THE LUMINOSITY PROFILE AND STRUCTURAL PARAMETERS OF THE ANDROMEDA GALAXY

By S. Courteau, L. Widrow, M. McDonald, P. Guhathakurta, K. Gilbert, Yucong Zhu, R. Beaton, S. Majewski. 2011

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We have constructed an extended composite luminosity profile for the Andromeda galaxy, M31, and have decomposed it into three basic luminous structural components: a bulge, a disk, and a halo. The dust-free Spitzer/Infrared Array Camera (IRAC) imaging and extended spatial coverage of ground-based optical imaging and deep star counts allow us to map M31's structure from its center to 22 kpc along the major axis. We apply, and address the limitations of, different decomposition methods for the one-dimensional luminosity profiles and two-dimensional images. These methods include nonlinear least-squares and Bayesian Monte Carlo Markov chain analyses. The basic photometric model for M31 has a Sérsic bulge with shape index n ≃ 2.2 ± .3 and effective radius Re = 1.0 ± 0.2 kpc, and a dust-free exponential disk of scale length Rd = 5.3 ± .5 kpc; the parameter errors reflect the range between different decomposition methods. Despite model covariances, the convergence of solutions based on different methods and current data suggests a stable set of structural parameters. The ellipticities (ϵ = 1 − b/a) of the bulge and the disk from the IRAC image are 0.37 ± 0.03 and 0.73 ± 0.03, respectively. The bulge parameter n is rather insensitive to bandpass effects and its value (2.2) suggests a first rapid formation via mergers followed by secular growth from the disk. The M31 halo has a two-dimensional power-law index ≃ − 2.5 ± 0.2 (or −3.5 in three-dimensional), comparable to that of the Milky Way. We find that the M31 bulge light is mostly dominant over the range Rmin ≲ 1.2 kpc. The disk takes over in the range 1.2 kpc ≲ Rmin ≲ 9 kpc, whereas the halo dominates at Rmin ≳ 9 kpc. The stellar nucleus, bulge, disk, and halo components each contribute roughly 0.05%, 23%, 73%, and 4% of the total light of M31 out to 200 kpc along the minor axis. Nominal errors for the structural parameters of the M31 bulge, disk, and halo amount to 20%. If M31 and the Milky Way are at all typical, faint stellar halos should be routinely detected in galaxy surveys reaching below μi ≃ 27 mag arcsec−2. We stress that our results rely on this photometric analysis alone. Structural parameters may change when other fundamental constraints, such as those provided by abundance gradients and stellar kinematics, are considered simultaneously.

Subfields: Astronomy and Astrophysics, Ecology

View Paper: https://www.semanticscholar.org/paper/b210a337709acee4e34e7ea418d3aa85574a25b5

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Citations in the corpus

Galaxy Masses: A Review (2013, background): “While the value of h depends on the assumed distance to the galaxy and details of surface brightness profile fitting (Courteau et al. 2011), Figure 10 makes clear that tilted ring models are required for rotation curves extending beyond 5-6 optical disk scale lengths.”
The SAGA Survey. I. Satellite Galaxy Populations around Eight Milky Way Analogs (2017, background): “For M 31, we assume physical properties from Hammer et al. (2007); Walterbos & Kennicutt (1987); Lewis et al. (2015); Courteau et al. (2011).”
Galactic accretion and the outer structure of galaxies in the CDM model (2013, background): “13 by M31 (black point; Watkins et al. 2010; Courteau et al. 2011) and the Milky Way (grey box; Smith et al. 2007; Bell et al. 2008; Li & White 2008).”
THE OBSERVED PROPERTIES OF DWARF GALAXIES IN AND AROUND THE LOCAL GROUP (2012, unknown): “The content and structure of the Andromeda Galaxy (M31) provide an excellent comparison (and, increasingly, contrast) to our own Galaxy (e.g., Courteau et al. 2011; Huxor et al. 2011; Watkins et al. 2010; McConnachie et al. 2009; Yin et al. 2009; Ibata et al. 2007; Chapman et al. 2007;…”
THE LARGE-SCALE STRUCTURE OF THE HALO OF THE ANDROMEDA GALAXY. I. GLOBAL STELLAR DENSITY, MORPHOLOGY AND METALLICITY PROPERTIES (2013, methodology): “To take a concrete example, if we adopt a core radius value of Rc = 5.2 kpc, which is the best-fit value of the preferred M31 model by Courteau et al. (2011), and extrapolate inwards using the fitted power laws, we estimate the total stellar mass in the smooth component over all radii to be ∼ 8 ×…”
THE PANCHROMATIC HUBBLE ANDROMEDA TREASURY (2012, methodology): “Recent work by Courteau et al. (2011) uses I band and Spitzer 3.6 µm integrated light to fit the inner profile of M31.”