2019/11/05 by Len Hartsuiker, Sylvia Ploeckinger · 11 citations
Physics and Astronomy · #Astronomy #Astronomy and Astrophysical Research #Astrophysics #Astrophysics and Star Formation Studies #Coalescence (physics) #Galaxies: Formation, Evolution, Phenomena #Galaxy #Galaxy formation and evolution #Galaxy group #Merge (version control) #Physics #astro-ph.CO #astro-ph.GA
paper · pdf · doi:10.1093/mnrasl/slz171
published in Monthly Notices of the Royal Astronomical Society Letters 491(1), L66-L71 (Oxford University Press) · accepted for publication in MNRAS letters
arxiv created 2019/11/05 · openalex publication_date 2019/11/14 · arxiv updated 2020/01/08 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
ABSTRACT Observations of compact groups of galaxies (CGs) indicate that their abundance has not significantly changed since z = 0.2. This balance between the time-scales for formation and destruction of CGs is challenging if the typical time-scale for CG members to merge into one massive galaxy is as short as historically assumed (<0.1 Hubble times). Following the evolution of CGs over time in a cosmological simulation (EAGLE), we quantify the contributions of individual processes that in the end explain the observed abundance of CGs. We find that despite the usually applied maximum line-of-sight velocity difference of 1000 km s–1 within the group members, the majority of CGs (≈60 per cent) are elongated along the line of sight by at least a factor of 2. These CGs are mostly transient as they are only compact in projection. In more spherical systems ≈80 per cent of galaxies at z > 0.4 merge into one massive galaxy before the simulation end (z = 0) and we find that the typical time-scale for this process is 2–3 Gyr. We conclude that the combination of large fractions of interlopers and the longer median group coalescence time-scale of CGs alleviates the need for a fast formation process to explain the observed abundance of CGs for z < 0.2.