Physics Commons^™

Machine Learning Based Predictions Of Dissolved Oxygen In A Small Coastal Embayment, Manuel Valera, Ryan K. Walter, Barbara A. Bailey, Jose E. Castillo

Physics

Coastal dissolved oxygen (DO) concentrations have a profound impact on nearshore ecosystems and, in recent years, there has been an increased prevalance of low DO hypoxic events that negatively impact nearshore organisms. Even with advanced numerical models, accurate prediction of coastal DO variability is challenging and computationally expensive. Here, we apply machine learning techniques in order to reconstruct and predict nearshore DO concentrations in a small coastal embayment while using a comprehensive set of nearshore and offshore measurements and easily measured input (training) parameters. We show that both random forest regression (RFR) and support vector regression (SVR) models accurately reproduce …

A Significant Excess In Major Merger Rate For Agns With The Highest Eddington Ratios At Z < 0.2, Victor Marian, Knud Jahnke, Irham Andika, Eduardo Bañados, Vardha N. Bennert, Seth Cohen, Bernd Husemann, Melanie Kaasinen, Anton M. Koekemoer, Mira Mechtley, Masafusa Onoue, Jan-Torge Schindler, Malte Schramm, Andreas Schulze, John D. Silverman, Irina Smirnova-Pinchukova, Arjen Van Der Wel, Carolin Villforth, Rogier A. Windhorst

Physics

Observational studies are increasingly finding evidence against major mergers being the dominant mechanism responsible for triggering an active galactic nucleus (AGN). After studying the connection between major mergers and AGNs with the highest Eddington ratios at z = 2, we here expand our analysis to z < 0.2, exploring the same AGN parameter space. Using ESO VLT/FORS2 B-, V-, and color images, we examine the morphologies of 17 galaxies hosting AGNs with Eddington ratios , and 25 mass- and redshift-matched control galaxies. To match the appearance of the two samples, we add synthetic point sources to the inactive comparison galaxies. The combined sample of AGN and inactive galaxies was …

Space Telescope And Optical Reverberation Mapping Project. Xii. Broad-Line Region Modeling Of Ngc 5548, P. R. Williams, A. Pancoast, T. Treu, B.J. Brewer, Vardha N. Bennert, Y. Zu

Physics

We present geometric and dynamical modeling of the broad line region (BLR) for the multi-wavelength reverberation mapping campaign focused on NGC 5548 in 2014. The data set includes photometric and spectroscopic monitoring in the optical and ultraviolet, covering the Hβ, C iv, and Lyα broad emission lines. We find an extended disk-like Hβ BLR with a mixture of near-circular and outflowing gas trajectories, while the C iv and Lyα BLRs are much less extended and resemble shell-like structures. There is clear radial structure in the BLR, with C iv and Lyα emission arising at …

Large-Scale Erosion Driven By Intertidal Eelgrass Loss In An Estuarine Environment, Ryan K. Walter, Jennifer K. O'Leary, Sean Vitousek, Mohsen Taherkhani, Carolyn Geraghty, Ann Kitajima

Physics

Seagrasses influence local hydrodynamics by inducing drag on the flow and dampening near-bed velocities and wave energy. When seagrasses are lost, near-bed currents and wave energy can increase, which enhances bottom shear stresses, destabilizes sediment, and promotes suspension and erosion. Though seagrasses are being lost rapidly globally, the magnitude of change in sediment stabilization following ecosystem-wide eelgrass loss has rarely been measured. In this study, we explored the geomorphological changes associated with an unprecedented estuary-wide collapse of a seagrass (eelgrass, Zostera marina) in Morro Bay, CA, USA. Morro Bay has historically suffered from accelerated sedimentation and accretion. However, following …

Abalone Recruitment In Abalone Recruitment In Low-Density And Aggregated Populations Facing Climatic Stress, Ryan K. Walter

Physics

Understanding spatial and temporal patterns in the recruitment of marine invertebrates with complex life histories remains a critical knowledge gap in marine ecology and fisheries. As marine invertebrates are facing multiple stressors from overfishing and climatic stress, it is important to evaluate the conditions that facilitate recruitment in low-density populations. The red abalone Haliolis rufescens historically supported an economically important fishery in California, but the fishery was sequentially closed as stocks declined, and the last fished area was closed in 2018 following the collapse of the kelp forests in Northern California. Here, red abalone recruitment was evaluated annually from 2012 …

An [O Iii] Search For Extended Emission Around Agn With Hi Mapping: A Distant Cloud Ionized By Mkn 1, Erin Darnell Knese, William C. Keel, Greg Knese, Vardha N. Bennert, Alexei Moiseev, Aleksandra Grokhovskaya, Sergei N. Dodonov

Physics

Motivated by the discovery of large ionized clouds around AGN, and particularly the large fraction of those that are consistent with photoionized gaseous tidal debris, we searched for [O III] emission around Seyfert galaxies previously mapped in H I, many with extended gas features. Of 26 Seyfert galaxies, we find one spatially extended emission feature, a discrete cloud projected ≈12 kpc SW from the centre of Mkn 1 and spanning a transverse extent of 8 kpc. Optical spectroscopy (Kast/Lick and SCORPIO/BTA) of this cloud confirms its association with the Mkn 1–NGC 451 galaxy pair, closely matching the kinematics of nearby …

Seasonal And Interannual Variability Of Phytoplankton Abundance And Community Composition On The Central Coast Of California, Alex Barth, Ryan K. Walter, Ian C. Robbins, Alexis Pasulka

Physics

Variations in the abundance and composition of phytoplankton greatly impact ecosystem structure and function. Within the California Current System (CCS), phytoplankton community structure is tightly coupled to seasonal variability in wind-driven coastal upwelling, a process that drives changes in coastal water temperatures and nutrient concentrations. Based on approximately a decade (2008-2018) of weekly phytoplankton measurements, this study provides the first characterization of the seasonal and interannual variability of phytoplankton abundance and composition in San Luis Obispo (SLO) Bay, an understudied region within the CCS. Overall, the seasonality of phytoplankton in SLO Bay mirrored that of the larger CCS; diatoms dominated …

Llama: The MBh–Σ⋆ Relation Of The Most Luminous Local Agns, Turgay Caglar, Leonard Burtscher, Bernhard Brandl, Jarle Brinchmann, Richard I. Davies, Erin K. S. Hicks, Michael Koss, Ming-Yi Lin, Witold Maciejewski, Francisco MüLler-Sánchez, Rogemar A. Riffel, Rogério Riffel, David J. Rosario, Marc Schartmann, Allan Schnorr-MüLler, T. Taro Shimizu, Thaisa Storchi-Bergmann, Sylvain Veilleux, Gilles Orban De Xivry, Vardha N. Bennert

Physics

Context. The MBH–σ_⋆ relation is considered a result of coevolution between the host galaxies and their supermassive black holes. For elliptical bulge hosting inactive galaxies, this relation is well established, but there is still discussion concerning whether active galaxies follow the same relation.

Aims. In this paper, we estimate black hole masses for a sample of 19 local luminous active galactic nuclei (AGNs; LLAMA) to test their location on the MBH–σ_⋆ relation. In addition, we test how robustly we can determine the stellar velocity dispersion in the presence of an AGN continuum and AGN emission lines, …

Hydrologic Response Of A Montane Meadow From Conifer Removal And Upslope Forest Thinning, Christopher Surfleet, Noel Fie, John Jasbinsek

Physics

This study evaluates the hydrologic response of restoration of a montane meadow by removal of encroached Pinus contorta and thinning of the adjacent forest. It is now a follow-up with four years of post-restoration data, on a previous analysis of a hydrologic response of the same meadow one year following restoration. A hydrologic change was evaluated through a statistical comparison of soil moisture and depth to groundwater between the restored Marian Meadow and a Control Meadow. Meadow water budgets and durations of water table depths during the growing season were evaluated. The four years following restoration of Marian Meadow had …

The Mass Relations Between Supermassive Black Holes And Their Host Galaxies At 1 < Z < 2 With Hst-Wfc3, Xuheng Ding, John Silverman, Tommaso Treu, Andreas Schulze, Malte Schramm, Simon Birrer, Daeseong Park, Knud Jahnke, Vardha N. Bennert, Jeyhan S. Kartaltepe, Anton M. Koekemoer, Matthew A. Malkan, David Sanders

Physics

Correlations between the mass of a supermassive black hole (SMBH) and the properties of its host galaxy (e.g., total stellar mass M*, luminosity Lhost) suggest an evolutionary connection. A powerful test of a coevolution scenario is to measure the relations –Lhost and –M* at high redshift and compare with local estimates. For this purpose, we acquired Hubble Space Telescope (HST) imaging with WFC3 of 32 X-ray-selected broad-line (type 1) active galactic nuclei at 1.2 < z < 1.7 in deep survey fields. By applying state-of-the-art tools to decompose the HST images including available ACS data, we measured the host galaxy luminosity and stellar mass along with …