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arXiv 0910.4168astro-ph.CO
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NGC 4649(M60)的超大质量黑洞和暗物质晕

The Supermassive Black Hole and Dark Matter Halo of NGC 4649 (M60)

Juntai Shen, Karl Gebhardt

摘要:

我们应用轴对称轨道叠加模型估算了NGC 4649的超大质量黑洞质量和暗物质晕轮廓。我们包括了哈勃太空望远镜、恒星和球状星团观测的数据集。我们的模型给出了黑洞质量= 4.5 \pm 1.0 10^9 \Msun和M/L = 8.7 \pm 1.0(或8.0 \pm 0.9后,前景银河系消光校正)。我们确认存在一个暗物质晕,但恒星质量占主导地位的有效半径内。由于大半径下球状星团数据的稀疏性,暗晕的参数受到的限制较少。我们发现,在NGC 4649的动力学质量剖面,从我们的建模是一致的大于从X射线数据在大多数的径向范围约60%至80%。这意味着,要么某些形式的非热压力需要包括在内,假设的流体静力平衡可能不是一个很好的近似在NGC 4649的X射线模型,或我们的假设中使用的动力学模型是有偏见的。我们的新黑洞质量大约是先前公布的值的两倍;早期的模型没有充分地对所需的轨道进行采样,以匹配星系中心的大切向各向异性。如果我们假设没有暗物质,黑洞质量和M/L的结果并没有显着变化,我们归因于包含HST光谱,稀疏的球状星团运动学和弥漫的暗物质晕。没有HST数据,黑洞探测的意义就大大降低。

英文摘要:

We apply the axisymmetric orbit superposition modeling to estimate the mass of the supermassive black hole and dark matter halo profile of NGC 4649. We have included data sets from the Hubble Space Telescope, stellar, and globular cluster observations. Our modeling gives the black hole mass = 4.5 \pm 1.0 10^9 \Msun and M/L = 8.7 \pm 1.0 (or 8.0 \pm 0.9 after foreground Galactic extinction is corrected). We confirm the presence of a dark matter halo, but the stellar mass dominates inside the effective radius. The parameters of the dark halo are less constrained due to the sparse globular cluster data at large radii. We find that in NGC 4649 the dynamical mass profile from our modeling is consistently larger than that derived from the X-ray data over most of the radial range by roughly 60% to 80%. It implies that either some forms of non-thermal pressure need to be included, the assumed hydrostatic equilibrium may not be a good approximation in the X-ray modelings of NGC 4649, or our assumptions used in the dynamical models are biased. Our new black hole mass is about two times larger than the previous published value; the earlier model did not adequately sample the orbits required to match the large tangential anisotropy in the galaxy center. If we assume that there is no dark matter, the results on the black hole mass and M/L do not change significantly, which we attribute to the inclusion of HST spectra, the sparse globular cluster kinematics, and a diffuse dark matter halo. Without the HST data, the significance of the black hole detection is greatly reduced.

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