Studies For High Energy Gamma Emission Of Star-Forming Galaxies And Its Interior Objects

High energy gamma rays are one of the important probes in the exploration of the universe.The study of gamma rays will help us understand the high energy physics phenomena in the universe,particle acceleration mechanism and identify the source of cosmic rays.The number of star-forming galaxies detected in the gamma band is relatively small compared to other wavelengths.The study of gamma-ray radiation from star-forming galaxies helps us to understand star-forming galaxies and their interactions with the surrounding environment,expand the directivity relationship between gamma-ray luminosity and total infrared luminosity of star-forming galaxies,and understand the physical properties of possible counterparts of unproven radiation sources.This master’s thesis is based on 64 star forming galaxies as samples.Through 13.4 years of Fermi-LAT observation data,it searches for high energy gamma ray radiation in the sample galaxies,and then studies the properties of gamma ray radiation.We found only one Ge V gamma-ray source in the northeast of NGC 4631.By analyzing the energy spectrum,pulse and light variation of this gamma-ray source,we proved that this source is a stable point source with an energy spectrum index of-1.6 and no pulse.There are several X-ray and radio observations within the 95% confidence range of its location,using the X-ray and radio fluxes closest to the source as the upper limit of the flux of the gamma ray source over the low energy band,We found that gamma-ray data can be reproduced by proton-proton collisions between cosmic rays and the interstellar medium in star-forming galaxies or by inverse Compton radiation from electrons in background blazar.Although the inferred luminosity is consistent with the empirical relationship between infrared luminosity and gamma ray luminosity of star-forming galaxies,the large systematic deviation from the center of the galaxy and the unusually rigid energy spectrum compared to other star-forming galaxies suggest that the source is more likely to be a background blazar than a star-forming galaxy.The first chapter introduces the composition,discovery,energy spectrum,origin and other related knowledge of cosmic rays,and then gives a brief introduction to the radiation mechanism of gamma rays.In chapter 2,Fermi-LAT correlation structure and data analysis methods as well as gamma-ray radiation candidates are introduced.Finally,the present situation of gamma-ray radiation observation in star-forming galaxies is introduced.In chapter 3,the research process of searching for high energy gamma-ray radiation from star-forming galaxies is described from the aspects of sample selection and data screening,and the spectrum,pulsation and light variation of the gamma-ray radiation are analyzed.Finally,the possible physical origin of the gamma-ray source is discussed.In the last chapter,I summarize my work during my master’s degree and give a prospect for the research of high energy gamma ray radiation in star-forming galaxies.