arXiv subjects

Nicole Thomas

Publications and source records attributed to Nicole Thomas.

7 recordsLinked to original sources

arXiv2026

Cosmological Galaxy Formation Modelling in the Era of the Square Kilometre Array

Over the past decade, galaxy formation simulations have advanced dramatically, transforming our ability to model the interstellar medium (ISM) and predict galaxies' radio emission. Yet the challenge of bridging physical scales--from sub-parsec star formation to gigaparsec cosmic structure--remains. The Square Kilometre Array (SKA) will map the cold gas and radio continuum of galaxies across cosmic time, demanding models that couple physical realism with cosmological reach. This chapter reviews the state-of-the-art in cosmological galaxy formation modelling in preparation for the SKA. We outline progress in simulating atomic hydrogen (HI), molecular gas, and radio continuum emission from both star formation and active galactic nuclei, highlighting how cosmological hydrodynamical simulations and semi-analytic models now jointly reproduce many observed gas properties. We emphasise the need for a coordinated, ``wedding-cake'' strategy that unites simulations of different scales, for forward modelling of observables to ensure fair comparison with data, and for the integration of new technologies such as AI-driven emulators to accelerate progress. Together, these efforts will enable theoretical models to both interpret and guide SKA science, turning simulations from passive interpreters into active engines for discovery.

astro-ph.GA↗

arXiv2022

The environments of the radio galaxy population in SIMBA

We investigate the environmental properties of the $z=0$ radio galaxy population using the Simba cosmological hydrodynamic simulation. We identify centrals and satellites from a population of high and low excitation radio galaxies (HERGs and LERGs) in Simba, and study their global properties. We find that $\sim 20 \%$ of radio galaxies are satellites, and that there are insignificant differences in the global properties of LERGs based on their central/satellite classification. HERG satellites display lower values of star formation, 1.4GHz radio luminosity, and Eddington fractions than HERG centrals. We further investigate the environments of radio galaxies and show that HERGs typically live in less dense environments, similar to star-forming galaxies. The environments of high-mass LERGs are similar to non-radio galaxies, but low-mass LERGs live in underdense environments similar to HERGs. LERGs with over-massive black holes reside in the most dense environments, while HERGs with over-massive black holes reside in underdense environments. The richness of a LERG's environment decreases with increasing Eddington fraction, and the environments of all radio galaxies do not depend on radio luminosity for $P_{\rm 1.4~GHz} < 10^{24} \rm{~W~Hz}^{-1}$. Complementing these results, we find that LERGs cluster on the same scale as the total galaxy population, while multiple HERGs are not found within the same dark matter halo. Finally, we show that high density environments support the growth of HERGs rather than LERGs at $z=2$. Simba predicts that with more sensitive surveys, we will find populations of radio galaxies in environments much similar to the total galaxy population.

astro-ph.GA↗

arXiv2021

The Radio Galaxy Population in the SIMBA SImulations

We examine the 1.4GHz radio luminosities of galaxies arising from star formation and active galactic nuclei (AGN) within the state-of-the-art cosmological hydrodynamic simulation Simba. Simba grows black holes via gravitational torque limited accretion from cold gas and Bondi accretion from hot gas, and employs AGN feedback including jets at low Eddington ratios. We define a population of radio loud AGN (RLAGN) based on the presence of ongoing jet feedback. Within RLAGN we define high and low excitation radio galaxies (HERGs and LERGs) based on their dominant mode of black hole accretion: torque limited accretion representing feeding from a cold disk, or Bondi representing advection-dominated accretion from a hot medium. Simba predicts good agreement with the observed radio luminosity function (RLF) and its evolution, overall as well as separately for HERGs and LERGs. Quiescent galaxies with AGN-dominated radio flux dominate the RLF at > $\sim 10^{22-23}$ W Hz$^{-1}$, while star formation dominates at lower radio powers. Overall, RLAGN have higher black hole accretion rates and lower star formation rates than non-RLAGN at a given stellar mass or velocity dispersion, but have similar black hole masses. Simba predicts a LERG number density of 8.53 Mpc$^{-3}$, $\sim 10\times$ higher than for HERGs, broadly as observed. While LERGs dominate among most massive galaxies with the largest black holes and HERGs dominate at high specific star formation rates, they otherwise largely populate similar-sized dark matter halos and have similar host galaxy properties. Simba thus predicts that deeper radio surveys will reveal an increasing overlap between the host galaxy demographics of HERGs and LERGs.

astro-ph.GA↗

arXiv2019

Black Hole -- Galaxy Correlations in Simba

We examine the co-evolution of galaxies and supermassive black holes in the Simba cosmological hydrodynamic simulation. Simba grows black holes via gravitational torque-limited accretion from cold gas and Bondi accretion from hot gas, while feedback from black holes is modeled in radiative and jet modes depending on the Eddington ratio ($f_{Edd}$). Simba shows generally good agreement with local studies of black hole properties, such as the black hole mass--stellar velocity dispersion ($M_{BH}-σ$) relation, 2 the black hole accretion rate vs. star formation rate (BHAR--SFR), and the black hole mass function. $M_{BH}-σ$ evolves such that galaxies at a given $M_{BH}$ have higher $σ$ at higher redshift, consistent with no evolution in $M_{BH}-M_*$. For $M_{BH}<\sim 10^8 M_\odot$, $f_{Edd}$ is anti-correlated with $M_{BH}$ since the BHAR is approximately independent of $M_{BH}$, while at higher masses $f_{Edd}-M_{BH}$ flattens and has a larger scatter. BHAR vs. SFR is invariant with redshift, but $f_{Edd}$ drops steadily with time at a given $M_{BH}$, such that all but the most massive black holes are accreting in a radiatively efficient mode at $z>\sim 2$. The black hole mass function amplitude decreases with redshift and is locally dominated by quiescent galaxies for $M_{BH}>10^{8}M_{\odot}$, but for $z>\sim 1$ star forming galaxies dominate at all $M_{BH}$. The $z=0$ $f_{Edd}$ distribution is roughly lognormal with a peak at $f_{Edd}<\sim 0.01$ as observed, shifting to higher $f_{Edd}$ at higher redshifts. Finally, we study the dependence of black hole properties with \HI\ content and find that the correlation between gas content and star formation rate is modulated by black hole properties, such that higher SFR galaxies at a given gas content have smaller black holes with higher $f_{Edd}$

astro-ph.GA↗

arXiv2015

A Large-Scale GaP-on-Diamond Integrated Photonics Platform for NV Center-Based Quantum Information

We present chip-scale transmission measurements for three key components of a GaP-on-diamond integrated photonics platform: waveguide-coupled disk resonators, directional couplers, and grating couplers. We also present proof-of-principle measurements demonstrating nitrogen-vacancy (NV) center emission coupled into selected devices. The demonstrated device performance, uniformity and yield place the platform in a strong position to realize measurement-based quantum information protocols utilizing the NV center in diamond.

cond-mat.mes-hall↗

arXiv2014

Waveguide-integrated single-crystalline GaP resonators on diamond

Large-scale entanglement of nitrogen-vacancy (NV) centers in diamond will require integration of NV centers with optical networks. Toward this goal, we present the fabrication of single-crystalline gallium phosphide (GaP) resonator-waveguide coupled structures on diamond. We demonstrate coupling between 1 μm diameter GaP disk resonators and waveguides with a loaded Q factor of 3,800, and evaluate their potential for efficient photon collection if integrated with single photon emitters. This work opens a path toward scalable NV entanglement in the hybrid GaP/diamond platform, with the potential to integrate on-chip photon collection, switching, and detection for applications in quantum information processing.

cond-mat.mes-hall↗

arXiv2014

Room-temperature detection of single 20 nm super-paramagnetic nanoparticles with an imaging magnetometer

We demonstrate room temperature detection of single 20 nm super-paramagnetic nanoparticles (SPNs) with a wide-field optical microscope platform suitable for biological integration. The particles are made of magnetite (Fe3O4) and are thus non-toxic and biocompatible. Detection is accomplished via optically detected magnetic resonance imaging using nitrogen-vacancy defect centers in diamond, resulting in a DC magnetic field detection limit of 2.3 μT. This marks a large step forward in the detection of SPNs, and we expect that it will allow for the development of magnetic-field-based biosensors capable of detecting a single molecular binding event.

cond-mat.mes-hall↗