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

Creators: van de Sande, Jesse; Scott, Nicholas; Bland-Hawthorn, Joss; Brough, Sarah; Bryant, Julia J.; Colless, Matthew; Cortese, Luca; Croom, Scott M.; d'Eugenio, Francesco; Foster, Caroline; Goodwin, Michael; Konstantopoulos, Iraklis S.; Lawrence, Jon S.; McDermid, Richard M.; Medling, Anne M.; Owers, Matt S.; Richards, Samuel N.; Sharp, Rob

Abstract

Stellar population and stellar kinematic studies provide unique but complementary insights into how galaxies build-up their stellar mass and angular momentum. 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 dynamics trace the change in angular momentum due to mergers, but major mergers tend to obscure the effect of earlier interactions. With the rise of large multi-object integral field spectroscopic surveys, such as SAMI and MaNGA, and single-object integral field spectroscopic surveys (for example, ATLAS3D (ref. 8), CALIFA, MASSIVE), 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 environment. 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, ϵ_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.

Additional Information

© 2018 Macmillan Publishers Limited. Received: 25 July 2017; Accepted: 1 March 2018; Published online: 23 April 2018. 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. Author 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. Code availability: The data reduction package used to process the SAMI data is available at http://ascl.net/1407.006, and makes use of 2dfdr: http://www.aao.gov.au/science/software/2dfdr. To derive the stellar kinematic parameters and the Lick absorption-line strengths, we used the publicly available penalized pixel-fitting (pPXF) code from M. Capppellari: http://www-astro.physics.ox.ac.uk/~mxc/software/#ppxf. For the adaptive LOESS smoothing, we use the code from M. Cappellari obtained from http://www-astro.physics.ox.ac.uk/~mxc/software/#loess. Data availability: All reduced data cubes in the GAMA fields used in this paper are available on http://datacentral.aao.gov.au/asvo/surveys/sami/ as part of the first SAMI Galaxy Survey data release53. Stellar kinematic and stellar population data products will become available in the second SAMI Galaxy Survey data release. The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request. The authors declare no competing interests.

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