Galaxy And Mass Assembly (GAMA): refining the local galaxy merger rate using morphological information

Abstract

We use the Galaxy And Mass Assembly (GAMA) survey to measure the local Universe mass dependent merger fraction and merger rate using galaxy pairs and the CAS structural method, which identifies highly asymmetric merger candidate galaxies. Our goals are to determine which types of mergers produce highly asymmetrical galaxies, and to provide a new measurement of the local galaxy major merger rate. We examine galaxy pairs at stellar mass limits down to M * = 10 8 M ⊙ with mass ratios of <100:1 and line of sight velocity differences of ∆V < 500 km s −1 . We find a significant increase in mean asymmetries for projected separations less than the sum of the individual galaxy's Petrosian 90 radii. For systems in major merger pairs with mass ratios of <4:1 both galaxies in the pair show a strong increase in asymmetry, while in minor merger systems (with mass ratios of >4:1) the lower mass companion becomes highly asymmetric, while the larger galaxy is much less affected. The fraction of highly asymmetric paired galaxies which have a major merger companion is highest for the most massive galaxies and drops progressively with decreasing mass. We calculate that the mass dependent major merger fraction is fairly constant at ∼ 1.3 − 2% between 10 9.5 < M * < 10 11.5 M ⊙ , and increases to ∼ 4% at lower masses. When the observability time scales are taken into consideration, the major merger rate is found to approximately triple over the mass range we consider. The total co-moving volume major merger rate over the range 10 8.0 < M * < 10 11.5 M ⊙ is (1.2 ± 0.5) × 10 −3 h 3 70 Mpc −3 Gyr −1 . Key words: galaxies: general -galaxies: evolution -galaxies: interactions -galaxies: statistics ⋆ E-mail: kcasteels@gmail.com (KRVC) 2 K. R. V. Casteels et al.

The Stripe 82 Massive Galaxy Project. III. A Lack of Growth among Massive Galaxies

“…The role of such mergers in driving high-mass galaxy growth at z 2 has been the subject of recent observational work (e.g., Bundy et al 2009;Lotz et al 2011;Casteels et al 2014;Mundy et al 2017) and the basis of theoretical explanations for how massive compact spheroidals at z ≈ 2 grow significantly in size by the present day (e.g., Hopkins et al 2010;Nipoti et al 2012;Hilz et al 2013;Welker et al 2017). Comparisons of the predicted growth in diffuse outer components required to drive increasing size estimates appear to be consistent with observed (minor) merger rates, at least for z 1 (Newman et al 2012;López-Sanjuan et al 2012;Ownsworth et al 2014).…”

Galaxy And Mass Assembly (GAMA): the effect of close interactions on star formation in galaxies

“…Such merger events are ubiquitous throughout the Universe, and as such probing the details of the merger process is key to our understanding of galaxy formation and evolution (e.g. Casteels et al 2014). For example, SF initiated by interactions could well be a key factor in transforming blue star-forming discs into red, passively evolving quiescent spheroids.…”

Pixel Color–Magnitude Diagram Analysis of the Brightest Cluster Galaxies in Dynamically Young and Old Clusters Abell 1139 and Abell 2589

“…It is probable that these galaxies will merge into the BCG in the future, since they already show evidence of ongoing interactions with the BCG. If the massto-light ratio is not so different between the BCG and the non-BCGs, the merging with the two close galaxies will be major mergers, which are often defined as mergers with mass ratio smaller than 4:1 (e.g., Casteels et al 2014). Then, the pCMD of the A1139-BCG will suffer significant changes because the stellar orbits will be largely mixed and redistributed (e.g., Di Mateo et al 2009).…”