A PECULIAR FAINT SATELLITE IN THE REMOTE OUTER HALO OF M31
- Research School of Astronomy and Astrophysics, Australian National University, Mount Stromlo Observatory, via Cotter Road, Weston, ACT 2611 (Australia)
- Astronomisches Rechen-Institut, Universitaet Heidelberg, Moenchhofstrasse 12-14, D-69120 Heidelberg (Germany)
- Observatoire astronomique de Strasbourg, Universite de Strasbourg, CNRS, UMR 7550, 11 rue de l'Universite, F-67000 Strasbourg (France)
- Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom)
- NRC Herzberg Institute for Astrophysics, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada)
- Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom)
- Sydney Institute for Astronomy, School of Physics, A28, University of Sydney, NSW 2006 (Australia)
- Department of Physics and Astronomy, University of Victoria, 3800 Finnerty Road, Victoria, BC V8P 1A1 (Canada)
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.
- OSTI ID:
- 22118773
- Journal Information:
- Astrophysical Journal Letters, Vol. 770, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 2041-8205
- Country of Publication:
- United States
- Language:
- English
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