arXiv subjects

Claire Kopenhafer

Publications and source records attributed to Claire Kopenhafer.

7 recordsLinked to original sources

arXiv2026

Figuring Out Gas & Galaxies in Enzo (FOGGIE). XV. Examining the Spatial and Kinematic Relationship between Circumgalactic Mg II and O VI

Understanding the thermodynamic properties of the circumgalactic medium (CGM) is key to uncovering the baryon cycle in galaxies. Here we present spatial and kinematic relationships between Mg II and O VI as representatives for low and high ion-bearing gas, in the cosmological zoom-in galaxy simulation suite FOGGIE, a set of Milky-way-like galaxy simulations with high CGM resolution. We find the O VI-bearing gas exists as a diffuse halo around the galactic disk, while the Mg II-bearing gas is more centrally located. We investigate the covering fraction, probability of co-observation, co-kinematic correspondence of these ions using two different analysis methods. We make both mock sightlines using two-dimensional projections of our simulations treating these cells as integrated lines of sight and we create one-dimensional ray objects and use the SALSA (Boyd et al. 2020) code to investigate individual gas structures that contribute most to the line of sight column densities, which we call mock absorbers. We explore the relative kinematics of these mock absorbers and find Mg II and O VI appear to have a co-kinematic relationship when looking at absorber pairs with the closest relative velocity like in Werk et al. (2016). However, this does not necessarily correspond with a close spatial separation meaning many O VI and Mg II absorber pairs only appear to be co-kinematic but are physically unrelated. Taking a more holistic look at Mg II and O VI absorber pairs reveals a much weaker correlation between these two ions.

astro-ph.GA↗

arXiv2025

Metagalactic Ultraviolet Background Tables for Calculating Diffuse Astrophysical Plasma Properties

In developing a deeper understanding of the Circumgalactic Medium, one feature that is poorly understood is the nature of the ultraviolet background (UVB) and its impact on observed column densities. A wide array of UVB models have been created over the years by many different authors, each based on the latest observational data available at the time. In addition to having a large variance between model properties, the formatting between released models is also inconsistent. This data release provides reformatted versions of several widely-used ultraviolet background models-Faucher-Giguère et al. 2009, Haardt and Madau 2012, Puchwein et al. 2019, and Faucher-Giguère 2020-such that each model is in the same units and thus can be utilized to directly compare these models over a wide redshift range. This release also includes code to run a 'cloudy_cooling_tools' pipeline to generate ionization tables for different UVB models.

astro-ph.CO↗

arXiv2025

Impacts of the Metagalactic Ultraviolet Background on Circumgalactic Medium Absorption Systems

Among the many different pieces of physics that go into simulations of the circumgalactic medium (CGM), the metagalactic ultraviolet background (UVB) plays a significant role in determining the ionization state of different metal species. However, the UVB is uncertain with multiple models having been developed by various research groups over the past several decades. In this work, we examine how different UVB models influence the ionic column densities of CGM absorbers. We use these UVB models to infer ion number densities in the FOGGIE galaxy simulations at $z=2.5$ and use the Synthetic Absorption Line Surveyor Application (SALSA) package to identify absorbers. Absorbers are then matched across UVB models based on their line of sight position so that their column densities can be compared. From our analysis, we find that changing the UVB model produces significant changes in ionization, specifically at lower gas densities and higher temperatures where photoionization dominates over collisional ionization. We also find that the scatter of column density differences between models tends to increase with increasing ionization energy, with the exception of \hi, which has the highest scatter of all species we examined.

astro-ph.GA↗

arXiv2022

Seeking Self-Regulating Simulations of Idealized Milky Way-Like Galaxies

Precipitation is potentially a mechanism through which the circumgalactic medium (CGM) can regulate a galaxy's star formation. Here we present idealized simulations of isolated Milky Way-like galaxies intended to examine the ability of galaxies to self-regulate their star formation, particularly via precipitation. Our simulations are the first CGM-focused idealized models to include stellar feedback due to the explicit formation of stars. We also examine the impact of rotation in the CGM. Using six simulations, we explore variations in the initial CGM $t_{\rm cool}/t_{\rm ff}$ ratio and rotation profile. Those variations affect the amount of star formation and gas accretion within the galactic disk. Our simulations are sensitive to their initial conditions, requiring us to gradually increase the efficiency of stellar feedback to avoid destroying the CGM before its gas can be accreted. Despite this gradual increase, the resulting outflows still evacuate large, hot cavities within the CGM and even beyond $r_{200}$. Some of the CGM gas avoids interacting with the cavities and is able to feed the disk along its midplane, but the cooling of feedback-heated gas far from the midplane is too slow to supply the disk with additional gas. Our simulations illustrate the importance of physical mechanisms in the outer CGM and IGM for star formation regulation in Milky Way-scale halos.

astro-ph.GA↗

arXiv2021

KODIAQ-Z: Metals and Baryons in the Cool Intergalactic and Circumgalactic Gas at 2.2<z<3.6

We present the KODIAQ-Z survey aimed to characterize the cool, photoionized gas at 2.2 100) between absorbers separated by less than 500 km/s imply that the metals are poorly mixed in 14.6<log N(HI)<20 gas. We show that these photoionized absorbers contribute to about 10% of the cosmic baryons and 30% of the cosmic metals at 2.2<z<3.6. We find the mean metallicity increases with N(HI), consistent with what is found in z<1 gas. The metallicity of gas in this column density regime has increased by a factor ~8 from 2.2<z<3.6 to z<1, but the contribution of the 14.6<log N(HI)<19 absorbers to the total metal budget of the universe at z<1 is half that at 2.2<z<3.6, indicating a substantial shift in the reservoirs of metals between these two epochs. We compare the KODIAQ-Z results to FOGGIE cosmological zoom simulations. The simulations show an evolution of [X/H] with N(HI) similar to our observational results. Very metal-poor absorbers with [X/H]<-2.4 at z~2-3 in these simulations are excellent tracers of inflows, while higher metallicity absorbers are a mixture of inflows and outflows.

astro-ph.GA↗

arXiv2020

The breakBRD Breakdown: Using IllustrisTNG to Track the Quenching of an Observationally-Motivated Sample of Centrally Star-Forming Galaxies

The observed breakBRD ("break bulges in red disks") galaxies are a nearby sample of face-on disk galaxies with particularly centrally concentrated star formation: they have red disks but recent star formation in their centers as measured by the D$_n$4000 spectral index (Tuttle & Tonnesen 2020). In this paper, we search for breakBRD analogues in the IllustrisTNG simulation and describe their history and future. We find that a small fraction (${\sim}4\%$ at $z=0$; ${\sim}1\%$ at $z=0.5$) of galaxies fulfill the breakBRD criteria, in agreement with observations. In comparison with the mass-weighted parent IllustrisTNG sample, these galaxies tend to consist of a higher fraction of satellite and splashback galaxies. However, the central, non-splashback breakBRD galaxies show similar environments, black hole masses, and merger rates, indicating that there is not a single formation trigger for inner star formation and outer quenching. We determine that breakBRD analogue galaxies as a whole are in the process of quenching. The breakBRD state - with its highly centrally concentrated star formation - is uncommon in the history of either currently quiescent or star-forming galaxies; however, approximately 10% of $10^{10} < M_\ast/M_{\odot} < 10^{11}$ quiescent galaxies at $z=0$ have experienced SFR concentrations comparable to those of the breakBRDs in their past. Additionally, the breakBRD state is short-lived, lasting a few hundred Myr up to ${\sim}2$ Gyr. The observed breakBRD galaxies may therefore be a unique sample of outside-in quenching galaxies.

astro-ph.GA↗

arXiv2019

What Is Inside Matters: Simulated Green Valley Galaxies Have Centrally Concentrated Star Formation

In spatially resolved galaxy observations, star formation rate radial profiles are found to correlate with total specific star formation rates. A central depletion in star formation is thought to correlate with the globally depressed star formation rates of, for example, galaxies within the Green Valley. We present, for the first time, radial specific star formation rate profiles for a statistical sample of simulated galaxies from the Illustris and EAGLE large cosmological simulations. For galaxies on the star-forming sequence, simulated specific star formation rate profiles are in loose agreement with observations, although galaxies from the EAGLE simulation are too centrally peaked, and galaxies from Illustris have a steeper decline at large radii. However, both galaxy samples show centrally concentrated star formation for galaxies in the Green Valley at all galaxy stellar masses, indicating that quenching occurs from the outside-in, in strong conflict with observations of inside-out quenching. These results appear in spite of the different feedback models in these two simulations. We conclude that the distribution of star formation within galaxies is a strong additional constraint for star formation and feedback models in simulations, in particular related to the quenching of star formation.

astro-ph.GA↗