AI 中文总结
本研究利用Pantheon+超新星数据，发现H₀偶极振幅随红移增大而减小，低红移（z_min≲0.032）时存在2-3σ偶极信号，其方向接近Shapley超星系团与CMB偶极方向，证实H₀偶极为低红移特征。
AI 中文摘要
我们利用Ia型超新星的Pantheon+汇编数据，研究局域宇宙膨胀率H₀中的偶极结构。我们在低红移区间z_min < z < 0.2（在CMC静止系中评估）内重构全天H₀的方向图。为进行层析分析，我们在z_min∈[0.015, 0.045]范围内选取10个不同值。我们发现，对于最低红移区间，偶极振幅A_dip=1.16±0.28 km/s/Mpc；随着z_min增大，A_dip单调降至0.35±0.52 km/s/Mpc。由于A_dip是正定的，在各向同性宇宙中A_dip>0是固有属性，因此为评估统计显著性，我们将结果与基于ΛCDM模型及相同红移区间生成的1000次蒙特卡洛模拟得到的A_dip进行比较。我们的结果显示，当z_min≲0.032时，存在2-3σ的偶极模式（取决于显著性水平的计算方式）。对于信号仍保持统计显著性（>2σ）的红移阈值，推断出的偶极方向接近Shapley超星系团和CMB偶极方向。随着z_min增大，偶极振幅减小，符合更高红移宇宙各向同性的预期，但最大对跖点H₀测量值的差值ΔH₀^max保留了各向异性的信号，该信号在偶极假设中消失。所有估计量的统计显著性随z_min增大而降低，表明任何H₀偶极都是低红移特征。
英文摘要
We examine the dipole structure in the local cosmic expansion rate $H_0$ using the Pantheon+ compilation of Type Ia supernovae. We reconstruct directional maps of $H_0$ across the sky within the low-redshift regime, $z_{\rm min} < z < 0.2$, evaluated in the CMB rest frame. To perform a tomographic analysis, we choose 10 different values for $z_{\rm min}\in [0.015 , 0.045]$ range. We find a dipole amplitude $A_{\rm dip}=1.16\pm0.28\ {\rm km/s/Mpc}$ for the lowest bin, monotonically decreasing to $A_{\rm dip} =0.35\pm0.52\ {\rm km/s/Mpc}$, as we increase $z_{\rm min}$. Since $A_{\rm dip}$ is positive-definite, by construction $A_{\rm dip} > 0$ even in an isotropic universe, thus to assess the statistical significance, we compare to $A_{\rm dip}$ generated from 1000 Monte Carlo simulations based on the $Λ$CDM model and the same redshift ranges. Our results reveal a $2-3σ$ dipole pattern (depending on how the significance level is computed) for $z_{\rm min}\lesssim 0.032$. For redshift thresholds where the signal remains statistically significant ($>2σ$), the inferred dipole direction points close to Shapley supercluster and CMB dipole directions. As $z_{\rm min}$ increases, the dipole amplitude diminishes in line with expectations of a higher redshift isotropic Universe, but the difference in maximal antipodal $H_0$ determinations, $Δ\text{H}_0^{\rm max}$, retain a signal of an anisotropy that disappears in the dipole ansatz. The decreasing statistical significance of all estimators with increasing $z_{\rm min}$ suggests that any $H_0$ dipole is a low-redshift feature.
Comments17pages, 8 Figures, 3 Tables
