arXiv 1406.41302014-06astro-ph.GAastro-ph.COhep-ph

用RAVE恒星约束银河系的暗晕

Constraining the Galaxy's dark halo with RAVE stars

T. Piffl, J. Binney, P. J. McMillan, M. Steinmetz, A. Helmi, R. F. G. Wyse, O. Bienaymé, J. Bland-Hawthorn, K. Freeman, B. Gibson, G. Gilmore, E. K. Grebel, G. … 展开作者

T. Piffl, J. Binney, P. J. McMillan, M. Steinmetz, A. Helmi, R. F. G. Wyse, O. Bienaymé, J. Bland-Hawthorn, K. Freeman, B. Gibson, G. Gilmore, E. K. Grebel, G. Kordopatis, J. F. Navarro, Q. Parker, W. A. Reid, G. Seabroke, A. Siebert, F. Watson, T. Zwitter

备注：: 20 pages, 17 figures, accepted for publication in MNRAS
DOI：: 10.1093/mnras/stu1948

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摘要：

我们使用的$\sim200\,000$巨星，位于$\sim 1.5$千秒差距的平面内的运动学来测量太阳附近的质量密度的垂直剖面。我们发现暗晕穿过太阳的等密度面（$(6\pm0.9)\times10^{10}\,\mathrm{M_\odot}$）内的暗质量和面内密度（$0.9$）几乎与（扁）晕的轴比$q$无关。如果光环是球形的，那么太阳上46%的径向力是由重子提供的，银河系只有4.3%的质量是重子。如果晕是扁平的，重子对局部径向力和星系质量的贡献就更小了。太阳所在位置的暗物质密度为$0.0126\,q^{-0.89}\,\mathrm{M_\odot\,pc^{-3}}=0.48\,q^{-0.89}\,\mathrm{GeV\,cm^{-3}}$。当结合其他文献结果，我们发现一个温和的扁圆暗晕与$q \simeq 0.8$的提示。我们的太阳半径内的暗物质的值是大于宇宙学暗物质的模拟预测，但在良好的协议与模拟，一旦重子的影响被考虑在内。我们的质量模型包括三个双指数盘，一个扁球形凸起和Navarro-Frenk-White暗物质晕，我们通过找到依赖于三个作用积分的分布函数$f(\mathbf{J})$来模拟RAVE星在相应引力场中的动力学。统计误差完全被系统的不确定性所淹没，其中最重要的是光度和光谱样本中恒星的距离以及太阳到银河系中心的距离。除了暗晕变平以外的其他系统学产生的总体不确定度为$\sim 15$ %。

英文摘要：

We use the kinematics of $\sim200\,000$ giant stars that lie within $\sim 1.5$ kpc of the plane to measure the vertical profile of mass density near the Sun. We find that the dark mass contained within the isodensity surface of the dark halo that passes through the Sun ($(6\pm0.9)\times10^{10}\,\mathrm{M_\odot}$), and the surface density within $0.9$ kpc of the plane ($(69\pm10)\,\mathrm{M_\odot\,pc^{-2}}$) are almost independent of the (oblate) halo's axis ratio $q$. If the halo is spherical, 46 per cent of the radial force on the Sun is provided by baryons, and only 4.3 per cent of the Galaxy's mass is baryonic. If the halo is flattened, the baryons contribute even less strongly to the local radial force and to the Galaxy's mass. The dark-matter density at the location of the Sun is $0.0126\,q^{-0.89}\,\mathrm{M_\odot\,pc^{-3}}=0.48\,q^{-0.89}\,\mathrm{GeV\,cm^{-3}}$. When combined with other literature results we find hints for a mildly oblate dark halo with $q \simeq 0.8$. Our value for the dark mass within the solar radius is larger than that predicted by cosmological dark-matter-only simulations but in good agreement with simulations once the effects of baryonic infall are taken into account. Our mass models consist of three double-exponential discs, an oblate bulge and a Navarro-Frenk-White dark-matter halo, and we model the dynamics of the RAVE stars in the corresponding gravitational fields by finding distribution functions $f(\mathbf{J})$ that depend on three action integrals. Statistical errors are completely swamped by systematic uncertainties, the most important of which are the distance to the stars in the photometric and spectroscopic samples and the solar distance to the Galactic centre. Systematics other than the flattening of the dark halo yield overall uncertainties $\sim 15$ per cent.

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