UMBC Physics Department

Permanent URI for this collection

The mission of the Department of Physics at UMBC is based on three pillars: education, research and service to society. We strive to provide outstanding educational opportunities, through instruction and research, for undergraduate physics majors seeking preparation for graduate school or entry into the workforce. We also aim to train graduate students to be leaders in their field of research. Our research goal is to grow and sustain internationally recognized research groups in atmospheric physics, astrophysics, condensed matter physics and quantum optics and information science. Through our teaching of physics to non-science and non-physics majors and through our Physics for Secondary Education Teachers program, we provide professional service to the university community and the State.


Recent Submissions

Now showing 1 - 20 of 1935
  • Item
    AGN Jets are X-ray Variable on kpc scales
    (2023-05-29) Meyer, Eileen T.; Shaik, Aamil; Tang, Y.; Reid, N.I.; Reddy, K.; Breiding, P.; Georganopoulos, M.
    Super-massive black holes residing at the centres of galaxies can launch powerful radio-emitting plasma jets which reach scales of hundreds of thousands of light-years, well beyond their host galaxies. The advent of Chandra, the only X-ray observatory capable of sub-arcsecond-scale imaging, has lead to the surprising discovery of strong X-ray emission from jets on kpc scales. The origin of this X-ray emission, which appears as a second spectral component from that of the radio emission, has been debated for over two decades. The most commonly assumed mechanism is inverse Compton upscattering of the CMB by very low energy electrons in a still highly relativistic jet (IC/CMB). Under this mechanism no variability in the X-ray emission is expected. Here we report the detection of X-ray variability in the large-scale jet population, using a novel statistical analysis of 53 jets with multiple Chandra observations.
  • Item
    Exploiting Machine Learning and Disequilibrium in Galaxy Clusters to Obtain a Mass Profile
    (AAS, 2024-01-25) Henriksen, Mark; Panda, Prajwal
    We use 3D k-means clustering to characterize galaxy substructure in the A2146 cluster of galaxies (z = 0.2343). This method objectively characterizes the cluster's substructure using projected position and velocity data for 67 galaxies within a 2.305 Mpc circular region centered on the cluster's optical center. The optimal number of substructures is found to be four. Four distinct substructures with rms velocity typical of galaxy groups or low-mass subclusters, when compared to cosmological simulations of galaxy cluster formation, suggest that A2146 is in the early stages of formation. We utilize this disequilibrium, which is so prevalent in galaxy clusters at all redshifts, to construct a radial mass distribution. Substructures are bound but not virialized. This method is in contrast to previous kinematical analyses, which have assumed virialization, and ignored the ubiquitous clumping of galaxies. The best-fitting radial mass profile is much less centrally concentrated than the well-known Navarro–Frenk–White profile, indicating that the dark-matter-dominated mass distribution is flatter pre-equilibrium, becoming more centrally peaked in equilibrium through the merging of the substructure.
  • Item
    Observations of rapid aerosol optical depth enhancements in the vicinity of polluted cumulus clouds
    (EGU, 2014-11-06) Eck, Thomas; Holben, B. N.; Reid, J. S.; Arola, A.; Berkoff, T. A.; Lolli, Simone; Wang, Y.; et al.
    During the July 2011 Deriving Information on Surface conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) field experiment in Maryland, significant enhancements in Aerosol Robotic Network (AERONET) sun–sky radiometer measured aerosol optical depth (AOD) were observed in the immediate vicinity of non-precipitating cumulus clouds on some days. Both measured Ångström exponents and aerosol size distribution retrievals made before, during and after cumulus development often suggest little change in fine mode particle size; therefore, implying possible new particle formation in addition to cloud processing and humidification of existing particles. In addition to sun–sky radiometer measurements of large enhancements of fine mode AOD, lidar measurements made from both ground-based and aircraft-based instruments during the experiment also measured large increases in aerosol signal at altitudes associated with the presence of fair weather cumulus clouds. These data show modifications of the aerosol vertical profile as a result of the aerosol enhancements at and below cloud altitudes. The airborne lidar data were utilized to estimate the spatial extent of these aerosol enhancements, finding increased AOD, backscatter and extinction out to 2.5 km distance from the cloud edge. Furthermore, in situ measurements made from aircraft vertical profiles over an AERONET site during the experiment also showed large increases in aerosol scattering and aerosol volume after cloud formation as compared to before. The 15-year AERONET database of AOD measurements at the Goddard Space Flight Center (GSFC), Maryland site, was investigated in order to obtain a climatological perspective of this phenomenon of AOD enhancement. Analysis of the diurnal cycle of AOD in summer showed significant increases in AOD from morning to late afternoon, corresponding to the diurnal cycle of cumulus development.
  • Item
    FRAMEx. V. Radio Spectral Shape at Central Subparsec Region of Active Galactic Nuclei
    (AAS, 2024-01-18) Shuvo, Onic Islam; Johnson, Megan C.; Secrest, Nathan J.; Gliozzi, Mario; Cigan, Phillip J.; Fischer, Travis C.; Van Der Horst, Alexander J.
    We present results from the Very Long Baseline Array multifrequency (1.6, 4.4, 8.6, and 22 GHz), high-sensitivity (∼25 μJy beam⁻¹), subparsec-scale (<1 pc) observations and spectral energy distributions for a sample of 12 local active galactic nuclei (AGNs), a subset from our previous volume-complete sample with hard-X-ray (14–195 keV) luminosities above 10⁴² erg s⁻¹, out to a distance of 40 Mpc. All 12 of the sources presented here were detected in the C (4.4 GHz) and X (8.6 GHz) bands, 75% in the L band (1.6 GHz), and 50% in the K band (22 GHz). Most sources showed compact, resolved/slightly resolved, central subparsec-scale radio morphology, except for a few with extended outflow-like features. A couple of sources have an additional component that may indicate the presence of a dual-core, single or double-sided jet or a more intricate feature, such as radio emission resulting from interaction with the nearby interstellar medium. The spectral slopes are mostly gigahertz-peaked or curved, with a few showing steep, flat, or inverted spectra. We found that at the subparsec scale, the gigahertz-peaked spectra belong to the low-accreting, radio-loud AGNs, with a tendency to produce strong outflows, possibly small-scale jets, and/or have a coronal origin. In contrast, flat/inverted spectra suggest compact radio emission from the central regions of highly accreting AGNs, possibly associated with radio-quiet AGNs producing winds/shocks or nuclear star formation in the vicinity of black holes.
  • Item
    Mineral dust optical properties for remote sensing and global modeling: A review
    (Elsevier, 2024-01-20) Castellanos, Patricia; Colarco, Peter; Espinosa, W. Reed; Guzewich, Scott D.; Levy, Robert C.; Miller, Ron L.; Chin, Mian; Kahn, Ralph A.; Kemppinen, Osku; Moosmüller, Hans; Nowottnick, Edward P.; Rocha-Lima, Adriana; Smith, Michael D.; Yorks, John E.; Yu, Hongbin
    Dust plays a key role in many Earth system processes and is ubiquitous in the Martian atmosphere. Various intensive field campaigns, laboratory analyses, space-based remote sensing missions, and global modeling efforts aim to characterize dust optical properties. This is a bountiful time for dust scientists, and yet the interpretation of retrievals and comparison to models remains complicated by various conflicting assumptions that are part of each algorithm. For example, the conversion of satellite radiance measurements into products like aerosol optical depth for model evaluation depends upon aerosol properties like particle size and shape that are often prescribed and not part of the retrieval. Conversely, the model calculation of aerosol optical depth often uses different assumptions. The goal of this review is to first document algorithmic assumptions by various satellite retrieval products and models, and identify where there is consistency and where there are differences. In general, the differences documented in this paper reflect uncertainties resulting from incomplete observational characterization of dust aerosols and limitations in our understanding. Second, we note what observations might reduce uncertainties in our knowledge and bring greater consistency to retrievals and models, allowing for a more rigorous and harmonious comparison. The lack of comprehensive and realistic shape models for dust is an outstanding issue, such that closure between forward modeling from particle refractive index, shape, and size and observed optical properties cannot be achieved. Limitations in the computational methods that must be applied to model scattering from complex shapes also makes accurate optical modeling for dust challenging. Field observations indicate the persistence of coarse and giant dust particles at higher altitudes and farther downwind from their source than previously expected. Remote sensing retrieval algorithms based on observations at visible wavelengths have limited sensitivity to these particles and generally do not consider them, although a recent product based on longwave radiances is encouraging. Current measurements of the refractive index of bulk dust and fundamental dust minerology components such as hematite vary widely, inhibiting attempts to represent the variability in dust optical properties and forcing, as expected from different major dust source regions on Earth that have varying mineralogical composition. Some remote sensing retrieval algorithms allow for limited refractive index variability in their inversion solutions through mixing with other fine mode aerosol models, or optimizing the single scattering albedo, but Earth system models surveyed for this paper assume a globally uniform, size-invariant refractive index. Although no Martian dust samples have yet been returned to Earth, remote sensing observations indicate that Martian dust is globally homogenous in composition, and a single spectral refractive index assumption has been widely adopted to represent Martian dust. The lack of comprehensive, statistically representative measurements of dust particle microphysical properties (size distribution, morphology, complex index of refraction spectra, internal structure heterogeneity), and the resulting optical properties, limits our ability to verify the fidelity of these assumptions. A chain of measurements is needed, ranging from characterizing individual dust mineralogy components (e.g., pure hematite and goethite) to in situ sampling of complex atmospheric aerosol mixtures. Such results could be applied to both remote sensing retrievals that characterize the optical properties of the total aerosol burden in the atmosphere from total radiance measurements, and to global models that represent the total aerosol burden in the atmosphere by building it up from the balance of individual aerosol sources and sinks.
  • Item
    Quantum information scrambling in two-dimensional Bose-Hubbard lattices
    (2024-01-16) Tripathy, Devjyoti; Touil, Akram; Gardas, Bartłomiej; Deffner, Sebastian
    It is a well-understood fact that the transport of excitations throughout a lattice is intimately governed by the underlying structures. Hence, it is only natural to recognize that also the dispersion of information has to depend on the lattice geometry. In the present work, we demonstrate that two-dimensional lattices described by the Bose-Hubbard model exhibit information scrambling for systems as little as two hexagons. However, we also find that the OTOC shows the exponential decay characteristic for quantum chaos only for a judicious choice of local observables. More generally, the OTOC is better described by Gaussian-exponential convolutions, which alludes to the close similarity of information scrambling and decoherence theory.
  • Item
    Modeling Chemical Exfoliation of Non-van der Waals Chromium Sulfides by Machine Learning Interatomic Potentials and Monte Carlo Simulations
    (ACS, 2024-1-10) Ibrahim, Akram; Wines, Daniel; Ataca, Can
    The chemical exfoliation of non-van der Waals (vdW) materials to ultrathin nanosheets remains a formidable challenge. This difficulty arises from the strong preference of these materials to engage in three-dimensional chemical bonding, resulting in uncontrolled atomic migration into the vdW gaps during cation deintercalation from the bulk structure, ultimately leading to unpredictable structural disorder. Computational models capable of comprehending the widespread nonstoichiometric local environments resulting from disordered atomic migrations during the exfoliation of non-vdW materials are crucial for understanding the underlying mechanisms. Here, we propose a generic framework using neural network potentials (NNPs) to accurately model nonstoichiometric systems over a broad range of vacancy concentrations. We apply our framework to investigate the crystal structures and phase transformations occurring during the exfoliation of non-vdW nonstoichiometric Cr₍₁₋ₓ₎S systems, a compelling material category with substantial potential for two-dimensional (2D) magnetic applications. The efficacy of the NNP outperforms conventional cluster expansion, exhibiting superior accuracy and transferability to unexplored crystal structures and compositions. By employing the NNP in simulated annealing optimizations, we predict low-energy Cr₍₁₋ₓ₎S structures anticipated to result from experimental synthesis. A notable structural transition is discerned at the Cr₀.₅S composition, with half of the Cr atoms preferentially migrating to vdW gaps. This aligns with experimental observations in the chemical exfoliation of 2D CrS₂ and emphasizes the vital role of excess Cr atoms beyond the Cr/S = 1/2 composition ratio in stabilizing vdW gaps. Additionally, we utilize the NNP in a large-scale vacancy diffusion Monte Carlo simulation to illustrate the impact of lateral compressive strains in catalyzing the formation of vdW gaps within non-vdW CrS₂ slabs through Poisson’s axial expansion. This provides a direct pathway for more facile exfoliation of ultrathin nanosheets from non-vdW materials through strain engineering. The implemented methodology, leveraging machine learning potentials, is imperative to bridge the quantum-level accuracy to large scales necessary for modeling the intricate mechanisms underlying the chemical exfoliation of non-vdW materials.
  • Item
    Information scrambling -- a quantum thermodynamic perspective
    (2024-01-10) Touil, Akram; Deffner, Sebastian
    Recent advances in quantum information science have shed light on the intricate dynamics of quantum many-body systems, for which quantum information scrambling is a perfect example. Motivated by considerations of the thermodynamics of quantum information, this perspective aims at synthesizing key findings from several pivotal studies and exploring various aspects of quantum scrambling. We consider quantifiers such as the Out-of-Time-Ordered Correlator (OTOC), the quantum Mutual Information, and the Tripartite Mutual Information (TMI), their connections to thermodynamics, and their role in understanding chaotic versus integrable quantum systems. With a focus on representative examples, we cover a range of topics, including the thermodynamics of quantum information scrambling, and the scrambling dynamics in quantum gravity models such as the Sachdev-Ye-Kitaev (SYK) model. Examining these diverse approaches enables us to highlight the multifaceted nature of quantum information scrambling and its significance in understanding the fundamental aspects of quantum many-body dynamics at the intersection of quantum mechanics and thermodynamics.
  • Item
    Using Satellite and ARM Observations to Evaluate Cold Air Outbreak Cloud Transitions in E3SM Global Storm-Resolving Simulations
    (2023-12-27) Zheng, Xue; Zhang, Yunyan; Klein, Stephen A.; Zhang, Meng; Zhang, Zhibo; Deng, Min; Terai, Christopher Ryutaro; Tian, Jingjing; Geerts, Bart; Caldwell, Peter Martin; Bogenschutz, Peter A
    This study evaluates the performance of a global storm-resolving model (GSRM), the Simple Cloud-Resolving E3SM Atmosphere Model (SCREAM). We analyze marine boundary layer clouds in a cold air outbreak over the Norwegian Sea in a 40-day simulation, and compare them to observations from satellite and a field campaign of the Atmospheric Radiation Measurement program (ARM). SCREAM qualitatively captures the cold air outbreak cloud transition in terms of the boundary layer growth, cloud mesoscale structure, and phase partitioning. SCREAM also correctly locates the greatest ice and liquid in the mesoscale updraft. However, the study finds that SCREAM might underestimate cloud supercooled liquid water in the cumulus cloud regime. This study showcases the promise of employing high-resolution and high-frequency observations under similar large-scale conditions for evaluating GSRMs. This approach can help identify model features for future process-level studies before allocating extra resources for a time-matched model intercomparison of a specific case.
  • Item
    Assessment of dust size retrievals based on AERONET: A case study of radiative closure from visible-near-infrared to thermal infrared
    (2023-12-26) Zheng, Jianyu; Zhang, Zhibo; Desouza-Machado, Sergio; Ryder, Claire L; Garnier, Anne; Biagio, Claudia Di; Yang, Ping; Welton, Ellsworth J; Yu, Hongbin; Barreto, Africa; Gonzalez, Margarita Y
    Super-coarse dust particles (diameters > 10 µm) are evidenced to be more abundant in the atmosphere than model estimates and contribute significantly to the dust climate impacts. Since super-coarse dust accounts for less dust extinction in the visible-to-near-infrared (VIS-NIR) than in the thermal infrared (TIR) spectral regime, they are suspected to be underestimated by remote sensing instruments operates only in VIS-NIR, including Aerosol Robotic Networks (AERONET), a widely used dataset for dust model validation. In this study, we perform a radiative closure assessment using the AERONET-retrieved size distribution in comparison with the collocated Atmospheric Infrared Sounder (AIRS) TIR observations with comprehensive uncertainty analysis. The consistently warm bias in the comparisons suggests a potential underestimation of supercoarse dust in the AERONET retrievals due to the limited VIS-NIR sensitivity. An extra super coarse mode included in the AERONET-retrieved size distribution helps improve the TIR closure without deteriorating the retrieval accuracy in the VIS-NIR.
  • Item
    Hot Gas Outflow Properties of the Starburst Galaxy NGC 4945
    (2023-12-13) Barrera, Natalia Porraz; Lopez, Sebastian; Lopez, Laura A.; Foord, Adi; Nguyen, Dustin D.; Thompson, Todd A.; Bolatto, Alberto D.
    We analyze 330 ks of {\it Chandra} X-ray imaging and spectra of the nearby, edge-on starburst and Seyfert Type 2 galaxy NGC~4945 to measure the hot gas properties along the galactic outflows. We extract and model spectra from 15 regions extending from −0.55 kpc to +0.85 kpc above and below the galactic disk to determine the best-fit parameters and metal abundances. We find that the hot gas temperatures and number densities peak in the central regions and decrease along the outflows. These profiles are inconsistent with a spherical, adiabatically-expanding wind model, suggesting the need to include mass loading and/or a non-spherical outflow geometry. We estimate the mass outflow rate of the hot wind to be 2.1M⊙ yr⁻¹. Emission from charge exchange is detected in the northern outflow, and we estimate it contributes 12\% to the emitted, broad-band (0.5−7~keV) X-ray flux.
  • Item
    Proper motions in the sub-kiloparsec jet of 3C 78: novel constraints on the physical nature of relativistic jets
    (Oxford University Press, 2023-12-18) Roychowdhury, Agniva; Meyer, Eileen T.; Georganopoulos, Markos; Kollmann, Kassidy
    Jets from active galactic nuclei are thought to play a role in the evolution of their host and local environments, but a detailed prescription is limited by the understanding of the jets themselves. Proper motion studies of compact bright components in radio jets can be used to produce model-independent constraints on their Lorentz factor, necessary to understand the quantity of energy deposited in the intergalactic medium. We present our initial work on the jet of radio–galaxy 3C 78, as part of Catalogue of proper motions in active galactic nuclei using Very Large Array Studies (CAgNVAS), with a goal of constraining nature of jet plasma on larger (>100 parsec) scales. In 3C 78, we find three prominent knots (A, B, and C), where knot B undergoes sub-luminal longitudinal motion (∼0.6c at ∼ 200 pc), while knot C undergoes extreme (apparent) backward motion and eventual forward motion (∼−2.6c, 0.5c, at ∼ 300 pc). Assuming knots are shocks, we infer the bulk speeds from the pattern motion of Knots B and C. We model the spectral energy distribution of the large-scale jet and observe that a physically motivated two-zone model can explain most of the observed emission. We also find that the jet profile remains approximately conical from parsec to kiloparsec scales. Using the parsec-scale speed from very long baseline interferometry studies (∼0.1c) and the derived bulk speeds, we find that the jet undergoes bulk acceleration between the parsec and the kiloparsec scales providing the first direct evidence of jet acceleration in a conical and matter-dominated jet.
  • Item
    Characteristics of dust aerosol properties using CALIOP and thermal infrared satellite observations
    (2023-01-01) Zheng, Jianyu; Zhang, Zhibo; Physics; Physics
    Mineral dust aerosol transport in the atmosphere impacts the radiation budget of Earth, cloud formations, ocean and terrestrial biogeochemical processes, visibility and human health. The satellite-retrieved spatiotemporal variation records of dust aerosol optical depth (DAOD) in the thermal infrared spectrum (TIR) and dust microphysical properties, such as coarse-mode particle size distribution (PSD), are critical yet remain insufficient for advancing the understanding of these dust impacts. The focus of my Ph.D. study is to develop novel retrieval algorithms of dust optical and microphysical properties, including DAOD and dust coarse-mode PSD, and distribute our retrieval products to a broader scientific community. We first develop a simple approach to retrieve the DAODTIR over the oceans during nighttime through synergistic use of observations from the Infrared Imaging Radiometer (IIR) and the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), both onboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) mission. The retrieval results are evaluated through climatological comparisons with two independent DAODTIR retrieval products based on the Infrared Atmospheric Sounding Interferometer (IASI) and ground-based Aerosol Robotic Networks (AERONET) over the active dust transport regions. The synergic IIR and CALIOP observation offers a unique prospect of collocated active lidar and passive IR observations for retrieving dust DAODTIR. To overcome the limitations and advance the IIR-CALIOP retrieval, we developed a novel algorithm based on the collocated Moderate Resolution Imaging Spectroradiometer (MODIS) TIR observations and dust vertical profiles from CALIOP to simultaneously retrieve dust aerosol optical depth at 10 µm (DAOD10µm) and the coarse-mode dust effective diameter (Deff) over global oceans. The accuracy of the Deff retrieval is assessed by comparing the dust lognormal volume PSD corresponding to retrieved Deff with the in situ-measured dust PSDs from three independent in-situ measurements at various locations and time through case studies. The new DAOD10µm retrievals are well-agreed with the IIR-CALIOP DAOD10.6µm retrieval (R ? 0.7) with a significant reduction in (? 50 %) retrieval uncertainties largely thanks to the better constraint on dust size. Using the new retrievals from 2013 to 2017, we performed a climatological analysis of coarse-mode dust Deff over global oceans and revealed a significant regional difference of Deff among North Atlantic, Indian Ocean and North Pacific. To the best of our knowledge, this study is the first to retrieve both DAOD and coarse-mode dust particle size over global oceans for multiple years. This retrieval dataset provides insightful information for evaluating dust longwave radiative effects and coarse-mode dust particle size in models. Lastly, in order to distribute our retrieval data in a more efficient and user-friendly way, we developed a service-oriented, flexible and efficient satellite remote sensing aggregation framework by taking MODIS products as an example. Using this framework, users only need to get aggregated MODIS L3 data based on their unique requirements, and the aggregation can run in parallel to achieve speedup. The experiments show our aggregation results are almost identical to the current MODIS L3 products, and our parallel execution with 8 computing nodes can achieve 88.63 times faster than serial code execution on a single node. The developed framework has great potential to be applied to aggregations for other satellite remote sensing products.
  • Item
    Variability and spectral properties of large-scale extragalactic X-ray jets
    (2023-01-01) Shaik, Aamil; Meyer, Eileen T; Physics; Physics
    At the center of most massive galaxies lies a supermassive black hole (10^6-10^10 solar masses). A small percentage of these accrete matter at a high rate and are consequently called active galactic nuclei (AGN). In some AGN, this accretion powers large jets of relativistic plasma which can extend up to lengths of Megaparsecs. While these kpc-scale jets were initially detected at radio frequencies where they emit brightly via synchrotron radiation, they have since been found to produce high luminosities across the electromagnetic spectrum. Of particular interest to this thesis is the Chandra X-ray Observatory's discovery of bright X-ray emission from most high-power kpc-scale jets which appears as a separate spectral component from the primary synchrotron component that extends from radio to infrared to optical. Despite two decades of research, the origin of this X-ray emission remains unknown, with competing models such as relativistic beaming of inverse-Compton upscattering of Cosmic Microwave Background (IC-CMB) photons and synchrotron radiation from a high-energy electron population predicting vastly different conditions within the jet. In this dissertation, I present two studies investigating the mechanism behind the bright X-ray emission from kpc-scale jets. The first study is a population survey of X-ray emitting jets for X-ray variability over time which is impossible to reconcile with a beamed IC-CMB model. I used a novel statistical method based on a maximum likelihood model to analyze archival Chandra data for a sample of 53 jets. Ultimately, I find significant evidence to suggest that a significant fraction of kpc-scale jets are variable X-ray emitters and thus reject IC-CMB as the dominant source of X-rays within those jets. The second project is a case study of the western hot spot of the nearby jetted AGN Pictor A using recent deep NuSTAR exposures in combination with archival Chandra data. This study represents the first study of a kpc-scale jet at hard X-ray energies (>10 keV). Using a Bayesian approach, I achieved the strongest constraints on the wide X-ray spectrum to date. I also applied our variability analysis from the previous study using both our NuSTAR and Chandra data, and found the most significant detection of variability in a kpc-scale X-ray jet yet. Collectively, these results suggest a synchrotron origin for the kpc-scale X-ray emission from extremely compact and highly magnetized unresolved emitting regions within the jet. This represents a fundamental change in how we view jet structure and particle acceleration.
  • Item
    Investigating the Dynamics of Extragalactic Jets from Parsec to Kiloparsec Scales: Novel Constraints on Jet Acceleration and Emission
    (2023-01-01) Roy Chowdhury, Agniva; Meyer, Eileen; Physics; Physics
    Actively accreting super-massive black holes, known as active galactic nuclei or AGN, are known to produce bipolar jets of relativistic plasma which carry matter and energy out of the central nucleus of a galaxy to scales far beyond the host to distances of a megaparsec or more, close to 10 orders of magnitude in gravitational radius. However, in spite of tremendous progress over the last several decades in astronomical observations of jets, it is relatively unknown how these jets form, accelerate and maintain strong collimation through the kiloparsec scale. Studies of motions of bright compact inhomogeneities at different positions in these jets (``proper motions") can, in principle, be used to produce model-independent constraints on the Lorentz factor ($\Gamma$) of the bulk motion at different spatial scales in the jet. This inferred velocity profile of the jet, in addition to constraining theories of jet acceleration-deceleration, is vital in understanding the origin of high-energy emission (X-rays and beyond) from extragalactic jets. With a view to leveraging the rich decades-spanning archive of the Very Large Array (VLA) telescope in particular, this thesis develops new radio interferometric techniques to measure jet velocities accurately beyond the few hundred parsec scale. I have initiated a catalogue of such measurements known as CAgNVAS: Catalogue of proper motions in AGN jets with Very large Array Studies. In this thesis I present in detail the velocity profiles of two extragalactic jets along with theoretical models of the observations. In both the jets, I find evidence of acceleration in a kpc-scale matter-dominated jet for the first time, with insights into the nature of the multi-wavelength spectrum of kpc-scale jets. The techniques developed and the science produced from this thesis will enable a much richer study of large-scale jets as seen by moderate-baseline interferometers like the Very Large Array.
  • Item
    (2023-01-01) Kaluappuwa Hannadige, Neranga Prasadi; Zhai, Pengwang; Physics; Physics, Atmospheric
    The atmospheric correction (AC) is an essential step in ocean color remote sensing. The heritage AC processes applied to MODIS-like spectrometers degrade over optically complex scenes involving absorbing aerosols and/or coastal waters. The rich information content of MAPs has made MAPs a powerful instrument to characterize aerosols and perform AC over optically complex scenes. The MAPs in synergy with the spectrometers such as in NASAÕs PACE and ESAÕs MetOp-SG future satellite missions are examples of the synergistic use of MAPs to improve the AC of the multi- or hyper-spectral radiometers. The first part of this dissertation presents an AC scheme, Polynomial-based Atmospheric Correction (POLYAC), for hyperspectral radiometers based on aerosol and surface information retrieved from collocated MAPs. POLYAC is expected to provide a robust and computationally efficient AC scheme for future satellite missions. One-step AC algorithms are implemented for MAP measurements. These al- gorithms include a forward RT model, with sub-models to represent the optics of the atmosphere, water surface, and water body. The retrieval performances of joint retrieval algorithms partially depend on the balance between model fidelity and the number of forward model parameters. More intricate models can closely resem- ble an observed scene while it becomes computationally demanding and unstable for retrieval algorithms. The ocean color bio-optical models that characterize the water-leaving signal are important. Bio-optical models with more than a single pa- rameter are required to represent the optical properties of coastal waters. Up to date, the number of parameters that are used in these bio-optical models is arbi- trary. The second part of this dissertation evaluates the information content of the water-leaving signal and the water bio-optical models. This work is expected to provide constraints on ocean bio-optical models. The third part of this disserta- tion evaluates the impact of the bio-optical models on MAP retrievals based on the MAPOL algorithm with airborne MAP measurements. The study evaluates three bio-optical models representing open and coastal waters. This work is expected to contribute to the development of MAP retrieval algorithms for aerosols and ocean color retrievals. The bio-optical models can also be easily applied to other retrieval algorithms as well.
  • Item
    Environmental Controls on Isolated Convection during the Amazonian Wet Season
    (EGU, 2023-12-12) Viscardi, Leandro Alex Moreira; Torri, Giuseppe; Adams, David K.; Barbosa, H. M. J.
    The Amazon rainforest is a vital component of the global climate system, influencing the hydrological cycle and tropical circulation. However, understanding and modeling the evolution of convection in this region remains a scientific challenge. Here, we assess the environmental conditions associated with shallow, congestus, and isolated deep convection days during the wet season (December to April) employing measurements from the GoAmazon (2014–2015) experiment and large-scale wind field from the constrained variational analysis. Composites of deep days show moister than average conditions below 3 km early in the morning. Analyzing the water budget at the surface through only observations, we estimated the water vapor convergence term as a residual of the water balance closure. Convergence remains nearly zero during the deep days until early afternoon (13 LST), when it becomes a dominant factor in their water budget. At 14 LST, the deep days experience a robust upward large-scale vertical velocity, especially above 4 km, which supports the shallow-to-deep convective transition occurring around 16–17 LST. In contrast, shallow and congestus days exhibit preconvective drier conditions, along with diurnal water vapor divergence and large-scale subsidence that extend from the surface to the lower free troposphere. Moreover, afternoon precipitation exhibits the strongest linear correlation (0.6) with large-scale vertical velocity, nearly double the magnitude observed for other environmental factors, even moisture at different levels and periods of the day. Precipitation also exhibits a moderate increase with low-level wind shear, while upper-level shear has a relatively minor negative impact on convection.
  • Item
    Advanced X-ray Imaging Satellite science team hits major milestone
    (UMBC News, 2023-12-05) Hansen, Sarah
  • Item
    FRAMEx. V. Radio Spectral Shape at Central Sub-parsec Region of AGNs
    (2023-12-07) Shuvo, Onic Islam; Johnson, Megan C.; Secrest, Nathan J.; Gliozzi, Mario; Cigan, Phillip J.; Fischer, Travis C.; Horst, Alexander J. Van Der
    We present results from the Very Long Baseline Array (VLBA) multi-frequency (1.6, 4.4, 8.6, 22 GHz), high-sensitivity (∼25 µJy beam⁻¹ ), sub-parsec scale (<1 pc) observations and Spectral Energy Distributions (SEDs) for a sample of 12 local active galactic nuclei (AGNs), a subset from our previous volume-complete sample with hard X-ray (14–195 keV) luminosities above 10⁴² erg s⁻¹ , out to a distance of 40 Mpc. All 12 of the sources presented here were detected in the C (4.4 GHz) and X (8.6 GHz) bands, 75% in the L band(1.6 GHz), and 50% in the K band (22 GHz). Most sources showed compact, resolved/slightly resolved, central sub-parsec scale radio morphology, except a few with extended outflow-like features. A couple of sources have an additional component that may indicate the presence of a dual-core, single or double-sided jet or a more intricate feature, such as radio emission resulting from interaction with nearby ISM. The spectral slopes are mostly GHz-peaked or curved, with a few showing steep, flat, or inverted spectra. We found that in the sub-parsec scale, the GHz-peaked spectra belong to the low-accreting, radio-loud AGNs with a tendency to produce strong outflows, possibly small-scale jet, and/or have a coronal origin. In contrast, flat/inverted spectra suggest compact radio emission from highly-accreting AGNs’ central region, possibly associated with radio-quiet AGNs producing winds/shocks or nuclear star formation in the vicinity of black holes.
  • Item
    Searching for the Highest-z Dual AGN in the Deepest Chandra Surveys
    (2023-12-04) Sandoval, Brandon; Foord, Adi; Allen, Steven W.; Volonteri, Marta; Stemo, Aaron; Chen, Nianyi; Matteo, Tiziana Di; Gultekin, Kayhan; Habouzit, Melanie; Puerto-Sanchez, Clara; Hodges-Kluck, Edmund; Dubois, Yohan
    We present an analysis searching for dual AGN among 62 high-redshift (2.5