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The SLUGGS survey: the mass distribution in early-type galaxies within five effective radii and beyond

机译：SLUGGS调查：五个有效半径以内及以外的早期型星系的质量分布

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We study mass distributions within and beyond 5 effective radii (Re) in 23 early-type galaxies from the SAGES Legacy Unifying Globulars and Galaxies Survey, using their globular cluster (GC) kinematic data. The data are obtained with Keck/DEep Imaging Multi-Object Spectrograph, and consist of line-of-sight velocities for ∼3500 GCs, measured with a high precision of ∼15 km s−1 per GC and extending out to ∼13 Re. We obtain the mass distribution in each galaxy using the tracer mass estimator of Watkins et al. and account for kinematic substructures, rotation of the GC systems and galaxy flattening in our mass estimates. The observed scatter between our mass estimates and results from the literature is less than 0.2 dex. The dark matter fraction within 5 Re (fDM) increases from ∼0.6 to ∼0.8 for low- and high-mass galaxies, respectively, with some intermediate-mass galaxies (M* ∼ 1011 M⊙) having low fDM ∼ 0.3, which appears at odds with predictions from simple galaxy models. We show that these results are independent of the adopted orbital anisotropy, stellar mass-to-light (M/L) ratio, and the assumed slope of the gravitational potential. However, the low fDM in the ∼1011 M⊙ galaxies agrees with the cosmological simulations of Wu et al. where the pristine dark matter distribution has been modified by baryons during the galaxy assembly process. We find hints that these M* ∼ 1011 M⊙ galaxies with low fDM have very diffuse dark matter haloes, implying that they assembled late. Beyond 5 Re, the M/L gradients are steeper in the more massive galaxies and shallower in both low and intermediate mass galaxies.
机译：我们使用SAGES旧版统一球状星系和星系调查研究了23个早期星系中5个有效半径（Re）之内和之外的质量分布，并使用它们的球状星团（GC）运动数据。数据是使用Keck / DEep成像多目标光谱仪获得的，包括约3500个GC的视线速度，每个GC的测量精度为〜15 km s-1，并扩展到了约13 Re。我们使用Watkins等人的示踪质量估计器获得每个星系中的质量分布。并在我们的质量估算中考虑了运动学的子结构，GC系统的旋转和星系展平。我们的质量估计与文献结果之间的分散度小于0.2 dex。对于低质量和高质量星系，5 Re（fDM）内的暗物质分数分别从〜0.6增至〜0.8，而某些中等质量星系（M *〜1011M⊙）的fDM则低至0.3。与简单星系模型的预测不一致。我们表明，这些结果与所采用的轨道各向异性，恒星质光比（M / L）和重力势的假定斜率无关。然而，在约1011M⊙星系中的低fDM与Wu等人的宇宙学模拟相符。在星系组装过程中，原始的暗物质分布已被重子改变。我们发现这些fDM较低的M *〜1011M⊙星系具有非常弥散的暗物质晕，这意味着它们组装较晚。超过5 Re，M / L梯度在质量较大的星系中较陡，而在中低质量的星系中均较浅。

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