Early Structure Formation from Primordial Density Fluctuations with a Blue, Tilted Power Spectrum: High-redshift Galaxies

Abstract

Recent observations by the James Webb Space Telescope (JWST) discovered unexpectedly abundant luminous galaxies at high redshift, posing possibly a severe challenge to popular galaxy formation models. We study early structure formation in a cosmological model with a blue, tilted power spectrum (BTPS) given by P ( k ) ∝ k m s with m s > 1 at small length scales. We run a set of cosmological N-body simulations and derive the abundance of dark matter halos and galaxies under simplified assumptions on star formation efficiency. The enhanced small-scale power allows rapid nonlinear structure formation at z > 7, and galaxies with stellar mass exceeding 1010 M ⊙ can be formed by z = 9. Because of frequent mergers, the structure of galaxies and galaxy groups appears clumpy. The BTPS model reproduces the observed stellar mass density at z = 7–9, and thus eases the claimed tension between galaxy formation theory and recent JWST observations. The large-scale structure of the present-day Universe is largely unaffected by the modification of the small-scale power spectrum. We conduct a systematic study by varying the slope of the small-scale power spectrum to derive constraints on the BTPS model from a set of observations of high-redshift galaxies.

High Redshift $\Lambda$Cdm Cosmology: To Bin or Not to Bin?

“…This unforeseen finding has seeded investigations into observational systematics [9][10][11][12][13][14][15] and speculations on new astrophysics. The latter musings range from more mundane changes to the star formation rate [16][17][18][19][20][21][22] to exotic physics that could explain the origin of the galaxies, such as accelerated growth through massive seed black holes [23,24] and primordial black holes [25][26][27]; invoking primordial magnetic fields [28]; primordial density fluctuations [29]; cosmic string loops [30][31][32]; changes to the dark matter (DM) paradigm [33][34][35][36][37][38][39][40]. While DM represents a cornerstone in the Lambda-Cold Dark Matter (ΛCDM) cosmological model, one could also consider relaxing other ΛCDM assumptions, notably dark energy described by the cosmological constant Λ [41][42][43][44][45][46], in order to alleviate any tension.…”