The UV escape fraction from high-redshift galaxies plays a key role in models of cosmic reionisation. Because it is currently not possible to deduce the escape fractions during the epoch of reionisation from observations, we have to rely on numerical simulations. Our aim is to better constrain the escape fraction from high-redshift dwarf galaxies, as these are the most likely sources responsible for reionising the Universe. We employ a N-body/SPH method that includes realistic prescriptions for the physical processes that are important for the evolution of dwarf galaxies. These models are post-processed with radiative transfer to determine the escape fraction of ionising radiation. We perform a parameter study to assess the influence of the spin parameter, gas fraction and formation redshift of the galaxy and study the importance of numerical parameters as resolution, source distribution and local gas clearing. We find that the UV escape fraction from high-redshift dwarf galaxies that have formed a rotationally supported disc lie between 1e-5 and 0.1. The mass and angular momentum of the galaxy are the most important parameters that determine the escape fraction. We compare our results to previous work and discuss the uncertainties of our models. The low escape fraction we find for high-redshift dwarf galaxies is balanced by their high stellar content, resulting in an efficiency parameter for stars that is only marginally lower than the values found by semi-analytic models of reionisation. We therefore conclude that dwarf galaxies play an important role in cosmic reionisation also after the initial starburst phase, when the gas has settled into a disc.
High redshift AGNs and HI reionisation: limits from the unresolved X-ray background
z~3处明亮类星体数量的迅速减少似乎对HI莱曼极限的电离背景的贡献越来越小。因此，一般认为（前）星系系统中的大质量恒星可能提供额外的电离通量，以在z>6时完成HI再电离。然而，一个星系主导的背景，可能需要从高红移星系的莱曼连续辐射的逃逸分数高达10%，一个值有点不一致（公认的稀缺）的观测约束。矮星系的高逃逸分数一直被提倡，或者，一个迄今未被发现（或几乎未被发现）的人口的无遮蔽，高红移微弱AGN。在这里，我们质疑后者的假设，并表明，这样的来源，是一致的，在z=0的未解决的X射线背景的测量水平，可以提供一个分数的HII填充因子不大于13%的z=6。分数上升到<27% in the somewhat extreme case of a constant comoving redshift evolution of the AGN emissivity. This still calls for a mean escape fraction of ionising photons from high-z galaxies >10%。
Feedback to the interstellar medium (ISM) from ionising radiation, stellar winds and supernovae is central to regulating star formation in galaxies. Due to their low mass ($M_{*} < 10^{9}$\,M$_\odot$), dwarf galaxies are particularly susceptible to such processes, making them ideal sites to study the detailed physics of feedback. In this perspective, we summarise the latest observational evidences for feedback from star forming regions and how this drives the formation of 'superbubbles' and galaxy-wide winds. We discuss the important role of external ionising radiation -- 'reionisation' -- for…
In recent years, interstellar dust has become a crucial topic in the study of the high and very high redshift Universe. Evidence points to the existence of high dust masses in massive star forming galaxies already during the Epoch of Reionization, potentially affecting the escape of ionising photons into the intergalactic medium. Moreover, correctly estimating dust extinction at UV wavelengths is essential for precise ultra-violet luminosity function (UVLF) prediction and interpretation. In this paper, we investigate the impact of dust on the observed properties of high redshift galaxies, and …
Identifying and characterising reionised bubbles enables us to track both their size distribution, which depends on the primary ionising sources, and the relationship between reionisation and galaxy evolution. We demonstrate that spectrally resolved $z\gtrsim6$ Lyman-alpha (Ly$α$) emission can constrain properties of reionised regions. Specifically, the distant from a source to a neutral region sets the minimum observable Ly$α$ velocity offset from systemic. Detection of flux on the blue side of the Ly$α$ resonance implies the source resides in a large, sufficiently ionised region that photons…
Context: Population III (Pop III) stars may be fast rotating. An expected consequence of fast rotation is strong internal mixing that deeply affects their evolutionary tracks in the Hertzsprung-Russell diagram and hence their ionising power. aims: We investigate the impact on the ionising power of Pop III stars in an extreme case of internal mixing, the one leading to chemically homogeneous evolution (CHE). In that situation, during the main sequence phase, the star keeps the same chemical composition from its center to its surface. Homogeneous stars have larger effective temperatures and lumi…
Although low-mass star-forming galaxies are the leading candidates of the reionisation process, we cannot conclusively rule out high-mass star-forming galaxies as candidates. While most simulations indicate the former is the best candidate some models suggest that at z > 6 massive, UV-bright galaxies - "oligarchs" - account for at least 80% of the ionising budget. To test this hypothesis we target massive (log10 (M*[Msol]) > 10), UV-bright (MUV ~ -22) Lya emitters at z > 7 in archival data, observed with similar resolution spectrographs (VLT/X-shooter and Keck/MOSFIRE). To increase the reliabi…
The ionizing photon escape fraction (LyC $f_{\rm{esc}}$) of star-forming galaxies is the single greatest unknown in the reionization budget. Stochastic sightline effects prohibit the direct separation of LyC leakers from non-leakers at significant redshift. Here we circumvent this uncertainty by inferring $f_{\rm{esc}}$ with resolved (R>4000) LyA profiles from the X-SHOOTER LyA survey at z=2 (XLS-z2). We select leakers ($f_{\rm{esc}}>20$%) and non-leakers ($f_{\rm{esc}}<5$%) from a representative sample of $>0.2 L^{*}$ LyA emitters (LAEs). With median stacked spectra of these subsets covering …
