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Discovery and analysis of three faint dwarf galaxies and a globular cluster in the outer halo of the Andromeda galaxy

Martin, N. F. and Ibata, R. A. and Irwin, M. J. and Chapman, S. and Lewis, G. F. and Ferguson, A. M. N. and Tanvir, N. and McConnachie, A. W. (2006) Discovery and analysis of three faint dwarf galaxies and a globular cluster in the outer halo of the Andromeda galaxy. Monthly Notices of the Royal Astronomical Society, 371 (4). pp. 1983-1991. ISSN 0035-8711. https://resolver.caltech.edu/CaltechAUTHORS:20110623-151117121

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Abstract

We present the discovery of three faint dwarf galaxies and a globular cluster in the halo of the Andromeda galaxy (M31), found in our MegaCam survey that spans the southern quadrant of M31, from a projected distance of ~50 to ~150 kpc. Though the survey covers 57 deg^2, the four satellites lie within 2° of one another. From the tip of the red giant branch (RGB), we estimate that the globular cluster lies at a distance of 631 ± 58 kpc from the Milky Way and along with a ~100 kpc projected distance from M31 we derive a total distance of 175 ± 55 kpc from its host, making it the farthest M31 globular cluster known. It also shows the typical characteristics of a bright globular cluster, with a half-light radius of 2.3 ± 0.2 pc and an absolute magnitude in the V band of M_(V,0)=−8.5 ± 0.3. Isochrone fitting reveals that it is dominated by a very old population with a metallicity of [Fe/H]~−1.3. The three dwarf galaxies are revealed as overdensities of stars that are aligned along the RGB tracks in their colour–magnitude diagrams. These satellites are all very faint, with absolute magnitudes in the range −7.3 ≲M_(V,0)≲−6.4, and show strikingly similar characteristics with metallicities of [Fe/H]∼−1.4 and half-light radii of ∼120 ± 45 pc, making these dwarf galaxies two to three times smaller than the smallest previously known satellites of M31. Given their faintness, their distance is difficult to constrain, but we estimate them to be between 740 and 955 kpc which places them well within the virial radius of the host galaxy. The panoramic view of the MegaCam survey can provide an unbiased view of the satellite distribution of the Andromeda galaxy and, extrapolating from its coverage of the halo, we estimate that up to 45 ± 20 satellites brighter than M_(V)~−6.5 should be orbiting M31. Hence faint dwarf galaxies cannot alone account for the missing satellites that are predicted by Λ cold dark matter models, unless they reside in dark matter minihaloes that are more massive than the typical masses of 10^7 M_⊙ currently inferred from their central radial velocity dispersion.


Item Type:Article
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http://dx.doi.org/10.1111/j.1365-2966.2006.10823.xDOIArticle
ORCID:
AuthorORCID
Martin, N. F.0000-0002-1349-202X
Additional Information:© 2006 The Authors. Journal compilation © 2006 Royal Astronomical Society. Accepted 2006 July 19. Received 2006 July 19; in original form 2006 June 6. Article first published online: 31 Aug. 2006. Based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada–France–Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institut National des Science de l’Univers of the Centre National de la Recherche Scientifique (CNRS) of France and the University of Hawaii. We wish to thank the CFHT staff for performing the MegaCam observations in queue mode.
Subject Keywords:galaxies: dwarf – galaxies: formation – galaxies: individual: And XI – galaxies: individual: And XII – galaxies: individual: And XIII – galaxies: structure
Issue or Number:4
Record Number:CaltechAUTHORS:20110623-151117121
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20110623-151117121
Official Citation:Martin, N. F., Ibata, R. A., Irwin, M. J., Chapman, S., Lewis, G. F., Ferguson, A. M. N., Tanvir, N. and McConnachie, A. W. (2006), Discovery and analysis of three faint dwarf galaxies and a globular cluster in the outer halo of the Andromeda galaxy. Monthly Notices of the Royal Astronomical Society, 371: 1983–1991. doi: 10.1111/j.1365-2966.2006.10823.x
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:24188
Collection:CaltechAUTHORS
Deposited By: Jason Perez
Deposited On:23 Jun 2011 22:45
Last Modified:03 Oct 2019 02:54

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