We investigate the three-point correlation function (3PCF) in the squeezed limit by considering galaxy pairs as discrete objects and cross-correlating them with the galaxy field. We develop an efficient algorithm using Fast Fourier Transforms to compute such cross-correlations and their associated pair-galaxy bias bpg and the squeezed 3PCF coefficient Qeff. We implement our method using N-body cosmological simulations and a fiducial Halo Occupation Distribution (HOD) and present the results in both the real space and redshift space. In real space, we observe a peak in bpg and Qeff at pair separation of ~ 2 Mpc, attributed to the fact that galaxy pairs at 2 Mpc separation trace the most massive dark matter halos. We also see strong anisotropy in the bpg and Qeff signals that track the large-scale filamentary structure. In redshift space, both the 2 Mpc peak and the anisotropy are significantly smeared out along the line-of-sight due to Finger-of-God effect. In both the real space and redshift space, the squeezed 3PCF shows a factor of 2 variation, contradicting the hierarchical ansatz but offering rich information on the galaxy-halo connection. Thus, we explore the possibility of using the squeezed 3PCF to constrain the HOD. When we compare two simple HOD models that are closely matched in their projected two-point correlation function (2PCF), we do not yet see a strong variation in the 3PCF that is clearly disentangled from variations in the projected 2PCF. Nevertheless, we propose that more complicated HOD models, e.g. those incorporating assembly bias, can break degeneracies in the 2PCF and show a distinguishable squeezed 3PCF signal.
Assuming a LCDM universe in a single-field inflationary scenario, we compute the three-point correlation function of the observed matter density fluctuation in the squeezed triangular configuration, accounting for all the relativistic effects at the second order in perturbations. This squeezed three-point correlation function characterizes the local-type primordial non-Gaussianity, and it has been extensively debated in literature whether there exists a prominent feature in galaxy clustering on large scales in a single-field inflationary scenario either from the primordial origin or the intrin…
2MASS/SDSS Close Major-Merger Galaxy Pairs: Luminosity Functions and Merger Mass Dependence
我们选择了一个密切的“主要合并候选人”的星系对样本，以计算的K_{s}光度函数（LF）和对分数的合并/相互作用的组成部分，在本地宇宙中的星系演化。对样本（投影间隔5 h $^{-1}$ kpc $\leq$ r $\leq$ 20 h $^{-1}$ kpc，$K_{s}$ -带星等差$Δ$ $K_{s}$ $\leq$ 1等）是通过结合2微米全天巡天（2 MASS）和斯隆数字巡天（SDSS）数据发布5（DR 5）选择的。由此产生的数据集包含340个星系，覆盖5800平方米。度一个恒星质量函数也是从LF转换而来的。微分对分数显示了星系对的比例几乎是恒定的，作为星系质量的函数，从10 $^{9}$到10 $^{11.5}$ M $_{\sun}$。由于测量的限制，差分对分数比标准的总对分数更少受到绝对幅度偏差的影响。这些结果表明，在0 $<$ z $<$ 0.1宇宙中的主要合并候选对是从$\sim$ 1.6%的星系人口发展而来的，而不依赖于星系质量的对组件低于10 $^{11}$ M $_{\sun}$。合并模型的时间尺度结合LF推导出当地合并率每单位体积的质量大于10 $^{11}$ M $_{\sun}$减少。
We analyze the galaxy pairs in a volume limited sample ($M_r \leq -21$) from the SDSS to study the effects of galaxy interactions on the star formation rate and colour of galaxies in different environments. We study the star formation rate and colour of the paired galaxies as a function of projected separation and compare the results with their control samples matched in stellar mass, redshift and local density. We find that the major interactions significantly enhance the star formation rate in paired galaxies and turn them bluer with decreasing pair separation within $30$ kpc. The impact of …
Observational studies of pairs of galaxies have uncovered that their differential line-of-sight velocities indicate the presence of a peak in their three-dimensional intervelocity distribution at 130-150 km/s. It had been argued that galaxy pairs in the standard model of cosmology, $Λ$CDM, should not exhibit such an intervelocity peak, while Modified Newtonian Dynamics (MOND) predicts such a preferred intervelocity for paired galaxies. However, no direct comparison with $Λ$CDM applying the same selection criteria and methodology as the observational studies has been performed yet, placing the …
