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Title: A PECULIAR FAINT SATELLITE IN THE REMOTE OUTER HALO OF M31

Abstract

We present Hubble Space Telescope imaging of a newly discovered faint stellar system, PAndAS-48, in the outskirts of the M31 halo. Our photometry reveals this object to be comprised of an ancient and very metal-poor stellar population with age {approx}> 10 Gyr and [Fe/H] {approx}< -2.3. Our inferred distance modulus (m - M){sub 0} = 24.57 {+-} 0.11 confirms that PAndAS-48 is most likely a remote M31 satellite with a three-dimensional galactocentric radius of 149{sup +19}{sub -8} kpc. We observe an apparent spread in color on the upper red giant branch that is larger than the photometric uncertainties should allow, and briefly explore the implications of this. Structurally, PAndAS-48 is diffuse, faint, and moderately flattened, with a half-light radius r{sub h}=26{sup +4}{sub -3} pc, integrated luminosity M{sub V} = -4.8 {+-} 0.5, and ellipticity {epsilon}=0.30{sup +0.08}{sub -0.15}. On the size-luminosity plane it falls between the extended globular clusters seen in several nearby galaxies and the recently discovered faint dwarf satellites of the Milky Way; however, its characteristics do not allow us to unambiguously classify it as either type of system. If PAndAS-48 is a globular cluster then it is among the most elliptical, isolated, and metal-poor of any seen inmore » the Local Group, extended or otherwise. Conversely, while its properties are generally consistent with those observed for the faint Milky Way dwarfs, it would be a factor of {approx}2-3 smaller in spatial extent than any known counterpart of comparable luminosity.« less

Authors:
;  [1];  [2]; ;  [3];  [4];  [5];  [6];  [7]; ;  [8]
  1. Research School of Astronomy and Astrophysics, Australian National University, Mount Stromlo Observatory, via Cotter Road, Weston, ACT 2611 (Australia)
  2. Astronomisches Rechen-Institut, Universitaet Heidelberg, Moenchhofstrasse 12-14, D-69120 Heidelberg (Germany)
  3. Observatoire astronomique de Strasbourg, Universite de Strasbourg, CNRS, UMR 7550, 11 rue de l'Universite, F-67000 Strasbourg (France)
  4. Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom)
  5. NRC Herzberg Institute for Astrophysics, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada)
  6. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom)
  7. Sydney Institute for Astronomy, School of Physics, A28, University of Sydney, NSW 2006 (Australia)
  8. Department of Physics and Astronomy, University of Victoria, 3800 Finnerty Road, Victoria, BC V8P 1A1 (Canada)
Publication Date:
OSTI Identifier:
22118773
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal Letters
Additional Journal Information:
Journal Volume: 770; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 2041-8205
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTRONOMY; ASTROPHYSICS; COLOR; COMPARATIVE EVALUATIONS; DISTANCE; HYDROGEN; IRON; LUMINOSITY; MILKY WAY; PHOTOMETRY; STAR CLUSTERS; TELESCOPES

Citation Formats

Mackey, A. D., Dotter, A., Huxor, A. P., Martin, N. F., Ibata, R. A., Ferguson, A. M. N., McConnachie, A. W., Irwin, M. J., Lewis, G. F., Sakari, C. M., Venn, K. A., and Tanvir, N. R., E-mail: dougal@mso.anu.edu.au. A PECULIAR FAINT SATELLITE IN THE REMOTE OUTER HALO OF M31. United States: N. p., 2013. Web. doi:10.1088/2041-8205/770/2/L17.
Mackey, A. D., Dotter, A., Huxor, A. P., Martin, N. F., Ibata, R. A., Ferguson, A. M. N., McConnachie, A. W., Irwin, M. J., Lewis, G. F., Sakari, C. M., Venn, K. A., & Tanvir, N. R., E-mail: dougal@mso.anu.edu.au. A PECULIAR FAINT SATELLITE IN THE REMOTE OUTER HALO OF M31. United States. doi:10.1088/2041-8205/770/2/L17.
Mackey, A. D., Dotter, A., Huxor, A. P., Martin, N. F., Ibata, R. A., Ferguson, A. M. N., McConnachie, A. W., Irwin, M. J., Lewis, G. F., Sakari, C. M., Venn, K. A., and Tanvir, N. R., E-mail: dougal@mso.anu.edu.au. Thu . "A PECULIAR FAINT SATELLITE IN THE REMOTE OUTER HALO OF M31". United States. doi:10.1088/2041-8205/770/2/L17.
@article{osti_22118773,
title = {A PECULIAR FAINT SATELLITE IN THE REMOTE OUTER HALO OF M31},
author = {Mackey, A. D. and Dotter, A. and Huxor, A. P. and Martin, N. F. and Ibata, R. A. and Ferguson, A. M. N. and McConnachie, A. W. and Irwin, M. J. and Lewis, G. F. and Sakari, C. M. and Venn, K. A. and Tanvir, N. R., E-mail: dougal@mso.anu.edu.au},
abstractNote = {We present Hubble Space Telescope imaging of a newly discovered faint stellar system, PAndAS-48, in the outskirts of the M31 halo. Our photometry reveals this object to be comprised of an ancient and very metal-poor stellar population with age {approx}> 10 Gyr and [Fe/H] {approx}< -2.3. Our inferred distance modulus (m - M){sub 0} = 24.57 {+-} 0.11 confirms that PAndAS-48 is most likely a remote M31 satellite with a three-dimensional galactocentric radius of 149{sup +19}{sub -8} kpc. We observe an apparent spread in color on the upper red giant branch that is larger than the photometric uncertainties should allow, and briefly explore the implications of this. Structurally, PAndAS-48 is diffuse, faint, and moderately flattened, with a half-light radius r{sub h}=26{sup +4}{sub -3} pc, integrated luminosity M{sub V} = -4.8 {+-} 0.5, and ellipticity {epsilon}=0.30{sup +0.08}{sub -0.15}. On the size-luminosity plane it falls between the extended globular clusters seen in several nearby galaxies and the recently discovered faint dwarf satellites of the Milky Way; however, its characteristics do not allow us to unambiguously classify it as either type of system. If PAndAS-48 is a globular cluster then it is among the most elliptical, isolated, and metal-poor of any seen in the Local Group, extended or otherwise. Conversely, while its properties are generally consistent with those observed for the faint Milky Way dwarfs, it would be a factor of {approx}2-3 smaller in spatial extent than any known counterpart of comparable luminosity.},
doi = {10.1088/2041-8205/770/2/L17},
journal = {Astrophysical Journal Letters},
issn = {2041-8205},
number = 2,
volume = 770,
place = {United States},
year = {2013},
month = {6}
}