Revisiting Stephan's Quintet with deep optical images

TL;DR

This study uses deep optical imaging to uncover new low surface brightness features in Stephan's Quintet, revealing a diffuse halo and filaments that suggest an earlier formation and complex interactions within the galaxy group.

Contribution

It provides new deep optical observations revealing previously undetected low surface brightness structures and a diffuse halo, offering fresh insights into the group's formation history.

Findings

Detection of a diffuse, reddish halo around NGC 7317

Identification of new low surface brightness filaments

Evidence of Galactic cirrus contamination in the observed structures

Abstract

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 multi-wavelength 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 multi-band deep optical images obtained with MegaCam on the Canada-France-Hawaii Telescope (CFHT), focusing on the detection of low surface brightness (LSB) structures. They reveal a number of extended LSB features, some new, and some already visible in published images but not discussed before. An extended diffuse, reddish, lopsided, halo is detected towards the early-type galaxy NGC 7317, the role of which had so far been ignored in models. The presence of this halo made of old stars may indicate that the group formed earlier than previously thought. Finally, a number of additional diffuse filaments are visible, some close to the foreground galaxy NGC 7331 located in the same field. Their structure and association with mid--IR emission suggest contamination by emission from Galactic cirrus.