Early growth of massive black holes in dynamical dark energy models with negative cosmological constant

TL;DR

The paper investigates whether dynamical dark energy models with a negative cosmological constant can jointly explain JWST-era observations of high-redshift galaxies, supermassive black holes, and AGN, without invoking exotic accretion physics or massive seeds. It builds a transparent analytic framework that ties dark matter halo growth to maximal black hole growth under continuous Eddington-limited accretion from Pop III seeds, within NCC cosmologies constrained by ACT, Planck, DESI, and SNIa data using a CPL parametrization $w_x(a)=w_0+w_a(1-a)$. The results show that for $\Omega_{\Lambda}\approx -1$, BHs can reach $M_{BH}\sim 10^{7}\,M_{\odot}$ by $z\sim 10$, and the AGN and UV luminosity functions are boosted relative to ΛCDM in a way that can align with JWST measurements, though the brightest high-$z$ end remains challenging. The study suggests NCC models offer a theoretically motivated and observationally viable background that can unify early structure formation with JWST findings, while highlighting the need to include reionization constraints in future work.

Abstract

Recent results from combined cosmological probes indicate that the Dark Energy component of the Universe could be dynamical. The simplest explanation envisages the presence of a quintessence field rolling into a potential, where the Dark Energy energy density parameter $Ω_{DE}=Ω_Λ+Ω_{x}$ results from the contribution of the ground state energy $Ω_Λ$ and the scalar field energy $Ω_{x}$. Provided that $Ω_{DE}\approx 0.7$, negative values of $Ω_Λ$ can be consistent with current measurements from cosmological probes, and could help in explaining the large abundance of bright galaxies observed by JWST at $z> 10$, largely exceeding the pre-JWST expectations in a $ΛCDM$ Universe. Here we explore to what extent such a scenario can account also for the early presence of massive Black Holes (BHs) with masses $M_{BH}\gtrsim 10^7\,M_{\odot}$ observed at $z\gtrsim 8$, and for the large over-abundance of AGN with respect to pre-JWST expectations. Our aim is not to provide a detailed description of BH growth, but rather to compute the maximal BH growth that can occur in cosmological models with negative $Ω_Λ$ under the simple assumption of Eddington-limited accretion onto initial light Black Hole seeds with mass $M_{seed}\sim 10^2\,M_{\odot}$ originated from PopIII stars. To this aim we develop a simple analytic framework to connect the growth of dark matter halos to the maximal growth of BHs within the above assumptions. We show such models can account for present observations assuming values of $Ω_Λ\approx -1$, simultaneously boosting both galaxy and AGN number counts without invoking any additional physics. This would allow us to trace the observed excess of bright and massive galaxies and the early formation of massive Black Holes and the abundance of AGN to the same cosmological origin.

Figures (6)

• Figure 1: 2D confidence contour in the $w_{0}-w_{a}$ plane for our model using CMB+DESI+DES data combination. The Dash-Dotted line is phantom line. Above this line, the allowed region is always non-phantom, where as below this line, the allowed region is early phantom and late non-phantom. Dots represents different Monte Carlo realizations. The color code shows the value of $\Omega_{\Lambda}$ that allows for consistency with the above cosmological probes
• Figure 2: Top-Left Panel: Based on our Monte Carlo procedure for the selection of ($w_0$-$w_a$, $\Omega_{\Lambda}$) combinations combinations consistent (at 2-$\sigma$ level) with the considered cosmological probes, we show as colored contours the average $\Omega_{\Lambda}$ as a function of ($w_0$-$w_a$). The color code is shown by the bar in the bottom-right of the figure. Top-Right Panel: for the combinations ($w_0\geq -1$, $w_a\geq 0$) considered here, we show the values of $\Omega_m$ and $\sigma_8$ consistent (at 2-$\sigma$ level) with the considered cosmological probes. The color code refers to the average values of $\Omega_{\Lambda}$ corresponding to each combination, as shown by the bottom bar. Bottom-Left Panel: the probability distribution of $\Omega_{\Lambda}$ resulting from our Monte Carlo procedure for the combinations ($w_0\geq -1$, $w_a\geq 0$) considered here.
• Figure 3: The high redshift UV luminosity functions of galaxies for our fiducial combination of ($w_0$, $w_a$) in the different redshift bins shown in the labels. The color code corresponds the different values of $\Omega_{\Lambda}$ as shown in the top bar, while the dashed line mark the results for the standard $\Lambda$CDM cosmology. We compare with measurements from Finkelstein_2023 (diamonds) Donnan_2023 (stars) McLeod_2023a (upward triangle) Harikane_2023 (open square) adams24 (pentagon) Bouwens_2022 (circle) Robertson_2024 (downward triangle).
• Figure 4: The maximal growth of BHs from $M_{seed}=10^2\,M_{\odot}$ at $z_{seed }= 25$ is shown for the different values of $\Omega_{\Lambda}$ shown in the color bar for our fiducial combination $w_0=-0.98$, $w_a=0.08$; the dashed line mark the result for the standard $\Lambda$CDM cosmology. To maximize the BH mass we assume continue Eddington-limited accretion. We compare these models to black holes measured by Bogdan_2024NatAs (solid square) Furtak2024Nature (cross) Greene2024ApJ (empty petagons) Juod_balis_2024 (upward triangle) Harikane_2023 (filled diamonds) Maiolino2024a (downward triangles) Maiolino2024Nature (solid circle) Kocevski2023ApJ (solid pentagon)
• Figure 5: The bolometric luminosity function of AGN under the assumption of continuous accretion at the Eddington rate is shown for the different values of $\Omega_{\Lambda}$ shown in the color bar for our fiducial combination $w_0=-0.98$, $w_a=0.08$; the dashed line mark the result for the standard $\Lambda$CDM cosmology. We compare with the measurements by Akins2024 based on JWST observations (red circles), derived under the assumption that the emission of LRD is entirely contributed by AGN, and by Harikane_2023 (orange pentagon). For comparison, we also show the pre-JWST measurements by shen2020 as a shaded area, by Glikman (square), Grazian2023 (diamonds), and the X-ray measurement through Chandra COSMOS data by Barlow (triangles) and barlow2023 (star).