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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.

Continue reading “MATLAS Dwarfs I: Hunting for Dwarf Galaxies and Ultra Diffuse Galaxies in Low Density Environments”

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.

Continue reading “The molecular gas content of shell galaxies (associated paper)”

Stephan’s Quintet, a compact group of galaxies, is often used as a laboratory to study a number of phenomena, including physical processes in the interstellar medium, star formation, galaxy evolution, and the formation of fossil groups. As such, it has been subject to intensive multiwavelength observation campaigns. Yet, models lack constrains to pin down the role of each galaxy in the assembly of the group. We revisit here this system with multiband deep optical images obtained with MegaCam on the Canada-France-Hawaii Telescope (CFHT), focusing on the detection of low surface brightness (LSB) structures.

Continue reading “Revisiting Stephan’s Quintet with deep optical images (associated paper)”