Seminar – Satadru Bag (IUCAA)

December 14, 2017 @ 12:00 pm – 1:00 pm

PhD student, IUCAA, India

Title:   Studying the morphology of HI isodensity surfaces with shapefinders during reionization
Shapefinders, derived from Minkowski functionals, are very powerful and widely applied tool to quantify a closed 2D surface embedded in 3-dimensions. We developed a very sophisticated code, named SURFGEN2, which can identify clusters in HI overdense (or underdense) region corresponding to some density threshold and precisely calculate the shapefinders of each individual cluster by triangulating its surface using Marching cube 33 algorithm. One of our prime interest is to apply this diagnostic on simulated HI density fields, in the anticipation of upcoming HI intensity map data from future radio surveys, like SKA. We studied the HI density fields, simulated using semi-numerical technique (inside-out), at various stages of reionization; redshift starting from z=7 to z=13. Accompanying shapefinders, we also performed the largest cluster statistics (LCS) to study the percolation. We found that the large clusters in both HI overdense and underdense regions are overwhelmingly filament like in the entire range of redshift considered. As we lower (rise) the density threshold for neutral (ionized) region, large clusters start to appear from the onset of percolation, which leads to sharp rise in volume-averaged “filamentarity” during percolation transition while “planarity” does not rise sharply. In the vicinity of percolation, when there are many large clusters, we found that the cross section of these large clusters do not vary much with volume, i.e. their “thickness” and “breadth” remain similar but the third shapefinder, “length”, becomes proportional to volume. This feature is more profound at low redshifts (advanced stages of reionization) and more vivid in overdense region (than in underdense region).