May 8, 2024: Mapping the Velocities of Stars in Distant Lensing Galaxies

In this dedicated session for students in Bogotá, Colombia, the team will utilize the W. M. Keck Observatory to conduct observations using the Keck II 10-meter telescope and Keck Cosmic Web Imager (KCWI) instrument.
The gravity from massive distant galaxies can act like magnifying lenses to blow up and distort the image of bright galaxies behind them, often showing multiple copies of the same galaxy. Astronomers use this gravitational lensing to weigh the galaxy in front. They can also observe the effect of gravity in distant galaxies by measuring the speeds of the stars in their orbits.
These galaxies contain billions of stars, so researchers measure their combined speeds by measuring how their motions change the spectrum of light in the galaxy. Modern telescopes can measure the spectrum in different locations across the galaxy, so they can extract a map of the speeds of stars throughout the galaxy. These maps show precisely where the gravity is concentrated and tell us about the structure and evolution of these galaxies. Astronomers have an advantage; since they are measuring this for a galaxy that acts like a gravitational lens, they can compare the measurements from lensing and the velocities to be more precise than either can accomplish on their own. Beyond that, researchers can even use these galaxies to measure how fast the Universe is expanding, which is one of the most controversial topics in astronomy!