arXiv subjects

Sophie L. Newman

Publications and source records attributed to Sophie L. Newman.

13 recordsLinked to original sources

arXiv2026

Stellar photoionisation modelling in SYNTHESIZER

Emission from photoionised gas surrounding young stellar populations ($H\text{II}$ regions) provides critical diagnostics of the physical conditions in star forming galaxies. This emission constrains the gas properties, the nature of ionising sources, and generates essential features for determining galaxy redshifts. To leverage spectroscopic observations to test galaxy formation models, it is essential to incorporate these emissions into synthetic datasets. Here, we present the integration of photoionised gas emission into the SYNTHESIZER package (https://synthesizer-project.github.io) and demonstrate its application. We quantify the impact of key modelling assumptions - including stellar population synthesis models, initial mass functions, ionisation parameter, gas density, geometry, abundance pattern, elemental depletion, and dust - on spectral diagnostics. Furthermore, we demonstrate the versatility of SYNTHESIZER through its application in different scenarios ranging from exploring emission in toy parametric models to large-volume cosmological simulations with realistic star formation and metal enrichment histories. Taken together, SYNTHESIZER provides a flexible, physically motivated framework to model stellar and nebular emissions, serving as a vital link between theory and observations in the era of next-generation spectroscopic missions.

astro-ph.GA↗

arXiv2026

Cloudy-Maraston: Integrating nebular continuum and line emission with the Maraston stellar population synthesis models

The James Webb Space Telescope has ushered in an era of abundant high-redshift observations of young stellar populations characterized by strong emission lines, motivating us to integrate nebular emission into the new Maraston stellar population model which incorporates the latest Geneva stellar evolutionary tracks for massive stars with rotation. We use the photoionization code Cloudy to obtain the emergent nebular continuum and line emission for a range of modelling parameters, then compare our results to observations on various emission line diagnostic diagrams. We carry out a detailed comparison with several other models in the literature assuming different input physics, including modified prescriptions for stellar evolution and the inclusion of binary stars, and find close agreement in the H$\rm β$, H$\rm α$, [N II]$λ6583$, and [S II]$λ6731$ luminosities between the models. However, we find significant differences in lines with high ionization energies, such as He II$λ$1640 and [O III]$λ5007$, due to large variations in the hard ionizing photon production rates. The models differ by a maximum of $\hat{Q}_{\rm [O III]λ5007} = \rm 6 \times 10^9 \; s^{-1} \, M_{\odot}^{-1}$, where these differences are mostly caused by the assumed stellar rotation and effective temperatures for the Wolf Rayet phase. Interestingly, rotation and uncorrected effective temperatures in our single star population models alone generate [O III] ionizing photon production rates higher than models including binary stars with ages between 1 to 8 Myr. These differences highlight the dependence of derived properties from SED fitting on the assumed model, as well as the sensitivity of predictions from cosmological simulations.

astro-ph.GA↗

arXiv2026

CROCS Data Release I: Constraints on the Hubble Constant

Recent cosmological surveys and datasets have highlighted a variety of tensions to the concordance model of our universe, $Λ$CDM. Of particular interest is the Hubble tension, the $5.5σ$ discrepancy between measurements of the Hubble constant $H_0$ using high redshift CMB data from Planck ($67.27\pm0.60$km$\text{s}^{-1}\text{Mpc}^{-1}$) and low redshift supernovae from SH0ES ($73.2\pm1.3$km$\text{s}^{-1}\text{Mpc}^{-1}$). To avoid stepping on any toes, we have initiated the CROCS collaboration to resolve this tension, gathering experts from across many fields of cosmology, astrophysics, astronomy, machine learning, data science, philosophy, and astrology. In this paper, we present findings from CROCS Data Release 1, corresponding to the first $\sim3$ days and 27 minutes (rest frame) of observation. We perform a robust statistical analysis, showing that Planck and SH0ES both suffer from imperial biasing systematics (IBS) at $5σ$ significance. Accounting for these errors by converting to metric units reconciles the high and low redshift data, with $H_0 = 69.00\pm0.420$km$\text{s}^{-1}\text{Mpc}^{-1}$. We thus report that our results are sufficient to end the Hubble tension for good.

astro-ph.CO↗

arXiv2026

The Nature of High-Redshift Massive Quiescent Galaxies -- Searching for RUBIES-UDS-QG-z7 in FLARES

RUBIES-UDS-QG-z7 (RQG) is the earliest massive quiescent galaxy identified to date, inferred to have formed its abundant stellar mass in a single burst that ceases rapidly before $z\sim8$. An object of such extreme nature challenges our understanding of galaxy formation, requiring rapid growth and quenching mechanisms only $0.6 \ \rm{Gyr}$ after the Big Bang and implying number densities $2 \ \rm{dex}$ higher than currently predicted by simulations. We use synthetic observables to identify analogous systems within the First Light And Reionisation Epoch Simulations (FLARES) and find two massive galaxies ($M_{\ast}>10^{9} \ \mathrm{M_{\odot}}$) dominated by rapidly quenched bursts. One of these demonstrates excellent agreement with the inferred physical properties of RQG and implies a number density of analogous systems $\log_{10}(\mathrm{N_{Q}} \ / \ \mathrm{Mpc}^{-3}) = -7.92^{\ +0.52}_{\ -0.76}$. Beyond demonstrating that the current FLARES model is capable of producing RQG-like systems, these analogues provide a laboratory within which to study the underlying physics. Their active galactic nuclei (AGN) heat and expel gas, inducing rapid quenching and preventing timely rejuvenation. This causes above-average chemical enrichment at a given stellar mass, with super solar levels predicted for RQG. These metallicities are underestimated by spectral energy distribution fitting and we show that $α$-enhancement cannot be solely responsible. Degeneracies with age and dust attenuation appear the more likely causes. Tensions between observed and simulated number densities can be alleviated in part by considering systematics, but adjustments to AGN feedback, such as allowing super-Eddington accretion rates, may be required for full agreement.

astro-ph.GA↗

arXiv2025

Resolving the ionizing photon budget crisis with JWST/NIRCam HII clumping constraints at z=6

We present a comprehensive study of the ionizing properties of 1721 galaxies at $5.6<z<6.5$ using deep JWST/NIRCam photometric imaging from the NEP, JADES, and PRIMER surveys spanning an unmasked area $\sim550$arcmin$^2$ across UV magnitudes $-22\lesssim M_{\rm UV}\lesssim-17.5$. Our $90\%$ stellar mass complete sample suggests little relation of UV slope with magnitude, $β_{\rm UV}=(-0.040\pm0.022)M_{\rm UV}-2.88^{+0.43}_{-0.44}$, implying $f_{\rm esc}^{\rm LyC}\simeq5\%$ based on calibrations from the Low-redshift Lyman Continuum Survey (LzLCS). We measure a constant ionizing photon production efficiency with UV magnitude, $\log_{10}(ξ_{\rm ion, 0}/\rm Hz\,erg^{-1}) = -0.006^{+0.019}_{-0.017}~M_{\rm UV} + 25.05^{+0.39}_{-0.34}$, consistent with HST canonical values. The total production rate of photons escaping into the IGM is computed as $\log_{10}(\dot{n}_{\rm ion}/\rm s^{-1}Mpc^{-3})=50.31^{+0.07}_{-0.06}$ for $M_{\rm UV}<-17$ galaxies from our star forming and smouldering UV luminosity functions (UVLFs), which differ in the faint-end slope ($α_{\rm SFG}=-2.2\pm0.2$; $α_{\rm sm}=-1.7\pm0.2$). Extrapolating to the latest UVLF turnover limits from the massive lensing galaxy cluster Abell S1063 ($M_{\rm UV, lim}=-13.5$) implies that a recombination-weighted HII clumping factor $C_{\rm HII, rec}=6.2^{+4.1}_{-2.1}$ is required to produce fully stably reionized at $z\simeq6$. A clumping factor of this magnitude resolves the ionizing photon budget crisis. Our methodology paves the way for indirect clumping measurements from galaxies which will provide insight into earlier stages of the EoR when the Ly$α$-forest becomes saturated and more direct quasar measurements become impossible.

astro-ph.GA↗

arXiv2025

Discovery of a Little Red Dot candidate at $z\gtrsim10$ in COSMOS-Web based on MIRI-NIRCam selection

JWST has revealed a new high-redshift population called little red dots (LRDs). Since LRDs may be in the early phase of black hole growth, identifying them in the early universe is crucial for understanding the formation of the first supermassive black holes. However, no robust LRD candidates have been identified at $z>10$, because commonly-used NIRCam photometry covers wavelengths up to $\sim5\,{\rm μm}$ and is insufficient to capture the characteristic V-shaped spectral energy distributions (SEDs) of LRDs. In this study, we present the first search for $z\gtrsim10$ LRD candidates using both NIRCam and MIRI imaging from COSMOS-Web, which provides the largest joint NIRCam-MIRI coverage to date ($0.20\,{\rm deg^2}$). Taking advantage of MIRI/F770W to remove contaminants, we identify one robust candidate, CW-LRD-z10 at $z_{\rm phot}=10.5^{+0.7}_{-0.6}$ with $M_{\rm UV}=-19.9^{+0.1}_{-0.2}\,{\rm mag}$. CW-LRD-z10 exhibits a compact morphology, a distinct V-shaped SED, and a non-detection in F115W, all consistent with being an LRD at $z\sim10$. Based on this discovery, we place the first constraint on the number density of LRDs at $z\sim10$ with $M_{\rm UV}\sim-20$ of $1.2^{+2.7}_{-1.0}\times10^{-6}\,{\rm Mpc^{-3}\,mag^{-1}}$, suggesting that the fraction of LRDs among the overall galaxy population increases with redshift, reaching $\sim3\%$ at $z\sim10$. Although deep spectroscopy is necessary to confirm the redshift and the nature of CW-LRD-z10, our results imply that LRDs may be a common population at $z>10$, playing a key role in the first supermassive black hole formation.

astro-ph.GA↗

arXiv2025

First Light And Reionization Epoch Simulations (FLARES) -- XIX: Supermassive black hole mergers in the early Universe and their environmental dependence

The upcoming space-based gravitational wave (GW) observatory, LISA, is expected to detect GW signals from supermassive black hole (SMBH) mergers occurring at high redshifts. However, understanding the origin and growth of SMBHs in the early Universe remains an open problem in astrophysics. In this work, we utilize the First Light And Reionization Epoch Simulations (FLARES), a suite of cosmological hydrodynamical zoom-in simulations, to study SMBH mergers at $5 \lesssim z \lesssim 10$ across a wide range of environments. Most mergers in FLARES involve secondary SMBHs near the seed mass ($m_{\rm seed} \approx 1.5 \times 10^{5}~{\rm M}_{\odot}$) while primary SMBHs span up to $10^{9}~{\rm M}_{\odot}$, resulting in mass ratios from $q \sim 10^{-4}$ to $1$, with a peak at $q \sim 1$. The number of mergers increases rapidly towards lower redshifts, and the comoving total number density scales with overdensity as $n_{\rm merger} = 10^{-3.81} (1 + δ)^{4.78}$. Denser regions host more massive mergers, with higher merger redshifts and lower mass ratios. Within the FLARES redshift range, LISA is expected to detect mergers with $10^{5} \lesssim M_{\rm tot}/{\rm M}_{\odot} \lesssim 10^{8}$ and $q \gtrsim 10^{-2}$, corresponding to a detection rate of $0.030~{\rm yr}^{-1}$ for events with signal-to-noise ratio ${\rm SNR} \geq 10$. Our study demonstrates the sensitivity of GW predictions at high redshifts to SMBH seed models and merger time delays, highlighting the need for improved modeling in future cosmological simulations to maximize LISA's scientific return.

astro-ph.GA↗

arXiv2025

The COSMOS-Web Lens Survey (COWLS) III: forecasts versus data

We compare forecasts for the abundance and properties of strong gravitational lenses in the COSMOS-Web survey, a $0.54$ deg$^2$ survey of the COSMOS field using the NIRCam and MIRI instruments aboard JWST, with the first catalogue of strong lens candidates identified in the observed NIRCam data, COWLS. We modify the lenspop package to produce a forecast for strong lensing in COSMOS-Web. We add a new mock galaxy catalogue to use as the source population, as well as the COSMOS-Web survey specifications, including the transmission data for the four NIRCam filters used. We forecast 107 strong lenses can be detected in COSMOS-Web across all bands, assuming complete subtraction of the lens galaxy light. The majority of the lenses are forecast to have small Einstein radii ($θ_{\rm E} < 1$ arcsecond) and lie at redshifts between $0 < z <2$, whilst the source redshift distribution peaks at $z\sim 3$ and has a long tail extending up to $z \sim 11$, unambiguously showing that strong lensing in JWST can probe the entirety of the epoch of reionisation. We compare our forecast with the distributions of Einstein radii, lens photometric redshifts, and lens and source magnitudes in the observed lenses, finding that whilst the forecast and observed Einstein radii distributions match, the redshifts and magnitudes do not. The observed lens redshift distribution peaks at a slightly lower redshift than the forecast one, whilst the lens magnitudes are systematically brighter in the observed data than in the forecast.

astro-ph.GA↗

arXiv2025

Using white dwarf lensing to resolve accretion flows

Microlensing is one of the most powerful tools for probing the nature of dark halo objects and the sources they lens. As our nearest massive galaxy, M31 provides a rich source population with many potential lenses in its halo crossing our field of view at any one time. In this paper we explore the probability that X-ray sources in M31 will be lensed by white dwarfs in M31's halo. We find an expected lensing rate of 2.6/year within the mean archival Swift XRT field-of-view, and 6.3/year for the whole galaxy. For X-ray emitting sources harboring accreting neutron stars and black holes, we find that microlensing offers a unique opportunity to constrain the properties of the inner accretion flow. Our results demonstrate that it is feasible to recover both the spin of the black hole and the temperature profile of the accretion disk by discerning their effects upon the profile of the microlensing magnification. We show that these parameters have a significant effect on the shape of the light curve, with the effect of spin being more pronounced at smaller impact parameters and higher energies, while the effect of the temperature profile is larger at lower energies and larger impact parameters. This suggests that multi-band observations of a single lensing event could be used to robustly constrain both parameters.

astro-ph.GA↗

arXiv2025

Physical properties of galaxies and the UV Luminosity Function from $z\sim6$ to $z\sim14$ in COSMOS-Web

We present measurements of the rest-frame ultraviolet luminosity function (UVLF) in three redshift bins over $z\sim5.5$-14 from the JWST COSMOS-Web survey. Our samples, selected using the dropout technique in the HST/ACS F814W, JWST/NIRCam F115W, and F150W filters, contain a total of 3099 galaxies spanning a wide luminosity range from faint ($M_{\rm UV}\sim-19$ mag) to bright ($M_{\rm UV}\sim-22.5$ mag). The galaxies are undergoing rapid star formation, with blue stellar populations. Surprisingly, their median UV spectral slope $β$ does not evolve at $z>8$, suggesting minimal dust, or physical separation of dust and star formation at early epochs. The measured UVLF exhibits an excess at the bright-end ($M_{\rm UV}<-21$ mag) compared to pre-JWST empirical results and theoretical predictions of an evolving Schechter function, with the excess beginning at $z\sim9$ and becoming increasingly prominent toward $z\sim12$. Our analysis suggests that reproducing the observed abundance of UV-bright galaxies at high redshift requires a combination of physical processes, including elevated star formation efficiencies, moderate levels of stochasticity in galaxy luminosities, and minimal dust attenuation.

astro-ph.GA↗

arXiv2025

A Swift analysis of the Eras tour set list and implications for astrophysics research (Taylor's version)

Popular culture plays a significant role in shaping public interest in science, and Taylor Swift's discography frequently incorporates astrophysics terminology. This study examines the occurrence of astrophysics-related words in her lyrics and their representation in the Eras tour set list. By analyzing the frequency of words in Swift's total discography, we identify that astrophysics is promoted the most within her most recent album, The Tortured Poets Department, whereas songs from Midnights promoted astrophysics the most throughout the Eras tour. We catagorize words into various disciplines of astrophysics and find that multimessenger astronomy is promoted the most, both in Swift's total discography and throughout the Eras tour. We perform Taylor expansion and predict $12 \pm 5$ astrophysical terms in Swift's next album. This analysis offers a unique perspective on the intersection of music and science, revealing how Swift's artistry may unintentionally promote interest in different fields of astrophysics.

astro-ph.GA↗

arXiv2025

First Light and Reionization Epoch Simulations (FLARES) -- XV: The physical properties of super-massive black holes and their impact on galaxies in the early universe

Understanding the co-evolution of super-massive black holes (SMBHs) and their host galaxies remains a key challenge of extragalactic astrophysics, particularly the earliest stages at high-redshift. However, studying SMBHs at high-redshift with cosmological simulations, is challenging due to the large volumes and high-resolution required. Through its innovative simulation strategy, the First Light And Reionisation Epoch Simulations (FLARES) suite of cosmological hydrodynamical zoom simulations allows us to simulate a much wider range of environments which contain SMBHs with masses extending to $M_{\bullet}>10^{9}\ M_{\odot}$ at $z=5$. In this paper, we use FLARES to study the physical properties of SMBHs and their hosts in the early Universe ($5\le\, z \le10$). FLARES predicts a sharply declining density with increasing redshift, decreasing by a factor of 100 over the range $z=5\to 10$. Comparison between our predicted bolometric luminosity function and pre-\emph{JWST} observations yield a good match. However, recent \emph{JWST} observations appear to suggest a larger contribution of SMBHs than previously observed, or predicted by FLARES. Finally, by using a re-simulation with AGN feedback disabled, we explore the impact of AGN feedback on their host galaxies. This reveals that AGN feedback results in a reduction of star formation activity, even at $z>5$, but only in the most massive galaxies. A deeper analysis reveals that AGN are also the cause of suppressed star formation in passive galaxies but that the presence of an AGN doesn't necessarily result in the suppression of star formation.

astro-ph.GA↗

arXiv2024

FOOD I: A New Division Scheme For The Stelliferous Era

In recent years the James Webb Space Telescope has enabled the frontier of observational galaxy formation to push to ever higher redshift, deep within cosmic dawn. However, what is high-redshift, and when was cosmic dawn? While widely used, these terms (as well as many other confusing terms) are not consistently defined in the literature; this both hampers effective communication but also impedes our ability to precisely characterize and understand the phenomena under investigation. In this article we seek to address this issue of utmost importance. We begin by definitively defining terms such as ``high-redshift'', ``cosmic dawn'', etc. However, despite the rigorous definitions for them we present, both the adjective-based redshift and diurnal marker (time-of-day) division schemes suffer from issues including not being sufficiently granular, angering cosmologists, being arbitrary, and having a geocentric bias. To overcome these we introduce the \textit{redshiFt epOchs fOr everyboDy} (FOOD) framework, a revolutionary new division scheme based on eating occasions, i.e. meals.

astro-ph.GA↗