Modeling emission lines from clouds irradiated by Cosmic Rays in the Solar neighborhood of Milky Way

Abstract

Cosmic rays are protons and electrons accelerated to a speed closer to the speed of light. It has been detected directly only in the vicinity of the Sun. However, they are present all across the galaxy, emphasizing the need to devise approaches to detect their spectrum indirectly. One of the most common ways to do this is to model the gamma-ray and gas emissions from clouds to derive the incident CR spectrum on them ([33]). In my thesis, we have come up with new methodologies to overcome the constraints of the existing model and improve the accuracy. We test the reliability of the new cloud model, which estimates the conversion factor from CO intensity to H2 column density. This cloud model is crucial since the fixed standard value of the conversion factor used in the conventional method could cause errors as it changes depending on environmental conditions. Moreover, 2D and 3D dust extinction and emission maps have been employed to distinguish passive clouds from active ones since the former is best suited for modeling the emission. Additionally, the background subtraction in gamma-ray maps is done using a new approach without employing the standard diffuse models as they could bias the results. This is done in a way that the background emission does not include the emission from the clouds, which could be the case in standard models. Finally, 12 passive clouds in the Solar neighborhood are selected, among which the most suitable one is used to test the cloud model.