arXiv subjects

Renier Hough

Publications and source records attributed to Renier Hough.

3 recordsLinked to original sources

arXiv2025

The Nature and Evolution of Early Massive Quenched Galaxies in the Simba-C Simulation

We examine the nature, origin, and fate of early ($z\geq 2$) massive ($M_\star>10^{10}M_\odot$) quenched galaxies (EQGs) in a new $(100h^{-1}{\rm Mpc}^3)$ run of the Simba-C galaxy formation model. We define ``quenched'' to be $>4σ$ below an iterative polynomial fit to the star-forming sequence (SFS), and find that Simba-C produces EQGs as early as $z\sim 5$ and number densities agreeing with observations at $z\leq 3$ (though slightly low at $z\geq 4$). Using a photometric-based EQG selection or a fixed sSFR cut of $10^{-10}$yr$^{-1}$ yields similar results. EQGs predominantly arise in central galaxies with stellar mass $M_\star\sim 10^{10.5-11.3}M_\odot$, not necessarily the most massive systems. A UMAP projection shows that quenched galaxies have notably large black hole-to-stellar mass ratios, lower rotational support, and less dust, but are not atypical versus similar-mass non-EQGs in their environments, halo mass, or halo gas temperatures at the time of quenching. However, via galaxy tracking we show that the progenitor environments of EQGs are significantly more overdense than that of non-EQGs, which drives higher black hole mass fractions and stellar-to-halo mass ratios. This results in the Eddington ratio dropping sufficiently low for Simba-C's jet mode feedback to turn on, which quickly quenches the host galaxies. EQGs thus seem to be galaxies that grow their black holes quickly within highly dense environments, but end up in moderately-dense environments where black hole feedback can quench effectively. We find that $\geq 30\%$ of EQGs rejuvenate, but the rejuvenating fraction drops quickly at $z\leq 2$. By $z=0$ it is difficult to distinguish the descendants of EQGs vs. non-EQGs.

astro-ph.GA↗

arXiv2023

Confronting the Chaplygin gas with data: background and perturbed cosmic dynamics

In this paper, we undertake a unified study of background dynamics and cosmological perturbations in the presence of the Chaplygin gas. This is done by first constraining the background cosmological parameters of different Chaplygin gas models with SNIa and $H(z)$ data for detailed statistical analysis of the CG models. Based on the statistical criteria we followed, none of the models has substantial observational support, but we show that the so-called `original' and `extended/generalised' Chaplygin gas models have {\it some observational support} and {\it less observational support}, respectively, whereas the `modified and `modified generalised Chaplygin gas models miss out on the category {\it less observational support}, but cannot be ruled out. The so-called `generalised cosmic Chaplygin gas model, on the other hand, falls under the {\it no observational support} category of the statistical criterion and can be ruled out. The models which are statistically accepted are considered for perturbation level in both theoretical and observational aspects. We also apply the $1+3$ covariant formalism of perturbation theory and derive the evolution equations of the fluctuations in the matter density contrast of the matter-Chaplygin gas system for the models with some or less statistical support. The solutions to these coupled systems of equations are then computed in both short-wavelength and long-wavelength modes. Then feed these observationally restricted parameters into the analysis of cosmological perturbations {to address the growth of density contrast through redshift}. Using the most recent linear growth of the data $f_{σ8}$, CG models are considered to study the linear growth of the structure.

gr-qc↗

arXiv2020

Viability tests of \textit{f(R)}-gravity models with Supernovae Type 1A data

In this work, we will be testing four different general \textit{f(R)}-gravity models, two of which are the more realistic models (namely the Starobinsky and the Hu-Sawicki models), to determine if they are viable alternative models to pursue a more vigorous constraining test upon them. For the testing of these models, we use 359 low- and intermediate-redshift Supernovae Type 1A data obtained from thRede SDSS-II/SNLS2 Joint Light-curve Analysis (JLA). We develop a Markov Chain Monte Carlo (MCMC) simulation to find a best-fitting function within reasonable ranges for each \textit{f(R)}-gravity model, as well as for the Lambda Cold Dark Matter ($Λ$CDM) model. For simplicity, we assume a flat universe with a negligible radiation density distribution. Therefore, the only difference between the accepted $Λ$CDM model and the \textit{f(R)}-gravity models will be the dark energy term and the arbitrary free parameters. By doing a statistical analysis and using the $Λ$CDM model as our "true model", we can obtain an indication whether or not a certain \textit{f(R)}-gravity model shows promise and requires a more in-depth view in future studies. In our results, we found that the Starobinsky model obtained a larger likelihood function value than the $Λ$CDM model, while still obtaining the cosmological parameters to be $Ω_{m} = 0.268^{+0.027}_{-0.024}$ for the matter density distribution and $\bar{h} = 0.690^{+0.005}_{-0.005}$ for the Hubble uncertainty parameter. We also found a reduced Starobinsky model that are able to explain the data, as well as being statistically significant.

gr-qc↗