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A relation between the characteristic stellar ages of galaxies and their intrinsic shapes

Nature Astronomy volume 2, pages 483–488 (2018)Cite this article

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Abstract

Stellar population and stellar kinematic studies provide unique but complementary insights into how galaxies build-up their stellar mass and angular momentum1,2,3. A galaxy’s mean stellar age reveals when stars were formed, but provides little constraint on how the galaxy’s mass was assembled. Resolved stellar dynamics4 trace the change in angular momentum due to mergers, but major mergers tend to obscure the effect of earlier interactions5. With the rise of large multi-object integral field spectroscopic surveys, such as SAMI6 and MaNGA7, and single-object integral field spectroscopic surveys (for example, ATLAS3D (ref. 8), CALIFA9, MASSIVE10), it is now feasible to connect a galaxy′s star formation and merger history on the same resolved physical scales, over a large range in galaxy mass, morphology and environment4,11,12. Using the SAMI Galaxy Survey, here we present a combined study of spatially resolved stellar kinematics and global stellar populations. We find a strong correlation of stellar population age with location in the (V/σ, \({\boldsymbol{\epsilon}}_{{\boldsymbol{e}}}\)) diagram that links the ratio of ordered rotation to random motions in a galaxy to its observed ellipticity. For the large majority of galaxies that are oblate rotating spheroids, we find that characteristic stellar age follows the intrinsic ellipticity of galaxies remarkably well.

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Fig. 1: Ratio between stellar ordered rotation and random orbital motion in a galaxy (V/σ)e as a function of total stellar mass.
Fig. 2: Linking stellar dynamics (V/σ)e and observed shape (ellipticity \({{\boldsymbol{\epsilon }}}_{{\bf{e}}}\)) with luminosity-weighted stellar age within one effective radius.
Fig. 3: Luminosity-weighted stellar age in the (V/σ, \({{\boldsymbol{\epsilon }}}_{{\bf{e}}}\)) diagram, split by visual morphological type.
Fig. 4: Intrinsic ellipticity and inclination derived from theoretical predictions and our data from within the (V/σ, \({{\boldsymbol{\epsilon }}}_{{\bf{e}}}\)) diagram.

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Acknowledgements

The SAMI Galaxy Survey is based on observations made at the Anglo-Australian Telescope. The Sydney–Australian Astronomical Observatory Multi-object Integral field spectrograph (SAMI) was developed jointly by the University of Sydney and the Australian Astronomical Observatory. The SAMI input catalogue is based on data taken from the Sloan Digital Sky Survey, the GAMA Survey and the VST ATLAS Survey. The SAMI Galaxy Survey is funded by the Australian Research Council Centre of Excellence for All-sky Astrophysics (CAASTRO), through project number CE110001020, and other participating institutions. The SAMI Galaxy Survey website is http://sami-survey.org/. Parts of this research were conducted by the Australian Research Council Centre of Excellence for All-sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number CE170100013. J.v.d.S. is funded under Bland-Hawthorn′s Australian Research Council Laureate Fellowship (FL140100278). N.S. acknowledges support of a University of Sydney Postdoctoral Research Fellowship. S.B. acknowledges the funding support from the Australian Research Council through a Future Fellowship (FT140101166). M.S.O. acknowledges the funding support from the Australian Research Council through a Future Fellowship (FT140100255). J.v.d.S. and N.S. thank all SAMI team members for valuable discussions. A.M.M. is a Hubble Fellow.

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Authors and Affiliations

  1. Sydney Institute for Astronomy, School of Physics, The University of Sydney, Sydney, New South Wales, Australia

    Jesse van de Sande, Nicholas Scott, Joss Bland-Hawthorn, Julia J. Bryant, Scott M. Croom & Caroline Foster

  2. ARC Centre of Excellence for All-sky Astrophysics (CAASTRO), The University of Sydney, Sydney, New South Wales, Australia

    Nicholas Scott, Sarah Brough, Julia J. Bryant, Matthew Colless, Scott M. Croom, Francesco d′Eugenio & Rob Sharp

  3. School of Physics, University of New South Wales, Sydney, New South Wales, Australia

    Sarah Brough

  4. Australian Astronomical Observatory, North Ryde, New South Wales, Australia

    Julia J. Bryant, Michael Goodwin, Iraklis S. Konstantopoulos, Jon S. Lawrence, Richard M. McDermid & Matt S. Owers

  5. Research School of Astronomy and Astrophysics, Australian National University, Canberra, Australian Capital Territory, Australia

    Matthew Colless, Francesco d′Eugenio, Anne M. Medling & Rob Sharp

  6. International Centre for Radio Astronomy Research, The University of Western Australia, Crawley, Western Australia, Australia

    Luca Cortese

  7. ARC Centre of Excellence for All-sky Astrophysics in 3 Dimensions (ASTRO 3D), The University of Sydney, Sydney, New South Wales, Australia

    Caroline Foster

  8. Atlassian , Sydney, New South Wales, Australia

    Iraklis S. Konstantopoulos

  9. Department of Physics and Astronomy, Macquarie University, Sydney, New South Wales, Australia

    Richard M. McDermid & Matt S. Owers

  10. Cahill Center for Astronomy and Astrophysics California Institute of Technology, Pasadena, CA, USA

    Anne M. Medling

  11. SOFIA Operations Center, USRA, NASA Armstrong Flight Research Center, Palmdale, CA, USA

    Samuel N. Richards

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  1. Jesse van de Sande
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Contributions

J.v.d.S. and N.S. led the interpretation. J.v.d.S. measured the stellar kinematic parameters from the SAMI Galaxy Survey spectra and wrote the text. N.S. measured the Lick indices from the spectra, and derived the stellar population ages. F.E. measured the structural parameters. All authors contributed to the analysis and interpretation of the data, and contributed to overall team operations, including target catalogue and observing preparation, instrument maintenance, observing at the telescope, writing data reduction and analysis software, managing various pieces of team infrastructure such as the website and data storage systems, and innumerable other tasks critical to the preparation and presentation of a large dataset presented here.

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Correspondence to Jesse van de Sande.

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van de Sande, J., Scott, N., Bland-Hawthorn, J. et al. A relation between the characteristic stellar ages of galaxies and their intrinsic shapes. Nat Astron 2, 483–488 (2018). https://doi.org/10.1038/s41550-018-0436-x

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