arXiv subjects

Pedro G Ferreira

Publications and source records attributed to Pedro G Ferreira.

4 recordsLinked to original sources

arXiv2026

The functional form of galaxy and halo luminosity and mass functions

The galaxy luminosity and stellar mass function (LF, SMF), and halo mass function (HMF), are fundamental quantities in astrophysics and crucial inputs to a range of astrophysical and cosmological analyses. They are typically parametrised by fitting functions that have been chosen "by eye" to match observed or simulated data. We apply symbolic regression -- specifically the Exhaustive Symbolic Regression (ESR) algorithm -- to automate the search for optimal LF, SMF and HMF functional forms. ESR scores all functions up to a maximum complexity composed of a user-defined basis set of operators using the description length, an approximation to the Bayesian evidence that balances accuracy with complexity. We find many functions outperforming the Schechter and double Schechter functions for the LF and SMF, and that outperform the Press--Schechter and Warren/Tinker functions for the HMF. By additionally imposing "physicality checks" on functions' extrapolation and integration properties, we identify the optimal, low-complexity functional forms in terms of accuracy, simplicity and behaviour beyond the data range. As well as providing drop-in replacements for literature LF, SMF and HMF fitting functions, and identifying robust behaviour across well-fitting functions, we present a framework with which symbolic regression may be used to automate the discovery of optimal functions for any astrophysical dataset.

astro-ph.GA↗

arXiv2018

The Fifth Force in the Local Cosmic Web

Extensions of the standard models of particle physics and cosmology often lead to long-range fifth forces with properties dependent on gravitational environment. Fifth forces on astrophysical scales are best studied in the cosmic web where perturbation theory breaks down. We present constraints on chameleon- and symmetron-screened fifth forces with Yukawa coupling and megaparsec range -- as well as unscreened fifth forces with differential coupling to galactic mass components -- by searching for the displacements they predict between galaxies' stars and gas. Taking data from the Alfalfa HI survey, identifying galaxies' gravitational environments with the maps of Desmond et al. (2018a) and forward-modelling with a Bayesian likelihood framework, we set upper bounds on fifth-force strength relative to Newtonian gravity from $ΔG/G_N < \text{few} \: \times 10^{-4}$ for range $λ_C = 50$ Mpc, to $ΔG/G_N \lesssim 0.1$ for $λ_C = 500$ kpc. In $f(R)$ gravity this requires $f_{R0} < \text{few} \: \times \: 10^{-8}$. The analogous bounds without screening are $ΔG/G_N < \text{few} \: \times 10^{-4}$ and $ΔG/G_N < \text{few} \times 10^{-3}$. These are the tightest and among the only fifth-force constraints on galaxy scales. We show how our results may be strengthened with future survey data and identify the key features of an observational programme for furthering fifth-force tests beyond the Solar System.

astro-ph.CO↗

arXiv2018

Fifth force constraints from galaxy warps

Intra-galaxy signals contain a wealth of information on fundamental physics, both the dark sector and the nature of gravity. While so far largely unexplored, such probes are set to rise dramatically in importance as upcoming surveys provide data of unprecedented quantity and quality on galaxy structure and dynamics. In this paper, we use warping of stellar disks to test the chameleon- or symmetron-screened fifth forces which generically arise when new fields couple to matter. We take r-band images of mostly late-type galaxies from the Nasa Sloan Atlas and develop an automated algorithm to quantify the degree of U-shaped warping they exhibit. We then forward-model the warp signal as a function of fifth-force strength $ΔG/G_N$ and range $λ_C$, and the gravitational environments and internal properties of the galaxies, including full propagation of the non-Gaussian uncertainties. Convolving this fifth-force likelihood function with a Gaussian describing astrophysical and observational noise and then constraining $ΔG/G_N$ and $λ_C$ by Markov Chain Monte Carlo, we find the overall likelihood to be significant increased ($Δ\log(\mathcal{L}) \simeq 20$) by adding a screened fifth force with $λ_C \simeq 2$ Mpc, $ΔG/G_N \simeq 0.01$. The variation of $Δ\log(\mathcal{L})$ with $λ_C$ is quantitatively as expected from the correlation of the magnitude of the fifth-force field with the force's range, and a similar model without screening achieves no increase in likelihood over the General Relativistic case $ΔG=0$. Although these results are in good agreement with a previous analysis of the same model using offsets between galaxies' stellar and gas mass centroids (Desmond et al. 2018), we caution that the effects of confounding baryonic and dark matter physics must be thoroughly investigated for the results of the inference to be unambiguous.

astro-ph.CO↗

arXiv2018

Fifth force constraints from the separation of galaxy mass components

One of the most common consequences of extensions to the standard models of particle physics or cosmology is the emergence of a fifth force. While generic fifth forces are tightly constrained at Solar System scales and below, they may escape detection by means of a screening mechanism which effectively removes them in dense environments. We constrain the strength $ΔG/G_N$ and range $λ_C$ of a chameleon- or symmetron-screened fifth force with Yukawa coupling -- as well as an unscreened fifth force with differential coupling to galactic mass components -- by searching for the displacement it predicts between galaxies' stellar and gas mass centroids. Taking data from the Alfalfa HI survey, identifying galaxies' gravitational environments with the maps of Desmond et al. (2018a) and forward-modelling with a Bayesian likelihood framework, we find $6.6σ$ evidence for $ΔG>0$ at $λ_C \simeq 2$ Mpc, with $ΔG/G_N = 0.025$ at maximum-likelihood. A similar fifth-force model without screening gives no increase in likelihood over the case $ΔG = 0$ for any $λ_C$. Although we validate these results by several methods, we do not claim screened modified gravity to provide the only possible explanation for the signal: this would require knowing that "galaxy formation" physics could not be responsible. We show also the results of a more conservative -- though less well motivated -- noise model which yields only upper limits on $ΔG/G_N$, ranging from $\sim10^{-1}$ for $λ_C \simeq 0.5$ Mpc to $\sim \: \text{few} \times 10^{-4}$ at $λ_C \simeq 50$ Mpc. We show how these constraints may be improved by future galaxy surveys and identify the key features of an observational programme for directly constraining fifth forces on galactic scales. This paper provides a complete description of the analysis summarised in Desmond et al. (2018b).

astro-ph.CO↗