An Empirical Model For Intrinsic Alignments: Insights From Cosmological Simulations

Journal Article · Tue Jun 04 00:00:00 EDT 2024 · The Open Journal of Astrophysics

DOI:https://doi.org/10.33232/001c.118783· OSTI ID:2483459

Van Alfen, Nicholas ^[1]; Campbell, Duncan ^[2]; Blazek, Jonathan ^[3]; Leonard, C. Danielle ^[4]; Lanusse, Francois ^[5]; Hearin, Andrew ^[6]; Mandelbaum, Rachel ^[2]

---

1. Northeastern University, Boston, MA (United States); Carnegie Mellon University, Pittsburgh, PA 15213
2. Carnegie Mellon University, Pittsburgh, PA (United States)
3. Northeastern University, Boston, MA (United States)
4. Newcastle University (United Kingdom)
5. Universit´e Paris-Saclay, Gif-sur-Yvette (France)
6. Argonne National Laboratory (ANL), Argonne, IL (United States)

We extend current models of the halo occupation distribution (HOD) to include a flexible, empirical framework for the forward modeling of the intrinsic alignment (IA) of galaxies. A primary goal of this work is to produce mock galaxy catalogs for the purpose of validating existing models and methods for the mitigation of IA in weak lensing measurements. This technique can also be used to produce new, simulation-based predictions for IA and galaxy clustering. Our model is probabilistically formulated, and rests upon the assumption that the orientations of galaxies exhibit a correlation with their host dark matter (sub)halo orientation or with their position within the halo. We examine the necessary components and phenomenology of such a model by considering the alignments between (sub)halos in a cosmological dark matter only simulation. We then validate this model for a realistic galaxy population in a set of simulations in the Illustris-TNG suite. We create an HOD mock with Illustris-like correlations using our method, constraining the associated IA model parameters, with the $$\mathcal{X}$$$$^{2}_{dof}$$ between our model’s correlations and those of Illustris matching as closely as 1.4 and 1.1 for orientation–position and orientation–orientation correlation functions, respectively. By modeling the misalignment between galaxies and their host halo, we show that the 3-dimensional two-point position and orientation correlation functions of simulated (sub)halos and galaxies can be accurately reproduced from quasi-linear scales down to 0.1 $$\mathcal{h}$$^–1 Mpc. We also find evidence for environmental influence on IA within a halo. Our publicly-available software provides a key component enabling efficient determination of Bayesian posteriors on IA model parameters using observational measurements of galaxy-orientation correlation functions in the highly nonlinear regime.

• Research Organization: Carnegie Mellon University, Pittsburgh, PA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), High Energy Physics (HEP)
• Contributing Organization: LSST Dark Energy Science Collaboration
• Grant/Contract Number: SC0010118
• OSTI ID: 2483459
• Journal Information: The Open Journal of Astrophysics, Journal Name: The Open Journal of Astrophysics Vol. 7; ISSN 2565-6120
• Publisher: Maynooth Academic Publishing
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
79 ASTRONOMY AND ASTROPHYSICS
Cosmology
Intrinsic Alignments
Weak Gravitational Lensing