Term Project: Analyzing Euclid Space Telescope Images

Project Overview

One of the biggest mysteries in astronomy is how galaxies form. and develop over time. The James Web Space Telescope (JWST; launched in late 2021) was designed in part to solve this mystery by peering back near the beginning of time, to the era when modern galaxies were just forming. As you may have read in the news, the results from JWST have provoked significant controversy, as they appeared to challenge our standard thinking about how galaxies form. More recent work has revised that assessment, bringing the JWST results more in line with existing theories (for example, see: https://science.nasa.gov/missions/webb/webb-finds-early-galaxies-werent-too-big-for-their-britches-after-all/ (https://science.nasa.gov/missions/webb/webb-finds-early-galaxies-werent-too-big-for-their-britches-after-all/) ). So, there are still many mysteries about galaxy formation, some of which can be explored by carefully scrutinizing images of galaxies across cosmic time. That's a big part of what you'll be doing in this project.

JWST is a very powerful telescope but, like all telescopes, it's optimized for a particular kind of science. JWST is designed to provide extremely detailed images of very small portions of the sky. This is useful if you want to study a small number of objects in unprecedented detail. But it's less useful if you need to study huge numbers of objects. To understand galaxies generally, we need to examine millions or billions of them. You can think of this a little like the difference between psychology and sociology: psychologists analyze the minds of individual humans, while sociologists look for patterns in the behavior. of many humans. If JWST is a galaxy psychologist, the European Space Agency's Euclid Space Telescope is a galaxy sociologist.

Launched in 2023, Euclid (https://www.esa.int/Science_Exploration/Space_Science/Euclid (https://www.esa.int/Science_Exploration/Space_Science/Euclid) ) was designed to map billions of galaxies across the universe. One of its goals is to build a map that will allow us to understand how dark energy has shaped the cosmos over time. To do this, Euclid is optimized in a very different way from JWST. JWST has a larger mirror that it uses to observe the universe at infrared wavelengths. Infrared wavelengths are very useful if you want to see light from the early ages of the cosmos. Euclid has a smaller mirror and it gathers visible and near-infrared light. Euclid's smaller mirror doesn't allow it to see each individual galaxy in as much detail as JWST, or to look as far back in time, but it can see vastly more galaxies over a long stretch of the history of the universe.

When we try to unravel the history of galaxies, we face a hard physical limit: galaxies evolve over billions of years, which is far longer than a human lifetime. Our photos of the cosmos show galaxies in "freeze-frame", at some random moment in their extraordinarily long lifespans. this means we can't actually watch one type of galaxy evolve and change into another. We can't see the stars in a galaxy flare to life for the first time, then dwindle as the galaxy runs out of gas to form. new stars. Here a biological analogy is helpful. A developmental botanist might take individual seeds and study them as they germinate, grow to seedlings, flower, and ultimately die. But a forest ecologist can't watch the entire lifecycle of a forest. Instead of following a single plant for a long period of time, she might hike through a forest, taking photos and measurements of everything she sees, later assembling it into a consistent story of what is going on in that forest. In this project, you're going to become galactic ecologists.

Each of you will be assigned a high-resolution snapshot of a segment of the sky recently taken by the Euclid space telescope. Your goal will be to analyze the photo to learn everything you can about galaxies, their formation, and their evolution.

Because this project relates to content that won't be covered until later in the course, we recommend that you don't finish it until closer to the end of the semester. However, you should look it over early in the semester so you have an idea what's involved, what you should be focusing on learning in class, and the overall time commitment.

Accessing Your Image

Every student is provided TWO unique images to work on. To earn grades, you must choose ONE AND ONLY ONE of your own personalized images. Make sure to state in your report which of your images you are choosing. It's totally up to you to decide which image to analyze. The images are generated randomly, so we provide two in case you find one of them too tricky to analyze. But in the end, you must only analyze ONE of them.

You will find your two images in this directory, labeled with your utorid:

AST201_winter2025_student_Euclid_images (https://utoronto.sharepoint.com/:f:/s/ArtSci-AST/adminsite/EhsXh0aLF0pHl3zBvzOBbasBSccmCO-xvQ-Yfl1SCBF-Bg?e=GbaMUP)

If you registered for this project late, your personalized image might not appear here. If that's the case, please contact us at the email address given in the syllabus (https://q.utoronto.ca/courses/377762/assignments/syllabus) .

Understanding Your Image

When interpreting your image, it's crucial you keep several factors in mind.

The objects in your image are probably spread out over billions of years of cosmic time.

Astronomical images capture whatever objects happen to lie along the line of sight, each potentially at a very different distance from the others. This means that they may also be at very different points in time. Two objects that appear side-by-side in an image might be separated by billions of years in time. That is, they might have very different "lookback times". This video does a great job of explaining this concept:

https://www.youtube.com/watch?v=yfWYXY85mBk (https://www.youtube.com/watch? v=yfWYXY85mBk)

(https://www.youtube.com/watch?v=yfWYXY85mBk)

Don't confuse brightness and distance

You can't necessarily assume that something is distant because it is faint. An object that appears faint in your image may be a very bright object seen from a very great distance, or it may actually be a very faint object seen from up close. That means you might see a little fuzzy patch in your image and be unsure whether it is a distant galaxy halfway across the universe or some little cloud of gas within our own Milky Way galaxy. This is a genuine ambiguity you will have to grapple with, and should factor into your interpretations.

Your image is made of visible and near-infrared light

Your image is a 1000 pixel by 1000 pixel PNG file. Each image is composed of both visible and near-infrared light. That means that the colors are NOT true to the colors the human eye would see. You will need to take this into account in your analysis. Here is how the Euclid team describe the color-coding of these images:

"The blue, green, red channels capture the Universe seen by Euclid around the wavelength 0.7, 1.1, and 1.7 micron respectively. This gives Euclid a distinctive colour palette: hot stars have a white-blue hue, excited hydrogen gas appears in the blue channel, and regions rich in dust and molecular gas have a clear red hue. Distant redshifted background galaxies appear very red. In the image, the stars have six prominent spikes due to how light interacts with the optical system of the telescope in the process of diffraction. Another signature of Euclid's special optics is the presence of a few, very faint and small round regions of a fuzzy blue colour. These are normal artefacts of complex optical systems, so-called ‘optical ghost’; easily identifiable during data analysis, they do not cause any problem for the science goals."

For reference, your eye would perceive light with a wavelength of 0.7 microns as red. Your eye cannot perceive light of 1.1 or 1.7 microns, as these are both infrared. That makes these "false color" images. The Euclid team have followed the general astronomical convention of color coding the shortest wavelength as blue, and longer wavelengths as red (as is the case for wavelengths in the visible part of the spectrum). Correctly interpreting what the colors mean will be crucial to your analysis.

Each image covers a patch of sky about 0.2 degrees on a side, which means the whole image is around 20% the size of the full Moon on the sky.

There are certain well-understood "artifacts" in your images

The design of a telescope affects the appearance of objects it photographs. You must be aware of this to correctly interpret what you are seeing. "Diffraction spikes" are a very common type of visual artifact that is entirely produced by the telescope itself. They typically appear around the brightest objects in the image and they look like this:

Those six bright spikes emanating from the star are caused by the structure of the telescope. You should not mistake them for celestial phenomena. Similarly, the fact that the star appears as a little circle instead of a single-pixel dot is also an effect of the telescope. Stars are "point sources" to Euclid, meaning that the telescope isn't actually capable of "resolving" the surface of the star. The round shape of the star in the image is caused by an intrinsic "blur" present in all astronomical images to differing degrees.

There are other known image artifacts in the Euclid data. You should do some reading about the telescope to inform. your interpretation of your images. Don't misinterpret data artifacts as real physical objects.

What to Do With Your Image

Your main task is to very carefully scrutinize your image. You should be looking for evidence about the structure and evolution of galaxies in the universe, while carefully screening out unrelated objects and image artifacts. You should try to identify at least one of each of the following types of objects, and always include the BEST candidates for each category:

1. A star that you believe is in the nearby universe (e.g. the Milky Way)

2. A spiral galaxy

3. An elliptical galaxy

4. A galaxy whose type is ambiguous.

5. Two galaxies of the same type that you believe are being seen at very different points in time (that is, separated by billions of years in time)

6. Two or more galaxies that appear to be physically interacting with one another (e.g. in the process of colliding or merging).

7. Gravitationally lensed galaxies

8. At least one anomalous celestial object you can’t identify, with an evidence-based hypothesis as to what it might be. This should NOT be an image defect (including any of the ones described in the previous section).

9. An estimate (or count) of the total number of galaxies

For each of the above (except the last), you should include the following:

1. One or more images. If you want to present more than one image from the same category in an efficient way please consider making a small mosaic, like this one:

2. A brief description of the object and your rationale for selecting it as an example of the category.

3. A clear and definitive assessment of your confidence that the object is what you have claimed it is. For example, you might say "I'm very confident that this is a spiral galaxy because the spiral pattern of its arms is unambiguous" or "I'm moderately confident that this is an elliptical galaxy, given its shape and colour, but it could also be ______ or ______."

It's possible you might not find objects in one or more of these categories in your image. If you believe they are entirely absent, you should say so clearly. If you believe that they might be present but you can't be sure, include them as described above, but with a low confidence assessment.

For full marks, your answers to the above should be informed by additional research concerning the telescope itself, the interpretation of the images, and the general topic of galaxy types and evolution.

What to Hand In

Hand in a report formatted as a single PDF file, no more than 5 pages in length. Your report should have these components:

1. A very brief introduction (one paragraph or less).

2. Answers to the questions in the previous section (identification of different types of objects, plus an estimate of the total number of galaxies in the image).

3. A bibliography listing all of the sources you used for your background research. You MAY cite the course textbook, but you MAY NOT cite the lecture notes from this or any other course. All of your sources should be current, written by an identifiable expert in the subject area, and preferably either edited or peer-reviewed by someone other than the author. You must include inline citations for EVERY fact, concept, or image derived from external sources, as well as a bibliography of your sources. Your bibliography can be in any common format (APA, MLA, Chicago, etc.), but all online sources MUST include a clickable link to the source, even if that is not required by your bibliography style. guide.

All images should have brief descriptive captions, including a figure number (Fig. 1, Fig. 2, etc.). If you choose to use images from an external source, they must be clearly marked as such. Where there is any possibility of ambiguity, you are encouraged to annotate your images to draw attention to specific details. For example, if you were to show the following image and refer in your description to "the spiral galaxy on the left side of the image", we would consider this ambiguous and you would potentially lose marks:

A better strategy would be to annotate the image as shown below and then refer to "the galaxy circled in red".