Halo Intrinsic Alignment: Dependence on Mass, Formation Time, and Environment

Abstract

In this paper we use high-resolution cosmological simulations to study halo intrinsic alignment and its dependence on mass, formation time and large-scale environment. In agreement with previous studies using N-body simulations, it is found that massive halos have stronger alignment. For the first time, we find that for given halo mass, older halos have stronger alignment and halos in cluster regions also have stronger alignment than those in filament. To model these dependencies we extend the linear alignment model with inclusion of halo bias and find that the halo alignment with its mass and formation time dependence can be explained by halo bias. However, the model can not account for the environment dependence, as it is found that halo bias is lower in clusters and higher in filaments. Our results suggest that halo bias and environment are independent factors in determining halo alignment. We also study the halo alignment correlation function and find that halos are strongly clustered along their major axes and less clustered along the minor axes. The correlated halo alignment can extend to scale as large as 100h−1 Mpc where its feature is mainly driven by the baryon acoustic oscillation effect.

Revisiting the Galaxy Shape and Spin Alignments with the Large-scale Tidal Field: An Effective Practical Model

“…Investigating the dependence of the strength of the tidally induced shape alignments on M, R f , and the type of the cosmic web, it has been found that the more massive galactic halos yield strongerû 3 -ê alignments (û 1 -ê anti-alignments) and that the increment of R f weakens the alignment tendency (see Figures 4). These numerical results are consistent with what the previous works already found (Joachimi et al 2013;Zhang et al 2013;Chen et al 2016;Hilbert et al 2017;Xia et al 2017;Piras et al 2018).…”

“…Figure 4 shows quantitatively how the increment of R f weakens the shape alignments. Although the alignment tendency becomes weaker as R f increases, the shape vector,ê, still shows significant alignment (antialignment) withû 3 (û 1 ) even for the case of R f = 30 h −1 Mpc, which is consistent with the findings of the previous works (e.g., Xia et al 2017).…”

“…It is interesting to note that the results shown in Figures 5-9 are in direct contradiction with that of Xia et al (2017) who found the strongest shape alignments of the halos in the knot environments. We think that this apparent inconsistency between our and their results may be related the difference in the web classification scheme.…”

Anisotropies of galaxy ellipticity correlations in real and redshift space: angular dependence in linear tidal alignment model

“…y4,0(k) − 8 21 y2,0(k) + 4 15 y0,0(k). After applying the orthogonality condition of y m , the two components of the II correlation function, ξ±(r), are given as (see Xia et al 2017, for an similar expression for the monopole moment)…”

Testing tidal alignment models for anisotropic correlations of halo ellipticities with N-body simulations

“…The intrinsic alignment (IA) of galaxy images (Heavens et al 2000;Croft & Metzler 2000;Lee & Pen 2000;Catelan et al 2001;Crittenden et al 2001;Hirata & Seljak 2004) (See Troxel & Ishak 2015;Joachimi et al 2015;Kirk et al 2015;Kiessling et al 2015, for reviews) is known to contaminate cosmological parameter estimations from weak lensing surveys, by 5 − 10% (Mandelbaum et al 2006;Hirata et al 2007;Joachimi et al 2011;Singh et al 2015). Precise modeling of the intrinsic alignments (IAs) is thus crucial for the cosmic shear to be a useful cosmological tool (Jing 2002;Smith & Watts 2005;Bridle & King 2007;Zhang 2010;Schneider & Bridle 2010;Blazek et al 2011Blazek et al , 2015Xia et al 2017;Codis et al 2018;Yao et al 2019b,a;Vlah et al 2019;Blazek et al 2019;). On the other hand, less focus has been drawn to the cosmological information IAs encode.…”