Accurate modeling of galaxy distributions is paramount for cosmological analysis using galaxy redshift surveys. However, this endeavor is often hindered by the computational complexity of resolving the dark matter halos that host these galaxies. To address this challenge, we propose the development of effective assembly bias models down to small scales, i.e., going beyond the local density dependence capturing non-local cosmic evolution. We introduce a hierarchical cosmic web classification that indirectly captures up to third-order long- and short-range non-local bias terms. This classification system also enables us to maintain positive definite parametric bias expansions. Specifically, we subdivide the traditional cosmic web classification, which is based on the eigenvalues of the tidal field tensor, with an additional classification based on the Hessian matrix of the negative density contrast. We obtain the large-scale dark matter field on a mesh with $\sim3.9\,h^{-1}$ Mpc cell side resolution through Augmented Lagrangian Perturbation Theory. To assess the effectiveness of our model, we conduct tests using a reference halo catalogue extracted from the UNIT project simulation, which was run within a cubical volume of 1 $h^{-1}$ Gpc side. The resulting mock halo catalogs, generated through our approach, exhibit a high level of accuracy in terms of the one-, two- and three-point statistics. They reproduce the reference power-spectrum within better than 2 percent accuracy up to wavenumbers $k\sim0.8\,h$ Mpc$^{-1}$ and provide accurate bispectra within the scales that are crucial for cosmological analysis. This effective bias approach provides a forward model appropriate for field-level cosmological inference and holds significant potential for facilitating cosmological analysis of galaxy redshift surveys, particularly in the context of projects such as DESI, EUCLID, and LSST.
Direct evidence of hierarchical assembly at low masses from isolated dwarf galaxy groups
矮星系的人口统计数据长期以来一直与冷暗物质（CDM）范式的预测相矛盾。如果原始密度波动像预测的那样是无标度的，那么矮星系本身就应该有暗物质暗晕，其中最大的暗物质可能经历了恒星形成，从而形成矮星系群。矮星系的集合体被观测为更大质量星系的卫星，并且有观测和理论证据表明，这些卫星在z=0时被大质量主晕作为一个群体捕获。然而，矮星系的演化是非常容易受到环境的影响，使这些卫星群不完善的CDM探测器在低质量的制度。我们已经确定了迄今为止在低质量下形成等级结构的最清晰的例子之一：七个孤立的，光谱证实的群体，只有矮星系作为成员。每个星系群都有3-5个已知成员，重子质量约为4.4 x 10^9 ~ 2 x 10^10 Msun，并且需要质光比<100才能被引力束缚。这样的星系群在理论上是罕见的，在当前的时代观测上也是罕见的，因此为更大质量的孤立星系的可能形成机制提供了一个独特的窗口。
