Release notes of ERO data for the Euclid Consortium

    Euclid Early Release Observations (EROs)

    The ERO programme is an initiative of the Euclid Science Team / ESA to collect 1 day of observations to showcase the Euclid mission and its capabilities before the start of the nominal survey. These observations are not part of the nominal survey, addressing legacy science, and the data are meant to be released to the general community as soon as possible after the programme is completed.

    A call for proposals was issued for Euclid observations with both communication/outreach and scientific merit, with priority to the communication/outreach merit. The call was addressed to the Euclid Science Collaboration consisting of the Euclid Consortium and the Independent Legacy Scientists. A total of 6 proposals were selected covering observations including a variety of objects at different distances covering different scales in the Universe. The teams supporting these proposals will carry out the first analyses of the data based on the science proposed.

    Selected ERO Projects

    The projects and best feasible targets were selected by the ERO programme committee:

    • A first glance at free-floating baby Jupiters with Euclid - Lead scientist: E. Martín (Instituto de Astrofísica de Canarias)
    • Euclid view of Milky Way globular clusters - Lead scientist: D. Massari (INAF-OAS Bologna)
    • A Euclid showcase of nearby galaxies - Lead Scientist: L. Hunt (INAF-AO Arcetri, Firenze)
    • A galaxy cluster seen with Euclid - Lead scientist: A. Lancon (Strasbourg Observatory)
    • A cluster of galaxies - Lead scientist: J.-C. Cuillandre (CEA, AIM, Université Paris-Saclay)
    • A Glimpse Into Euclid’s Universe Through a Giant Magnifying Lens - Lead scientist: H. Atek (Institut d’Astrophysique de Paris)

    Data Collection

    The ERO proposals and initial observations were selected before Euclid launch assuming the pre-launch schedule for the commissioning and the start of the nominal survey. The actual schedule had to account for the update of the FGS guiding software update, causing the start of the performance verification phase several weeks later than planned.

    Before the re-start of the Performance Verification Phase, the operations teams managed to schedule a number of observations because selected targets would move out of the visibility window of Euclid. A subset of these observations could be executed successfully without guiding errors, and are used as ERO showcase. However, the majority of the successful ERO observations have been collected during the Performance Verification Phase.

    Data Products and usage

    The imaging data have been processed using processing pipelines developed by J.-C. Cuillandre (CEA, AIM, Université Paris-Saclay) based on the Euclid Level 1 data. The detailed description of the ERO processing will be published as a separate paper which will be part of the set of the ERO papers to be released in January 2024.

    The ERO pipeline is designed from the ground up for diffuse emission science (low surface brightness Universe, LSB) and standard point/compact source science. It is a direct legacy from proven imaging pipelines developed for CCD and FPA mosaics at the CFHT over the past two decades with several steps relying on E. Bertin's AstrOmatic toolbox. It is fully independent from the processing functions developed by the Euclid Science Ground Segment, which are optimised for the generation of data products supporting the core cosmology.

    If you simply wish to explore visually the images, the LSB stacks are best. However, these LSB stacks are suitable only for diffuse emission precision science (surface brightness measurements): compact source photometry from these images will be off compared to the flattened stacks which must be adopted instead.

    Internal astrometry precision is on average (across these 5 fields) 7mas for VIS and 24 mas for NISP (less than 1/10th of a pixel for both). Astrometry was derived through the combo Astrometry.net + SCAMP.

    The VIS images being affected by cosmic rays, all images are healed by DeepCR prior to stacking (in-painting trained on HST images perfectly preserving photometry). DeepCR for NISP is currently under investigation.

    The zero point for all stacks is arbitrarily set to 30.00 through the transfer of a zero point derived from raw data during the commissioning phase by the Euclid mission calibration scientist. The ERO science teams are currently working at refining the photometric calibration. For now the absolute photometric precision is assumed to be within 10% while the internal precision (photometric flatness across the FOV) is within 5%.

    There are various artifacts/blemishes remaining in the stacks, from the dichroic ghosts on VIS to traces of persistence on NISP: due to the low number of input frames from a single ROS (except Perseus which is four ROS on a single pointing), some parts of the sky are exposed only once on NISP and remain affected by CR hits.

    The FITS files made available here are only accessible to all active Euclid Consortium members who are interested in assessing and possibly exploring the first Euclid data. Please take the following instructions into account:

    • Do not share the data with persons who are not part of the Euclid Collaboration until the public data release of the EROs in 2024
    • In case you wish to carry out research with these data, first consult the relevant EC Portal project page where all on-going projects are listed. If you are interested in joining the ERO team to contribute to an existing project or develop your own program by accessing its internal advanced data products, you should contact the proposal lead scientist. Alternatively, if joining the ERO team is not the preferred option after contacting the proposal lead scientist, you can provide a description of your project in the EC project portal.
    • Do not share images (JPEGs, PNGs TIFF, etc) before the embargo date imposed by ESA communications, on social media, mass media, or other media (e.g. slack).

    Data released on 2 Nov 2023

    These data are associated with the communications products released during the media briefing on 7 Nov 2023. The data sets are processed stacks of the images taken in the VIS, Y, J, and H Euclid bands.

    Instruction on access to the data files:

    • Register for access by opening a ticket at the ESA Euclid Helpdesk: https://support.cosmos.esa.int/euclid/
      • Please select ‘General’ as the department and ‘Euclid ERO access’ with your COSMOS username in the subject.
      • If you do not have a COSMOS account yet or do not have the account details, please open a ticket in the ‘Accounts’ department.
    • Access the data : https://euclid.esac.esa.int/dr/ero/ You will need to log in with your COSMOS username and password.

    We anticipate a high level of interest in this release. In order keep help everybody please download only the data which you are immediately interested in; the files will be available through this website for the indefinite future. If you are working at an institute with other Euclideans, please download the data files and distribute locally and let others know. Thanks!

    Please use the #early-release-observations channel on the Euclid Consortium Slack workspace for questions, prompt updates will be posted there.