Galaxy Zoo Cosmic Dawn

**Galaxy Zoo Cosmic Dawn** uses tens of thousands of new galaxy images taken by the Hyper Suprime-Cam (HSC) on board the 8.2m Subaru telescope on the summit of Mauna Kea in Hawaii, as part of the Hawaii Two-0 (H20) survey, a key component to the more ambitious Cosmic Dawn survey. This effort from Galaxy Zoo will therefore also help prepare for the upcoming launch of the Euclid space telescope by the European Space Agency (ESA) in 2023, with the classifications volunteers make now helping to guide what Euclid will observe in more detail with its even higher resolution imaging in visible light and the infrared. This alliteration's goal can help the team understand the period of intense star formation that took place in the early Universe, and tag bright red galaxies. These are rare objects that is very important in the alliteration especially for such distant galaxies!

## Classification System

Galazy Zoo Cosmic Dawn's questions has been modified so that people's classifications can help refine the software used by the H20 team, and perhaps that of future Galaxy Zoo incarnations as well. For example, the “Star or Artifact” question now includes a “Bad Image Zoom” option, while selecting “Non-star Artifact” will allow you to classify the type of any image artifact you come across, such as satellite trails. In the future, Galaxy Zoo will also be running a simplified decision tree of questions for some of the fainter distant galaxies, as their lower resolution prevents many features from being identified. The workflow asks questions to look out for any galaxies containing bright clumps! We’ve added a question about these, as they can help us understand the period of intense star formation that took place in the early Universe. Finally, the project is also asking volunteers to tag any extremely red objects, or those with a lens or arc features, in the Talk board, using the “Done & Talk” option. These are rare objects that we don’t want to miss, especially for such distant galaxies!

## #bright-red Galaxies

For Galaxy Zoo: Cosmic Dawn, the team is collecting extremely red objects that can be tagged with #bright-red when the "Done And Talk" button was clicked. The H20 team are eager to discover these very distant galaxies. While many red objects can be found from classifying based on their colour, the crowded fields seen in many of these deep H20 images can make this challenging to automate. Red galaxies can even be entirely misclassified by automated algorithms if they are overlapping or otherwise too near other objects. By tagging these extremely red galaxies, the volunteers will be aiding in both their discovery and helping improve the H20 team's automated algorithms.

### Updates in tagging #bright-red

Based on these tagged images, The H20 team asks the team to refining the search and have updated the Field Guide entry “How red is #bright-red?” with new examples of the sorts of objects we would like tagging. The H2O team notes that you should now only focus on the central object in the image. There is also the #dim-red tag you can use for extremely red but faint objects, and a couple of extra things that more advanced users can have a go at. The reason for the update is due to duplications, sunce there are over 10,000 subjects.

## Known issues in Cosmic Dawn

Due to the high number of subjects, foreground stars are the same appearance as galaxies because they have no diffraction spikes which many volunteers misclassify as galaxies. Because of this, an update was added to consider stars without diffraction spikes. The same thing also applies to #bright-red galaxies.

Also due to the high number of visible objects in the H2O survey, galaxies are zoomed out too much that are unclassifiable. The imaging collection algorithm appears as one large object. This is the main reason for the addition of the Bad Zoom.

The result is less galaxies and more stars/artifacts. with 60% are galaxies while the remaining 40% are not galaxies (eg. stars, artifacts, or bad zooms)