Norma集群（ACO3627）-- III。近红外KS波段基平面的距离和特征速度
The Norma cluster (ACO3627) -- III. The Distance and Peculiar Velocity via the Near-Infrared Ks-band Fundamental Plane
摘要：
虽然Norma（ACO 3627）是大吸引子（GA）区域中最丰富的集群，但其在局部动力学中的作用却知之甚少。Norma星系团的平均红移（z_CMB）为0.0165，被认为是GA的“核心”。我们利用K波段的基平面（FP）测量了Norma星系团相对于Coma星系团的距离。我们报告FP测光参数（有效半径和表面亮度），来自ESO NTT SOFI图像，和速度色散，从AAT 2dF光谱，为31个早型星系团。对于后发座星系团，我们使用2 MASS图像和SDSS速度色散测量的121个早型星系生成校准FP数据集。对于合并的正常昏迷样本，我们测量的FP系数为a=1.465+/-0.059和b=0.326+/-0.020。我们发现一个均方根散射，在日志（中心速度色散）为0.08德克斯，对应于每个星系的距离不确定性为28%。Norma和Coma FP之间的零点偏移为0.154+/-0.014 dex。假设后发座星系团相对于宇宙微波背景坐标系是静止的，z_CMB（Coma）=0.0240，我们得到它到诺玛星系团的距离为5026+/-160 km/s，其特有速度为-72+/-170 km/s，即：与零一致。这是低于以前报道的积极特有的速度集群/集团/星系在GA地区，因此诺玛集群可能确实代表GA的“核心”。
英文摘要：
While Norma (ACO3627) is the richest cluster in the Great Attractor (GA) region, its role in the local dynamics is poorly understood. The Norma cluster has a mean redshift (z_CMB) of 0.0165 and has been proposed as the "core" of the GA. We have used the Ks-band Fundamental Plane (FP) to measure Norma cluster's distance with respect to the Coma cluster. We report FP photometry parameters (effective radii and surface brightnesses), derived from ESO NTT SOFI images, and velocity dispersions, from AAT 2dF spectroscopy, for 31 early-type galaxies in the cluster. For the Coma cluster we use 2MASS images and SDSS velocity dispersion measurements for 121 early-type galaxies to generate the calibrating FP dataset. For the combined Norma-Coma sample we measure FP coefficients of a=1.465+/-0.059 and b=0.326+/-0.020. We find an rms scatter, in log(central velocity dispersion) of 0.08 dex which corresponds to a distance uncertainty of 28% per galaxy. The zero point offset between Norma's and Coma's FPs is 0.154+/-0.014 dex. Assuming that the Coma cluster is at rest with respect to the cosmic microwave background frame and z_CMB(Coma)=0.0240, we derive a distance to the Norma cluster of 5026+/-160 km/s, and the derived peculiar velocity is -72+/-170 km/s, i.e., consistent with zero. This is lower than previously reported positive peculiar velocities for clusters/groups/galaxies in the GA region and hence the Norma cluster may indeed represent the GA's "core".
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