arXiv subjects

Cameron Heather

Publications and source records attributed to Cameron Heather.

3 recordsLinked to original sources

arXiv2026

Extreme Values of Black Hole to Stellar Mass Ratio for High-Redshift Galaxies

With recent data from the \emph{James Webb Space Telescope} (JWST), it is possible to calculate the mass of the supermassive black holes at the center of galaxies, and the stellar mass of the host galaxies at redshift $z \gtrsim 5$. In this work, we apply extreme-value statistics to calculate the distributions of extreme black-hole and stellar masses for galaxies in the redshift range $3 \lesssim z \lesssim 8$. We show that under certain assumptions about the stellar and black-hole mass functions, a high ratio of $M_\text{BH}/M_*\sim0.3-0.5$ can be obtained without invoking additional black-hole growth physics. Nevertheless, surveying a range of extreme-value methodologies, we find predictions of the extreme ratio $M_\text{BH}/M_*$ to still be in slight tension with the high values observed by JWST.

astro-ph.GA↗

arXiv2025

The brightest X-ray AGNs at redshift $3\lesssim z \lesssim 6$

Given recent X-ray observations of high-redshift active galactic nuclei (AGNs), we consider whether the extreme luminosities of these AGNs are consistent with current semi-analytical models. In particular, we apply extreme-value statistics (EVS) to obtain predictions of extreme X-ray luminosities of AGNs in the redshift range $3\lesssim z\lesssim 6$. We apply this formalism using different X-ray luminosity functions and compare the predicted extreme luminosities to AGNs in the Stripe 82 X-ray catalogue. We find a general consistency between data and the EVS predictions although there is some tension with certain luminosity functions. We discuss possible extensions to this model, including extrapolating our results to even higher redshifts ($z\gtrsim10$) where AGNs have recently been observed.

astro-ph.GA↗

arXiv2024

Extreme-value modelling of the brightest galaxies at $z\gtrsim9$

Data from the James Webb Space Telescope have revealed an intriguing population of bright galaxies at high redshifts. In this work, we use extreme-value statistics to calculate the distribution (in UV magnitude) of the brightest galaxies in the redshift range $9 \lesssim z \lesssim 16$. We combine the Generalised Extreme Value (GEV) approach with modelling of the galaxy luminosity function. We obtain predictions of the brightest galaxies for a suite of luminosity functions, including the Schechter and double power law functions, as well as a model parametrised by the stellar formation efficiency $f_*$. We find that the JWST data is broadly consistent with $f_*$ of $5\%-10\%$, and that the brightest galaxy at $z\sim16$ will have $M_{\rm UV}\approx -23.5^{0.8}_{0.4}$. If $f_*$ is dependent on halo mass, we predict $M_{\rm UV}\approx -22.5^{0.5}_{1.5}$ for such an object. We show that extreme-value statistics not only predicts the magnitude of the brightest galaxies at high redshifts, but may also be able to distinguish between models of star formation in high-redshift galaxies.

astro-ph.GA↗