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Faculty Scholarship

2020

Articles 1 - 18 of 18

Full-Text Articles in Physical Sciences and Mathematics

Higher Order Interactions In Complex Networks Of Phase Oscillators Promote Abrupt Synchronization Switching, Per Sebastian Skardal, Alex Arenas Dec 2020

Higher Order Interactions In Complex Networks Of Phase Oscillators Promote Abrupt Synchronization Switching, Per Sebastian Skardal, Alex Arenas

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© 2020, The Author(s). Synchronization processes play critical roles in the functionality of a wide range of both natural and man-made systems. Recent work in physics and neuroscience highlights the importance of higher-order interactions between dynamical units, i.e., three- and four-way interactions in addition to pairwise interactions, and their role in shaping collective behavior. Here we show that higher-order interactions between coupled phase oscillators, encoded microscopically in a simplicial complex, give rise to added nonlinearity in the macroscopic system dynamics that induces abrupt synchronization transitions via hysteresis and bistability of synchronized and incoherent states. Moreover, these higher-order interactions can stabilize …

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Galaxy And Mass Assembly (Gama): A Wise Study Of The Activity Of Emission-Line Systems In G23, H. F.M. Yao, T. H. Jarrett, M. E. Cluver, L. Marchetti, Edward N. Taylor, M. G. Santos, Matt S. Owers, Angel R. Lopez-Sanchez, Y. A. Gordon, M. J.I. Brown, S. Brough, S. Phillipps, Benne Holwerda, A. M. Hopkins, L. Wang Nov 2020

Galaxy And Mass Assembly (Gama): A Wise Study Of The Activity Of Emission-Line Systems In G23, H. F.M. Yao, T. H. Jarrett, M. E. Cluver, L. Marchetti, Edward N. Taylor, M. G. Santos, Matt S. Owers, Angel R. Lopez-Sanchez, Y. A. Gordon, M. J.I. Brown, S. Brough, S. Phillipps, Benne Holwerda, A. M. Hopkins, L. Wang

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We present a detailed study of emission-line systems in the Galaxy And Mass Assembly (GAMA) G23 region, making use of Wide-field Infrared Survey Explorer (WISE) photometry that includes carefully measured resolved sources. After applying several cuts to the initial catalog of. 41,000 galaxies, we extract a sample of 9809 galaxies. We then compare the spectral diagnostic Baldwin, Philips & Terlevich (BPT) classification of 1154 emission-line galaxies (38% resolved in W1) to their location in the WISE color-color diagram, leading to the creation of a new zone for mid-infrared "warm"galaxies located 2μm above the star-forming sequence, below the standard WISE active …

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Diversity Patterns Associated With Varying Dispersal Capabilities As A Function Of Spatial And Local Environmental Variables In Small Wetlands In Forested Ecosystems, Brett M. Tornwall, Amber L. Pitt, Bryan L. Brown, Joanna Hawley-Howard, Robert F. Baldwin Nov 2020

Diversity Patterns Associated With Varying Dispersal Capabilities As A Function Of Spatial And Local Environmental Variables In Small Wetlands In Forested Ecosystems, Brett M. Tornwall, Amber L. Pitt, Bryan L. Brown, Joanna Hawley-Howard, Robert F. Baldwin

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© 2020 by the authors. Licensee MDPI, Basel, Switzerland. The diversity of species on a landscape is a function of the relative contribution of diversity at local sites and species turnover between sites. Diversity partitioning refers to the relative contributions of alpha (local) and beta (species turnover) diversity to gamma (regional/landscape) diversity and can be influenced by the relationship between dispersal capability as well as spatial and local environmental variables. Ecological theory predicts that variation in the distribution of organisms that are strong dispersers will be less influenced by spatial properties such as topography and connectivity of a region and …

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Galaxy And Mass Assembly: Luminosity And Stellar Mass Functions In Gama Groups, J. A. Vazquez-Mata, J. Loveday, S. D. Riggs, I. K. Baldry, L. J.M. Davies, A. S.G. Robotham, Benne W. Holwerda, M. J.I. Brown, M. E. Cluver, L. Wang, M. Alpaslan, J. Bland-Hawthorn, S. Brough, S. P. Driver, A. M. Hopkins, E. N. Taylor, A. H. Wright Nov 2020

Galaxy And Mass Assembly: Luminosity And Stellar Mass Functions In Gama Groups, J. A. Vazquez-Mata, J. Loveday, S. D. Riggs, I. K. Baldry, L. J.M. Davies, A. S.G. Robotham, Benne W. Holwerda, M. J.I. Brown, M. E. Cluver, L. Wang, M. Alpaslan, J. Bland-Hawthorn, S. Brough, S. P. Driver, A. M. Hopkins, E. N. Taylor, A. H. Wright

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How do galaxy properties (such as stellar mass, luminosity, star formation rate, and morphology) and their evolution depend on the mass of their host dark matter halo? Using the Galaxy and Mass Assembly group catalogue, we address this question by exploring the dependence on host halo mass of the luminosity function (LF) and stellar mass function (SMF) for grouped galaxies subdivided by colour, morphology, and central/satellite. We find that spheroidal galaxies in particular dominate the bright and massive ends of the LF and SMF, respectively. More massive haloes host more massive and more luminous central galaxies. The satellites LF and …

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Galaxy And Mass Assembly: A Comparison Between Galaxy⇓Galaxy Lens Searches In Kids/Gama, Shawn Knabel, Rebecca L. Steele, Benne W. Holwerda, Joanna S. Bridge, Alice Jacques, Andrew M. Hopkins, Stephen P. Bamford, Michael J.I. Brown, Sarah Brough, Lee Kelvin, Maciej Bilicki, John Kielkopf Nov 2020

Galaxy And Mass Assembly: A Comparison Between Galaxy⇓Galaxy Lens Searches In Kids/Gama, Shawn Knabel, Rebecca L. Steele, Benne W. Holwerda, Joanna S. Bridge, Alice Jacques, Andrew M. Hopkins, Stephen P. Bamford, Michael J.I. Brown, Sarah Brough, Lee Kelvin, Maciej Bilicki, John Kielkopf

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Strong gravitational lenses are a rare and instructive type of astronomical object. Identification has long relied on serendipity, but different strategies—such as mixed spectroscopy of multiple galaxies along the line of sight, machine-learning algorithms, and citizen science—have been employed to identify these objects as new imaging surveys become available. We report on the comparison between spectroscopic, machine-learning, and citizen-science identification of galaxy–galaxy lens candidates from independently constructed lens catalogs in the common survey area of the equatorial fields of the Galaxy and Mass Assembly survey. In these, we have the opportunity to compare high completeness spectroscopic identifications against high-fidelity imaging …

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The Sizes Of Z ∼ 9-10 Galaxies Identified In The Brightest Of Reionizing Galaxies (Borg) Survey, Benne W. Holwerda, Joanna S. Bridge, Rebecca L. Steele, Samir Kusmic, Larry Bradley, Rachael Livermore, Stephanie Bernard, Alice Jacques Oct 2020

The Sizes Of Z ∼ 9-10 Galaxies Identified In The Brightest Of Reionizing Galaxies (Borg) Survey, Benne W. Holwerda, Joanna S. Bridge, Rebecca L. Steele, Samir Kusmic, Larry Bradley, Rachael Livermore, Stephanie Bernard, Alice Jacques

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Redshift z = 9-10 object selection is the effective limit of Hubble Space Telescope (HST) imaging capability, even when confirmed with Spitzer. If only a few photometry data points are available, it becomes attractive to add criteria based on their morphology in these J- and H-band images. One could do so through visual inspection, a size criterion, or alternate morphometrics. We explore a vetted sample of Brightest of Reionizing Galaxies (BoRG) z ∼ 9 and z ∼ 10 candidate galaxies and the object rejected by Morishita+ to explore the utility of a size criterion in z = 9-10 candidate selection. …

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Chess As A Testing Grounds For The Oracle Approach To Ai Safety, James D. Miller, Roman Yampolskiy, Olle Häggström, Stuart Armstrong Sep 2020

Chess As A Testing Grounds For The Oracle Approach To Ai Safety, James D. Miller, Roman Yampolskiy, Olle Häggström, Stuart Armstrong

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To reduce the danger of powerful super-intelligent AIs, we might make the first such AIs oracles that can only send and receive messages. This paper proposes a possibly practical means of using machine learning to create two classes of narrow AI oracles that would provide chess advice: those aligned with the player's interest, and those that want the player to lose and give deceptively bad advice. The player would be uncertain which type of oracle it was interacting with. As the oracles would be vastly more intelligent than the player in the domain of chess, experience with these oracles might …

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Review Of Student-Built Spectroscopy Instrumentation Projects, Michelle L. Kovarik, Julia R. Clapis, K. Ana Romano-Pringle Aug 2020

Review Of Student-Built Spectroscopy Instrumentation Projects, Michelle L. Kovarik, Julia R. Clapis, K. Ana Romano-Pringle

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Copyright © 2020 American Chemical Society and Division of Chemical Education, Inc. One challenge of teaching chemical analysis is the proliferation of sophisticated, but often impenetrable, instrumentation in the modern laboratory. Complex instruments, and the software that runs them, distance students from the physical and chemical processes that generate the analytical signal. A solution to this challenge is the introduction of a student-driven instrument-building project. Visible absorbance spectroscopy is well-suited to such a project due to its relative simplicity and the ubiquity of absorbance measurements. This Article reviews simple instructor- A nd student-built instruments for spectroscopy, providing an overview of …

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Is Ngc 300 A Pure Exponential Disk Galaxy?, In Sung Jang, Roelof S. De Jong, Ivan Minchev, Eric F. Bell, Antonela Monachesi, Benne W. Holwerda, Jeremy Bailin, Adam Smercina, Richard D'Souza Aug 2020

Is Ngc 300 A Pure Exponential Disk Galaxy?, In Sung Jang, Roelof S. De Jong, Ivan Minchev, Eric F. Bell, Antonela Monachesi, Benne W. Holwerda, Jeremy Bailin, Adam Smercina, Richard D'Souza

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NGC 300 is a low-mass disk galaxy in the Sculptor group. In the literature, it has been identified as a pure exponential disk galaxy, as its luminosity profile can be well fit with a single exponential law over many disk scale lengths (Type I). We investigate the stellar luminosity distribution of NGC 300 using Hubble Space Telescope archive data, reaching farther and deeper than any other previous studies. Color-magnitude diagrams show a significant population of old red giant branch (RGB) stars in all fields out to R ∼ 19 kpc (32′), as well as younger populations in the inner regions. …

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Galaxy And Mass Assembly (Gama): Demonstrating The Power Of Wise In The Study Of Galaxy Groups To Z < 0.1, M. E. Cluver, T. H. Jarrett, E. N. Taylor, A. M. Hopkins, S. Brough, S. Casura, B. W. Holwerda, J. Liske, K. A. Pimbblet, A. H. Wright Jul 2020

Galaxy And Mass Assembly (Gama): Demonstrating The Power Of Wise In The Study Of Galaxy Groups To Z < 0.1, M. E. Cluver, T. H. Jarrett, E. N. Taylor, A. M. Hopkins, S. Brough, S. Casura, B. W. Holwerda, J. Liske, K. A. Pimbblet, A. H. Wright

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Combining high-fidelity group characterization from the Galaxy and Mass Assembly survey and source-tailored z < 0.1 photometry from the Wide-Field Infrared Survey Explorer (WISE) survey, we present a comprehensive study of the properties of ungrouped galaxies, compared to 497 galaxy groups (4 ≤ N FoF ≤ 20) as a function of stellar and halo mass. Ungrouped galaxies are largely unimodal in WISE color, the result of being dominated by star-forming, late-type galaxies. Grouped galaxies, however, show a clear bimodality in WISE color, which correlates strongly with stellar mass and morphology. We find evidence for an increasing early-type fraction, in stellar mass bins between 1010 M o˙ ≲ M stellar ≲ 1011 M o˙, with increasing halo mass. Using ungrouped, late-type galaxies with star-forming colors (W2-W3 > 3), we define a star-forming main sequence (SFMS), which we use to delineate systems that have moved below the sequence ("quenched"for the purposes of this work). We find that with increasing halo mass, the relative number of late-type systems on the SFMS decreases, with a corresponding increase in early-type, quenched systems at high stellar mass (M stellar > 1010.5 M o˙), consistent with mass quenching. Group galaxies with masses M stellar < 1010.5 M o˙ show evidence of quenching consistent with environmentally driven processes. The stellar mass distribution of late-type, quenched galaxies suggests that it may be an intermediate population as systems transition from being star-forming and late-type to the "red sequence."Finally, we use the projected area of groups on the sky to extract groups that are (relatively) compact for their halo mass. Although these show a marginal increase in their proportion of high-mass and early-type galaxies compared to nominal groups, a clear increase in quenched fraction is not evident.

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Wallaby – An Ska Pathfinder H I Survey, Bärbel S. Koribalski, L. Staveley-Smith, T. Westmeier, P. Serra, K. Spekkens, O. I. Wong, K. Lee-Waddell, C. D.P. Lagos, D. Obreschkow, E. V. Ryan-Weber, M. Zwaan, V. Kilborn, G. Bekiaris, K. Bekki, F. Bigiel, A. Boselli, A. Bosma, B. Catinella, G. Chauhan, M. E. Cluver, M. Colless, H. M. Courtois, R. A. Crain, W. J.G. De Blok, H. Dénes, A. R. Duffy, A. Elagali, C. J. Fluke, B. Q. For, G. Heald, P. A. Henning, K. M. Hess, Benne W. Holwerda Jul 2020

Wallaby – An Ska Pathfinder H I Survey, Bärbel S. Koribalski, L. Staveley-Smith, T. Westmeier, P. Serra, K. Spekkens, O. I. Wong, K. Lee-Waddell, C. D.P. Lagos, D. Obreschkow, E. V. Ryan-Weber, M. Zwaan, V. Kilborn, G. Bekiaris, K. Bekki, F. Bigiel, A. Boselli, A. Bosma, B. Catinella, G. Chauhan, M. E. Cluver, M. Colless, H. M. Courtois, R. A. Crain, W. J.G. De Blok, H. Dénes, A. R. Duffy, A. Elagali, C. J. Fluke, B. Q. For, G. Heald, P. A. Henning, K. M. Hess, Benne W. Holwerda

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The Widefield ASKAP L-band Legacy All-sky Blind surveY (wallaby) is a next-generation survey of neutral hydrogen (H i) in the Local Universe. It uses the widefield, high-resolution capability of the Australian Square Kilometer Array Pathfinder (ASKAP), a radio interferometer consisting of 36 × 12 -m dishes equipped with Phased-Array Feeds (PAFs), located in an extremely radio-quiet zone in Western Australia. wallaby aims to survey three-quarters of the sky (− 90 ∘< δ< + 30 ∘) to a redshift of z≲ 0.26 , and generate spectral line image cubes at ∼30 arcsec resolution and ∼1.6 mJy beam−1 per 4 km s−1 channel sensitivity. ASKAP’s instantaneous field of view at 1.4 GHz, delivered by the PAF’s 36 beams, is about 30 sq deg. At an integrated signal-to-noise ratio of five, wallaby is expected to detect around half a million galaxies with a mean redshift of z∼ 0.05 (∼200 Mpc). The scientific goals of wallaby include: (a) a census of gas-rich galaxies in the vicinity of the Local Group; (b) a study of the H i properties of galaxies, groups and clusters, in particular the influence of the environment on galaxy evolution; and (c) the refinement of cosmological parameters using the spatial and redshift distribution of low-bias gas-rich galaxies. For context we provide an overview of recent and planned large-scale H i surveys. Combined with existing and new multi-wavelength sky surveys, wallaby will enable an exciting new generation of panchromatic studies of the Local Universe. — First results from the wallaby pilot survey are revealed, with initial data products publicly available in the CSIRO ASKAP Science Data Archive (CASDA).

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Mergers Trigger Active Galactic Nuclei Out To Z ∼0.6, F. Gao, L. Wang, W. J. Pearson, Y. A. Gordon, Benne W. Holwerda, A. M. Hopkins, M. J.I. Brown, J. Bland-Hawthorn, M. S. Owers May 2020

Mergers Trigger Active Galactic Nuclei Out To Z ∼0.6, F. Gao, L. Wang, W. J. Pearson, Y. A. Gordon, Benne W. Holwerda, A. M. Hopkins, M. J.I. Brown, J. Bland-Hawthorn, M. S. Owers

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Aims. The fueling and feedback of active galactic nuclei (AGNs) are important for understanding the co-evolution between black holes and host galaxies. Mergers are thought to have the capability to bring gas inward and ignite nuclear activity, especially for more powerful AGNs. However, there is still significant ongoing debate on whether mergers can trigger AGNs and, if they do, whether mergers are a significant triggering mechanism. Methods. We selected a low-redshift (0.005  <   z  <   0.1) sample from the Sloan Digital Sky Survey and a high-redshift (0  <   z  <   0.6) sample from the Galaxy And Mass Assembly survey. We took advantage of the convolutional neural network technique to identify mergers. We used mid-infrared (MIR) color cut and optical emission line diagnostics to classify AGNs. We also included low excitation radio galaxies (LERGs) to investigate the connection between mergers and low accretion rate AGNs. Results. We find that AGNs are more likely to be found in mergers than non-mergers, with an AGN excess up to 1.81 ± 0.16, suggesting that mergers can trigger AGNs. We also find that the fraction of mergers in AGNs is higher than that in non-AGN controls, for both MIR and optically selected AGNs, as well as LERGs, with values between 16.40 ± 0.5% and 39.23 ± 2.10%, implying a non-negligible to potentially significant role of mergers in triggering AGNs. This merger fraction in AGNs increases as stellar mass increases, which supports the idea that mergers are more important for triggering AGNs in more massive galaxies. In terms of merger fraction as a function of AGN power we find a positive trend for MIR selected AGNs and a complex trend for optically selected AGNs, which we interpret under an evolutionary scenario proposed by previous studies. In addition, obscured MIR selected AGNs are more likely to be hosted in mergers than unobscured MIR selected AGNs.

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Tracing The Anemic Stellar Halo Of M 101, In Sung Jang, Roelof S. De Jong, Benne W. Holwerda, Antonela Monachesi, Eric F. Bell, Jeremy Bailin May 2020

Tracing The Anemic Stellar Halo Of M 101, In Sung Jang, Roelof S. De Jong, Benne W. Holwerda, Antonela Monachesi, Eric F. Bell, Jeremy Bailin

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Models of galaxy formation in a cosmological context predict that massive disk galaxies should have structured extended stellar halos. Recent studies in integrated light, however, report that a few galaxies, including the nearby disk galaxy M 101, have no measurable stellar halos to the detection limit. We aim to quantify the stellar content and structure of M 101's outskirts by resolving its stars. We present the photometry of its stars based on deep F606W and F814W images taken with Hubble Space Telescope (HST) as part of the GHOSTS survey. The HST fields are placed along the east and west sides …

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Galaxy And Mass Assembly (Gama): Defining Passive Galaxy Samples And Searching For The Uv Upturn, S. Phillipps, S. S. Ali, M. N. Bremer, R. De Propris, A. E. Sansom, M. E. Cluver, M. Alpaslan, S. Brough, M. J.I. Brown, L. J.M. Davies, S. P. Driver, M. W. Grootes, Benne W. Holwerda, A. M. Hopkins, P. A. James, K. Pimbblet, A. S.G. Robotham, E. N. Taylor, L. Wang Feb 2020

Galaxy And Mass Assembly (Gama): Defining Passive Galaxy Samples And Searching For The Uv Upturn, S. Phillipps, S. S. Ali, M. N. Bremer, R. De Propris, A. E. Sansom, M. E. Cluver, M. Alpaslan, S. Brough, M. J.I. Brown, L. J.M. Davies, S. P. Driver, M. W. Grootes, Benne W. Holwerda, A. M. Hopkins, P. A. James, K. Pimbblet, A. S.G. Robotham, E. N. Taylor, L. Wang

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We use data from the GAMA and GALEX surveys to demonstrate that the UV upturn, an unexpected excess of ultraviolet flux from a hot stellar component, seen in the spectra of many early-type galaxies, arises from processes internal to individual galaxies with no measurable influence from the galaxies' larger environment. We first define a clean sample of passive galaxies without a significant contribution to their UV flux from low-level star formation. We confirm that galaxies with the optical colours of red sequence galaxies often have signs of residual star formation, which, without other information, would prevent a convincing demonstration of …

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Remaking Environmental Justice, Clifford Villa Jan 2020

Remaking Environmental Justice, Clifford Villa

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From movements for civil rights in the 1960s and environmental protection in the 1970s, the environmental justice movement emerged in the 1980s and 1990s to highlight the disparate impacts of pollution, principally upon people of color and low-income communities. Over time, the scope of environmental justice expanded to address concerns for other dimensions of diversity. New and continuing challenges tell us that we need to reframe our understanding of environmental justice to ensure better protection for people going forward. One way to reframe this understanding may be to apply the heuristic of vulnerability analysis as proposed by legal theorist Martha …

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Modeling And Counteracting Exposure Bias In Recommender Systems, Sami Khenissi, Olfa Nasraoui Jan 2020

Modeling And Counteracting Exposure Bias In Recommender Systems, Sami Khenissi, Olfa Nasraoui

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What we discover and see online, and consequently our opinions and decisions, are becoming increasingly affected by automated machine learned predictions. Similarly, the predictive accuracy of learning machines heavily depends on the feedback data that we provide them. This mutual influence can lead to closed-loop interactions that may cause unknown biases which can be exacerbated after several iterations of machine learning predictions and user feedback. Machine-caused biases risk leading to undesirable social effects ranging from polarization to unfairness and filter bubbles. In this paper, we study the bias inherent in widely used recommendation strategies such as matrix factorization. Then we …

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Galaxy And Mass Assembly (Gama): Properties And Evolution Of Red Spiral Galaxies, Smriti Mahajan, Kriti Kamal Gupta, Rahul Rana, M. J.I. Brown, S. Phillipps, Joss Bland-Hawthorn, M. N. Bremer, S. Brough, Benne W. Holwerda, A. M. Hopkins, J. Loveday, Kevin Pimbblet, Lingyu Wang Jan 2020

Galaxy And Mass Assembly (Gama): Properties And Evolution Of Red Spiral Galaxies, Smriti Mahajan, Kriti Kamal Gupta, Rahul Rana, M. J.I. Brown, S. Phillipps, Joss Bland-Hawthorn, M. N. Bremer, S. Brough, Benne W. Holwerda, A. M. Hopkins, J. Loveday, Kevin Pimbblet, Lingyu Wang

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We use multiwavelength data from the Galaxy And Mass Assembly (GAMA) survey to explore the cause of red optical colours in nearby (0.002 < z < 0.06) spiral galaxies. We show that the colours of red spiral galaxies are a direct consequence of some environment-related mechanism(s) that has removed dust and gas, leading to a lower star formation rate. We conclude that this process acts on long time-scales (several Gyr) due to a lack of morphological transformation associated with the transition in optical colour. The specific star formation rate (sSFR) and dust-to-stellar mass ratio of red spiral galaxies is found to be statistically lower than blue spiral galaxies. On the other hand, red spirals are on average 0.9 dex more massive, and reside in environments 2.6 times denser than their blue counterparts. We find no evidence of excessive nuclear activity, or higher inclination angles to support these as the major causes for the red optical colours seen in ≳47 per cent of all spirals in our sample. Furthermore, for a small subsample of our spiral galaxies that are detected in H I, we find that the SFR of gas-rich red spiral galaxies is lower by ∼1 dex than their blue counterparts.

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Fossil Fortunes: Regulating Commercial Paleontology & Incentivizing Fossil Discovery, Ashlee A. Paxton-Turner Jan 2020

Fossil Fortunes: Regulating Commercial Paleontology & Incentivizing Fossil Discovery, Ashlee A. Paxton-Turner

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No abstract provided.

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