About Me

I aim to reveal the processes governing galaxy evolution by precisely mapping out the properties and history of the raw material for star formation - cool atomic and molecular gas. I design instruments, carry out surveys, and produce models to measure and understand cool gas in galaxies from today to the dawn of the universe.

I am currently a postdoctoral researcher at the Max Planck Institute for Astronomy in Heidelberg, Germany. I completed my graduate studies at the University of Arizona, where I was a National Science Foundation Graduate Research Fellow, and my undergraduate work at the University of Michigan.

You can find an overview of my various projects below. I'm always happy to chat about any of these topics - send me an email or better yet, if you find yourself in Heidelberg, drop by my office.

Research Interests

The History of Star Forming Gas

My primary research interest is understanding the processes that form and shape galaxies over cosmic time. Clouds cool atomic and molecular hydrogen gas play a particularly significant role in this history: cold molecular gas is the precursor to the birth of new stars, while reservoirs of atomic gas surround and fill star forming disks and sit at the interface between galaxies and the intergalactic medium. Tracing the properties of this gas will allow us to understand how the barryonic matter has been processed and transformed to create the galaxies we see today.

Study of molecular gas in the early universe requires extremely sensitive millimeter and sub-millimeter wavelength observations with telescopes such as the Atacama Large Millimiter/submillimeter Array (ALMA). Because of the long observation times required to do this type of research, studies to date have focused on extremely small regions of the sky. This may result in sampling biases and uncertainties that hinder our understanding. I use cosmological simulations to understand the extent of these biases and develop tools to account for them.

Related Publications
"Biases and Cosmic Variance in Molecular Gas Abundance Measurements at High Redshift", R. P. Keenan, D. P. Marrone, & G. K. Keating 2020, The Astrophysical Journal, 904, 127
"An Intensity Mapping Constraint on the CO-Galaxy Cross Power Spectrum at Redshift ~ 3" , R. P. Keenan, G. K. Keating, & D. P. Marrone 2020, The Astrophysical Journal, 927, 161

Gas Properties of Nearby Galaxies

In addition to observing gas in the past, we also need to understand its behavior in the present. Many properties of molecular gas, such as the relationships between different spectral lines that are used to trace its abudnance, are poorly understood even in nearby galaxies. To this end, I am conducting a survey of multiple tracers of molecular gas in nearby galaxies to understand how they can be used in concert to better understand both the abundance and conditions of star forming gas.

Related Publications
"The Arizona Molecular ISM Survey with the SMT: Survey Overview and Public Data Release", R. P. Keenan, D. P. Marrone, G. K. Keating, E. C. Mayer, K. Bays, J. Downey, L. C. Dunn, J. C. Flores, T. W. Folkers, D. C. Forbes, B. C. Guvenen, C. Holmstedt, R. M. Moulton, & P. Sullivan 2023, The Astrophysical Journal, submitted
"Biases and Cosmic Variance in Molecular Gas Abundance Measurements at High Redshift", R. P. Keenan, D. P. Marrone, & G. K. Keating 2020, The Astrophysical Journal, 904, 127

Line Intensity Mapping

Schematic illustration of intensity mapping

Intensity mapping is a novel tool for studying gas in the distant universe. The traditional approach to studying distant galaxies has been to select a small number of targets to observe in great detail; this provides a wealth of information about individual objects, but may miss important statistical trends. Line intensity mapping (LIM) allows us to study large samples of galaxies, many too faint to be detected in the traditional approach, by combining their light statistically. This tool will provide complimenatry information to the detailed traditonal studies by surveying galaxies over enormous volumes of space.

I build models to predict the signal that will be seen by LIM surveys at a variety of wavelengths. These models are being used to inform instrument design and survey strategy for upcoming LIM projects. I also work on developing data analysis techniques for existing and future LIM datasets.

I am a collaborator in a number of ongoing intensity mapping projects. These include the Millimeter Intensity Mapping Experiment (mmIME), Tomographic Ionized-carbon Mapping Experiment (TIME), and the Terahertz Intensity Mapper (TIM).

Related Publications
"An Intensity Mapping Constraint on the CO-Galaxy Cross Power Spectrum at Redshift ~ 3" , R. P. Keenan, G. K. Keating, & D. P. Marrone 2020, The Astrophysical Journal, 927, 161
"An Intensity Mapping Detection of Aggregate CO Line Emission at 3 mm", G. K. Keating, D. P. Marrone, G. C. Bower, & R. P. Keenan 2020, The Astrophysical Journal, 901, 141