Studying the post reionization universe using marked statistics

Abstract

The present day cosmology is built on the statistical analysis of the large scale and large volume observations of our Universe conducted over a wide span of wavelengths. To this effect, various statistical tools such as the two and three point correlation functions in real space and power spectra and bispectra in Fourier space have been developed and used to understand the history and the process of structure formation in our Universe. In this project we try to explore the possibility of using one such statistical tool, namely, the marked correlation function to understand and analyse the structures in the post reionization Universe. Any marked statistic, defined either in real or Fourier space, is defined on the basis of a “mark” or the property of the specific target observable. Here we consider two such mark that can be used to observe the present day galaxy distribution around us. One is some line emission from the galaxies, the brightness and spectroscopic or photometric identification of which will determine whether the specific galaxy will be identified in a specific galaxy redshift survey. The other is the intensity map of the HI 21-cm line from the neutral hydrogen content within the galaxy, which will provide a rather coarser view of the galaxy distribution around us. In this project, using a dark matter only N-body simulation, Friends-of-Friends halo identification technique, we have simulated mock surveys of such marked galaxy distributions. Next, we have estimated the power spectrum statistic for both of these observable marks of the galaxies mentioned above. Next, from these marked power spectra estimated the ratio of the marked biases in the galaxy distribution. Further, we provide an interpretation of the estimated ratio of the marked biases using the halo bias obtained from the linear perturbation model of the structure formation. This project can be further extended by considering realistic survey volumes, survey sensitivity and noise estimates of these surveys and their impact on the detectability of the galaxies based on their specific line luminosity.