Intrinsic alignments of bulges and discs

Abstract

Galaxies exhibit coherent alignments with local structure in the Universe. This effect, called Intrinsic Alignments (IA), is an important contributor to the systematic uncertainties for wide-field weak lensing surveys. On cosmological distance scales, intrinsic shape alignments have been observed in red galaxies, which are usually bulge-dominated; while blue galaxies, which are mostly disc-dominated, exhibit shape alignments consistent with a null detection. However, disc-dominated galaxies typically consist of two prominent structures: disc and bulge. Since the bulge component has similar properties as elliptical galaxies and is thought to have formed in a similar fashion, naturally one could ask whether the bulge components exhibit similar alignments as ellipticals? In this paper, we investigate how different components of galaxies exhibit IA in the TNG100-1 cosmological hydrodynamical simulation, as well as the dependence of IA on the fraction of stars in rotation-dominated structures at $z=0$. The measurements were controlled for mass differences between the samples. We find that the bulges exhibit significantly higher IA signals, with a nonlinear alignment model amplitude of $A_I=2.98_{-0.37}^{+0.36}$ compared to the amplitude for the galaxies as a whole (both components), $A_I=1.13_{-0.35}^{+0.37}$. The results for bulges are statistically consistent with those for elliptical galaxies, which have $A_I=3.47_{-0.57}^{+0.57}$. These results highlight the importance of studying galaxy dynamics in order to understand galaxy alignments and their cosmological implications.

14 pages, 7 figures. Matches the version published at MNRAS

References in corpus (12)

• Structural Properties of Pseudo-Bulges, Classical Bulges and Elliptical Galaxies: an SDSS Perspective
• Dark energy constraints from cosmic shear power spectra: impact of intrinsic alignments on photometric redshift requirements
• Intrinsic galaxy alignments from the 2SLAQ and SDSS surveys: luminosity and redshift scalings and implications for weak lensing surveys
• The Intrinsic Alignment of Galaxies and its Impact on Weak Gravitational Lensing in an Era of Precision Cosmology
• Constraints on intrinsic alignment contamination of weak lensing surveys using the MegaZ-LRG sample
• Intrinsic alignments of SDSS-III BOSS LOWZ sample galaxies
• Potential sources of contamination to weak lensing measurements: constraints from N-body simulations
• Galaxy Shapes and Intrinsic Alignments in The MassiveBlack-II Simulation
• Intrinsic alignments of galaxies in the MassiveBlack-II simulation: analysis of two-point statistics
• Alignments between galaxies, satellite systems and haloes
• KiDS-1000: Constraints on the intrinsic alignment of luminous red galaxies
• Intrinsic alignments of the extended radio continuum emission of galaxies in the EAGLE simulations

Cited by in corpus (3)

• Galaxies and Halos on Graph Neural Networks: Deep Generative Modeling Scalar and Vector Quantities for Intrinsic Alignment
• Merger Effects on the Spin and Shape Alignments of Galaxy Stellar, Cold and Hot Gas, and Dark Matter Components
• Anisotropic correlation functions as tracers of central galaxy alignments in simulations