My research focuses on understanding properties of galaxy populations and particularly the relationship between galaxies' gaseous and stellar content. These comparisons are based on observations carried out at radio wavelengths to study the gas, and at optical and infrared wavelengths to study the stars. I've carried out observations at 21-cm at the Arecibo, Green Bank, the VLA, and Nançay radio telescopes. My optical studies have used Kitt Peak and Sierra San Pedro de Mártir Observatories. I was part of the original science team that designed the 2-Micron All Sky Survey (2MASS) and created the extended-source catalog, which I used as the basis for several follow-up studies at radio wavelengths. More recently I've used the large database of visual-wavelength observations in the Sloan Digital Sky Survey to complement the 21-cm observations. 

My interest in this area of research was piqued when as a graduate student I discovered a large intergalactic hydrogen cloud that showed no traces of stars despite having billions of solar masses of gas. This cloud is twice the size on the sky as the full moon, yet virtually invisible at optical wavelengths, and I discovered it accidentally during calibration observations at Arecibo. This raised questions in my mind about the kinds of biases we have in our studies of galaxies based on our focus on visible light.