Author: matlas

Several detailed observations, such as those carried out at the Canada-France-Hawaii Telescope (CFHT), have revealed prominent Low Surface Brightness (LSB) fine structures that lead to a change in the apparent morphology of galaxies. Previous photometry surveys have developed observational techniques which make use of the diffuse light detected in the external regions of galaxies. In these studies, the outer perturbations have been identified and classified. These include tidal tails, stellar streams, and shells. These structures serve as tracers for interacting events and merging events and retain some memory of the mass assembly of galaxies. Cosmological numerical simulations are required to estimate their visibility timescale, among other properties, in order to reconstruct the merger history of galaxies. In the present work, we analyze a hydrodynamical cosmological simulation to build up a comprehensive interpretation of the properties of fine structures.

The MATLAS project explores the surroundings of a complete sample of nearby massive early-type galaxies with multi-colour deep optical images obtained at the Canada- France Hawaii Telescope. The observing and data reduction techniques ensured the detection of extended low-surface-brightness (LSB) structures, while the high image quality allowed us to identify associated compact objects such as star clusters. A number of scientific topics are addressed with this data-set that are briefly presented in this review: the study of foreground Galactic cirrus at high spatial resolution, telling us about the ISM structure; the characterisation of collisional debris around the galaxies (streams, tails, shells, stellar halos), giving hints on their past merger history; the distribution of dwarf galaxy satellites, including the ultra-diffuse ones, together with their globular cluster population, which are additional tracers of the formation and mass assembly of galaxies.

Published in IAU S355, The real of low surface brightness universe, La Laguna, 2019

The properties of low surface brightness dwarf galaxies found in low-density environments are poorly constrained observationally. This problem is two-fold, as many studies (1) focus on dwarfs in the Local Group or cluster environments, or (2) lack either the depth or coverage to detect a large sample of dwarf galaxies. These issues can be overcome using the Mass Assembly of early Type gaLAxies with their fine Structures (MATLAS) large observing program, which has imaged ∼142 deg2 of the sky around nearby [primarily] isolated early type galaxies (ETGs) down to surface brightnesses of ∼ 28.5 in the g-band using MegaCam on the Canada France Hawaii Telescope. This is the first of a series of papers in which we intend to fully characterize the properties of the 2210 dwarf candidates we have identified in the MATLAS imaging.

Shells are fine stellar structures identified by their arc-like shapes present around a galaxy and currently thought to be vestiges of galaxy interactions and/or mergers. The study of their number, geometry, stellar populations and gas content can help to derive the interaction/merger history of a galaxy. Numerical simulations have proposed a mechanism of shell formation through phase wrapping during a radial minor merger. Alternatively, there could be barely a space wrapping, when particles have not made any radial oscillation yet, but are bound by their radial expansion, or produce an edge-brightened feature. These can be distinguished, because they are expected to keep a high radial velocity. While shells are first a stellar phenomenon, HI and CO observations have revealed neutral gas associated with shells. Some of the gas, the most diffuse and dissipative, is expected to be driven quickly to the center if it is travelling on nearly radial orbits. Molecular gas, distributed in dense clumps, is less dissipative, and may be associated to shells, and determine their velocity, too difficult to obtain from stars.