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Recent observations by the James Webb Space Telescope (JWST) discoveredunexpectedly abundant luminous galaxies at high redshift, posing possibly asevere challenge to popular galaxy formation models. We study early structureformation in a cosmological model with a blue, tilted power spectrum (BTPS)given by $P(k) \propto k^{m_{\rm s}}$ with $m_{\rm s} > 1$ at small lengthscales. We run a set of cosmological $N$-body simulations and derive theabundance of dark matter halos and galaxies under simplified assumptions onstar formation efficiency. The enhanced small-scale power allows rapidnonlinear structure formation at $z>7$, and galaxies with stellar massexceeding $10^{10}\,M_\odot$ can be formed by $z=9$. Because of frequentmergers, the structure of galaxies and galaxy groups appears clumpy. The BTPSmodel reproduces the observed stellar mass density at $z=7-9$, and thus easesthe claimed tension between galaxy formation theory and recent JWSTobservations. The large-scale structure of the present-day Universe is largelyunaffected by the modification of the small-scale power spectrum. We conduct asystematic study by varying the slope of the small-scale power spectrum toderive constraints on the BTPS model from a set of observations ofhigh-redshift galaxies.

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