Radio Observations of Ultra Luminous Infra Red Galaxies (ULIRGs)

Abstract

ULIRGs, or Ultra-Luminous Infra Red Galaxies, are incredibly bright galaxies that emit intense Infra Red (IR) radiation due to the merger of two gas-rich galaxies. The intense star formation due to the merger generates a significant amount of ultraviolet radiation, absorbed by surrounding dust and re-emitted in the IR range, making galaxies look very bright at this wavelength. Observations of the galaxies show that they are evolving into elliptical galaxies. While star formation is the primary source of energy for ULIRGs, it has been discovered that nearly half of all ULIRGs detected also contain active galactic nuclei (AGNs). Furthermore, ULIRGs are considered the low-redshift counterparts of distant radio-loud galaxies, making them a valuable research topic. Understanding the behaviour of AGN in these galaxies is critical for studying our nearby Universe and its cosmological consequences. Despite extensive research on ULIRGs at optical and IR wavelengths, detailed radio maps of these galaxies have not been studied. In this study, we intend to make radio frequency maps of a sample of ULIRGs, enabling us to observe their radio morphologies and search for extended features like jets. We will also determine the emission’s spectral index, turnover frequency and break frequency, which will provide vital information about the physical processes taking place within these galaxies. The break frequency will enable us to calculate the spectral age of the ULIRGs, helping us understand where it stands in the evolution of radio-loud galaxies. We find that ULIRGs have a low-frequency turnover comparable to Compact Steep Spectrum (CSS) sources, which are thought to be young radio sources that evolve into large radio galaxies. The measured spectral ages have a median of around 3 million years. This age is younger than large radio relic galaxies that are 107 −108 million years old. This fits with the claim that ULIRGs are new radio sources. The radio powers at 1.4 GHz is very near to log(P at 1.4GHz) = 25, the radio power that separates Fanaroff–Riley I and Fanaroff–Riley II radio sources.