The SAMI Galaxy Survey: the intrinsic shape of kinematically selected galaxies

C. Foster*, J. van de Sande, F. D'Eugenio, L. Cortese, R. M. McDermid, J. Bland-Hawthorn, S. Brough, J. Bryant, S. M. Croom, M. Goodwin, I. S. Konstantopoulos, J. Lawrence, A. R. Lopez-Sanchez, A. M. Medling, M. S. Owers, S. N. Richards, N. Scott, D. S. Taranu, C. Tonini, T. Zafar

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    37 Citations (Scopus)


    Using the stellar kinematic maps and ancillary imaging data from the Sydney AAO Multi Integral field (SAMI) Galaxy Survey, the intrinsic shape of kinematically selected samples of galaxies is inferred. We implement an efficient and optimized algorithm to fit the intrinsic shape of galaxies using an established method to simultaneously invert the distributions of apparent ellipticities and kinematic misalignments. The algorithm output compares favourably with previous studies of the intrinsic shape of galaxies based on imaging alone and our re-analysis of the ATLAS3D data. Our results indicate that most galaxies are oblate axisymmetric. We show empirically that the intrinsic shape of galaxies varies as a function of their rotational support as measured by the 'spin' parameter proxy λRe. In particular, low-spin systems have a higher occurrence of triaxiality, while high-spin systems are more intrinsically flattened and axisymmetric. The intrinsic shape of galaxies is linked to their formation and merger histories. Galaxies with high-spin values have intrinsic shapes consistent with dissipational minor mergers, while the intrinsic shape of low-spin systems is consistent with dissipationless multimerger assembly histories. This range in assembly histories inferred from intrinsic shapes is broadly consistent with expectations from cosmological simulations.

    Original languageEnglish
    Pages (from-to)966-978
    Number of pages13
    JournalMonthly Notices of the Royal Astronomical Society
    Issue number1
    Publication statusPublished - 21 Nov 2017


    • galaxies: fundamental parameters
    • galaxies: kinematics and dynamics


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