Dearth of dark matter or massive dark halo? Mass-shape-anisotropy degeneracies revealed by nmagic dynamical models of the elliptical galaxy NGC 3379
Dearth of dark matter or massive dark halo? Mass-shape-anisotropy degeneracies revealed by nmagic dynamical models of the elliptical galaxy NGC 3379
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DOI：
10.1111/j.1365-2966.2009.14553.x
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发表时间：
2008-04
影响因子：
4.8
通讯作者：
F. Lorenzi;O. Gerhard;L. Coccato;M. Arnaboldi;M. Capaccioli;N. Douglas;K. Freeman;K. Kuijken;M. Merrifield;N. Napolitano;E. Noordermeer;A. Romanowsky;V. Debattista
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作者：
F. Lorenzi;O. Gerhard;L. Coccato;M. Arnaboldi;M. Capaccioli;N. Douglas;K. Freeman;K. Kuijken;M. Merrifield;N. Napolitano;E. Noordermeer;A. Romanowsky;V. Debattista
行星状星云光谱仪（PNS）调查的最新结果显示，在附近的椭圆星系NGC 3379中，速度色散分布迅速下降，怀疑这个中等光度的星系是否具有冷暗物质（CDM）宇宙学中预期的暗物质（DM）晕。我们提出了一个详细的动力学研究这个星系，结合地面长缝光谱，积分场数据从光谱面积单位研究光学星云（SAURON）仪器和PNS数据达到超过7个有效半径。我们构造的动力学模型与灵活的χ 2 -量身定制（χ 2 M2M）粒子方法实现的NMAGIC代码。我们适合球形，轴对称和一些三轴模型的光度和结合的运动学数据在一个序列的引力势，其圆速度曲线在大半径的变化之间的近开普勒下降和大规模晕产生的近平坦的形状。我们发现，模型的晕质量，各向异性，形状和倾角的范围是很好的代表性的数据。特别是，这些数据与以恒星质量为主的近各向同性系统和具有强烈径向各向异性外部部分（在7 Re时β 0.8）的中等质量晕模型都是一致的。正式的似然极限将排除（在1σ）只有恒星的模型，以及vcirc（7 Re）250 km s −1的晕模型。所有拟合所有数据的有效模型在千兆年内都是动态稳定的，包括最各向异性的模型。总的来说，NGC 3379到7 Re的运动学数据与该星系的质量分布范围一致。NGC 3379很可能有一个DM光环，正如最近的合并所预测的那样。
Recent results from the Planetary Nebula Spectrograph (PNS) survey have revealed a rapidly falling velocity dispersion profile in the nearby elliptical galaxy NGC 3379, casting doubts on whether this intermediate-luminosity galaxy has the kind of dark matter (DM) halo expected in � cold dark matter (� CDM) cosmology. We present a detailed dynamical study of this galaxy, combining ground based long-slit spectroscopy, integral-field data from the Spectrographic Areal Unit for Research on Optical Nebulae (SAURON) instrument and PNS data reaching to more than seven effective radii. We construct dynamical models with the flexible χ 2 -made-to-measure (χ 2 M2M) particle method implemented in the NMAGIC code. We fit spherical, axisymmetric and some triaxial models to the photometric and combined kinematic data in a sequence of gravitational potentials whose circular velocity curves at large radii vary between a near-Keplerian decline and the nearly flat shapes generated by massive haloes. We find that models with a range of halo masses, anisotropies, shapes and inclinations are good representations of the data. In particular, the data are consistent both with nearisotropic systems dominated by the stellar mass and with models in moderately massive haloes with strongly radially anisotropic outer parts (β 0.8 at 7Re). Formal likelihood limits would exclude (at 1σ ) the model with stars only, as well as halo models with vcirc(7Re) 250 km s −1 . All valid models fitting all the data are dynamically stable over gigayears, including the most anisotropic ones. Overall the kinematic data for NGC 3379 out to 7Re are consistent with a range of mass distributions in this galaxy. NGC 3379 may well have a DM halo as predicted by recent merger ¯