On the Accretion Origin of a Vast Extended Stellar Disk around the Andromeda Galaxy

By R. Ibata, S. Chapman, A. Ferguson, Geraint F. Lewis, M. Irwin, N. Tanvir. 2005

182 citations recorded by the source corpus.

We present the discovery of an inhomogenous, low surface brightness, extended disklike structure around the Andromeda galaxy (M31) based on a large kinematic survey of more than 2800 stars with the Keck DEIMOS multiobject spectrograph. The stellar structure spans radii from 15 kpc out to ~40 kpc, with detections out to R ~ 70 kpc. The constituent stars have velocities close to the expected velocity of circular orbits in the plane of the M31 disk and typically have a velocity dispersion of ~30 km s-1. The color range on the upper red giant branch shows a large spread indicative of a population with a significant range of metallicity. The mean metallicity of the population, measured from Ca II equivalent widths, is [Fe/H] = -0.9 ± 0.2. The morphology of the structure is irregular at large radii and shows a wealth of substructures that must be transitory in nature and are almost certainly tidal debris. The presence of these substructures indicates that the global entity was formed by accretion. This extended disk follows smoothly on from the central parts of M31 disk out to ~40 kpc with an exponential density law with a scale length of 5.1 ± 0.1 kpc, which is similar to that of the bright inner disk. However, the population possesses similar kinematic and abundance properties over the entire region where it is detected in the survey. We estimate that the structure accounts for approximately 10% of the total luminosity of the M31 disk, and given the huge scale, contains ~30% of the total disk angular momentum. This finding indicates that at least some galactic stellar disks are vastly larger than previously thought and are formed, at least in their outer regions, primarily by accretion.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/d6eb58d7336885412b7c3cd7223a52adcf517dff

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Citations in the corpus

THE LUMINOSITY PROFILE AND STRUCTURAL PARAMETERS OF THE ANDROMEDA GALAXY (2011, result): “Other lines of evidence (e.g., Ibata et al. 2005; Worthey et al. 2005) point to the M31 stellar disk extending out to Rmaj ∼ 50 kpc, with occasional detections of features (not spatially continuous) with disk-like kinematics out to Rmaj ∼ 60 kpc (Ibata et al. 2005).”
THE M31 VELOCITY VECTOR. II. RADIAL ORBIT TOWARD THE MILKY WAY AND IMPLIED LOCAL GROUP MASS (2012, methodology): “This image can be compared to star-count maps of giant stars in M31, which show the same features (e.g., Ibata et al. 2005; Gilbert et al. 2009; or Paper I, which also shows the location of our PM fields).”
THE SPLASH SURVEY: SPECTROSCOPY OF 15 M31 DWARF SPHEROIDAL SATELLITE GALAXIES (2011, background): “The radial velocity of the peak broadly matches the expectations from Ibata et al. (2005) for this field, but some of the stars in the feature are in parts of the CMD that are not consistent with M31 expectations.”
Simulations of minor mergers - I. General properties of thick discs (2008, background): “For example, Ibata et al. (2005) discovered an extended and clumpy disk-like structure around M31 with a scalelength similar to that of the main disk, rotating ∼40 km/s slower and with a rather low velocity dispersion of ∼30 km/s.”
A KINEMATIC STUDY OF THE ANDROMEDA DWARF SPHEROIDAL SYSTEM (2013, background): “Not only are their measurements determined from 4 times the member stars that we possess, we also experienced problems with our radial velocity measurements for the stars observed with this mask, due to the use of the minislitlet approach pioneered by Ibata et al. (2005).”
The Haunted Halos of Andromeda and Triangulum: A Panorama of Galaxy Formation in Action (2007, methodology): “Further signs of this halo component were detected in the spectroscopic study of McConnachie et al. (2006) with Keck/DEIMOS, who distinguished halo field stars from stars in the disk via their kinematics, and deduce a mean metallicity for the halo component of 〈[Fe/H]〉 = −1.5, with a narrower spread”
Thin, thick and dark discs in ΛCDM (2008, background): “Indeed, this could provide an explanation for the extended disc seen in Andromeda (Ibata et al. 2005 and Section 1).9 From Section 2, we expect ∼15 such low inclination, low mass, mergers to occur in the Milky Way.”
The Metal-poor Halo of the Andromeda Spiral Galaxy (M31) (2006, background): “Ibata et al. (2005) find that this disk is a lowsurface brightess, kinematically cold (velocity dispersion, ∼30 km s−1) structure at R = 15–40 kpc and is an extention of the inner disk.”
THE OUTER DISKS OF EARLY-TYPE GALAXIES. I. SURFACE-BRIGHTNESS PROFILES OF BARRED GALAXIES (2007, background): “This diversity is probably telling us something important about galaxy formation and evolution — for example, the outer part of the disk may record useful information about past accretion and interactions or the lack thereof (e.g., Ibata et al. 2005; Younger et al. 2007).”
A Search for Extended Ultraviolet Disk (XUV-Disk) Galaxies in the Local Universe (2007, background): “Ibata et al. (2005) reported an exponential disk-like component in M 31 extending to at least 40 kpc radius (about twice the previously known size) having kinematics consistent with the expected circular motion at the radii probed.”
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…”
An Intermediate-Mass Black Hole in the Globular Cluster G1: Improved Significance from New Keck and Hubble Space Telescope Observations (2005, methodology): “Meylan et al. (2001) suggest G1 is similar to the nucleus of NGC 205, and Ferguson et al. (2002, 2005) and Ibata et al. (2005) report evidence for a disrupted galaxy that is centered on G1, although there is no evidence for a discrete system.”
A non-LTE study of neutral and singly-ionized calcium in late-type stars (2006, background): “…in globular clusters (e.g. Article published by EDP Sciences and available at http://www.aanda.org or http://dx.doi.org/10.1051/0004-6361:20065999 Armandroff& da Costa 1991; Rutledge et al. 1997) to stars and stellar populations in nearby galaxies (e.g. Tolstoy et al. 2001; Ibata et al. 2005).”
A wide-field H I mosaic of Messier 31 - II. The disk warp, rotation, and the dark matter halo (2009, background): “An faint stellar disk which extends as far as 40 kpc from the Andromeda nucleus has been recently pointed out by Ibata et al. (2005) with an exponential scale length of 5.1 kpc in the I-band.”
THE NUCLEUS OF THE SAGITTARIUS DSPH GALAXY AND M54: A WINDOW ON THE PROCESS OF GALAXY NUCLEATION (2008, methodology): “The radial velocities of the target stars were obtained by cross correlating the observed spectra against an artificial template of the Ca II lines, using the same approach described and discussed in detail in Ibata et al. (2005) and Battaglia et al. (2008).”
Galactic stellar haloes in the CDM model (2009, background): “Pritchet & van den Bergh (1994) measured a projected axial ratio of 0.5 for the M31 halo at ∼10 kpc. Ibata et al. (2005) describe a highly irregular and rotating inner halo component or ‘extended disc’ (to ∼40 kpc) of 27–31 mag arcsec−2, aligned with the thin disc and having an axial ratio of ∼0.6…”