FURTHER EVIDENCE FOR LARGE CENTRAL MASS-TO-LIGHT RATIOS IN EARLY-TYPE GALAXIES: THE CASE OF ELLIPTICALS AND LENTICULARS IN THE A262 CLUSTER
FURTHER EVIDENCE FOR LARGE CENTRAL MASS-TO-LIGHT RATIOS IN EARLY-TYPE GALAXIES: THE CASE OF ELLIPTICALS AND LENTICULARS IN THE A262 CLUSTER
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早型星系中较大的中心质光比的进一步证据：A262 星团中椭圆星系和透镜状星系的情况
DOI：
10.1088/0004-6256/144/3/78
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发表时间：
2012
期刊：
影响因子：
--
通讯作者：
S. Pu
中科院分区：
文献类型：
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作者：
G. Wegner;E. Corsini;J. Thomas;R. Saglia;R. Bender;S. Pu
我们提出了 A262 星团中八个早期型星系的新径向分辨光谱。测量结果包括恒星自转、速度色散、沿长轴、短轴和中间轴的视线速度分布的 H3 和 H4 系数以及 Mg、Fe 和 Hβ 的线强度指数分布。沿不同轴测量六个样本星系的电离气体速度和速度色散。我们从基于轨道的动力学模型中推导出动态质光比和暗物质密度，并从单个恒星种群模型中得到星系的年龄、金属丰度和α元素丰度。电离气体运动学为有关星系方向和固有形状的模型假设提供了有价值的一致性检查。四个星系对暗物质进行了显着的探测，它们的光晕比相同恒星质量的螺旋星系密度大约高 10 倍。通过将暗物质密度校准到宇宙学模拟，我们发现 zDM ≈ 1-3 的组装红移，如之前报道的后发星团。跟随光的动力质量比 Kroupa 恒星初始质量函数 (IMF) 的预期要大，特别是在有效半径 ref 内具有高速色散 σeff 的星系中。这可能表明巨大星系中存在“巨大”IMF。或者，大质量星系中的一些暗物质可能非常紧密地跟随光。结合我们的后发早期型星系的比较样本，我们现在有 24 个星系中的 5 个，其中（1）质量跟随光达到 1-3 reff，（2）所有跟随光的质量的动态质量与光之比很大（在 Kron-Cousins R 波段中约为 8-10），以及（3）暗物质分数可以忽略不计，达到 1-3 reff。除非这些星系中的IMF特别“巨大”并且以某种方式与暗物质含量耦合，否则至少在一些早期型星系中，发光物质和暗物质之间似乎存在显着的简并性。简要讨论了剧烈放松的作用。
We present new radially resolved spectroscopy of eight early-type galaxies in the A262 cluster. The measurements include stellar rotation, velocity dispersion, H3 and H4 coefficients of the line-of-sight velocity distribution along the major and minor axes and an intermediate axis as well as line-strength index profiles of Mg, Fe, and Hβ. The ionized-gas velocity and velocity dispersion is measured for six sample galaxies along different axes. We derive dynamical mass-to-light ratios and dark matter densities from orbit-based dynamical models, complemented by the galaxies’ ages, metallicities, and α-element abundances from single stellar-population models. The ionized-gas kinematics give a valuable consistency check for the model assumptions about orientation and intrinsic shape of the galaxies. Four galaxies have a significant detection of dark matter and their halos are about 10 times denser than in spirals of the same stellar mass. By calibrating dark matter densities to cosmological simulations we find assembly redshifts of zDM ≈ 1–3, as previously reported for the Coma Cluster. The dynamical mass that follows the light is larger than expected for a Kroupa stellar initial mass function (IMF), especially in galaxies with high velocity dispersion σeff inside the effective radius reff. This could indicate a “massive” IMF in massive galaxies. Alternatively, some of the dark matter in massive galaxies could follow the light very closely. In combination with our comparison sample of Coma early-type galaxies, we now have 5 of 24 galaxies where (1) mass follows light to 1–3 reff, (2) the dynamical mass-to-light ratio of all the mass that follows the light is large (≈8–10 in the Kron-Cousins R band), and (3) the dark matter fraction is negligible to 1–3 reff. Unless the IMF in these galaxies is particularly “massive” and somehow coupled to the dark matter content, there seems to be a significant degeneracy between luminous and dark matter in at least some early-type galaxies. The role of violent relaxation is briefly discussed.