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arXiv 1105.1209astro-ph.GA
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椭圆星系NGC 4649(M 60)中的行星状星云:运动学和距离重新测定

Planetary nebulae in the elliptical galaxy NGC 4649 (M 60): kinematics and distance redetermination

A. M. Teodorescu, R. H. Mendez, F. Bernardi, J. Thomas, P. Das, O. Gerhard

摘要:

利用8.2米斯巴鲁望远镜及其FOCAS卡塞格伦摄谱仪和欧洲南方天文台甚大望远镜(VLT)1号(Antu)及其FORS 2卡塞格伦摄谱仪的无狭缝光谱学方法,我们在巨大的室女座椭圆星系NGC 4649(M 60)中探测到了326个行星状星云(PN),并测量了它们的径向速度。在剔除了一些可能属于伴星系NGC 4647的PNs后,我们建立了一个包含M 60中298个PNs运动学信息的星表。利用这些径向速度,我们得出结论,他们支持的暗物质晕围绕M 60的存在。基于各向同性的双分量Hernquist模型,我们估计3个$R_{\rm e}$内的暗物质晕质量为4 $\times10^{11} M_{\odot}$,几乎是3个$R_{\rm e}$内约$10^{12} M_{\odot}$总质量的一半.这一总质量与球状星团、XMM-牛顿和钱德拉观测估计的质量相似。外部的暗物质占主导地位。更详细的动力学模型的PN数据发表在一个配套文件。我们还测量了其中许多PN的$m$(5007)幅度,并建立了218个PN的统计完整样本。得到的PN光度函数(PNLF)用于估计距离模数为30.7 $\pm$ 0.2 mag,相当于14 $\pm$ 1 Mpc。这证实了较早的PNLF距离测量,基于小得多的样本。PNLF距离模量保持比表面亮度波动(SBF)距离模量小0.4兆。

英文摘要:

Using a slitless spectroscopy method with (a) the 8.2 m Subaru telescope and its FOCAS Cassegrain spectrograph, and (b) the ESO Very Large Telescope (VLT) unit 1 (Antu) and its FORS2 Cassegrain spectrograph, we have detected 326 planetary nebulae (PNs) in the giant Virgo elliptical galaxy NGC 4649 (M 60), and we have measured their radial velocities. After rejecting some PNs more likely to belong to the companion galaxy NGC 4647, we have built a catalog with kinematic information for 298 PNs in M 60. Using these radial velocities we have concluded that they support the presence of a dark matter halo around M 60. Based on an isotropic, two-component Hernquist model, we estimate the dark matter halo mass within 3$R_{\rm e}$ to be 4$\times10^{11} M_{\odot}$, which is almost one half of the total mass of about $10^{12} M_{\odot}$ within 3$R_{\rm e}$. This total mass is similar to that estimated from globular cluster, XMM-Newton and Chandra observations. The dark matter becomes dominant outside. More detailed dynamical modeling of the PN data is being published in a companion paper. We have also measured the $m$(5007) magnitudes of many of these PNs, and built a statistically complete sample of 218 PNs. The resulting PN luminosity function (PNLF) was used to estimate a distance modulus of 30.7$\pm$0.2 mag, equivalent to 14$\pm$1 Mpc. This confirms an earlier PNLF distance measurement, based on a much smaller sample. The PNLF distance modulus remains smaller than the surface brightness fluctuation (SBF) distance modulus by 0.4 mag.

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