Testing Bump in the Cosmological Power Spectrum Using Dwarf Galaxies

TL;DR

This work tests whether a cosmological power-spectrum bump at a wavelength of $\lambda \approx 1.3\,\mathrm{Mpc}$ with amplitude $\mathcal{A}=2$ leaves observable imprints in local dwarf galaxies. By running $N$-body simulations in a $47\,\mathrm{Mpc}$ box and applying the GRUMPY semi-analytic model to predict $B$-band luminosity functions, the authors compare to the Local Volume data and find that the bump is strongly disfavored, yielding a 3$\sigma$ upper limit of $\mathcal{A} < 0.25$ for $\lambda=1.3\,\mathrm{Mpc}$. They also examine the dwarf-galaxy correlation function, which shows only modest differences on small scales and currently lacks robust observational constraints. The results constrain small-scale features in the initial power spectrum and illustrate how combining $N$-body simulations with baryonic modeling can test inflation-inspired spectrum features. If the bump is at a shorter wavelength, the associated luminosity-function feature would move into a regime with weaker existing constraints.

Abstract

We analyze the possibility of using observational data on nearby dwarf galaxies -- their luminosity functions and spatial distributions -- to constrain deviations of the cosmological power spectrum from the standard one. Specifically, we consider a cosmological model with a "bump" in the power spectrum at a wavelength of 1.3~Mpc and a dimensionless amplitude $\mathcal{A}=2.0$. Such a spectrum is motivated by observations of an excess number of galaxies at high redshifts. The bump leads to a noticeable increase in the luminosity function in the range $-13 > M_B > -17$ at $z=0$. Comparison with observations constrains the bump amplitude to $\mathcal{A} < 0.25$ at a 3-sigma significance level for a wavelength of 1.3~Mpc. For wavelengths smaller than 0.8~Mpc, the bump manifests only in the luminosity function of dwarfs with $M_B > -14$.

Figures (4)

• Figure 1: Dark matter halo mass functions at $z=0,6,11$ (dark to light lines). Solid lines: bump model; dashed lines: $\Lambda$CDM.
• Figure 2: Dwarf galaxy luminosity function in the bump model (solid line) and standard spectrum model (dashed line). Circles show measurements from klypin15. Filled circles correspond to $M_B < -14$, where the galaxy sample is complete. Shaded areas indicate Poisson errors at $1\sigma$ and $3\sigma$.
• Figure 3: Correlation function of galaxies with $M_B < -14$ in bump (solid line) and no-bump (dashed line) models. Points show measured correlation function from 2dF catalog for galaxies with $M_B < -20$.
• Figure 4: Mass-luminosity relation for galaxies in both models. The line shows $L \propto M_v^2$.