An international team of scientists has published the largest near-infrared image the Hubble telescope has ever captured. The image shows many very old galaxies that could be interesting candidates for the James Webb telescope.
Full-image galaxies up to 10 billion years old
The image is the result of the so-called 3D-DASH project. The Wide Field Camera 3 and the Advanced Camera for Surveys of the Hubble Space Telescope were used to achieve a complete near-infrared study of the entire Cosmos field. Cosmos here stands for Cosmological Evolution Survey and that is the name of the largest Hubble mosaic in the sky. It is one of the richest data fields for studying objects from outside the Milky Way. The 3D-DASH project built on these earlier Cosmos observations.
Because Hubble has a small field of view, many observations and images are required to be merged in order to study a larger area. The end result is an area of 1.35 square degrees in the sky, or an area slightly larger than six combined full moons in the sky as viewed from Earth.
It would normally have taken Hubble 2,000 hours to produce an image the size of the current end result, but the research team used a new technique called Drift and Shift, or Dash. This method creates an image that is eight times larger than the normal field of view (0.04 x 0.04 degrees) of the Wide Field Camera 3. It is achieved by taking multiple images and merging them into a large mosaic , more or less like a smartphone camera does when shooting a panorama. This Dash technique also makes the images faster: eight images per orbit, instead of one image. This meant that in 250 hours what would normally have taken 2000 hours was achieved. In total, 1256 individual images were used to create the complete mosaic.
The researchers emphasize that until now, such large mosaic images have only been possible from the ground, leading to poor resolution and limitations on what can be observed. According to researcher Lamiya Mowla, it was “extremely difficult” to study the most massive galaxies, formed by the merger of two galaxies, with existing images, partly because they are very rare. That was one of the motivations to start this big project.
The University of Toronto, among others, has collected a selection of observed galaxies and merged them into the above image. That’s not the full sighting of the area. This sighting can be viewed on a special page which contains the full mosaic and users can, among other things, zoom in and out.
This record of the 3D-DASH project will remain for some time to come, as the James Webb Space Telescope is primarily designed for more sensitive, closer shots. This new space telescope will therefore mainly lead to more detailed images of small areas. It is likely that a larger image in the near-infrared part of the spectrum will not be made until the next decade, for example by NASA’s Nancy Grace Roman Space Telescope and ESAs Euclid† These telescopes have larger fields of view of 0.8 x 0.4 degrees and 0.79 x 1.16 degrees respectively. The European telescope should go up in 2023 and the American one in 2027.
A slice of heaven as photographed by 3D-DASH. It shows the brightest and rarest objects in the universe, such as monster galaxies. The full mosaic is a lot bigger.