Action-based distribution function modelling for constraining the shape of the Galactic dark matter halo
Action-based distribution function modelling for constraining the shape of the Galactic dark matter halo
复制标题
用于约束银河暗物质晕形状的基于动作的分布函数建模
DOI：
10.1093/mnras/stab2898
复制
发表时间：
2021
影响因子：
4.8
通讯作者：
Vasiliev Eugene
中科院分区：
文献类型：
--
作者：
Hattori Kohei;Valluri Monica;Vasiliev Eugene
We estimate the 3D density profile of the Galactic dark matter (DM) halo withinr≲ 30 kpc from the Galactic centre by using the astrometric data for halo RR Lyrae stars from Gaia DR2. We model both the stellar halo distribution function and the Galactic potential, fully taking into account the survey selection function, the observational errors, and the missing line-of-sight velocity data for RR Lyrae stars. With a Bayesian method, we infer the model parameters, including the density flattening of the DM haloq, which is assumed to be constant as a function of radius. We find that 99 per cent of the posterior distribution ofqis located atq> 0.963, which strongly disfavours a flattened DM halo. We cannot draw any conclusions as to whether the Galactic DM halo atis prolate, because we restrict ourselves to axisymmetric oblate halo models withq≤ 1. Our DM density profile might be biased especially in the inner few kpc, due to the uncertainty in the baryonic distribution. Our result is in tension with predictions from cosmological hydrodynamical simulations that advocate more oblate (<q> ∼ 0.8 ± 0.15) DM haloes withinof the virial radius for Milky-Way-sized galaxies. An alternative possibility, based on our validation tests with a cosmological simulation, is that the true valueqof the Galactic halo could be consistent with cosmological simulations but that disequilibrium in the Milky Way potential is inflating our measurement ofqby 0.1–0.2. As a by-product, our model constrains the DM density in the Solar neighbourhood to be $\rho _{\mathrm{DM},\odot } = (9.01^{+0.18}_{-0.20})\times 10^{-3}{\,\rm M_\odot} \mathrm{pc}^{-3} = 0.342^{+0.007}_{-0.007}$ GeVcm−3, consistent with other recent measurements.
We estimate the 3D density profile of the Galactic dark matter (DM) halo withinr≲ 30 kpc from the Galactic centre by using the astrometric data for halo RR Lyrae stars from Gaia DR2. We model both the stellar halo distribution function and the Galactic potential, fully taking into account the survey selection function, the observational errors, and the missing line-of-sight velocity data for RR Lyrae stars. With a Bayesian method, we infer the model parameters, including the density flattening of the DM haloq, which is assumed to be constant as a function of radius. We find that 99 per cent of the posterior distribution ofqis located atq> 0.963, which strongly disfavours a flattened DM halo. We cannot draw any conclusions as to whether the Galactic DM halo atis prolate, because we restrict ourselves to axisymmetric oblate halo models withq≤ 1. Our DM density profile might be biased especially in the inner few kpc, due to the uncertainty in the baryonic distribution. Our result is in tension with predictions from cosmological hydrodynamical simulations that advocate more oblate (<q> ∼ 0.8 ± 0.15) DM haloes withinof the virial radius for Milky-Way-sized galaxies. An alternative possibility, based on our validation tests with a cosmological simulation, is that the true valueqof the Galactic halo could be consistent with cosmological simulations but that disequilibrium in the Milky Way potential is inflating our measurement ofqby 0.1–0.2. As a by-product, our model constrains the DM density in the Solar neighbourhood to be $\rho _{\mathrm{DM},\odot } = (9.01^{+0.18}_{-0.20})\times 10^{-3}{\,\rm M_\odot} \mathrm{pc}^{-3} = 0.342^{+0.007}_{-0.007}$ GeVcm−3, consistent with other recent measurements.