ΛCDM-based Models for the Milky Way and M31. I. Dynamical Models

By Anatoly Klypin, HongSheng Zhao, R. Somerville. 2001

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We apply standard disk formation theory with adiabatic contraction within cuspy halo models predicted by the standard cold dark matter (ΛCDM) cosmology. The resulting models are confronted with the broad range of observational data available for the Milky Way and M31 galaxies. We find that there is a narrow range of parameters that can satisfy the observational constraints, but within this range, the models score remarkably well. Our favored models have virial masses of 1012 and 1.6 × 1012 M☉ for the Galaxy and for M31, respectively, average spin parameters λ ≈ 0.03-0.05, and concentrations Cvir = 10-17, typical for halos of this mass in the standard ΛCDM cosmology. The models require neither dark matter modifications nor flat cores to fit the observational data. We explore two types of models, with and without the exchange of angular momentum between the dark matter and the baryons. The models without exchange give reasonable rotation curves, fulfill constraints in the solar neighborhood, and satisfy constraints at larger radii, but they may be problematic for fast rotating central bars. We explore models in which the baryons experience additional contraction due to loss of angular momentum to the surrounding dark matter. These models produce similar global properties, but the dark matter is only a 25% of the total mass in the central 3 kpc region, allowing a fast rotating bar to persist. According to preliminary calculations, our model galaxies probably have sufficient baryonic mass in the central ~3.5 kpc to reproduce recent observational values of the optical depth to microlensing events toward the Galactic center. Our dynamical models unequivocally require that about 50% of all the gas inside the virial radius must not be in the disk or in the bulge, a result that is obtained naturally in standard semianalytic models. Assuming that the Milky Way is "typical," we investigate whether the range of virial masses allowed by our dynamical models is compatible with constraints from the galaxy luminosity function. We find that if the Milky Way has a luminosity MK = -24.0, then these constraints are satisfied, but if it is more luminous (as expected if it lies on the Tully-Fisher relation), then the predicted space density is larger than the observed space density of galaxies of the corresponding luminosity by a factor of 1.5-2. We conclude that observed rotation curves and dynamical properties of "normal" spiral galaxies appear to be consistent with standard ΛCDM.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/4592f346927c8472067f516c97b2b5c41d09c46b

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Citations in the corpus

Dark Matter Subhalos and the Dwarf Satellites of the Milky Way (2008, background): “…Galaxy halo is still quite uncertain: since the effects of disk formation on the total mass distribution are still poorly constrained, the possible range of dark matter halo sizes that could form and host a 220 km s−1 disk is quite large, with Vhost between 150 and 220 km s−1 (Klypin et al. 2002).”
Scalar multiplet dark matter (2009, background): “ the galactic disk is believed to be the most concentrated, is the most promising region to probe for DM annihilations. If the halo is very cuspy, as simulations [52–54] and some dynamical mechanisms [55] suggest, observation of photons or neutrinos from the GC can provide a clean signature of the p”
CONSTRAINING THE MILKY WAY'S HOT GAS HALO WITH O vii AND O viii EMISSION LINES (2014, background): “Estimates of the Milky Way’s Rvir range between 207 kpc (Loeb et al. 2005) and 277 kpc (Shattow & Loeb 2009) with additional estimates in between (Klypin et al. 2002).”
On the Continuing Formation of the Andromeda Galaxy: Detection of H I Clouds in the M31 Halo (2003, result): “These two mass determinations are in good agreement with independent total mass estimates of 4× 1011 M⊙ within a radius of 30 kpc (Brinks & Burton 1984) and 1.6× 1012 M⊙ within Andromeda’s virial radius of 300 kpc (Klypin et al. 2002).”
Forming disc galaxies in ΛCDM simulations (2006, background): “GAL1, the largest halo, is more massive than that of our MW, as a recent analysis points to a MW halo of about 1012 M (Klypin et al. 2002).”
The formation of disc galaxies in a ΛCDM universe (2010, methodology): “We note that our own Galaxy and M31 also might be strong outliers in this analysis, considering the inferred η from mass modelling (Klypin et al. 2002; Seigar et al. 2008) as well as via recent MW halo mass estimates (Xue et al. 2008).”