A two-state model for galaxy bias. Issue 3 (27th February 2020)

• Record Type: Journal Article
• Authors: Repp, Andrew; Szapudi, István
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 493:Issue 3(2020)
• Page Start: 3449
• Page End: 3463
• Publication Date: 2020-02-27
• Subjects: galaxies: abundances -- galaxies: clusters: general -- cosmology: miscellaneous -- cosmology: theory; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/staa496
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: A reliable model of galaxy bias is necessary for interpreting data from future dense galaxy surveys. Conventional linear and quadratic bias models are unphysical, often predicting negative galaxy densities (δg < −1) in voids, which potentially contain half of a survey's available cosmological information. Here we present a physically motivated alternative by assuming two energetically distinct subhalo states. Our approximations – namely, local galaxy formation, rough equivalence of galaxy-hosting subhaloes, and universal energetic favourability for the galaxy-hosting state – result in a bias model with only two free parameters; mathematically, the model (in the correct variables) yields a Fermi–Dirac distribution or (equivalently) an interactionless Ising model with an external field. The model yields sensible (and physical) predictions for both high- and low-density regions. We test the model using a catalogue of Millennium Simulation galaxies in cubical survey pixels with side lengths from 2 h −1 –31 h −1 Mpc, at redshifts from 0 to 2. We find the two-state model markedly superior to linear and quadratic bias models on scales smaller than 10 h −1 Mpc, while those conventional models fare better on scales larger than 30 h −1 Mpc. Though the largest scale of applicability is likely to depend on the galaxy catalogue employed, the two-state model should be superior on any scale with a non-negligible fraction of cells devoid of galaxies.