Open AccessA revised Λ CDM mass model for the Andromeda Galaxy
Author(s) -
Seigar Marc S.,
Barth Aaron J.,
Bullock James S.
Publication year - 2008
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2008.13732.x
Subject(s) - physics , galaxy rotation curve , astrophysics , satellite galaxy , andromeda galaxy , virial mass , dark matter halo , galaxy , astronomy , dark matter , halo , interacting galaxy , virial theorem , galaxy formation and evolution , spiral galaxy
We present an updated mass model for M31 that makes use of a Spitzer 3.6‐μm image, a mass‐to‐light ratio gradient based on the galaxy's B − R colour profile, and observed rotation curve data from a variety of sources. We examine cases where the dark matter follows a pure Navarro, Frenk & White (NFW) profile and where an initial NFW halo contracts adiabatically in response to the formation of the galaxy. We find that both of these scenarios can produce a reasonable fit to the observed rotation curve data. However, a pure NFW model requires a concentration c vir = 51 which is well outside the range predicted in Λcold dark matter cosmology and is therefore disfavoured. An adiabatically contracted NFW halo favours an initial concentration c vir = 20 and virial mass 8.2 × 10 11 M ⊙ , and this is in line with the cosmological expectations for a galaxy of the size of M31. The best‐fitting mass is consistent with published estimates from Andromeda Stream kinematics, satellite galaxy radial velocities and planetary nebulae studies. Finally, using the known linear correlation between rotation curve shear and spiral arm pitch angle, we show that the stellar spiral arm pitch angle of M31 (which cannot be deduced from imaging data due to the galaxy's inclination) is P =247 ± 44.