The matter environment of GAMA galaxy pairs studied with galaxy-galaxy-galaxylensing and KiDS data

在暗物质的高密度区域或光晕中发现了不同类型的星系。观测到的星系类型的组成并没有被完全详细地理解，但很可能取决于物质密度场中的局部条件。这解释了星系的数密度和物质密度之间的强相关性，这可以用众所周知的引力透镜效应来研究：密度不均匀引起的潮汐扭曲会剪切背景星系的图像，从而探测物质场。因此，背景星系的观测形状和前景星系的位置之间的相关性编码了星系物理的统计信息，更有趣的是，如果我们考虑不同星系类型的相关信号，则更有趣的是。作为这种相关性分析的应用，我们建议测量星系对在星系与质量总成(GAMA)调查中的基洛度调查(KIDS)中的星系图像的平均引力切变。这个三点统计被称为星系-星系-星系透镜(G3L)，它量化了星系对周围的平均投射物质密度，超过了不相关星系的平均投射物质密度；星系对可以是相同类型的(非混合对)，也可以是不同类型的(混合对)。与传统的星系-星系透镜聚焦于单个星系周围的平均切变不同，G3L对同一晕内星系位置的相关性或占据该晕的星系类型相关的数量的相关性也很敏感。此外，G3L对星系对相对于晕物质分布的统计排列是主要敏感的，而两点统计只对堆叠晕的径向密度分布敏感。因此，一个显著测量的G3L信号及其解释将完善我们目前对星系晕占据的理解。这个新的星系研究工具的细节和适用性仍然需要确定，就像我们在这个项目中所做的那样。将特别关注混合对的G3L。为此，我们已经在建立混合对G3L的新理论模型方面做了几个步骤。我们还演示了在GAMA和CHILD中使用某些非混合配对进行G3L测量的可行性。现在，为了超越这个早期项目阶段，我们要求DFG提供资金，通过利用精确的GAMA星系红移来调查和改进可用的G3L估计器，成熟我们(尚未公布的)混合星系对的G3L模型，并对非混合星系对和首次混合的GAMA星系对进行系统的G3L测量。然后，这些测量结果将被用来测试现有星系模型的G3L预测，并改进星系的晕占据统计数据。总而言之，这个项目是一次很好的机会，让两位博士论文利用现成的最先进数据，致力于宇宙学和星系物理学中令人兴奋的科学。

Galaxies of different types are found inside the high-density regions, or halos, of dark matter. The observed composition of galaxy types is not fully understood in detail but very likely depends on the local conditions in the matter density field. This explains the strong correlation between the number density of galaxies and the matter density which can be studied with the well-established effect of gravitational lensing: tidal distortions caused by density inhomogeneities shear the images of background galaxies and thus probe the matter field. Correlations between the observed shapes of background galaxies and positions of foreground galaxies therefore encode statistical information on galaxy physics, more interestingly so if we consider the correlation signal for different galaxy types.As application of such a correlation analysis, we propose to measure the mean gravitational shear from galaxy images in the Kilo-Degree Survey (KiDS) around galaxy pairs in the Galaxy-and-Mass Assembly (GAMA) survey. This three-point statistic, dubbed galaxy-galaxy-galaxy lensing (G3L), quantifies the mean projected matter density around galaxy pairs in excess of that for uncorrelated galaxies; the pairs can either be of the same type (unmixed pairs) or different type (mixed pairs). In contrast to traditional galaxy-galaxy lensing, which focuses on the mean shear around single galaxies, G3L is also sensitive to the correlation of positions of galaxies inside the same halo or the correlation of the type-dependent numbers of galaxies that occupy the halo. In addition, G3L is principally sensitive to the statistical alignment of galaxy pairs with respect to the halo matter distribution, whereas two-point statistics are only sensitive to the radial density profiles of stacked halos. Thus, a significantly measured G3L signal and its interpretation will refine our current understanding of the galaxy halo occupation.The details and applicability of this new tool for galaxy research still have to be established as we will do in this project. A special focus will be given to G3L of mixed pairs. To this end, we have already done a few steps in direction of a new theoretical model for the mixed-pair G3L. We also have demonstrated the feasibility of G3L measurements with certain unmixed pairs in GAMA and KiDS. To now move beyond this early project phase, we ask for DFG funding to investigate and improve the available G3L estimator by utilising the precise GAMA galaxy redshifts, to mature our (unpublished) G3L model for mixed galaxy pairs, and to perform systematic G3L measurements for unmixed and, for the first time, mixed GAMA galaxy pairs. These measurements will then be used to test G3L predictions of existing galaxy models and to refine the halo occupation statistics of galaxies. All in all, this project is a great opportunity for a couple of doctoral theses to work on exciting science in cosmology and galaxy physics with readily availablestate-of-the-art data.