Surveys



Jafar has proved its usefulness in several projects listed below, using images from various instruments, from ground-based to space-based telescopes.



Canada-France-Hawaii Telescope (CFHT)


The Canada-France-Hawaii Telescope is a 3.6-m telescope on top of the Mauna Kea in Hawaii, at 4,200m above sea level. It is equipped of several instruments, including the MegaCam camera which is a wide-field optical imager. It has five broad-band filters, several narrow-band filters, a fied-of-view of one degree and a pixel size of 0.187 arcsecond.

Here, we describe the work conducted using four surveys conducted as CFHT Large Programs, with the aim of disclosing the faint, Low Surface Brightness Universe. A dedicated pipeline, Elixir-LSB, enabled to obtain deep images that preserve the LSB signal.

  • CFIS/UNIONS: the Canada-France Imaging Survey (CFIS) covers more than 5,000 square degrees in the Northern hemisphere in LSB-r band.
  • MATLAS: the Mass Assembly of early-type GaLAxies with their fine Structures (MATLAS) survey targeted nearby massive early-type galaxies between 2013 and 2015.
  • NGVS: The Next Generation Virgo cluster Survey (NGVS) is a CFHT Large Program than ran from 2008 to 2012 that imaged 104 square degrees of the Virgo galaxy clusters.
  • VESTIGE: the Virgo Environmental Survey Tracing Ionized Gas Emission (VESTIGE) Large Program surveyed the same footprint as NGVS of the Virgo cluster.

Related publications:

  • Sola+2022,2024 (submitted): These Papers introduce Jafar and its characteristics. The work aims at characterising faint, Low Surface Brightness tidal features in deep images from the CFHT. Tidal features are stars expelled from their host galaxies due to gravitational interactions during galaxy mergers. They are crucial to study as they hold the imprints of the merger history, which enables scientists to learn about the formation and evolution of galaxies.
    Jafar was utilised to annotate tidal features in images of 475 nearby massive galaxies. Their geometry (area, length), and luminosity were derived from the database. Cutout images and masks of these structures were created. This unique database of annotated LSB features, publicly released, can also be used for Deep Learning applications. The relationships between the properties of tidal features and the host galaxy’s mass and environment were studied.
  • Richards+2023: This Paper relies on the annotated LSB structures from Sola+2022 to train a Deep Learning algorithm to automatically detect and segment tidal features and sources of contamination (Galactic cirrus). Segmentation consists of finding the contours of the objects and is complicated for very faint objects.

Euclid


Euclid is an ESA mission designed to explore the composition and evolution of the dark Universe. Launched in July 2023, this space telecope offers an unprecedented combination of wide field-of-view, spatial resolution, wide coverage on the sky and stable PSF. This makes Euclid particularly well-suited for the study of the faint LSB Unvierse.

As a prelude to the mission, a first set of images of objects in the nearby Universe have been acquired as part of the Early Release Observations (ERO).

Related publications:

  • Marleau+2024 : This work explores the properties and characteristics of the population of dwarf galaxies in the Euclid ERO image of the Perseus cluster,. These small galaxies are crucial to study as their properties (number, morphology, luminosity, substructures) enable scientists to put constraints on the cosmology. They also enable to probe galaxy formation at low masses than galaxies such as our Milky Way.
    To identify the dwarf galaxies in the ERO image, seven expert users have used Jafar to label them and their substructures (nuclei). Once they agreed on a list of potential candidates, Jafar was used to validate the dwarfs and their properties (morphology, number of substructures). This led to a final catalogue of 1100 dwarf galaxy candidates, for which the properties have been computed.