SAMI Galaxy Survey: stellar and gas misalignments and the origin of gas in nearby galaxies

Creators: Bryant, J. J.; Croom, S. M.; van de Sande, J.; Scott, N.; Fogarty, L. M. R.; Bland-Hawthorn, J.; Bloom, J. V.; Taylor, E. N.; Brough, S.; Robotham, A.; Cortese, L.; Couch, W.; Owers, M. S.; Medling, A. M.; Federrath, C.; Bekki, K.; Richards, S. N.; Lawrence, J. S.; Konstantopoulos, I. S.

Abstract

Misalignment of gas and stellar rotation in galaxies can give clues to the origin and processing of accreted gas. Integral field spectroscopic observations of 1213 galaxies from the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey show that 11 per cent of galaxies with fitted gas and stellar rotation are misaligned by more than 30° in both field/group and cluster environments. Using SAMI morphological classifications and Sérsic indices, the misalignment fraction is 45 ± 6 per cent in early-type galaxies (ETGs), but only 5 ± 1 per cent in late-type galaxies (LTGs). The distribution of position angle offsets is used to test the physical drivers of this difference. Slower dynamical settling time of the gas in elliptical stellar mass distributions accounts for a small increase in misalignment in early-type galaxies. However, gravitational dynamical settling time is insufficient to fully explain the observed differences between ETGs and LTGs in the distributions of the gas/stellar position angle offsets. LTGs have primarily accreted gas close to aligned rather than settled from misaligned based on analysis of the skewed distribution of PA offsets compared to a dynamical settling model. Local environment density is less important in setting the misalignment fractions than morphology, suggesting that mergers are not the main source of accreted gas in these discs. Cluster environments are found to have gas misalignment driven primarily by cluster processes not by gas accretion.

Additional Information

© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model). Accepted 2018 November 14. Received 2018 August 31; in original form 2017 October 6. Published: 21 November 2018. The SAMI Galaxy Survey is based on observations made at the Anglo-Australian Telescope. The SAMI instrument was developed jointly by the University of Sydney and the Australian Astronomical Observatory. Initial seed funding came from Bland-Hawthorn's ARC Federation Fellowship (2008-13). The SAMI input catalogue is based on data taken from the SDSS, 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 supported by the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number CE170100013. We would like to thank the Australia Astronomical Observatory and University of Sydney instrumentation groups for their support and dedication to making the SAMI instrument. The SAMI Survey has greatly benefitted from the excellent technical support offered by the AAO in Sydney and by site staff at the Anglo-Australian Telescope. GAMA is a joint European-Australasian project based around a spectroscopic campaign using the Anglo-Australian Telescope. The GAMA input catalogue is based on data taken from the SDSS and the UKIRT Infrared Deep Sky Survey. Complementary imaging of the GAMA regions is being obtained by a number of independent survey programmes including GALEX MIS, VST KiDS, VISTA VIKING, WISE, Herschel-ATLAS, GMRT, and ASKAP, providing UV to radio coverage. GAMA is funded by the STFC (UK), the ARC (Australia), the AAO, and the participating institutions. The GAMA website is http://www.gama-survey.org/. JJB acknowledges support of an Australian Research Council Future Fellowship (FT180100231). SMC acknowledges the support of an Australian Research Council Future Fellowship (FT100100457). LC acknowledges support under the Australian Research Council's Discovery Projects funding scheme (DP130100664) and Future Fellowship (FT180100066) funded by the Australian Government. Support for AMM is provided by NASA through Hubble Fellowship grant #HST-HF2-51377 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. NS acknowledges support from a University of Sydney Postdoctoral Research Fellowship. SB acknowledges the funding support from the Australian Research Council through a Future Fellowship (FT140101166). JvdS is funded under Bland-Hawthorn's ARC Laureate Fellowship (FL140100278). MSO acknowledges the funding support from the Australian Research Council through a Future Fellowship (FT140100255). C.F. acknowledges funding provided by the Australian Research Council (Discovery Projects DP150104329 and DP170100603, and Future Fellowship FT180100495), and the Australia-Germany Joint Research Cooperation Scheme (UA-DAAD). This study is based on data products (VST/ATLAS) from observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 177.A-3011(A-J). This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, and the U.S. Department of Energy Office of Science. The SDSS-III website is http://www.sdss3.org/. We thank the referee for suggestions that improved the clarity and flow of this paper.

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