Color composite image of the data used in this work. In this picture images in three different filters have been combined to make a color image. The color channels use data from a NIRCam filter at approximate wavelengths of 3.6 (red), 2.0 (green), and 1.5 (blue) micrometers. The three filters used in this composite do not cover the same area, so the edges are only seen in blue and green. The image contain nearly 100000 galaxies in a region of the sky whose are is around 2% of the Moon, as shown in the bottom right corner of the image. Credit: ESA/Webb, NASA & CSA, Pablo Peréz-González.

Deep imaging surveys are the most efficient way to find very distant galaxies, by observing galaxies in filters of different wavelengths. Young galaxies contain stars that  emit most of their light from the ultraviolet to the visual and at wavelengths shorter than UV, the so called Lyman break, they emit little or no light. When galaxies are very far away, at high redshifts (z), the Lyman break is shifted to longer wavelengths and they become invisible in filters probing bluer light. For instance, when the universe was just 1.5 billion years old, galaxies become invisible or in the visual while still seen at longer wavelengths (these are called drop-out galaxies). The redder the filter where a galaxy drops out, the more distant it is likely to be.

Ultimately, a spectroscopic observation is required to confirm the redshift, but since these are more expensive in terms of observing time  and can only target a limited number of galaxies per observation, imaging surveys is the first step. Using this technique with the Hubble Space Telescope galaxies at redshifts up to approximately 10 could be found. With JWST, that probe wavelengths further into the infrared, many more very high redshift galaxy candidates have been found. Currently, the most distant spectroscopically confirmed galaxy is at a redshift of 14 (when the universe was just 300 million year old).

As a part of the MIDIS survey (led by professor Göran Östlin at Stockholm University), unprecedentedly deep imaging of the Hubble Ultra Deep Field was obtained at wavelengths larger than 5 micrometers. In this survey the Near IR Camera (NIRCam) at JWST was staring at an area of the sky which had partly already been covered by another deep survey (NGDEEP). The images were co-added to achieve an unprecedented depth (90 hours of observations in the filter with longest exposure time) which made it possible to find very high redshift galaxy candidates through the dropout technique.

I was scrutinizing the data with the hope to maybe find a few extreme redshift candidates a little bit further away than the most distant ones previously discovered, but to my surprise I found nine candidates that are all significantly more distant. JWST continues to surprise us, says lead author Pablo Pérez-González.

A smaller portion of the observed field with a zoom-in box on one of the candidates. The red color of the galaxy is due to the very high redshift, causing it to drop out from the bluer filters on NIRCam. The galaxy is not detected in these bluer filters and thus appears red in the color composite. Credit: ESA/Webb, NASA & CSA, Pablo Peréz-González.

After carefully investigating all possible candidates and error sources he ended up with a set of nine solid candidates, six at redshift 17 and three at redshift 25, corresponding to having emitted their light 200 and 100 million years after Big Bang, respectively. These results imply that there are more such galaxies, and that galaxy formation commenced earlier than theoretical models had anticipated.

The MIRI Deep Imaging Survey, and its parallel observations with NIRCam, were designed to push the frontiers of our understanding of galaxies in the early universe. Finding such distant galaxy candidates extends beyond our initial expectations but demonstrates the power of JWST in changing the astrophysics landscape, says Göran Östlin.

Learn more about this project

The results are published in the Astrophysical Journal.

Interactive image comparing the new JWST image to previous Hubble observations.

The MIDIS survey

Contacts

Pablo Pérez-González, Centro de Astrobiología, Spain, pgperez@cab.inta-csic.es 

Göran Östlin, Stockholm University, ostlin@astro.su.se, +46 8 553 785 13

Jens Melinder, Stockholm University, jens@astro.su.se, +46 70 6471856

Details on the JWST programme

The astronomers observed the Hubble Ultra Deep Field and parallels as part of the JWST Guaranteed Time Observation (GTO) Program 1283, “The MIRI HUDF Deep Imaging Survey” (Primary Investigators): Göran Östlin, Hans Ulrik Norgaard-Nielsen) and the GO5 Program 6511 “Galaxy mass buildup in the early universe - ultra deep imaging of the Hubble Ultra Deep Field to 10 microns” (Primary Investigator: Göran Östlin).

The MIDIS (MIRI Deep imaging Survey) collaboration consists of the following research institutions: Centro de Astrobiología, CSIC-INTA, Villanueva de la Cañada and Torrejón de Ardoz, Spain; Max Planck Institute for Astronomy, Heidelberg, Germany; Max Planck Institute for Extraterrestrial Physics, Garching, Germany; Physikalisches Institut, Universität zu Köln, Germany; Université Paris-Saclay, Orsay and Gif-sur-Yvette, France; Leiden Observatory, The Netherlands; KU Leuven, Belgium; Rijksuniversiteit Groningen, The Netherlands; University of Vienna, Austria; ETH Zürich, Switzerland; Université de Liege, Belgium; LESIA, Observatoire de Paris, Meudon, France; INAF, Napoli, Italy; Dublin Institute for Advanced Studies, Ireland; UK Astronomy Technology Centre, Edinburgh, UK; University of Leicester, UK; Radboud University, Nijmegen, The Netherlands; Space Research Institute, Graz, Austria; SRON, Groningen and Leiden, The Netherlands; Stockholm University Sweden; Cosmic Dawn Center (DAWN), DTU Space, Lyngby, Denmark; Onsala Space Observatory, Sweden; Amsterdam University, The Netherlands.

The James Webb Space Telescope (JWST) is the world's leading observatory for space research. JWST is an international programme led by NASA with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency). MIRI was built by a consortium involving research institutes and universities in 9 European countries and USA.