arXiv subjects

Tereasa Brainerd

Publications and source records attributed to Tereasa Brainerd.

8 recordsLinked to original sources

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).

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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.

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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 ($\Sigma_*-\Sigma_{\rm SFR}$, $\Sigma_*-\Sigma_{\rm gas}$, and $\Sigma_{\rm gas}-\Sigma_{\rm SFR}$) 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-$\Sigma_*$ is independent (within $2\sigma$) 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.

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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 $\Delta \Sigma_{SFR}$ 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.

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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.

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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.

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arXiv2021

Cosmic Voids in GAN-Generated Maps of Large-Scale Structure

A Generative Adversarial Network (GAN) was used to investigate the statistics and properties of voids in a $Λ$CDMuniverse. The total number of voids and the distribution of void sizes is similar in both sets of images and, within the formal error bars, the mean void properties are consistent with each other. However, the generated images yield somewhat fewer small voids than do the simulated images. In addition, the generated images yield far fewer voids with central density contrast $\sim$ $-$1. Because the generated images yield fewer of the emptiest voids, the distribution of the mean interior density contrast is systematically higher for the generated voids than it is for the simulated voids. The mean radial underdensity profiles of the largest voids are similar in both sets of images, but systematic differences are apparent. On small scales (r $< 0.5r_{v}$), the underdensity profiles of the voids in the generated images exceed those of the voids in the simulated images. On large scales (r $> 0.5r_{v}$), the underdensity profiles of the voids in the simulated images exceed those of the voids in the generated images. The discrepancies between the void properties in the two sets of images are attributable to the GAN struggling to capture absolute patterns in the data. In particular, the GAN produces too few pixels with density contrasts $\sim$ $-$1 and too many pixels with density contrasts in the range $\sim$ $-$0.88 to $\sim$ $-$0.63.

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arXiv1995

MEASURING GALAXY MASSES USING GALAXY-GALAXY GRAVITATIONAL LENSING

We report a significant detection of weak, tangential distortion of the images of cosmologically distant, faint galaxies due to gravitational lensing by foreground galaxies. A mean image polarisation of $ =0.011\pm 0.006$ is measured for 3202 pairs of source galaxies with magnitudes $23< r \le 24$ and lens galaxies with magnitudes $20\le r\le 23$. The signal remains strong for lens-source separations $\lo 90''$, consistent with quasi-isothermal galaxy halos extending to large radii ($\go 100h^{-1}$ kpc). Our observations thus provide the first evidence from weak gravitational lensing of large scale dark halos associated with individual galaxies. The observed polarisation is also consistent with the signal expected on the basis of simulations incorporating measured properties of local galaxies and modest extrapolations of the observed redshift distribution of faint galaxies. From the simulations we derive a best-fit halo circular velocity of $V\sim 220$ km/s and characteristic radial extent of $s \go 100h^{-1}$ kpc. Our best-fit halo parameters imply typical masses for the lens galaxies within a radius of $100h^{-1}$ kpc on the order of $1.0^{+1.1}_{-0.7}\times 10^{12}h^{-1} M_\odot$, in good agreement with recent dynamical estimates of the masses of local spiral galaxies. This is particularly encouraging as the lensing and dynamical mass estimators rely on different sets of assumptions. Contamination of the gravitational lensing signal by a population of tidally distorted satellite galaxies can be ruled out with reasonable confidence. The prospects for corroborating and improving this measurement seem good, especially using deep HST archival data.

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