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On October 11, 2022, NASA’s James Webb Space Telescope spent more than 20 hours observing the long-studied Hubble Ultra Deep Field for the first time. The General Observation Program (GO 1963) focused on field analysis 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 sighting of the Hubble Ultra Deep Field through Webb’s eyes.
What is important for people to know about these Webb observations?
Michael Maseda: The fact that we see hot, ionized gas tells us exactly where stars are born in these galaxies. Now we can separate these areas from those where the stars already existed. This information is very important because, billions of years later, we do not know exactly how the galaxies became what they are today. It’s important to note that we haven’t seen everything yet. Our whole program lasted about 24 hours, which is not a lot of time in the grand scheme of time spent by other observatories. But, even in this relatively short time, we are beginning to paint a new picture of galaxy growth at this really interesting time in the history of the Universe.
What are you interested in learning while exploring the Hubble Ultra Deep Field with Webb?
Christina Williams: We proposed to image the Ultra Deep Field using some of Webb NIRCam’s mid-band image filters, which allowed us to image spectral features more accurately than with wide-band filters. band, because mid-band filters cover a shorter wavelength range. This gives us more sensitivity 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 in the past. era of reionization. Measuring the energy produced by galaxies at this time will help us understand how the galaxies reionized the universe, turning it from neutral gas to ionized plasma as it was after the big bang.
Sandro Tacchella: One of the main outstanding questions in extragalactic astrophysics is how the first galaxies form. Since the middle bands cover a range of different wavelengths, we can either directly find some of the earliest galaxies in the early universe, or date the stars of galaxies when the universe was around a billion years old to understand when the galaxy actually formed its stars in the past. This survey helps to identify the formation of the first galaxies.
Michael Maseda: The capabilities we have with Webb’s midband filters are actually quite new. We get kind of a hybrid between imaging and spectroscopy, so we get detailed information for pretty much every galaxy in the field, as opposed to traditional spectroscopy where you can only select a few galaxies in the field of view to study . It really is a complete picture in the sense that this information complements a lot of existing data, not only from Hubble, but also from ground-based instruments like MUSE (the Multi Unit Spectroscopic Explorer) on the Very Large Telescope, where we have a spectroscopy at different wavelengths. for a number of these objects. MUSE is very good at finding galaxies that have Lyman-alpha emission, or light from ionized hydrogen in these galaxies, which are the type of galaxies that existed when reionization was complete. This new data is a missing piece that we didn’t have before to understand the full population of galaxies in this area.
Was there anything unexpected about this data that surprised you?
Michael Maseda: I don’t know if I was really surprised, but the pictures were even better than I expected. In these images you can actually see with the naked eye that it is ionized gas over a fairly wide area. I expected everything to be unresolved, but we have high enough resolution to actually see it. And I’m glad to see it because it could have been a lot harder to figure out what was going on.
Christina Williams: I think seeing how beautiful the footage looks and how high quality it ended up being was definitely a highlight. We calculated that we would be able to do things like that, but it was different seeing it and having the real data in practice.
Why did you choose to make the data immediately public?
Sandro Tacchella: Galaxies are very complex systems in which a wide range of different processes operate on different spatial and temporal scales, so there are many approaches that can be used to better understand the physics of galaxies. So making it accessible to many different groups will make it easier to find more information.
Christina Williams: Webb is still very new and people are still learning best practices for analyzing datasets. Thus, it is beneficial for everyone to have a few datasets available immediately to help people understand how best to use Webb data in the future and to better plan programs in future cycles based on a real experience with data.
Provided by the Webb Space Telescope
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