Galaxy And Mass Assembly (GAMA): galaxy close pairs, mergers and the future fate of stellar mass

A. S. G. Robotham*, S. P. Driver, L. J. M. Davies, A. M. Hopkins, I. K. Baldry, N. K. Agius, A. E. Bauer, J. Bland-Hawthorn, S. Brough, M. J. I. Brown, M. Cluver, R. De Propris, M. J. Drinkwater, B. W. Holwerda, L. S. Kelvin, M. A. Lara-Lopez, J. Liske, A. R. Lopez-Sanchez, J. Loveday, S. MahajanT. McNaught-Roberts, A. Moffett, P. Norberg, D. Obreschkow, M. S. Owers, S. J. Penny, K. Pimbblet, M. Prescott, E. N. Taylor, E. van Kampen, S. M. Wilkins

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

80 Citations (Scopus)


We use a highly complete subset of the Galaxy And Mass Assembly II (GAMA-II) redshift sample to fully describe the stellar mass dependence of close pairs and mergers between 10(8) and 10(12)M(circle dot). Using the analytic form of this fit we investigate the total stellar mass accreting on to more massive galaxies across all mass ratios. Depending on how conservatively we select our robust merging systems, the fraction of mass merging on to more massive companions is 2.0-5.6 per cent. Using the GAMA-II data we see no significant evidence for a change in the close pair fraction between redshift z = 0.05 and 0.2. However, we find a systematically higher fraction of galaxies in similar mass close pairs compared to published results over a similar redshift baseline. Using a compendium of data and the function gamma(M) = A(1 + z)(m) to predict the major close pair fraction, we find fitting parameters of A = 0.021 +/- 0.001 and m = 1.53 +/- 0.08, which represents a higher low-redshift normalization and shallower power-law slope than recent literature values. We find that the relative importance of in situ star formation versus galaxy merging is inversely correlated, with star formation dominating the addition of stellar material below M* and merger accretion events dominating beyond M*. We find mergers have a measurable impact on the whole extent of the galaxy stellar mass function (GSMF), manifest as a deepening of the 'dip' in the GSMF over the next similar to Gyr and an increase in M* by as much as 0.01-0.05 dex.

Original languageEnglish
Pages (from-to)3986-4008
Number of pages23
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Early online date18 Sept 2014
Publication statusPublished - 11 Nov 2014


  • galaxies: evolution
  • galaxies: fundamental parameters
  • galaxies: interactions
  • galaxies: kinematics and dynamics
  • galaxies: luminosity function, mass function
  • galaxies: stellar content
  • Digital sky survey
  • Supermassive black-holes
  • Luminous red galaxies
  • CNOC2 redshift survey
  • Early data release
  • VLT deep survey
  • Similat-to 1
  • Star-formation
  • Time-scales
  • Elliptic galaxies


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