early universe constraints on the detectability of scaling quintessence dynamics at late times, showing that such dynamics may well be invisible until the unveiling of the Stage-IV dark energy experiments (DUNE, JDEM, LSST, SKA). Nucleosynthesis strongly limits potential deviations from ΛCDM. Surprisingly, the standard Chevallier-Polarski-Linder (CPL) parametrisation, w(z) = w0 + waz/(1 + z), cannot match the nucleosynthesis bound for minimally coupled scaling fields. Given that such models are arguably the best-motivated alternatives to a cosmological constant these results may significantly impact future cosmological survey design and imply that dark energy may well be dynamical even if we do not detect any dynamics in the next decade.

Small fractions of isocurvature perturbations correlated with the dominant adiabatic mode are shown to be a significant primordial systematic for future Baryon Acoustic Oscillation (BAO) surveys, distorting the standard ruler distance by broadening and shifting the peak in the galaxy correlation function. Untreated this systematic leads to biases that can exceed 10σ in the dark energy parameters even for Planck-level isocurvature constraints. Accounting for the isocurvature modes corrects for this bias but degrades the dark energy figure of merit by at least 50%. The BAO data in turn provides extremely powerful new constraints on the nature of the primordial perturbations. Future large galaxy surveys will thus be powerful probes of the earliest phase of the universe in addition to helping pin down the nature of dark energy.

This paper presents storm time total electron content (TEC) modeling results based on artificial neural networks, for both low‐latitude and midlatitude African regions. The developed storm time TEC models were based on Global Positioning System (GPS) observations from GPS receiver stations selected in low latitude, Northern and Southern hemisphere midlatitude regions of the African sector. GPS data selection was based on a storm criterion of Dst≤ −50 nT and storm data sets used to develop the models were within the periods 2001–2015, 2000–2015, and 1998–2015, for African low latitude, Northern and Southern Hemisphere midlatitude regions, respectively. For the first time in storm time TEC modeling, the meridional wind velocity was introduced as an additional input to the well‐known TEC modeling inputs (diurnal variation, seasonal variation, solar activity, and geomagnetic activity representations) to take into account the effect of neutral winds in moving ionization within the ionosphere along the magnetic field lines. Results showed that the use of meridional wind as an additional input leads to overall percentage improvements of about 5%, 10%, and 5% for the low‐latitude, Northern and Southern Hemisphere midlatitude regions, respectively. High‐latitude storm‐induced winds and the interhemispheric blows of the meridional winds from summer to winter hemisphere may be associated with these improvements.

Baryon Acoustic Oscillation (BAO) surveys will be a leading method for addressing the dark energy challenge in the next decade. We explore in detail the effect of allowing for small amplitude admixtures of general isocurvature perturbations in addition to the dominant adiabatic mode. We find that non-adiabatic initial conditions leave the sound speed unchanged but instead excite different harmonics. These harmonics couple differently to Silk damping, altering the form and evolution of acoustic waves in the baryon-photon fluid prior to decoupling. This modifies not only the scale on which the sound waves imprint onto the baryon distribution, which is used as the standard ruler in BAO surveys, but also the shape, width and height of the BAO peak. We discuss these effects in detail and show how more general initial conditions impact our interpretation of cosmological data in dark energy studies. We find that the inclusion of these additional isocurvature modes leads to a decrease in the Dark Energy Task Force figure of merit (FoM) by 46% i.e., FoMISO = 0.54 × FoMAD and 53% for the Boss and Adept experiments respectively when considered in conjunction with Planck data. We also show that the incorrect assumption of adiabaticity has the potential to bias our estimates of the dark energy parameters by 2.7σ (2.2σ) for a single correlated isocurvature mode (CDM isocurvature), and up to 4.9σ (5.7σ) for three correlated isocurvature modes in the case of the Boss (Adept) experiment. We find that the use of the large scale structure data in conjunction with CMB data improves our ability to measure the contributions of different modes to the initial conditions by as much as 95% for certain modes in the fully correlated case.

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