THE LUMINOSITY PROFILE AND STRUCTURAL PARAMETERS OF THE ANDROMEDA GALAXY
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Courteau-2011-THE LUMINOSITY PROFI.pdf
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1.17 MB
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Checksum (MD5)
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Author(s)
Courteau, Stephane
Widrow, Lawrence M.
McDonald, Michael A.
Guhathakurta, Puragra
Gilbert, Karoline M.
Zhu, Yucong
Beaton, Rachael Lynn
Majewski, Steven R.
Date Issued
September 2011
Journal
Astrophysical Journal
Publisher
Institute of Physics/American Astronomical Society
Citation
Courteau, Stéphane, Lawrence M. Widrow, Michael McDonald, Puragra Guhathakurta, Karoline M. Gilbert, Yucong Zhu, Rachael Lynn Beaton, and Steven R. Majewski. “THE LUMINOSITY PROFILE AND STRUCTURAL PARAMETERS OF THE ANDROMEDA GALAXY.” The Astrophysical Journal 739, no. 1 (August 30, 2011): 20. © 2011 American Astronomical Society.
Version
Final published version
Abstract
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 sime 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 (epsilon = 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 sime – 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 R min lsim 1.2 kpc. The disk takes over in the range 1.2 kpc lsim R min lsim 9 kpc, whereas the halo dominates at R min gsim 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 μ i sime 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.
MIT Department
MIT Kavli Institute for Astrophysics and Space Research
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DOI of Published Version
https://doi.org/10.1088/0004-637x/739/1/20
