Dust Obscuration in the Most Massive Galaxies of Epoch of Reionization

Abstract

One of the biggest challenges in Cosmology is understanding the earliest galaxies formed in the Universe within one billion years of the Big Bang. This is a pressing issue because these galaxies are believed to be responsible for the last major cosmic phase transition, known as Cosmic Reionization, and for polluting the intergalactic medium with heavy elements. These processes significantly impact the subsequent formation of galaxies, governed by a complex network of physical processes collectively called “feedback.”

Recent advancements in technology and the availability of powerful instruments such as the JWST and ALMA interferometer have enabled us to explore the depths of space and study these early galaxies in greater detail. With the help of JWST, we have observed galaxies beyond z > 10, while ALMA has provided insights into the properties of galaxies beyond z > 7. Studies based on these new observations have discovered very bright sources at z > 10, which challenges the widely accepted model of large-scale structure formation known as the ΛCDM model. This raises questions about the physical processes involved in the rapid accumulation of large masses of these galaxies in a short period (around a few hundred million years after the Big Bang). In this thesis, we propose a simple solution to this problem by postulating the role of “Dust Obscuration” in the observations. We use theoretical and numerical approaches to develop a model of UV and IR luminosity and Dust Obscuration. The dust produced in these early galaxies absorbs the UV radiation from young, hot, metal-free stars, resulting in lower UV luminosity than predicted by existing theoretical models. The dust then warms up and irradiates in the IR wavelength. We propose a dust obscuration model that minimally affects the UV magnitude beyond z ≥ 10. We also extend this model to the IR band using a simple chain rule transformation. However, we observe a slight disagreement between the model and the IR luminosity data, which we hypothesize could be due to the presence of “UV dark” galaxies. These galaxies do not emit UV radiation but contribute heavily to the IR wavelength. We propose the number density of these missing galaxies from the IR data.