The upcoming radio interferometer Square Kilometre Array is expected to directly detect the redshifted 21-cm signal from the Cosmic Dawn for the first time. In this era temperature fluctuations from X-ray heating of the neutral intergalactic medium can impact this signal dramatically. Previously, in Ross et al. (2017), we presented the first large-volume, 244 h-1 Mpc=349 Mpc a side, fully numerical radiative transfer simulations of X-ray heating. This work is a follow-up where we now also consider QSO-like sources in addition to high mass X-ray binaries. Images of the two cases are clearly distinguishable at SKA1-LOW resolution and have RMS fluctuations above the expected noise. The inclusion of QSOs leads to a dramatic increase in non-Gaussianity of the signal, as measured by the skewness and kurtosis of the 21-cm signal. We conclude that this increased non-Gaussianity is a promising signature of early QSOs.

The future SKA1-Low radio telescope will be powerful enough to produce tomographic images of the 21-cm signal from the Epoch of Reionization. Here we address how to identify ionized regions in such data sets, taking into account the resolution and noise levels associated with SKA1-Low. We describe three methods of which one, superpixel oversegmentation, consistently performs best.

The matched filtering technique is an efficient method to detect H ii bubbles and absorption regions in radio interferometric observations of the redshifted 21-cm signal from the epoch of reionization and the Cosmic Dawn. Here, we present an implementation of this technique to the upcoming observations such as the SKA1-low for a blind search of absorption regions at the Cosmic Dawn. The pipeline explores four dimensional parameter space on the simulated mock visibilities using a MCMC algorithm. The framework is able to efficiently determine the positions and sizes of the absorption/H ii regions in the field of view.

The James Webb Space Telescope (JWST) will observe the rest-frame ultraviolet/optical spectra of galaxies from the epoch of reionization (EoR) in unprecedented detail. While escaping into the intergalactic medium, hydrogen-ionizing (Lyman continuum; LyC) photons from the galaxies will contribute to the bluer end of the UV slope and make nebular emission lines less prominent. We present a method to constrain leakage of the LyC photons using the spectra of high redshift (z ≳ 6) galaxies. We simulate JWST/NIRSpec observations of galaxies at z =6–9 by matching the fluxes of galaxies observed in the Frontier Fields observations of galaxy cluster MACS-J0416. Our method predicts the escape fraction fesc with a mean absolute error Δfesc ≈ 0.14. The method also predicts the redshifts of the galaxies with an error $\left\langle \frac{\Delta z}{(1+z)}\right\rangle \approx 0.0003$.

The propagation of cosmological ionisation fronts (I-fronts) during reionisation is strongly influenced by small-scale structure. Here we summarise our recent attempts to understand the effect of this small-scale structure. We present high resolution cosmological N-body simulations at high-z ($z>6$) which resolve a wide range of halo mass, from mini-halos to clusters of large, rare halos. We also study how mini-halos affect I-fronts, through simulations of mini-halo photo-evaporation including numerical gas dynamics with radiative transfer. Furthermore, we modify the I-front propagation equations to account for evolving small-scale structure, and incorporate these results into a semi-analytical reionisation model. When intergalactic medium clumping and mini-halo clustering around sources are included, small-scale structure affects reionisation by slowing it down and extending it in time. This helps to explain the observations of the Wilkinson Microwave Anisotropy Probe, which imply an early and extended reionisation epoch. We also study how source clustering affects the evolution and size of H II regions, finding, in agreement with simulations, that H II regions usually expand, and rarely shrink. Hence, “relic H II regions” are an exception, rather than the rule. When the suppression of small-mass sources in already-ionised regions by Jeans-mass filtering is accounted for, H II regions are smaller, delaying overlap. We also present a new numerical method for radiative transfer which is fast, efficient and easily coupled to hydrodynamics and N-body codes, along with sample tests and applications.

The formation of PNe around [WC] stars is modelled with a numerical hydrodynamics code. It is found that the PN around [WC] are expected to expand faster, and be more turbulent. It is shown that the observed lack of differences with ‘normal’ PNe, can have implications for models of the origin of asphericity in PNe.

We present the results of numerical hydrodynamic models for the collimation of outflows from young stellar objects. We show that the presence of a toroidal environment can lead to efficient formation of jets and bipolar outflows from initially uncollimated central winds. The interaction between the wind and the environment leads to two types of collimation, one which is dominated by radiative cooling effects, and one which works when cooling is less efficient. We describe the two types of jets as they appear in the simulations and we suggest a description for the long term evolution of these structures in more realistic time-dependent wind sources.

The are often inconsistencies between the results of different methods for deriving electron temperatures from line strengths in PNe. Temperatures derived from forbidden lines ratios such as [OIII]4363/5007, are on average higher than those calculated from permitted lines. This is normally explained by assuming the existence of areas of higher temperatures which have more weight in a forbidden line analysis, the so-called ‘temperature fluctuations’. The magnitude of these fluctuations is expressed by the t2 parameter. See Peimbert (1967). A typical value is about 0.03, corresponding to fluctuations of ∼ 10%. Photoionization models have difficulty in explaining fluctuations of this magnitude (Kingdon & Ferland 1995).

The formation of a Planetary Nebula is determined by the star which lives and evolves in the middle of it. The star produces both the winds and the photons which determine the shape and appearance of the nebula. Here I study how the shape of the PN depends on the stellar properties.