Understanding the Nature of the Diffuse Interstellar Bands in Extra-Galactic Sources

Brandon Lawton

The Diffuse Interstellar Bands (DIBs) are absorption features with rest-frame optical transition wavelengths and are likely due to organic molecules. Understanding these molecules has immense importance in understanding the nature of a galaxy's ISM as well as significance in astrobiology. I have obtained funding through the NASA GSRP and the New Mexico Space Grant Consortium to complete my thesis topics which aim to explore the nature of DIBs in extra-galactic sources.

• The first portion of my thesis is complete and explores DIBs as observed in damped Lyman alpha systems (DLAs) at relatively high redshift via QSO absorption-line systems. I have addressed several questions regarding DIBs in this portion of my project including the feasibility of observing DIBs at high redshifts, and the roles hydrogen and metallicity play in the DIB strengths we observe.

• The second portion of my project is currently underway in which I observe starburst galaxies at low redshifts. In this work I am comparing neutral sodium strengths to DIB strengths as well as the characteristics of the various galaxies including metallicity, ionization, reddening, and orientation.

• The third part of my project that is also currently underway is to observe ultra-luminous infrared galaxies (ULIRGs) for the DIBs. In this part of my project I am comparing the same galactic quantities as the starburst sample, but I will also compare the strengths of the DIBs with observed strengths of the known PAH IR emission lines. From these observations I will test the likelihood that the molecules responsible for creating the DIBs are the same types of PAH molecules responsible for the IR emission bands. This project holds the promise of independently determining the nature of the DIB carriers.

All three projects will significantly build our knowledge of DIBs, the environments conducive to housing the molecular carriers of the DIBs, and the nature of those molecules.