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Title: The hidden giant: discovery of an enormous Galactic dwarf satellite in Gaia DR2

Abstract

ABSTRACT We report the discovery of a Milky Way satellite in the constellation of Antlia. The Antlia 2 dwarf galaxy is located behind the Galactic disc at a latitude of b ∼ 11° and spans 1.26°, which corresponds to ∼2.9 kpc at its distance of 130 kpc. While similar in spatial extent to the Large Magellanic Cloud, Antlia 2 is orders of magnitude fainter at MV = −9 mag, making it by far the lowest surface brightness system known (at ∼31.9 mag arcsec−2), ∼100 times more diffuse than the so-called ultra diffuse galaxies. The satellite was identified using a combination of astrometry, photometry, and variability data from Gaia Data Release 2, and its nature confirmed with deep archival DECam imaging, which revealed a conspicuous BHB signal. We have also obtained follow-up spectroscopy using AAOmega on the AAT, identifying 159 member stars, and we used them to measure the dwarf’s systemic velocity, 290.9 ± 0.5 km s−1, its velocity dispersion, 5.7 ± 1.1 km s−1, and mean metallicity, [Fe/H] = −1.4. From these properties we conclude that Antlia 2 inhabits one of the least dense dark matter (DM) haloes probed to date. Dynamical modelling and tidal-disruption simulations suggest that a combination of a cored DM profile and strong tidal stripping may explain the observed properties of this satellite. Themore » origin of this core may be consistent with aggressive feedback, or may even require alternatives to cold dark matter (such as ultra-light bosons).« less

Authors:
ORCiD logo [1]; ORCiD logo [2]; ORCiD logo [3];  [4];  [5]; ORCiD logo [6];  [7];  [8];  [9];  [6]; ORCiD logo [10]
  1. Institute of Astronomy and Astrophysics, Academia Sinica, P.O. Box 23-141, Taipei 10617, Taiwan
  2. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK, Center for Computational Astrophysics, Flatiron Institute, 162 5th Avenue, New York, NY 10010, USA
  3. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK, McWilliams Center for Cosmology, Department of Physics, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213, USA
  4. Fermi National Accelerator Laboratory, P.O. Box 500, Batavia, IL 60510, USA, Kavli Institute for Cosmological Physics, University of Chicago, Chicago, IL 60637, USA
  5. McWilliams Center for Cosmology, Department of Physics, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213, USA
  6. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
  7. Department of Physics, Imperial College London, Blackett Laboratory, Prince Consort Road, London SW7 2AZ, UK
  8. Department of Physics & Astronomy, Macquarie University, Sydney, NSW 2109, Australia, Macquarie University Research Centre for Astronomy, Astrophysics and Astrophotonics, Macquarie University, Sydney, NSW 2109, Australia
  9. Australian Astronomical Optics, Macquarie University, North Ryde, NSW 2113, Australia
  10. Department of Physics & Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK, Sternwarte der Ludwig-Maximilians-Universität, Scheinerstrasse 1, München D-81679, Germany
Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
1544920
Resource Type:
Published Article
Journal Name:
Monthly Notices of the Royal Astronomical Society
Additional Journal Information:
Journal Name: Monthly Notices of the Royal Astronomical Society Journal Volume: 488 Journal Issue: 2; Journal ID: ISSN 0035-8711
Publisher:
Oxford University Press
Country of Publication:
United Kingdom
Language:
English

Citation Formats

Torrealba, G., Belokurov, V., Koposov, S. E., Li, T. S., Walker, M. G., Sanders, J. L., Geringer-Sameth, A., Zucker, D. B., Kuehn, K., Evans, N. W., and Dehnen, W. The hidden giant: discovery of an enormous Galactic dwarf satellite in Gaia DR2. United Kingdom: N. p., 2019. Web. doi:10.1093/mnras/stz1624.
Torrealba, G., Belokurov, V., Koposov, S. E., Li, T. S., Walker, M. G., Sanders, J. L., Geringer-Sameth, A., Zucker, D. B., Kuehn, K., Evans, N. W., & Dehnen, W. The hidden giant: discovery of an enormous Galactic dwarf satellite in Gaia DR2. United Kingdom. doi:10.1093/mnras/stz1624.
Torrealba, G., Belokurov, V., Koposov, S. E., Li, T. S., Walker, M. G., Sanders, J. L., Geringer-Sameth, A., Zucker, D. B., Kuehn, K., Evans, N. W., and Dehnen, W. Wed . "The hidden giant: discovery of an enormous Galactic dwarf satellite in Gaia DR2". United Kingdom. doi:10.1093/mnras/stz1624.
@article{osti_1544920,
title = {The hidden giant: discovery of an enormous Galactic dwarf satellite in Gaia DR2},
author = {Torrealba, G. and Belokurov, V. and Koposov, S. E. and Li, T. S. and Walker, M. G. and Sanders, J. L. and Geringer-Sameth, A. and Zucker, D. B. and Kuehn, K. and Evans, N. W. and Dehnen, W.},
abstractNote = {ABSTRACT We report the discovery of a Milky Way satellite in the constellation of Antlia. The Antlia 2 dwarf galaxy is located behind the Galactic disc at a latitude of b ∼ 11° and spans 1.26°, which corresponds to ∼2.9 kpc at its distance of 130 kpc. While similar in spatial extent to the Large Magellanic Cloud, Antlia 2 is orders of magnitude fainter at MV = −9 mag, making it by far the lowest surface brightness system known (at ∼31.9 mag arcsec−2), ∼100 times more diffuse than the so-called ultra diffuse galaxies. The satellite was identified using a combination of astrometry, photometry, and variability data from Gaia Data Release 2, and its nature confirmed with deep archival DECam imaging, which revealed a conspicuous BHB signal. We have also obtained follow-up spectroscopy using AAOmega on the AAT, identifying 159 member stars, and we used them to measure the dwarf’s systemic velocity, 290.9 ± 0.5 km s−1, its velocity dispersion, 5.7 ± 1.1 km s−1, and mean metallicity, [Fe/H] = −1.4. From these properties we conclude that Antlia 2 inhabits one of the least dense dark matter (DM) haloes probed to date. Dynamical modelling and tidal-disruption simulations suggest that a combination of a cored DM profile and strong tidal stripping may explain the observed properties of this satellite. The origin of this core may be consistent with aggressive feedback, or may even require alternatives to cold dark matter (such as ultra-light bosons).},
doi = {10.1093/mnras/stz1624},
journal = {Monthly Notices of the Royal Astronomical Society},
number = 2,
volume = 488,
place = {United Kingdom},
year = {2019},
month = {6}
}

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