Photometry and the Metallicity Distribution of the Outer Halo of M31. II. The 30 Kiloparsec Field

By P. Durrell, W. Harris, C. Pritchet. 2001

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We present the results of a wide-field (VI) photometric study of the red giant branch (RGB) stars in the outer halo of M31, in a field located 30–35 kpc from the center of the galaxy along the southeast minor axis. At this remote location, we find that RGB stars belonging to M31 are sparsely but definitely present, after statistical subtraction of field contamination. We derive the metallicity distribution function (MDF) for the halo stars using interpolation within a standard (I, V-I) grid of RGB evolutionary tracks. The halo MDF is quite broad but dominated by a moderately high-metallicity population peaking at [M/H] ∼ -0.5, strikingly different from the [M/H] ∼ -1.3 level that characterizes the outer halo of the Milky Way. However, the shape and peak metallicity for this region are entirely similar to those found in other studies for the inner regions of the M31 halo, particularly our previous study of a 20 kpc region employing similar data. In summary, we find no evidence for a metallicity gradient or systematic change in the MDF out to quite large distances in the M31 halo: it appears to be a homogeneous and moderately metal-rich subsystem of the galaxy at all locations. The star counts in the 30 kpc field are also consistent with the r1/4 law that fits the interior regions of the M31 spheroid surface brightness profile. The metal-rich MDF and the r1/4 spheroid suggests M31 more strongly resembles a giant elliptical galaxy than other, Milky Way–like, spirals.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/d27dda09a7488f21762e0707fad6a08248d1aebc

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Citations in the corpus

THE PANCHROMATIC HUBBLE ANDROMEDA TREASURY. X. ULTRAVIOLET TO INFRARED PHOTOMETRY OF 117 MILLION EQUIDISTANT STARS (2014, background): “…studies of M31 that have concentrated on the field star population, on OB associations, or on portions of the halo (Massey et al. 1986; Mould & Kristian 1986; Pritchet & van den Bergh 1988; Haiman et al. 1994; Davidge 1993; Durrell et al. 1994, 2001; Ibata et al. 2001; McConnachie et al. 2009).”
Chemical Abundance Distributions of Galactic Halos and Their Satellite Systems in a ΛCDM Universe (2005, background): “MDFs for different regions in the halo of M31 have been derived by a number of authors (Durrell et al. 2001; Reitzel & Guhathakurta 2002; Bellazzini et al. 2003; Durrell et al. 2004).”
Evidence for Stellar Substructure in the Halo and Outer Disk of M31 (2002, background): “…have now been calculated for stars in several fields, all of which are found to exhibit a similar shape, consisting of a peak at the metal-rich end and an extended tail toward lower metallicities (Holland et al. 1996; Durrell et al. 2001; Sarajedini & Van Duyne 2001; Reitzel & Guhathakurta 2002).”
The New Galaxy: Signatures of Its Formation (2002, background): “The halo of M31, for example, follows the r1/4 law (Pritchet & van den Bergh 1994) and is much more metal rich in the mean than the halo of our Galaxy (Durrell et al. 2001) although it does have stars that are very metal weak.”
The Metal-poor Halo of the Andromeda Spiral Galaxy (M31) (2006, result): “Our finding, however, is in contrast to previous observational work on M31 which has found no significant radial [Fe/H] gradient within R < 30 kpc (e.g., Durrell et al. 2001, 2004).”
The Detailed Star Formation History in the Spheroid, Outer Disk, and Tidal Stream of the Andromeda Galaxy (2006, methodology): “Furthermore, the metallicity distribution in our spheroid field is clearly very similar to the metallicity distribution in other fields throughout the inner spheroid of Andromeda (Ferguson et al. 2002; Durrell et al. 1994, 2001, 2004).”
The Effect of Metallicity on Cepheid-based Distances (2004, result): “…2000a; (2) Cioni et al. 2000; (3) Sakai et al. 1996; (4) Dolphin et al. 2003; (5) Sakai et al. 1997; (6) Méndez et al. 2002; (7) Lee et al. 1993; (8) Durrell et al. 2001; (9) this paper; (10) Kim et al. 2002; (11) Lee 1993; (12) Minniti et al. 1999; (13) Gallart et al. 1996; (14) Cole et al.…”
Gas physics, disk fragmentation, and bulge formation in young galaxies (2003, result): “This points to a relatively slow star formation process for the M31 halo stars.”