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arXiv 2310.02464astro-ph.GA
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本星系群及更远区域中矮星系空间分布与运动学的各向异性

Anisotropies in the spatial distribution and kinematics of dwarf galaxies in the Local Group and beyond

Isabel M. E. Santos-Santos, Julio F. Navarro, Alan McConnachie

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10 pages, 5 figures, submitted to MNRAS. [Fig. 1 is a video that will play on compatible software (e.g. Okular and Adobe Acrobat, but not Preview or browser viewers).]
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AI总结：

本研究利用APOSTLE宇宙学模拟分析本星系群矮星系分布与运动的各向异性，发现模拟与观测结果存在差异，推测可能由观测不完备导致，需深度全天巡天验证。

摘要：

本星系群（Local Group, LG）由M31与银河系（Milky Way, MW）的双星系统主导，这一构型表明本星系群及其周边的质量分布应具有高度各向异性。我们利用APOSTLE宇宙学模拟，研究这种各向异性如何在距离银河系3 Mpc范围内的矮星系的空间分布和运动学中体现。模拟结果显示，矮星系明显倾向于分布在靠近银河系-M31连线所定义的轴线上，即使是位于本星系群外围（LG periphery, LGP；即距离满足1.25<d/Mpc<3的矮星系）的矮星系也是如此。本星系群外围的“哈勃流”也受到影响；在距离银河系固定的位置，平均退行速度<V_{rad}>随与M31的角距离变化，在反M31方向达到峰值，在M31后方达到最小值。M31与银河系的联合质量会减缓局域膨胀；APOSTLE模拟中的本星系群“转向半径”（即<V_{rad}>=0的位置）位于距离本星系群质心约1.25 Mpc处，且至少在3 Mpc范围内都未达到纯哈勃流（即<V_{rad}> ~ H_0*d的状态）。预测的流动非常“冷”，质心速度弥散小于40 km/s。将这些预测特征与现有观测结果对比，得到的结果好坏参半。有明确的观测证据表明本星系群外围的视向速度V_{rad}存在角各向异性，但几乎没有证据显示本星系群外围的矮星系沿银河系-M31轴线存在偏好的空间分布。观测到的局域哈勃流也存在特殊性：尽管流动的冷度与模拟结果一致，但它的减速程度明显更低——相对于银河系，平均而言，距离d~1.25 Mpc以外的所有星系似乎都处于纯哈勃流状态。我们认为这些异常可能源于观测的不完备性和天空覆盖的不均匀性，但完整的解释可能需要等到深度全天巡天完成，以填补我们目前对近邻矮星系清查的空白。

英文摘要：

The Local Group (LG) of galaxies is dominated by the M31 and Milky Way (MW) pair, a configuration which suggests that the mass distribution in the LG and its surroundings should be highly anisotropic. We use the APOSTLE cosmological simulations to examine how this anisotropy manifests on the spatial distribution and kinematics of dwarf galaxies out to a distance of 3 Mpc from the MW. The simulations indicate a clear preference for dwarfs to be located close to the axis defined by the MW-M31 direction, even for dwarfs in the LG periphery (LGP; i.e., those at distances 1.25<d/Mpc<3). The LGP "Hubble flow" is also affected; at fixed distance from the MW the mean recession speed, <V_{rad} >, varies with angular distance to M31, peaking in the anti-M31 direction and reaching a minimum behind M31. The combined M31-MW mass decelerates the local expansion; the LG "turnaround radius" (where <V_{rad}>=0) in APOSTLE is located at r ~ 1.25 Mpc from the LG barycentre and the pure Hubble flow (where <V_{rad}> ~ H_0*d) is not reached out to at least 3 Mpc. The predicted flow is very cold, with a barycentric dispersion of <40 km/s. A comparison of these predicted features with existing observations gives mixed results. There is clear observational evidence for an angular anisotropy in V_{rad} around the LGP, but little evidence for a preferred spatial distribution of LGP dwarfs along the MW-M31 axis. The observed local Hubble flow is also peculiar. Although the coldness of the flow is consistent with the simulations, it is significantly less decelerated: relative to the MW, on average, all galaxies beyond d~1.25 Mpc seem to be on a pure Hubble flow. We argue that these oddities may result from incompleteness and inhomogeneous sky coverage, but a full explanation may need to await the completion of deep all-sky surveys able to fill the gaps in our current inventory of nearby dwarfs.

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