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arXiv 1609.05477astro-ph.GA
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通过透镜和动力学揭示的螺旋星系的质量分布

A spiral galaxy's mass distribution uncovered through lensing and dynamics

Wilma H. Trick, Glenn van de Ven, Aaron A. Dutton

摘要:

利用引力透镜和恒星动力学模型,研究了一个具有反向旋转恒星核的螺旋星系SDSS J1331+3628(J1331)的物质分布.通过将引力势模型拟合到J1331凸起周围的四组透镜图像,我们将爱因斯坦半径R_ein =(0.91 +/- 0.02 μ“(~= 1.83 +/- 0.04 kpc)内的质量严格限制在4%以内:M_ein =(7.8 +/- 0.3)x 10^10 M_Sun。我们观察到的长缝主轴恒星运动学在J1331的中心区域找到多高斯展开(MGE)模型的恒星和暗物质分布,解决轴对称的金斯方程。透镜模型和动力学模型是独立导出的,但在~R_ein附近彼此吻合得很好。我们发现,J1331的中心需要一个陡峭的总质光比梯度。一个包含NFW晕(维里速度v_200 ~= 240 +/- 40 km/s,浓度c_200 ~= 8 +/- 2)和中等切向速度各向异性(β_z ~= -0.4 +/- 0.1)的动力学模型可以再现J1331反旋核的特征,并预测更大半径处的恒星和气体旋转曲线。然而,我们的模型不同意在大半径的速度色散观察。我们推测,原因可能是一个不平凡的结构和运动学的变化,由于可能的合并事件,在J1331的最近的过去。

英文摘要:

We investigate the matter distribution of a spiral galaxy with a counter-rotating stellar core, SDSS J1331+3628 (J1331), independently with gravitational lensing and stellar dynamical modelling. By fitting a gravitational potential model to a quadruplet of lensing images around J1331's bulge, we tightly constrain the mass inside the Einstein radius R_ein = (0.91 +/- 0.02)'' (~= 1.83 +/- 0.04 kpc) to within 4%: M_ein = (7.8 +/- 0.3) x 10^10 M_Sun. We model observed long-slit major axis stellar kinematics in J1331's central regions by finding Multi-Gaussian Expansion (MGE) models for the stellar and dark matter distribution that solve the axisymmetric Jeans equations. The lens and dynamical model are independently derived, but in very good agreement with each other around ~R_ein. We find that J1331's center requires a steep total mass-to-light ratio gradient. A dynamical model including an NFW halo (with virial velocity v_200 ~= 240 +/- 40 km/s and concentration c_200 ~= 8 +/- 2) and moderate tangential velocity anisotropy (beta_z ~= -0.4 +/- 0.1) can reproduce the signatures of J1331's counter-rotating core and predict the stellar and gas rotation curve at larger radii. However, our models do not agree with the observed velocity dispersion at large radii. We speculate that the reason could be a non-trivial change in structure and kinematics due to a possible merger event in J1331's recent past.

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