Cassandra Lochhaas
A5074375776- Galaxies: Formation, Evolution, Phenomena
- Astronomy and Astrophysical Research
- Astrophysics and Star Formation Studies
- Stellar, planetary, and galactic studies
- Astrophysical Phenomena and Observations
- Astrophysics and Cosmic Phenomena
- Astronomical Observations and Instrumentation
- Gamma-ray bursts and supernovae
- Adaptive optics and wavefront sensing
- Radio Astronomy Observations and Technology
- Particle Detector Development and Performance
- Cosmology and Gravitation Theories
- Dark Matter and Cosmic Phenomena
- Statistical and numerical algorithms
- Calibration and Measurement Techniques
- Pulsars and Gravitational Waves Research
- Astro and Planetary Science
- Gear and Bearing Dynamics Analysis
Space Telescope Science Institute
2020-2024
Center for Astrophysics Harvard & Smithsonian
2024
The Ohio State University
2016-2021
We present the first results from an optical reverberation mapping campaign executed in 2014, targeting active galactic nuclei (AGN) MCG+08-11-011, NGC 2617, 4051, 3C 382, and Mrk 374. Our targets have diverse interesting observational properties, including a "changing look" AGN broad-line radio galaxy. Based on continuum-H$\beta$ lags, we measure black hole masses for all five targets. also obtain H$\gamma$ He{\sc ii}\,$\lambda 4686$ lags objects except 382. The indicate radial...
We present the results of an optical spectroscopic monitoring program targeting NGC 5548 as part a larger multi-wavelength reverberation mapping campaign. The campaign spanned six months and achieved almost daily cadence with observations from five ground-based telescopes. H$\beta$ He II $\lambda$4686 broad emission-line light curves lag that 5100 $\AA$ continuum by $4.17^{+0.36}_{-0.36}$ days $0.79^{+0.35}_{-0.34}$ days, respectively. relative to 1158 ultraviolet curve measured Hubble Space...
Abstract We present optical continuum lags for two Seyfert 1 galaxies, MCG+08-11-011 and NGC 2617, using monitoring data from a reverberation mapping campaign carried out in 2014. Our light curves span the ugriz filters over four months, with median cadences of 1.0 0.6 days respectively, combined roughly daily X-ray near-UV Swift 2617. find consistent geometrically thin accretion-disk models that predict lag-wavelength relation τ ∝ λ 4/3 . However, observed are larger than predictions based...
Abstract The circumgalactic medium (CGM) is often assumed to exist in or near hydrostatic equilibrium, with the regulation of accretion and effects feedback treated as perturbations a stable balance between gravity thermal pressure. We investigate global equilibrium CGM using four highly resolved L * galaxies from Figuring Out Gas & Galaxies Enzo (FOGGIE) project. FOGGIE simulations were specifically targeted at fine spatial mass resolution (Δ x ≲ 1 kpc h −1 M ≃ 200 ⊙ ). develop new...
Abstract Over the next decade, astronomical community will be commissioning multiple wide-field observatories well suited for studying stellar halos in both integrated light and resolved stars. In preparation this, we use five high-resolution cosmological simulations of Milky Way–like galaxies from FOGGIE suite to explore properties components halos. These are run with high time (5 Myr) mass (1000 M ⊙ ) resolution better model origins low-density regions like We find that have masses,...
Abstract Gas-phase metallicity gradients are a crucial element in understanding the chemical evolution of galaxies. We use FOGGIE simulations to study (∇ Z ) six Milky Way–like galaxies throughout their evolution. generally exhibit steep negative for most history, with only few short-lived instances reaching positive slopes that appear arise mainly from interactions other concurs simulation results but disagrees robust observational finding flat and common at z > 1. By tracking gradient...
Successful models of the low-redshift circumgalactic medium (CGM) must account for (1) a large amount gas, (2) relatively slow gas velocities, (3) high degree metal enrichment, (4) similar absorption properties around both star-forming and passive galaxies, (5) observationally inferred temperature densities CGM gas. We show that galactic wind-driven bubbles can these observed properties. develop model describing motion driven by hot, fast wind characteristic supernova energy injection. The...
The circumgalactic medium (CGM) is closely linked to galaxy formation and evolution, but difficult characterize observationally typically poorly resolved in cosmological simulations. We use spherically-symmetric, idealized, high-resolution simulations of the CGM $10^{12}M_\odot$ $10^{11}M_\odot$ dark matter halos gas pressure, turbulent radial velocities, degree thermal effective dynamic pressure support overall as well its high- low-temperature phases. find that halo contains a mostly...
We study ram pressure stripping in simulated Milky Way-like halos at z>=2 from the Figuring Out Gas & Galaxies In Enzo (FOGGIE) project. These simulations reach exquisite resolution their circumgalactic medium (CGM) gas owing to FOGGIE's novel refinement scheme. The CGM of each halo spans a wide dynamic range density and velocity over its volume---roughly 6 dex 1000 km/s, respectively---translating into 5 imparted interacting satellites. profiles are highly stochastic, kpc-scale variations...
We present geometric and dynamical modeling of the broad line region for multi-wavelength reverberation mapping campaign focused on NGC 5548 in 2014. The dataset includes photometric spectroscopic monitoring optical ultraviolet, covering H$\beta$, C IV, Ly$\alpha$ emission lines. find an extended disk-like H$\beta$ BLR with a mixture near-circular outflowing gas trajectories, while IV BLRs are much less resemble shell-like structures. There is clear radial structure BLR, arising at smaller...
We present the first results from a reverberation-mapping campaign undertaken during half of 2012, with additional data on one AGN (NGC 3227) 2014 campaign. Our main goals are (1) to determine black hole masses continuum-Hbeta reverberation signatures, and (2) look for velocity-dependent time delays that might be indicators gross kinematics broad-line region. successfully measure Hbeta five AGNs, four which have previous mass measurements. The values measured here in agreement earlier...
ABSTRACT Energy injection by supernovae may drive hot supersonic galactic winds in rapidly star-forming galaxies, driving metal-enriched gas into the circumgalactic medium and potentially accelerating cool gas. If sufficiently mass-loaded, such flows become radiative within wind-driving region, reducing overall mass outflow rate from host galaxy. We show that this sets a maximum on total momentum for energy-driven winds. For spherical wind of Solar metallicity driven continuous star...
Abstract The circumgalactic medium (CGM) of the Milky Way is mostly obscured by nearby gas in position–velocity space because we reside inside Galaxy. Substantial biases exist most studies Way’s CGM that focus on easier-to-detect high-velocity gas. With mock observations a analog from Figuring Out Gas & Galaxies Enzo (FOGGIE) simulation, investigate four observational related to CGM. First, QSO absorption-line probe limited amount mass: only 35% mass at high Galactic latitudes <?CDATA $|...
Following work by W\"unsch and collaborators, we investigate a self-enrichment scenario for second generation star formation in globular clusters wherein wind material from first massive stars rapidly radiatively cools. Radiative energy loss allows retention of fast winds within the central regions clusters, where it fuels formation. Secondary occurs $\sim3-5$ Myr, before supernovae, producing uniform iron abundances both populations. We derive critical criteria radiative cooling mass as...
Abstract Supermassive black holes (SMBHs) are thought to provide energy that prevents catastrophic cooling in the centers of massive galaxies and galaxy clusters. However, it remains unclear how this “feedback” process operates. We use high-resolution optical data study kinematics multiphase filamentary structures by measuring velocity structure function (VSF) filaments over a wide range scales three nearby clusters: Perseus, A2597, Virgo. find motions turbulent all clusters studied. There...
Abstract In this contribution, we achieve the primary goal of active galactic nucleus (AGN) STORM campaign by recovering velocity–delay maps for prominent broad emission lines (Ly α , C iv He ii and H β ) in spectrum NGC 5548. These are most detailed ever obtained an AGN, providing unprecedented information on geometry, ionization structure, kinematics broad-line region. Virial envelopes enclosing emission-line responses show that reverberating gas is bound to black hole. A stratified...
The classical definition of the virial temperature a galaxy halo excludes fundamental contribution to energy partition halo: kinetic non-thermal gas motions. Using simulations low-redshift, $\sim L^*$ galaxies from FOGGIE project (Figuring Out Gas & Galaxies In Enzo) that are optimized resolve low-density gas, we show motions is roughly equal thermal simulated halos have 2\times$ lower bulk temperatures than expected equilibrium, owing significant formally excluded $T_\mathrm{vir}$. We...
We use the Lyα Mass Association Scheme (LyMAS) to predict cross-correlations at z = 2.5 between dark matter haloes and transmitted flux in forest, compare measured for quasars damped systems (DLAs) from Baryon Oscillation Spectroscopic Survey (BOSS) by Font-Ribera et al. calibrate LyMAS using Horizon-AGN hydrodynamical cosmological simulations of a (100 h− 1 Mpc)3 comoving volume. apply this calibration (1 Gpc)3 simulation realized with 20483 particles. In 100 Mpc box, reproduces halo-flux...
Gas-phase metallicity gradients are a crucial element in understanding the chemical evolution of galaxies. We use FOGGIE simulations to study ($\nabla Z$) six Milky Way-like galaxies throughout their evolution. generally exhibit steep negative for most history, with only few short-lived instances reaching positive slopes that appear arise mainly from interactions other concurs simulation results but disagrees robust observational finding flat and common at $z>1$. By tracking gradient rapid...
We investigate the co-evolution of angular momentum Milky Way-like galaxies, their circumgalactic gas, and dark matter halos using zoom-in simulations from Figuring Out Gas & Galaxies in Enzo (FOGGIE) suite. examine how magnitude orientation varies over time within halo between components mass. From z~2 to today, general across simulated halos, specific momenta central galaxies cool gas media (T < 10^5 K) increase together. Over that same period, hot (>10^6 change minimally. By z~1, have...
High signal-to-noise spectra toward background quasars are crucial for uncovering weak absorption in the circumgalactic medium (CGM) of intervening galaxies, such as diagnostic lines N V that provide insight to ionization process warm gas but typically have low equivalent widths. We present a new spectrum from Hubble Space Telescope with ratio $\sim20-35$ quasar SDSS J1009+0713 and analyze systems CGM two $L^\star$ galaxies close line sight. identify additional these was not reported by...
Over the next decade, astronomical community will be commissioning multiple wide-field observatories well-suited for studying stellar halos in both integrated light and resolved stars. In preparation this, we use five high-resolution cosmological simulations of Milky Way-like galaxies from Figuring Out Gas & Galaxies Enzo (FOGGIE) suite to explore properties components halos. At $z=0$, find that FOGGIE have masses, metallicity gradients, surface brightness profiles are consistent with...
Abstract Cosmological simulations are a powerful tool to study galaxy evolution as they can span substantial fraction of the cosmic time. In this research note, we use Figuring Out Gas and Galaxies Enzo simulations—cosmological hydrodynamic simulation Milky Way-like galaxies—to measure radius disk. Additionally, analyze along three different lines sight. Lastly, show that disk size increases over time regardless angle projection.