KiDS-1000: Weak lensing and intrinsic alignment around luminous red galaxies

TL;DR

This study analyzes the relationship between intrinsic alignments of luminous red galaxies and their halo masses using KiDS-1000 data, revealing a power-law dependence and confirming random orientations of source galaxies.

Contribution

It introduces a halo model-based analysis linking intrinsic alignments directly to halo mass, extending previous work with new observational constraints from KiDS-1000.

Findings

Intrinsic alignment amplitude scales with halo mass as a power law.

Both red and blue source galaxies are randomly oriented relative to LRGs.

Halo mass estimates range from 2.7e12 to 2.6e13 h^{-1} M_sun.

Abstract

We study the properties of luminous red galaxies (LRGs) selected from the fourth data release of the Kilo Degree Survey (KiDS-1000) via galaxy-galaxy lensing of the background galaxies from KiDS-1000. We used a halo model formalism to interpret our measurements and obtain estimates of the halo masses as well as the satellite fractions of the LRGs, resulting in halo masses of $2.7 \times 10^{12} h^{-1} {\rm M}_{\odot}<M_{\rm h}< 2.6 \times 10^{13} h^{-1} {\rm M}_{\odot}$. We studied the strength of intrinsic alignments (IA) using the position-shape correlations as a function of LRG luminosity, where we used a double power law to describe the relation between luminosity and halo mass to allow for a comparison with previous works. Here, we directly linked the observed IA of the (central) galaxy to the mass of the hosting halo, which is expected to be a fundamental quantity in establishing the alignment. We find that the dependence of the IA amplitude on halo mass is described well by a single power law, with an amplitude of $A = 5.74\pm{0.32}$ and slope of $\beta_M = 0.44\pm{0.04}$, in the range of $1.9 \times 10^{12}h^{-1} {\rm M}_{\odot}<M_{\rm h}<3.7 \times 10^{14} h^{-1} {\rm M}_{\odot}$. We also find that both red and blue galaxies from the source sample associated with the LRGs are randomly oriented, with respect to the LRGs, although our detection significance is limited by the uncertainty in our photometric redshifts.