Hobby-Eberly望远镜对NGC 821暗晕的观测
Hobby-Eberly Telescope Observations of the Dark Halo in NGC 821
摘要：
我们目前的视线恒星速度分布的椭圆星系NGC 821获得约100弧秒（超过2个有效半径）的长缝光谱从霍比-埃伯利望远镜。我们测量的恒星视线的速度分布大于行星状星云在类似的半径测量。我们适合轴对称轨道叠加模型与一系列的黑暗晕密度分布，包括二维运动学在较小的半径从SAURON数据。在我们的假设范围内，最佳拟合模型在100弧秒内给出的总封闭质量为2.0 × 10^11 M_sun，精度为2%;该质量在晕和恒星之间平分。在1R_e处，最适合的暗物质晕占星系总质量的13%。这个暗晕与之前通过行星状星云测量得出的星系中几乎没有暗物质晕的说法不一致。我们发现，幂律暗晕与斜率0.1是最好的拟合模型，没有暗晕和NFW模型是更差的拟合在大于99%的置信水平。NGC 821似乎没有预期的暗晕密度分布。恒星速度分布的内部矩表明，没有暗晕的模型是径向各向异性在小半径和切向各向同性在大半径，而最佳拟合晕模型是轻微的径向各向异性在所有半径。我们测试了模型平滑的潜在影响，发现在误差范围内对我们的结果没有影响。最后，我们运行模型使用行星状星云的运动学，并假设我们的最佳拟合晕，并发现行星状星云需要径向轨道在整个星系。
英文摘要：
We present line-of-sight stellar velocity distributions of elliptical galaxy NGC 821 obtained to approximately 100 arcsec (over 2 effective radii) with long-slit spectroscopy from the Hobby-Eberly Telescope. Our measured stellar line-of-sight velocity distributions are larger than the planetary nebulae measurements at similar radii. We fit axisymmetric orbit-superposition models with a range of dark halo density profiles, including two-dimensional kinematics at smaller radii from SAURON data. Within our assumptions, the best-fitted model gives a total enclosed mass of 2.0x10^11 M_sun within 100 arcsec, with an accuracy of 2%; this mass is equally divided between halo and stars. At 1R_e the best-fitted dark matter halo accounts for 13% of the total mass in the galaxy. This dark halo is inconsistent with previous claims of little to no dark matter halo in this galaxy from planetary nebula measurements. We find that a power-law dark halo with a slope 0.1 is the best-fitted model; both the no dark halo and NFW models are worse fits at a greater than 99% confidence level. NGC 821 does not appear to have the expected dark halo density profile. The internal moments of the stellar velocity distribution show that the model with no dark halo is radially anisotropic at small radii and tangentially isotropic at large radii, while the best-fitted halo models are slightly radially anisotropic at all radii. We test the potential effects of model smoothing and find that there are no effects on our results within the errors. Finally, we run models using the planetary nebula kinematics and assuming our best-fitted halos and find that the planetary nebulae require radial orbits throughout the galaxy.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
