arXiv subjects

Bryanne McDonough

Publications and source records attributed to Bryanne McDonough.

12 recordsLinked to original sources

arXiv2026

A High-Mass Size Deficit for Void Galaxies in the Complete SDSS DR7

We characterize how environment shapes the sizes, luminosity functions, and mass functions of galaxies in large-scale underdensities by comparing the NSA catalog of the Sloan Digital Sky Survey Data Release 7 with an identically selected TNG300 sample, both built with the void finding algorithm VoidFinder, and by assigning a local average underdensity contrast to each galaxy via a spherical top-hat smoothed density field approximation. Void galaxies have fainter characteristic magnitudes than their non-void counterparts, and, at fixed stellar mass, redshift, and color, NSA void galaxies with $M_*>10^{11}h^{-1}M_\odot$ are about $11\pm3\%$ more compact than galaxies in the field, a deficit the TNG300 simulation reproduces. The galaxies that are responsible for this effect are almost all central and predominantly early type, i.e., the systems that are most likely to grow their outer envelopes via late-time mergers. These trends hold across two redshift bins to $z\leq0.114$. Crucially, this deficit is not a fixed property of the void sample but a steep function of the underdensity contrast, deepening toward the emptiest interiors and washing out at a typical density, implying that strict density control and sample selection are imperative when conducting environmental dependency studies like these. The same environmental dependence appears in the stellar mass function, which shifts to lower masses in the deepest voids, and in the close-pair (i.e., the ongoing merger) fraction, which falls toward the emptiest regions. Together, these point to a late-time, merger-driven growth of massive galaxies that is suppressed in voids, leaving their most massive members structurally distinct today.

astro-ph.GA↗

arXiv2026

Lensing-Reconstructed Dark Matter-Intracluster Medium Coherence as a Probe of Cluster Dynamical State: Application to HSTFF, RELICS, and CLASH Clusters

We present the first application of Fourier-space coherence analysis between the lensing-reconstructed projected mass distribution and the X-ray-emitting intracluster medium to a sample of 49 observed galaxy clusters. Using publicly available HST convergence maps from the Hubble Frontier Fields, CLASH, and RELICS programs, together with Chandra X-ray imaging, we measure the scale-dependent coherence between the dark-matter-dominated surface mass density and the hot baryonic gas. We use the coherence length, l_CR, defined as the scale above which the two maps remain at least 90% coherent, as a diagnostic of cluster dynamical state. Across the sample, dynamically relaxed systems exhibit high coherence over a broad range of scales and small l_CR/r500, while disturbed and merging systems show a loss of coherence on intermediate and small scales, yielding larger l_CR/r500. The inferred coherence lengths show sensitivity to lens-model assumptions and to the heterogeneous extent of the available convergence maps. Nevertheless, the coherence signal remains physically interpretable and provides a stringent measure of dark-matter-gas alignment. Applying a conservative threshold, l_CR/r500 < 0.2, we find that only 16% of the sample is relaxed; this fraction rises to 41% for a more permissive threshold of l_CR/r500 < 0.4. Relative to previous X-ray and morphological classifications, we find a 24% disagreement, with the coherence method identifying more systems as dynamically disturbed. These results demonstrate that lensing-X-ray coherence provides a complementary, scale-resolved probe of cluster dynamical state, while highlighting the need for homogeneous, wide-field weak-lensing maps to control reconstruction and field-of-view systematics.

astro-ph.CO↗

arXiv2026

Understanding the regulation of star formation within TNG100 galaxies on kpc-scales using machine learning I: Global versus local

We apply Random Forest and XGBoost machine learning algorithms to determine which galaxy properties most effectively predict star formation and quenching in simulated galaxies. Using spatially-resolved data from approximately 63,000 annular bins across 6,189 TNG100 galaxies, we train classification models to predict quenching states and regression models to predict star formation rate surface densities. Despite their different algorithmic approaches, both methods produce consistent feature importance rankings, with XGBoost distributing importance more evenly among correlated features. For central galaxies and high-mass satellites, black hole mass dominates quenching predictions, consistent with quenching via active galactic nuclei (AGN) feedback. Classification of low-mass satellites shows overwhelming importance for halo mass, indicating environmental quenching. Star formation predictions are dominated by local stellar mass surface density across all star-forming galaxy types, confirming that active star formation is a local process while quenching is driven by global properties.

astro-ph.GA↗

arXiv2025

Void Galaxies and AGN Activity in ZOBOV-identified TNG300 Voids Out to z=3.0

We study void galaxies in the TNG300 simulation between redshifts $z=3$ and $z=0$. Cosmic void catalogs were constructed using a watershed-based void-finding algorithm, and we define four populations of field galaxies for our investigation: [1] galaxies that are members of a watershed void, [2] galaxies that are located within a radius $r \leq 0.8 R_{\rm eff}$ of the center of a void, [3] galaxies interior to spheres centered on void centers that have underdensity contrasts $<-0.8$, and [4] non-void galaxies. We show that population statistics on void galaxy properties can be recovered from watershed-based void catalogs. Differences between galaxy populations are most pronounced interior to the shell-crossing surface (i.e., population [3]) where densities are intermediate to high. Compared to non-void galaxies at all redshifts, the density controlled galaxies are bluer, smaller, more actively star forming, more massive, and less metal enriched. At redshifts $\geq 1$, these differences are less apparent, likely caused by resolution and selection effects incurred by attempting to define a density-controlled sample from a watershed-based void finding algorithm. Further, we investigate the fraction of galaxies with Active Galactic Nuclei (AGN) and find that our density controlled population has AGN fractions that are significantly higher than those of non-void galaxy population ($79.8 \pm 0.4$\% higher at $z=0.0$ and $61.5\pm 0.7$\% higher at larger redshifts).

astro-ph.GA↗

arXiv2025

Measuring Scaling Relationships: Fitting Technique Matters

Scaling relationships, both integrated and spatially resolved, arise due to the physical processes that govern galaxy evolution and are frequently measured in both observed and simulated data. However, the accuracy and comparability of these measurements are hindered by various differences between studies such as spatial resolution, sample selection criteria, and fitting technique. Here, we compare variations of standard least squares techniques to the ridge line method for identifying spatially resolved scaling relations ($Σ_*-Σ_{\rm SFR}$, $Σ_*-Σ_{\rm gas}$, and $Σ_{\rm gas}-Σ_{\rm SFR}$) for TNG100 galaxies. We find that using the ridge line technique to fit these scaling relations with a double linear function results in significantly better fits than fitting with ordinary least squares. We further illustrate the utility of the ridge line technique with an investigation into the dependence of rSFMS measurements on spatial resolution and smoothing scale. Specifically, we find that the slope of the rSFMS at low-$Σ_*$ is independent (within $2σ$) of spatial resolution and smoothing scale. Finally, we discuss the need for a consistent re-analysis of resolved scaling relations in the literature and physically motivate adoption of the ridge line technique over other fitting methods.

astro-ph.GA↗

arXiv2025

Density Profiles of TNG300 Voids across Cosmic Time

We present radial density profiles, as traced by luminous galaxies and dark matter particles, for voids in eleven snapshots of the \texttt{TNG300} simulation. The snapshots span 11.65~Gyr of cosmic time, corresponding to the redshift range $0 \le z \le 3$. Using the comoving galaxy fields, voids were identified via a well-tested, watershed transformation-based algorithm. Voids were defined to be underdense regions that are unlikely to have arisen from Poisson noise, resulting in the selection of $\sim100-200$ of the largest underdense regions in each snapshot. At all redshifts, the radial density profiles as traced by both the galaxies and the dark matter resemble inverse top-hat functions. However, details of the functions (particularly the underdensities of the innermost regions and the overdensities of the ridges) evolve considerably more for the dark matter density profiles than for the galaxy density profiles. At all redshifts, a linear relationship between the galaxy and dark matter density profiles exists, and the slope of the relationship is similar to the bias estimates for \texttt{TNG300} snapshots. Lastly, we identify distinct environments in which voids can exist, defining ``void-in-void" and ``void-in-cloud" populations (i.e., voids that reside in larger underdense or overdense regions, respectively) and we investigate ways in which the relative densities of dark matter and galaxies in the interiors and ridges of these structures vary as a function of void environment.

astro-ph.GA↗

arXiv2025

Magnetic Fields of Satellite Galaxies Stronger Than Comparable Centrals in TNG100

Magnetic fields exist in and around galaxies, but the properties of these fields have not been fully explored due to the challenges inherent in observing and modeling them. In this Note, we explore the differences in magnetic field strength of central and satellite galaxies from the magnetohydrodynamic TNG100 simulation. We find that on average, magnetic fields in satellite galaxies are roughly an order of magnitude stronger than those of central galaxies with comparable masses. The difference is greater for satellites that have already approached within $1 R_{200}$ of their host galaxies. These results indicate that magnetic fields in satellite galaxies are amplified by environmental processes as they fall into a host halo.

astro-ph.GA↗

arXiv2024

Intrinsic and Environmental Effects on the Distribution of Star Formation in TNG100 Galaxies

We present radial profiles of luminosity-weighted age, $age_L$, and $ΔΣ_{SFR}$ for various populations of high- and low- mass central and satellite galaxies in the TNG100 cosmological simulation. Using these profiles, we investigate the impact of intrinsic and environmental factors on the radial distribution of star formation. For both central galaxies and satellites, we investigate the effects of black hole mass, cumulative AGN feedback energy, morphology, halo mass, and local galaxy overdensity on the profiles. In addition, we investigate the dependence of radial profiles of the satellite galaxies as a function of the redshifts at which they joined their hosts, as well as the net change in star-forming gas mass since the satellites joined their host. We find that high-mass ($M_*>10^{10.5} M_{\odot}$) central and satellite galaxies show evidence of inside-out quenching driven by AGN feedback. Effects from environmental processes only become apparent in averaged profiles at extreme halo masses and local overdensities. We find that the dominant quenching process for low-mass galaxies ($M_*<10^{10} M_{\odot}$) is environmental, generally occurring at low halo mass and high local galaxy overdensity for low-mass central galaxies and at high host halo masses for low-mass satellite galaxies. Overall, we find that environmental processes generally drive quenching from the outside-in.

astro-ph.GA↗

arXiv2024

Properties of Voids and Void Galaxies in the TNG300 Simulation

We investigate the properties of voids and void galaxies in the \texttt{TNG300} simulation. Using a luminous galaxy catalog and a spherical void finding algorithm, we identify 5,078 voids at redshift $z = 0$. Within the voids, mass does not directly trace light. Instead, the mean radial underdensity profile as defined by the locations of void galaxies is systematically lower than the mean radial underdensity profile as defined by the dark matter (i.e., the voids are more ``devoid'' of galaxies than they are of mass). Within the voids, the integrated underdensity profiles of the dark matter and the galaxies are independent of the local background density (i.e., voids-in-voids vs.\ voids-in-clouds). Beyond the void radii, however, the integrated underdensity profiles of both the dark matter and the galaxies exhibit strong dependencies on the local background density. Compared to non-void galaxies, void galaxies are on average younger, less massive, bluer in color, less metal enriched, and have smaller radii. In addition, the specific star formation rates of void galaxies are $\sim 20$\% higher than non-void galaxies and, in the case of galaxies with central supermassive black holes with $M_{\rm BH} \gtrsim 3\times 10^6 h^{-1} M_\odot$, the fraction of active void galaxies is $\sim 25$\% higher than active non-void galaxies.

astro-ph.GA↗

arXiv2023

Resolved star formation in TNG100 central and satellite galaxies

Recent cosmological hydrodynamical simulations have produced populations of numerical galaxies whose global star-forming properties are in good agreement with those of observed galaxies. Proper modeling of energetic feedback from supernovae and active galactic nuclei is critical to the ability of simulations to reproduce observed galaxy properties and, historically, such modelling has proven to be a challenge. Here, we analyze local properties of central and satellite galaxies in the $z=0$ snapshot of the TNG100 simulation as a test of feedback models. We generate a face-on projection of stellar particles in TNG100 galaxies, from which we demonstrate the existence of a resolved star-forming main sequence ($Σ_{SFR}$--$Σ_*$ relation) with a slope and normalization that is in reasonable agreement with previous studies. We also present radial profiles of various galaxy populations for two parameters: the distance from the resolved main sequence line ($ΔΣ_{SFR}$) and the luminosity-weighted stellar age ($age_L$). We find that, on average, high-mass central and satellite galaxies quench from the inside-out, while low-mass central and satellite galaxies have similar, flatter profiles.

astro-ph.GA↗

arXiv2022

The Distribution of Satellite Galaxies in the TNG100 Simulation

We investigate the spatial distribution of the satellites of isolated host galaxies in the TNG100 simulation. In agreement with a previous, similar analysis of the Illustris-1 simulation, the satellites are typically poor tracers of the mean host mass density. Unlike the Illustris-1 satellites, here the spatial distribution of the complete satellite sample is well-fitted by an NFW profile; however, the concentration is a factor of ~2 lower than that of the mean host mass density. The spatial distribution of the brightest 50% and faintest 50% of the satellites are also well-fitted by NFW profiles, but the concentrations differ by a factor of ~2. When the sample is subdivided by host color and luminosity, the number density profiles for blue satellites generally fall below the mean host mass density profiles while the number density profiles for red satellites generally rise above the mean host mass density profiles. These opposite, systematic offsets combine to yield a moderately good agreement between the mean mass density profile of the brightest blue hosts and the corresponding number density profile of their satellites. Lastly, we subdivide the satellites according to the redshifts at which they joined their hosts. From this, we find that neither the oldest one third of the satellites nor the youngest one third of the satellites faithfully trace the mean host mass density.

astro-ph.GA↗

arXiv2020

Modeling the Infrared Reverberation Response of the Circumnuclear Dusty Torus in AGNs: An Investigation of Torus Response Functions

The size and structure of the dusty circumnuclear torus in active galactic nuclei (AGN) can be investigated by analyzing the temporal response of the torus's infrared (IR) dust emission to variations in the AGN ultraviolet/optical luminosity. This method, reverberation mapping, is applicable over a wide redshift range, but the IR response is sensitive to several poorly constrained variables relating to the dust distribution and its illumination, complicating the interpretation of measured reverberation lags. We have used an enhanced version of our torus reverberation mapping code (TORMAC) to conduct a comprehensive exploration of the torus response functions at selected wavelengths, for the standard interstellar medium grain composition. The shapes of the response functions vary widely over the parameter range covered by our models, with the largest variations occurring at shorter wavelengths ($\leq 4.5\,μ$m). The reverberation lag, quantified as the response-weighted delay (RWD), is most affected by the radial depth of the torus, the steepness of the radial cloud distribution, the degree of anisotropy of the AGN radiation field, and the volume filling factor. Nevertheless, we find that the RWD provides a reasonably robust estimate, to within a factor of $\sim 3$, of the luminosity-weighted torus radius, confirming the basic assumption underlying reverberation mapping. However, overall, the models predict radii at $2.2\,μ$m that are a typically factor of $\sim 2$ larger than those derived from K-band reverberation mapping. This is likely an indication that the innermost region of the torus is populated by clouds dominated by large graphite grains.

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