Category: Publications

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.

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)”

Deep imaging of the diffuse light that is emitted by stellar fine structures and outer halos around galaxies is often now used to probe their past mass assembly. Because the extended halos survive longer than the relatively fragile tidal features, they trace more ancient mergers. We use images that reach surface brightness limits as low as 28.5-29 mag arcsec^-2 (g-band) to obtain light and color profiles up to 5-10 effective radii of a sample of nearby early-type galaxies.

Continue reading “A deconvolution technique to correct deep images of galaxies from instrumental scattered light”

Globular clusters (GCs) are some of the most visible tracers of the merging and accretion histories of galaxy halos. Metal-poor GCs, in particular, are thought to arrive in massive galaxies largely through dry, minor merging events, but it is rare to see a direct connection between GCs and visible stellar streams. NGC 474 is a post-merger early-type galaxy with dramatic fine structures made of concentric shells and radial streams that have been more clearly revealed by deep imaging. We present a study of GCs in NGC 474 to better establish the relationship between merger-induced fine structure and the GC system.

Continue reading “Globular Clusters as Tracers of Fine Structure in the Dramatic Shell Galaxy NGC 474”

Diffuse Galactic light has been observed in the optical since the 1930s. We propose that, when observed in the optical with deep imaging surveys, it can be used as a tracer of the turbulent cascade in the diffuse interstellar medium (ISM), down to scales of about 1 arcsec. Here we present a power spectrum analysis of the dust column density of a diffuse cirrus at high Galactic latitude (l ~ 198 deg, b ~ 32 deg) as derived from the combination of a MegaCam g-band image, obtained as part of the MATLAS large programme at the CFHT, with Planck radiance and Wise 12 micron data.

Continue reading “Probing interstellar turbulence in cirrus with deep optical imaging: no sign of energy dissipation at 0.01 pc scale”

Deep imaging programs, such as MATLAS which has just been completed at the CFHT, allows us to study with their diffuse light the outer stellar populations around large number of galaxies. We have carried out a systematic census of their fine structures, i.e. the collisional debris from past mergers.

Continue reading “Using deep images and simulations to trace collisional debris around massive galaxies”

NGC 4203 is a nearby early-type galaxy surrounded by a very large, low-column-density H I disc. In this paper, we study the star formation efficiency in the gas disc of NGC 4203 by using the UV, deep optical imaging and infrared data.

Continue reading “Star formation in the outer regions of the early-type galaxy NGC 4203”

Various programs aimed at exploring the still largely unknown low surface brightness Universe with deep imaging optical surveys have recently started. They open a new window for studies of galaxy evolution, pushing the technique of galactic archeology outside the Local Group (LG).

Continue reading “Applying galactic archeology to massive galaxies using deep imaging surveys”