External gas accretion provides a fresh gas supply to the active S0 galaxy NGC 5077

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In early-Type galaxies, externally accreted gas is thought to be the main source of gas replenishment at late times. We use MUSE integral field spectroscopy data to study the active S0 galaxy NGC 5077, which is known to have disturbed dynamics that are indicative of a past external interaction. We confirm the presence of a stellar kinematically distinct core with a diameter of 2.8 kpc that is counter-rotating with respect to the main stellar body of the galaxy. We find that the counter-rotating core consists of an old stellar population that is not significantly different from the rest of the galaxy. The ionised gas is strongly warped and extends out to 6.5 kpc in the polar direction and in a filamentary structure. The gas dynamics is complex, with significant changes in the position angle as a function of radius. The ionised gas line ratios are consistent with LINER excitation by the active galactic nucleus, both in the nucleus and at kiloparsec scales. We discover a nuclear outflow with projected velocity Vâ ∼â 400 km s-1, consistent with a hollow outflow cone intersecting the plane of the sky. The properties of the misaligned gas match predictions from numerical simulations of misaligned gas infall after a gas-rich merger. The warp and change in the gas orientation as a function of radius are consistent with gas relaxation due to stellar torques; these are stronger at small radii where the gas aligns faster than in the outer regions, driving gas to the nucleus. The stellar and gas dynamics indicate that NGC 5077 has had at least two external interactions, one that resulted in the formation of the counter-rotating core, followed by the second, late-Time external gas accretion. NGC 5077 illustrates the importance of external interactions in the replenishment of the galaxy gas reservoir and the nuclear gas content available for black hole fuelling.

Original languageEnglish
Article numberA34
JournalAstronomy and Astrophysics
Number of pages14
Publication statusPublished - 1 Jun 2021

Bibliographical note

Funding Information:
Acknowledgements. The author would like to thank the referee, for a thorough review of the paper and for the constructive comments and suggestions that have improved the quality of the paper. The author would also like to thank Mike Crenshaw, Ric Davies, Travis Fischer, Steven Kraemer, Joao Mendonca, and Marianne Vestergaard for useful discussions. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 891744. Based on observations collected at the European Southern Observatory under ESO programme 094.B-0298. This research has made use of the services of the ESO Science Archive Facility. 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. Based on observations made with the NASA/ESA Hubble Space Telescope, and obtained from the Hubble Legacy Archive, which is a collaboration between the Space Telescope Science Institute (STScI/NASA), the Space Telescope European Coordinating Facility (ST-ECF/ESA) and the Canadian Astronomy Data Centre (CADC/NRC/CSA). This research made use of Astropy (http://www.astropy.org), a community-developed core Python package for Astronomy (Astropy Collaboration 2013, 2018).

Publisher Copyright:
© ESO 2021.

    Research areas

  • Black hole physics, Galaxies: Active, Galaxies: elliptical and lenticular, cD, Galaxies: individual: NGC 5077, Galaxies: kinematics and dynamics, Quasars: supermassive black holes

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