Angular momentum-Large-scale structure alignments in LCDM models and the SDSS

TL;DR

This study investigates how the angular momentum of dark matter halos and galaxies aligns with large-scale cosmic structures using simulations and SDSS data, revealing scale- and mass-dependent alignment patterns.

Contribution

It provides the first detailed analysis of angular momentum alignments in both simulations and real galaxy data, highlighting scale and mass dependencies.

Findings

High-mass halos have spins perpendicular to matter distribution at large scales.

Lower mass halos show weaker or reversed alignment trends.

Galaxies in SDSS tend to have angular momentum perpendicular to large-scale structure.

Abstract

We study the alignments between the angular momentum of individual objects and the large-scale structure in cosmological numerical simulations and real data from the Sloan Digital Sky Survey, Data Release 6. To this end we measure anisotropies in the two point cross-correlation function around simulated halos and observed galaxies, studying separately the 1- and 2-halo regimes. The alignment of the angular momentum of dark-matter haloes in LCDM simulations is found to be dependent on scale and halo mass. At large distances (2-halo regime), the spins of high mass haloes are preferentially oriented in the direction perpendicular to the distribution of matter; lower mass systems show a weaker trend that may even reverse to show an angular momentum in the plane of the matter distribution. In the 1-halo term regime, the angular momentum is aligned in the direction perpendicular to the matter distribution; the effect is stronger than for the 1-halo term and increases for higher mass systems. On the observational side, we focus our study on galaxies in the Sloan Digital Sky Survey, Data Release 6 (SDSS-DR6) with elongated apparent shapes, and study alignments with respect to the major semi-axis. We find an excess of structure in the direction of the major semi-axis for all samples; the red sample shows the highest alignment (2.7+-0.08%) and indicates that the angular momentum of flattened spheroidals tends to be perpendicular to the large-scale structure. (Abridged)