2005/05/31 by Mike J. Irwin, Mike Irwin, Annette Ferguson +6 · 2 citations
Physics and Astronomy · #Astronomy #Astronomy and Astrophysical Research #Astrophysics #Brightness #Galaxies: Formation, Evolution, Phenomena #Galaxy #Photometry (optics) #Physics #Population #RADIUS #Star formation #Stars #Stellar population #Stellar, planetary, and galactic studies #Surface brightness #astro-ph
paper · pdf · doi:10.1086/432718
published as Astrophys.J. 628 (2005) L105-L108 · 11 pages, 3 figures, ApJ Letters in press, extremely minor modifications
arxiv created 2005/06/08 · openalex publication_date 2005/07/13 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We use data from the Isaac Newton Telescope Wide-Field Camera survey of M31 to determine the surface brightness profile of M31 along the southeast minor axis. We combine surface photometry and faint red giant branch star counts to trace the profile from the innermost regions out to a projected radius of 4° (≈55 kpc), where μ V ~ 32 mag arcsec -2 ; this is the first time the M31 minor-axis profile has been mapped over such a large radial distance using a single data set. We confirm the finding by Pritchet & van den Bergh that the minor-axis profile can be described by a single de Vaucouleurs law out to a projected radius of 1 4 or ≈20 kpc. Beyond this, the surface brightness profile flattens considerably and is consistent with either a power law of index about -2.3 or an exponential of scale length 14 kpc. The fraction of the total M31 luminosity contained in this component is ≈2.5%. While it is tempting to associate this outer component with a true Population II halo in M31, we find that the mean color of the stellar population remains roughly constant at V - i ≈ 1.6 from 0 5 to 3 5 along the minor axis. This result suggests that the same metal-rich stellar population dominates both structural components.