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

不同类型的星系位于暗物质的高密度区域或光晕内。观测到的星系类型的组成还没有完全被详细了解，但很可能取决于物质密度场的局部条件。这解释了星系数量密度和物质密度之间的强相关性，这种相关性可以用引力透镜效应来研究：由密度不均匀性引起的潮汐扭曲会剪切背景星系的图像，从而探测物质场。观测到的背景星系的形状和前景星系的位置之间的相关性因此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。作为这一相关性分析的应用，我们提出了在星系与质量组合（GAMA）巡天中测量千度巡天（KiDS）星系图像中围绕星系对的平均引力切变。这个三点统计，被称为星系-星系-星系透镜（G3L），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；这些数据对可以是相同类型（未混合数据对）或不同类型（混合数据对）。与关注单个星系周围平均剪切的传统星系-星系透镜不同，G3L对同一光晕内星系位置的相关性或占据光晕的星系类型相关数的相关性也很敏感。此外，G3L主要对星系对在晕物质分布方面的统计排列敏感，而两点统计仅对堆积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。这个新工具在星系研究中的细节和适用性仍然需要建立，正如我们在这个项目中所做的那样。将特别关注混合双人赛的G3L。为此，我们已经在建立混合对G3L的新理论模型的方向上做了一些工作。我们还证明了在GAMA和KiDS中使用某些未混合对测量G3L的可行性。现在，为了超越这个早期的项目阶段，我们要求DFG资助通过利用精确的GAMA星系红移来调查和改进可用的G3L估计器，以成熟我们的（未发表的）混合星系对的G3L模型，并对未混合的G3L进行系统的测量，这是第一次，混合的GAMA星系对。这些测量结果将用于测试G3L对现有星系模型的预测，并改进星系的晕占率统计数据。总而言之，这个项目为一些博士论文提供了一个很好的机会，可以用现成的最先进的数据来研究令人兴奋的宇宙学和星系物理学。

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.