Peeking into the Reionization era with Lyman-α transmission spikes

While visiting UCSC last year, I started working on a project with Piero Madau and Nick Gnedin. Some weeks ago we finally put the paper on arXiv.

For this paper, we used the radiation-hydrodynamical simulations of the CROC suite, and asked this question: what kind of gas produces the narrow transmission spikes we see in quasar spectra (embedded in large Gunn-Peterson trough)? Turns out that very special conditions are required in the IGM to produce spikes, namely underdense gas and above-average radiation field. This is not common, because the sources of photons (galaxies) live in overdense regions. We checked the number of spikes as a function of redshift, how their shape (height and width) of the peaks is linked to the IGM density, temperature and ionized state. We also checked how all these results change when we include a realistic observational setup. Finally, we compared our simulations to observations of the average flux around galaxies.

Left: slice through one simulation box showing gas temperature, overdensity and HI fraction.

Right: a synthetic spectrum extracted from one simulation box, showing the density field (top) around the line of sight (dashed line), the normalized transmitted flux (top-center), overdensity (center), HI fraction (bottom center) ans temperature (bottom) along the line of sight.