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外文期刊>The Astrophysical journal
>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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FURTHER EVIDENCE FOR LARGE CENTRAL MASS-TO-LIGHT RATIOS IN EARLY-TYPE GALAXIES: THE CASE OF ELLIPTICALS AND LENTICULARS IN THE A262 CLUSTER*
We present new radially resolved spectroscopy of eight early-type galaxies in the A262 cluster. The measurements include stellar rotation, velocity dispersion, H 3 and H 4 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 z DM ≈ 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 r eff. 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 r eff, (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 r eff. 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.
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机译：我们提出了A262集群中八个早期类型星系的新径向分辨光谱。测量包括恒星旋转，速度分散，沿主轴线和短轴以及中间轴的视线速度分布的H 3和H 4系数，以及Mg，Fe和Hβ的线强度指数分布。测量沿不同轴的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得出动力学的质光比和暗物质密度，并从单个恒星种群模型中补充了星系的年龄，金属性和α元素丰度。电离气体运动学为有关银河系的方向和本征形状的模型假设提供了有价值的一致性检查。四个星系具有明显的暗物质探测能力，其光晕的密度约为相同恒星质量旋涡中密度的10倍。通过校准暗物质密度以进行宇宙学模拟，我们发现z DM≈1-3的装配红移，如先前对昏迷星团的报道。跟随光的动态质量大于Kroupa恒星初始质量函数（IMF）的预期质量，尤其是在有效半径r eff内具有高速色散σeff的星系中。这可能表明大规模星系中的“大规模” IMF。另外，大质量星系中的某些暗物质可能会非常靠近光。结合我们的昏迷早期星系比较样本，我们现在拥有24个星系中的5个，其中（1）质量跟随光达到1-3 r eff，（2）所有质量的动态质量与光之比随光变大（在Kron-Cousins R波段中约为8-10），并且（3）暗物质分数可忽略不计1-3 r eff。除非这些星系中的IMF特别“庞大”并且以某种方式与暗物质含量耦合，否则至少在某些早期类型的星系中，发光物质和暗物质之间似乎存在明显的退化。简要讨论了暴力放松的作用。
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