Simulations play a vital role in testing and validating H i 21-cm power spectrum estimation techniques. Conventional methods use techniques like N-body simulations to simulate the sky signal which is then passed through a model of the instrument. This makes it necessary to simulate the H i distribution in a large cosmological volume, and incorporate both the light-cone effect and the telescope's chromatic response. The computational requirements may be particularly large if one wishes to simulate many realizations of the signal. In this paper we present an analytical method to simulate the H i visibility signal. This is particularly efficient if one wishes to simulate a large number of realizations of the signal. Our method is based on theoretical predictions of the visibility correlation which incorporate both the light-cone effect and the telescope's chromatic response. We have demonstrated this method by applying it to simulate the H i visibility signal for the upcoming Ooty Wide Field Array Phase I.

We study the prospects for extracting detailed statistical properties of the neutral hydrogen distribution during the era of reionization using the brightness temperature fluctuations from redshifted 21 cm line emission. Detection of this signal is complicated by contamination from foreground sources such as diffuse Galactic synchrotron and freefree emission at low radio frequencies, extragalactic free-free emission from ionized regions, and radio point sources. We model these foregrounds to determine the extent to which 21 cm fluctuations can be detected with upcoming experiments. We find that not only the level of correlation from one frequency to another but also the functional form of the foreground correlations has a substantial impact on foreground removal. We calculate how well the angular power spectra of the 21cm fluctuations can be determined. We also show that the large-scale bias of the neutral hydrogen gas distribution with respect to the density field can be determined with high precision and used to distinguish between different reionization histories. Subject headingg s: cosmology: theory -diffuse radiation -large-scale structure of universe

The Square Kilometre Array (SKA) will have a low frequency component (SKA-low) which has as one of its main science goals the study of the redshifted 21cm line from the earliest phases of star and galaxy formation in the Universe. This 21cm signal provides a new and unique window both on the time of the formation of the first stars and accreting black holes and the subsequent period of substantial ionization of the intergalactic medium. The signal will teach us fundamental new things about the earliest phases of structure formation, cosmology and even has the potential to lead to the discovery of new physical phenomena. Here we present a white paper with an Executive SummaryThe Square Kilometre Array (SKA) will have a low frequency component (AA-low/SKA-low 1 ) which has as one of its main science goals the study of the redshifted 21cm line from the earliest phases of star and galaxy formation in the Universe (see SKA Memo 125). It is during this phase that the first building blocks of the galaxies that we see around us today, including our own Milky Way, were formed. It is a crucial period for understanding the history of the Universe and one for which we have currently very little observational data.We divide the period into two different phases based on the physical processes which affect the Intergalactic Medium. The first period, which we call the Cosmic Dawn, saw the formation of the first stars and accreting black holes, which changed the quantum state of the still neutral Intergalactic Medium. The second period, known as the Epoch of Reionization, is the one during which large areas between the galaxies were photo-ionized by the radiation produced in galaxies and which ended when the Intergalactic Medium had become completely ionized.Observations of the redshifted 21-cm line with SKA will provide a new and unique window on the entire period of Cosmic Dawn and Reionization. The signal is sensitive to the emergence of the first stellar populations, radiation from growing massive black holes and the formation of larger groups of galaxies and bright quasars. At the same time it maps the distribution of most of the baryonic matter in the Universe. The study of the redshifted 21cm line will teach us fundamental new things about the earliest phases of structure formation and cosmology. It even has the potential to lead to the discovery of new physical phenomena. Here we present an overview of the science questions that SKA-low can address, how we plan to tackle these questions and what this implies for the basic design of the telescope.The redshifted 21cm signal will be analyzed with different techniques, which each come with their own requirements for the SKA: (i) Tomography, (ii) power-spectra and higher-order statistics, (iii) hydrogen absorption, (iv) global/total-intensity signal. Whereas all precursors/pathfinders aim to study the signal statistically through its power spectrum, SKA will be able to image the neutral hydrogen distribution directly and its focus will therefore be more on tomograph...

No abstract

We produce simulations of the atomic CII line emission in large sky fields in order to determine the current and future prospects for mapping this line during the high redshift epoch of reionization. We calculate the CII line intensity, redshift evolution and spatial fluctuations using observational relations between CII emission and the galaxy star formation rate (SFR) over the frequency range 200 -300 GHz. We estimate an averaged intensity of I CII = (4 ± 2) × 10 2 Jy sr −1 in the redshift range z ∼ 5.3 − 8.5. Observations of the CII emission in this frequency range will suffer contamination from emission lines at lower redshifts, in particular CO rotational lines. Using simulations, we estimated the CO contamination to be I CO ≈ 10 3 Jy sr −1 (originating from galaxies at z < 2.5). Using detailed simulations of the CII and CO emission across a range of redshifts, we generate maps as a function of angle and frequency, fully taking into account this resolution and light cone effects. In order to reduce the foreground contamination we find that we should mask galaxies below redshifts ∼ 2.5 with a CO(J:2-1) to CO(J:6-5) line flux density higher than 5 × 10 −22 W m −2 or a AB magnitude lower than m K = 22. We estimate that the additional continuum contamination originating in emission from stars and in dust, free-free, free-bound and two photon emission in the ISM is of the order of 10 5 Jy sr −1 however it can be removed from observation due to the smooth evolution of this foreground with frequency. We also consider the possibility of cross correlating foreground lines with galaxy surveys in order to probe the intensity of the foregrounds. Finally, we discuss the expected constraints from two experiments capable of measuring the expected CII power spectrum. Subject headings: cosmology: theory -diffuse radiation -intergalactic medium -large scale structure of universe

The atomic CII fine-structure line is one of the brightest lines in a typical star-forming galaxy spectrum with a luminosity ∼ 0.1% to 1% of the bolometric luminosity. It is potentially a reliable tracer of the dense gas distribution at high redshifts and could provide an additional probe to the era of reionization. By taking into account of the spontaneous, stimulated and collisional emission of the CII line, we calculate the spin temperature and the mean intensity as a function of the redshift. When averaged over a cosmologically large volume, we find that the CII emission from ionized carbon in individual galaxies is larger than the signal generated by carbon in the intergalactic medium (IGM). Assuming that the CII luminosity is proportional to the carbon mass in dark matter halos, we also compute the power spectrum of the CII line intensity at various redshifts. In order to avoid the contamination from CO rotational lines at low redshift when targeting a CII survey at high redshifts, we propose the cross-correlation of CII and 21-cm line emission from high redshifts. To explore the detectability of the CII signal from reionization, we also evaluate the expected errors on the CII power spectrum and CII-21 cm cross power spectrum based on the design of the future milimeter surveys. We note that the CII-21 cm cross power spectrum contains interesting features that captures physics during reionization, including the ionized bubble sizes and the mean ionization fraction, which are challenging to measure from 21-cm data alone. We propose an instrumental concept for the reionization CII experiment targeting the frequency range of ∼ 200 to 300 GHz with 1, 3 and 10 meter apertures and a bolometric spectrometer array with 64 independent spectral pixels with about 20,000 bolometers. Subject headings: cosmology: theory -diffuse radiation -intergalactic medium -large scale structure of universe

We study contributions from inhomogeneous (patchy) reionization to arcminute-scale (1000 < l < 10; 000) cosmic microwave background (CMB) anisotropies. We show that inhomogeneities in the ionization fraction, rather than in the mean density, dominate both the temperature and the polarization power spectra. Depending on the ionization history and the clustering bias of the ionizing sources, we find that rms temperature fluctuations range from 2 to 8 lK and the corresponding values for polarization are over 2 orders of magnitude smaller. Reionization can significantly bias cosmological parameter estimates and degrade gravitational lensing potential reconstruction from temperature maps but not from polarization maps. We demonstrate that a simple modeling of the reionization temperature power spectrum may be sufficient to remove the parameter bias. The high-l temperature power spectrum will contain some limited information about the sources of reionization.

Future surveys of large-scale structure will be able to measure perturbations on the scale of the cosmological horizon, and so could potentially probe a number of novel relativistic effects that are negligibly small on sub-horizon scales. These effects leave distinctive signatures in the power spectra of clustering observables and, if measurable, would open a new window on relativistic cosmology. We quantify the size and detectability of the effects for the most relevant future large-scale structure experiments: spectroscopic and photometric galaxy redshift surveys, intensity mapping surveys of neutral hydrogen, and radio continuum surveys. Our forecasts show that next-generation experiments, reaching out to redshifts z 4, will not be able to detect previously-undetected general-relativistic effects by using individual tracers of the density field, although the contribution of weak lensing magnification on large scales should be clearly detectable. We also perform a rigorous joint forecast for the detection of primordial non-Gaussianity through the excess power it produces in the clustering of biased tracers on large scales, finding that uncertainties of σ(f NL ) ∼ 1 − 2 should be achievable. We study the level of degeneracy of these large-scale effects with several tracer-dependent nuisance parameters, quantifying the minimal priors on the latter that are needed for an optimal measurement of the former. Finally, we discuss the systematic effects that must be mitigated to achieve this level of sensitivity, and some alternative approaches that should help to improve the constraints. The computational tools developed to carry out this study, which requires the full-sky computation of the theoretical angular power spectra for O(100) redshift bins, as well as realistic models of the luminosity function, are publicly available at