Evidence for Stellar Substructure in the Halo and Outer Disk of M31

By A. Ferguson, M. Irwin, R. Ibata, Geraint F. Lewis, N. Tanvir. 2002

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We report the discovery of significant stellar substructure in the halo and outer disk of our nearest large galactic neighbor, M31. Our deep panoramic survey with the Isaac Newton Telescope Wide Field Camera currently maps out an area of ≈25 deg2 around M31, extending along the semimajor axis to 55 kpc and is the first to allow an uninterrupted study of the density and color distribution of individual red giant branch stars across a large fraction of the halo of an external spiral galaxy. We find evidence for both spatial density and metallicity (as inferred from color information) variations, which are often, but not always, correlated. In addition to the previously reported giant stellar stream, the data reveal the presence of significant stellar overdensities at large radii close to the southwestern major axis, in the proximity of the very luminous globular cluster G1, and near the northeastern major axis, coinciding with and extending beyond the previously known northern spur. The most prominent metallicity variations are found in the southern half of the halo, where two large structures with above average metallicites are apparent; one of these coincides with the giant stellar stream while the other corresponds to a much lower level stellar enhancement. Our findings contrast with, but do not conflict with, past studies of the M31 halo and outer disk that have suggested a rather homogeneous stellar population at large radius: the bulk of our newly detected substructure lies in the previously uncharted far outer regions of the galaxy. We discuss the possible origin of the substructure observed and the implications it has for constraining the galaxy assembly process.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/509af5875e1147c467455ed2574d6597dd1816f6

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Citations in the corpus

Cosmological simulations of the formation of the stellar haloes around disc galaxies (2011, background): “Recent advances in observational techniques have allowed the detection of faint stellar haloes around external galaxies, such as M31 (Ferguson et al. 2002; Guhathakurta et al. 2005; Irwin et al. 2005; Ibata et al. 2007) and other nearby disc galaxies (Mouhcine et al. 2005a,b; de Jong et al. 2007;…”
Taking measure of the Andromeda halo: A Kinematic analysis of the giant stream surrounding M31 (2004, methodology): “To answer this, we have undertaken a large photometric study of M31, using the wide field cameras at the INT and CFHT telescopes to resolve stars over the entire disk and inner halo of that galaxy (Ibata et al. 2001b; Ferguson et al. 2002; McConnachie et al. 2003).”
STECKMAP: STEllar Content and Kinematics from high resolution galactic spectra via Maximum A Posteriori (2005, background): “The highly detailed stellar content and kinematical information that can be obtained for the Milky Way or for nearby galaxies that can be resolved into stars, such as M31 (Ferguson et al. 2002; Ibata et al. 2004), could be extended to a larger sample of more distant galaxies.”
The Haunted Halos of Andromeda and Triangulum: A Panorama of Galaxy Formation in Action (2007, methodology): “Purpose of the present study In this contribution we are building upon an earlier wide-field survey of Andromeda with the Wide Field Camera camera at the Isaac Newton Telescope (Ibata et al. 2001b; Ferguson et al. 2002; Irwin et al. 2005).”
The Milky Way’s stellar disk (2013, background): “The Outer Fringes of the Disk: The stellar disk of our neighbor galaxy, M31, is manifestly frayed in its very outer parts (Ferguson et al. 2002; Ibata et al. 2005), possibly because much of the material is tidally disrupted satellite debris or possibly because disk material has been grossly…”
The Secular Evolution of Disk Structural Parameters (2005, unknown): “…Electronic address: moore@physik.unizh.ch Electronic address: wadsley@mcmaster.ca Electronic address: trq@astro.washington.edu 1 current address: Astronomy Department, University of Washington, Box 351580, Seattle WA, 98195, USA 2 Brooks Prize Fellow et al. 1999) and M31 (Ferguson et al. 2002).”
Galactic stellar haloes in the CDM model (2009, background): “Recent surveys of M31 (e.g. Ferguson et al. 2002; Kalirai et al. 2006; Ibata et al. 2007; McConnachie et al. 2009) have revealed an extensive halo (to ∼150 kpc) also displaying abundant substructure.”
Distances and metallicities for 17 Local Group galaxies (2004, methodology): “Ferguson et al. (2002) and Irwin et al. (in preparation) present maps of the spatial distribution of red giant branch stars as seen in our INT WFC survey of this galaxy.”
THE GHOSTS SURVEY. I. HUBBLE SPACE TELESCOPE ADVANCED CAMERA FOR SURVEYS DATA (2011, background): “…55 kpc was first explored in the Isaac Newton Telescope 1 The Astrophysical Journal Supplement Series, 195:18 (27pp), 2011 August Radburn-Smith et al. Wide-Field Camera Panoramic Survey of M31, which revealed the massive infalling giant southern stream (Ibata et al. 2001; Ferguson et al. 2002).”
THE PANCHROMATIC HUBBLE ANDROMEDA TREASURY. X. ULTRAVIOLET TO INFRARED PHOTOMETRY OF 117 MILLION EQUIDISTANT STARS (2014, background): “Ground-based halo studies have taken advantage of the very large fields of view available on many telescopes, leading to the discovery of extended density features from accreted smaller galaxies (Ibata et al. 2001; Ferguson et al. 2002).”
On the Accretion Origin of a Vast Extended Stellar Disk around the Andromeda Galaxy (2005, methodology): “…this study was obtained with the Wide Field Camera at the 2.5m Isaac Newton Telescope; the survey and preliminary results were presented in Ibata et al. (2001b) and Ferguson et al. (2002), though the full completed survey will be discussed in detail in a forthcoming article (Irwin et al., in prep).”