On October 11, 2022, NASA’s James Webb Space Telescope observed the long-studied Hubble Ultra Deep Field for over 20 hours for the first time. The General Observation Program (GO 1963) focused on analyzing the field at wavelengths between about 2 and 4 microns. We spoke with Christina Williams (NOIRLab), Sandro Tacchella (University of Cambridge) and Michael Maseda (University of Wisconsin-Madison) to learn more about the first Webb-eyed observation of the Hubble Ultra Deep Field.

What is important for people to know about these Webb observations?

Michael Maseda : Our seeing of hot ionized gas tells us exactly where stars were born in these galaxies. We can now separate these regions from regions where stars already exist. This information is very important because we don’t know exactly how galaxies got to what they are today after billions of years. It is important to note that we do not see everything to see. Our entire schedule was ~24 hours, which is not so much in the grand scheme of how long other observatories have been looking at it. But even in this relatively short period of time, we are starting to form a new picture of how galaxies grew during this truly interesting period in the history of the universe.

What are you interested in learning as you explore the Hubble Ultra Deep Field with Webb?

Christina Williams: We proposed to display the ultra-deep field using some mid-pass filters of NIRCam Webb images; this allowed us to image the spectral features more precisely than we could with broadband filters, since midpass filters cover a smaller wavelength range. . This gives us greater precision in measuring colors, which helps us understand the history of star formation and the ionization properties of galaxies during the first billion years of the universe, such as the age of reionization. Measuring the energy produced by galaxies at that time will help us understand how galaxies reionized the universe by turning it from neutral gas to ionized plasma, just as it did after the Big Bang.

Sandro Tacella: One of the key unresolved questions in extragalactic astrophysics is how the first galaxies formed. Because the middle bands span a range of different wavelengths, we can either directly locate some of the first galaxies in the early universe or age the stars in galaxies when the universe was about a billion years old to figure out when galaxies actually were. They formed their stars in the past. This study helps determine the formation of the first galaxies.

Michael: Webb’s midband filter capabilities are actually fairly new. We’re getting a kind of hybrid between imaging and spectroscopy, so we get detailed information about almost all galaxies in the field of view, unlike traditional spectroscopy, where you can only select a few galaxies to work with in the field of view. . It’s a really complete picture in the sense that this information complements a lot of existing data that we have on spectroscopy on the Very Large Telescope, not only from Hubble, but also from ground-based instruments like MUSE (Multi-Unit Spectroscopic Explorer). different wavelengths. for some of these objects. MUSE is very good at detecting galaxies with Lyman-alpha emission or light from ionized hydrogen in these galaxies; what types of galaxies were present in these galaxies when the reionization ceased. This new data is a missing piece that we didn’t have before in understanding the entire population of galaxies in the field.

Did anything unexpected happen in the data that surprised you?

Michael : I don’t know if I was completely surprised, but the images turned out better than I expected. In these images, you can visually see that this is a fairly large area of ​​ionized gas. I would expect it to be unresolved but we have high enough resolution to see it. And I’m glad to see that, because it could have been much more difficult to understand what was going on.

Christina: I think it was definitely a high point to see how beautiful the images were and how high quality they were. We expected to be able to do such things, but seeing it in practice and having real data was different.

Why did you decide to publish the data immediately?

Sandro: Galaxies are very complex systems where a wide variety of different processes operate at different spatial and temporal scales, so there are many approaches that can be used to better understand the physics of galaxies. Therefore, making it available to many different groups will make it easier to find more information.

Christina: Webb is still a beginner and people are still learning best practices for analyzing datasets. Therefore, it is in everyone’s interest to have multiple data sets immediately available to help people understand how best to use Webb data in the future and better plan programs for future cycles based on real-world experience with the data.