Assistant Professor Ryan Sanders joined the Department of Physics and Astronomy in the fall of 2023.  He completed a B.S. degree in physics at the University of Louisville in 2012.  He received his Ph.D. in astronomy from the University of California, Los Angeles, in 2018 before moving to the University of California, Davis, as a postdoctoral scholar.  In 2020, Dr. Sanders was awarded a prestigious NASA Hubble Fellowship which he held at UC Davis until he joined the University of Kentucky in 2023.

Dr. Sanders’s research program focuses on understanding the population of galaxies in the Universe, their origin, and the physical mechanisms that control their change and growth over time; a field of astronomy known as galaxy formation and evolution.   Some open questions in this field include: What physical mechanisms control galaxy growth and evolve early-Universe populations into the diverse set of present-day galaxies?  How and when did the first generation of galaxies form?  What role does feedback from supernova explosions play in regulating star formation and galax growth?   How does the cycling of baryons into and out of galaxies vary over cosmic time and for galaxies of different masses?  Dr. Sanders’s group at UK uses observations nearby and distant galaxies from the world’s most advanced telescopes spanning the electromagnetic spectrum across radio, infrared, optical, ultraviolet, and X-ray wavelengths to answer these questions.

One of Dr. Sanders’s particular areas of expertise lies in characterizing the chemical makeup of gas and stars in distant galaxies using spectroscopy at ultraviolet, optical, and near-infrared wavelengths.  The abundance of chemical elements heavier than helium that astronomers refer to as “metals” (e.g., oxygen, carbon, nitrogen, iron) traces the buildup of stellar mass over time in a galaxy since these heavy elements were all produced in processes associated with the life and death of stars such as nuclear fusion in stellar cores, supernova explosions, or the mergers of neutron stars.  In contrast, the “light” elements hydrogen and helium have been around in roughly the present-day ratio since shortly after the Big Bang.  The spectrum of a galaxy can be decoded to derive the abundance of various chemical elements in its interstellar gas based on our understanding of atomic physics, from which we know the specific wavelengths of light emitted by different elements when their electrons move between energy levels and the relative strength of these transitions.  Dr. Sanders’s research has pioneered precision chemical abundance measurements of distant galaxies at high cosmological redshift. 

The recently launched James Webb Space Telescope (JWST) has been revolutionizing the field of galaxy formation and evolution since it began science operations July of 2022.  JWST is optimized for observations in the infrared region of the spectrum, ideal for studying distant galaxies in the early Universe because their light emitted in optical wavelengths will be stretched out (“redshifted”) due to the expansion of the Universe and arrive at our telescopes in infrared wavelengths.  The suite of imaging and spectroscopic instruments onboard JWST opens vast new possibilities to observe ancient galaxies in much more detail than was previously possible.  Dr. Sanders has been successful in securing observing time on JWST, leading two Cycle 1 programs as PI that are focused on spectroscopy of galaxies when the Universe was only 1-4 billion years old to characterize their chemical makeup and the properties of massive stars and star-forming gas in these objects.  Data from these programs have just arrived over the past few months and analysis is currently underway in Sanders’s group at UK.  Such observations place strong constraints on theories of galaxy formation and will lead to a better understanding of the origin of present-day galaxies like the Milky Way in which we live.