Shape asymmetry: a morphological indicator for automatic detection of galaxies in the post-coalescence merger stages

Milena Pawlik, Vivienne Wild, C. J. Walcher, P. H. Johansson, Carolin Villforth, Kate Elizabeth Rowlands, Jairo Mendez Abreu, Tim Hewlett

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We present a new morphological indicator designed for automated recognition of galaxies with faint asymmetric tidal features suggestive of an ongoing or past merger. We use the new indicator, together with pre-existing diagnostics of galaxy structure to study the role of galaxy mergers in inducing (post-) starburst spectral signatures in local galaxies, and investigate whether (post-) starburst galaxies play a role in the build-up of the ‘red sequence’. Our morphological and structural analysis of an evolutionary sample of 335 (post-) starburst galaxies in the Sloan Digital Sky Survey DR7 with starburst ages 0 < tSB < 0.6 Gyr, shows that 45 per cent of galaxies with young starbursts (tSB < 0.1 Gyr) show signatures of an ongoing or past merger. This fraction declines with starburst age, and we find a good agreement between automated and visual classifications. The majority of the oldest (post-) starburst galaxies in our sample (tSB ∼ 0.6 Gyr) have structural properties characteristic of early-type discs and are not as highly concentrated as the fully quenched galaxies commonly found on the ‘red sequence’ in the present day Universe. This suggests that, if (post-) starburst galaxies are a transition phase between active star-formation and quiescence, they do not attain the structure of presently quenched galaxies within the first 0.6 Gyr after the starburst.
Original languageEnglish
Pages (from-to)3032-3052
Number of pages21
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
Early online date12 Jan 2016
Publication statusPublished - 1 Mar 2016


  • Galaxies: evolution
  • Galaxies: interactions
  • Galaxies: starburst
  • Galaxies: structure


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