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Paper: The Dominant Role of Mergers in the Size Evolution of Massive Galaxies since z1
Volume: 477, Galaxy Mergers in an Evolving Universe
Page: 159
Authors: López-Sanjuan, C.; Le Fèvre, O.; Ilbert, O.; Tasca, L.; COSMOS Collaboration; zCOSMOS Collaboration
Abstract: We estimate the merger rate, both major (stellar mass ratio μ = M★,2/M★,1 ≥ 1/4) and minor (1/10 ≤ μ < 1/4), of massive (M ≥ 1011 M) early-type galaxies (ETGs) in the COSMOS field by close pairs statistics. The merger rate of massive ETGs evolves as a power-law (1+z)n, showing the minor merger little evolution with redshift, nmm ∼ 0, in contrast with the increase of major mergers, nMM = 1.8. Our results shows that massive ETGs have undergone 0.89 mergers (0.43 major and 0.46 minor) since z ∼ 1, leading to a mass growth of ∼ 30%. In addition, μ ≥ 1/10 mergers can explain ∼ 55% of the observed size evolution of these galaxies since z ∼ 1. Another ∼ 20% is due to the progenitor bias (younger galaxies are more extended) and we estimate that very minor mergers (μ < 1/10) could contribute with an extra ∼ 20%. The remaining ∼ 5% should come from other processes (e.g., adiabatic expansion or observational effects). These results suggest that mergers are the main contributor to the size evolution of massive ETGs, accounting for ∼ 55%–75% of that evolution in the last 8 Gyr. Nearly half of this merging evolution is related with minor (μ < 1/4) events.
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