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

¹ Leiden Observatory, Leiden University, PO Box 9513 Leiden, NL-2300 RA, The Netherlands
² Ruhr University Bochum, Faculty of Physics and Astronomy, Astronomical Institute (AIRUB), German Centre for Cosmological Lensing, 44780 Bochum, Germany
³ Institute for Theoretical Physics, Utrecht University, Princetonplein 5, 3584CC Utrecht, The Netherlands
⁴ School of Mathematics, Statistics and Physics, Newcastle University, Herschel Building, NE1 7RU Newcastle-upon-Tyne, UK
⁵ Center for Theoretical Physics, Polish Academy of Sciences, al. Lotników 32/46, 02-668 Warsaw, Poland
⁶ Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
⁷ Shanghai Astronomical Observatory (SHAO), Nandan Road 80, Shanghai 200030, China

^⋆ Corresponding author; dvornik@astro.rub.de

Received: 23 September 2024
Accepted: 14 January 2025

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 × 10¹² h⁻¹ M_⊙ < M_h < 2.6 × 10¹³ h⁻¹ M_⊙. 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 ± 0.32 and slope of β_M = 0.44 ± 0.04, in the range of 1.9 × 10¹² h⁻¹ M_⊙ < M_h < 3.7 × 10¹⁴ h⁻¹ M_⊙. 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.