Excess of high-z galaxies as a test for bumpy power spectrum of density perturbations

Abstract

Modified matter power spectra with approximately Gaussian bump on sub-Mpc scales can be a result of a complex inflation. We consider five spectra with different Gaussian amplitudes A and locations k0 and run N-body simulations in a cube (5 Mpc h−1)3 at z > 8 to reveal the halo mass functions and their evolution with redshift. We have found that the Sheth–Tormen formula provides a good approximation to a such kind of halo mass functions. In the considered models, the dark matter halo formation starts much more earlier than in Lambda cold dark matter (ΛCDM), which in turn can result in an earlier star formation and a nuclear activity in galaxies and can be detected and tested by, e.g. JWST. At z = 0, the halo mass functions are hardly distinguishable from the standard ΛCDM, therefore the models with the bumpy spectra can be identified in observations by their excess in number of bright sources at high redshift only.

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

“…Detailed galaxy formation models combined with a broad class of observations of subgalactic objects are necessary to understand the formation and evolution of small-scale structures and to place tight constraints on the PPS. Tkachev et al (2024) consider a modified matter power spectrum with an approximately Gaussian bump at submegaparsec scales and study the effect on the halo mass function. They argue that observations of high-redshift galaxies are crucial to infer the characteristics of the small-scale power spectrum.…”

Which Came First: Supermassive Black Holes or Galaxies? Insights from JWST

“…The early formation of a large population of (ultracompact) galaxies is problematic in the standard ΛCDM model. A possible resolution could involve excess small-scale power in the primordial density fluctuation power spectrum on dwarf galaxy scales, as has been explored in earlier studies of ways of boosting early formation of galaxies (Chevallard et al 2015) and AGN (Habouzit et al 2016) by primordial galaxy-scale non-Gaussianities (Sabti et al 2023) or by primordial spectral bumps (Tkachev et al 2024). It is well known that the formation of SMBH, especially at high z, cannot be explained if accretion growth from stellar-mass black holes is Eddington accretion-limited.…”

Quantifying the Tension between Cosmological Models and JWST Red Candidate Massive Galaxies

“…Plenty of beyond-ΛCDM models, including alternative dark energy (Menci et al 2022;Wang et al 2023b;Adil et al 2023), non-standard dark matter (Bird et al 2023;Dayal & Giri 2024;Lin et al 2024;Maio & Viel 2023), cosmic strings (Jiao et al 2023), primordial black holes (Gouttenoire et al 2023;Guo et al 2023;Hütsi et al 2023;Huang et al 2023;Yuan et al 2023) and many others (Lovyagin et al 2022;John & Babu Joseph 2023;Lei et al 2024;Melia 2023), have been confronted with the JWST highredshift candidate galaxies. Modification of primordial conditions may also lead to an overabundance of dark matter halos and hence more massive galaxies at high redshift (Huang 2019;Wang & Liu 2022;Forconi et al 2023;Keller et al 2023;Padmanabhan & Loeb 2023;Parashari & Laha 2023;Su et al 2023;Tkachev et al 2024).…”