Program Results

Introduction to the event

Dr. Andrew Cooper and his group at the NTHU Institute of Astronomy are participating in a large international astronomy collaboration, the Dark Energy Spectroscopic Instrument Milky Way Survey (DESI-MWS). The 5-year project is led by the USA’s Lawrence Berkeley National Laboratory. When it is complete, DESI MWS will be the largest ever spectroscopic survey of very faint stars in the most distant parts of the Milky Way Galaxy. 

The bottom right of the picture shows the latest measurements from the first full year of DESI MWS (May 2021 to April 2022), on top of an all-sky picture of the Milky Way taken by the European Space Agency’s Gaia satellite. 

DESI MWS is observing stars that are very far away. With DESI, we can measure very accurately how fast those stars are moving, relative to the Sun, by looking for very small changes in their color (the Doppler effect). The Sun orbits around the Galaxy very fast, but the distant stars move much more slowly. This means they look a little more blue when we see them in the same direction as the Sun is moving, and a little more red when we see them in the opposite direction.

Dr. Cooper and his group are now preparing papers based on the first year of DESI data. As expected, we can clearly see the blue-to-red pattern in the measurements we have made so far. However, that is not what we are most interested in. We want to take away that large-scale pattern and look for much smaller patterns in the motion of the distant stars that reveal groups of them moving together, in clumps.  

The standard model of cosmology predicts that many of those clumps are created by collisions between the Milky Way and other, smaller galaxies. Some of those collisions are thought to have happened more than eight billion years ago. By searching for the debris of those collisions, we can learn about the history of our Galaxy – this is ‘Galactic Archaeology’.

In the top right picture, Dr. Cooper and his students are reviewing the literature on techniques to discover these clumps. They specialize in using theory and computer models to interpret the DESI data and develop new ways to analyze it. As part of the project, they will run computer models on the high-performance computing cluster built by the NTHU Center for Informatics and Computation in astronomy (part of which is shown on the left of the picture). 

The DESI Milky Way Survey team are celebrating a successful first year of observations and looking forward to making new discoveries that will help us tell the story of the Galaxy we live in.

Caption: A snapshot of the average line-of-sight speeds of stars in different parts of the sky measured by the DESI Survey (lower right) superimposed on a picture of the Milky Way. Dr. Cooper and his group (upper right) are studying these results and planning their analysis of the data, which will use the newly upgraded CICA cluster at NTHU IoA (left).