arXiv subjects

Robert Thompson

Publications and source records attributed to Robert Thompson.

At least 19 recordsLinked to original sources

arXiv2026

$K$-Bad Spheres

In this paper we look at the $E$-completion of topological spaces where $E$ is a $p$-local ring spectrum. After a brief review of the concept of $E$-completion, we specialize to the case where $E=K$, $p$-local complex periodic $K$-theory, and consider the $K$-theory of the unstable sphere $S^{2n+1}$. We show that for certain values of $n$ and an odd prime $p$, the $K$-homology of the $K$-completion is not isomorphic to the $K$-homology of the sphere itself, thus in the terminology of Bousfield and Kan, these spheres are '$K$-bad'.

math.AT↗

arXiv2024

Deepest limits on scattered light emission from the Epsilon Eridani inner debris disk with HST/STIS

Epsilon Eridani ($\epsilon$ Eri) is one of the first debris disk systems detected by the Infrared Astronomical Satellite (IRAS). However, the system has thus far eluded detection in scattered light with no components having been directly imaged. Its similarity to a relatively young Solar System combined with its proximity makes it an excellent candidate to further our understanding of planetary system evolution. We present a set of coronagraphic images taken using the Space Telescope Imaging Spectrograph (STIS) coronagraph on the Hubble space telescope at a small inner working angle to detect a predicted warm inner debris disk inside 1". We used three different post-processing approaches; Non-negative Matrix Factorization (NMF), Karhunen-Lo`eve Image Processing (KLIP), and Classical reference differential imaging (RDI), to best optimize reference star subtraction, and find that NMF performed the best overall while KLIP produced the absolute best contrast inside 1". We present limits on scattered light from warm dust, with constraints on surface brightness at 6 mJy/as$^2$ at our inner working angle of 0.6". We also place a constraint of 0.5 mJy/as$^2$ outside 1", which gives us an upper limit on the brightness for outer disks and substellar companions. Finally, we calculated an upper limit on the dust albedo at $\omega <$ 0.487.

astro-ph.EP↗

arXiv2022

Optimizing Product Wheel Time in Lean Manufacturing Systems

Lean manufacturing is a production method focused on reducing production times, eliminating waste, and synchronizing production with fluctuating demand. A standard lean manufacturing methodology is the product wheel, a repeating sequence of production of various items. If this product wheel sequence is short, it is easier to interrupt or alter production to adjust for failures or fluctuations in demand, so the manufacturing process is leaner. However, a sequence that is too short results in frequent changeover from the production of one item to the next, yielding higher costs. This study formulates the product wheel methodology as an optimization problem and proposes two approaches to solving this problem: one via a relaxation to integer linear programming, and another via the probabilistic optimization technique of simulated annealing. We assess the performance of these two approaches through simulations and analyze the relationships between production leanness and costs.

math.OC↗

arXiv2022

Vehicle-to-Vehicle Charging Coordination over Information Centric Networking

Cities around the world are increasingly promoting electric vehicles (EV) to reduce and ultimately eliminate greenhouse gas emissions. For example, the city of San Francisco aims to increase the number of EVs from tens of thousands to over quarter of a million by 2025. This huge number of EVs will put unprecedented stress on the power grid. To efficiently serve the increased charging load, these EVs need to be charged in a coordinated fashion. One promising coordination strategy is vehicle-to-vehicle (V2V) charging coordination, enabling EVs to sell their surplus energy in an ad-hoc, peer to peer manner. Enabling V2V charging coordination requires new communication network protocols that can facilitate such charging coordination in a peer-to-peer fashion. This paper introduces an Information Centric Networking (ICN)-based protocol to support ad-hoc V2V charging coordination (V2V-CC). Our evaluations demonstrate that V2V-CC can provide added flexibility, fault tolerance, and reduced communication latency than a conventional centralized cloud based approach. We show that V2V-CC can achieve a 93\% reduction in protocol completion time compared to a conventional approach. We also show that V2V-CC also works well under extreme packet loss, making it ideal for V2V charging coordination.

cs.NI↗

arXiv2022

An Information Centric Framework for Weather Sensing Data

Weather sensing and forecasting has become increasingly accurate in the last decade thanks to high-resolution radars, efficient computational algorithms, and high-performance computing facilities. Through a distributed and federated network of radars, scientists can make high-resolution observations of the weather conditions on a scale that benefits public safety, commerce, transportation, and other fields. While weather radars are critical infrastructure, they are often located in remote areas with poor network connectivity. Data retrieved from these radars are often delayed or lost, or even lack proper synchronization, resulting in sub-optimal weather prediction. This work applies Named Data Networking (NDN) to a federation of weather sensing radars for efficient content addressing and retrieval. We identify weather data based on a hierarchical naming scheme that allows us to explicitly access desired files. We demonstrate that compared to the window-based mechanism in TCP/IP, an NDN based mechanism improves data quality, reduces uncertainty, and enhances weather prediction. Our evaluation demonstrates that this naming scheme enables effective data retrieval, while compared to the window-based mechanism in TCP/IP, an NDN based mechanism improves data quality, reduces uncertainty, and enhances weather prediction.

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arXiv2021

Application of integral invariants to apictorial jigsaw puzzle assembly

We present a method for the automatic assembly of apictorial jigsaw puzzles. This method relies on integral area invariants for shape matching and an optimization process to aggregate shape matches into a final puzzle assembly. Assumptions about individual piece shape or arrangement are not necessary. We illustrate our method by solving example puzzles of various shapes and sizes.

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arXiv2021

Iterative Respacing of Polygonal Curves

A $\textit{polygonal curve}$ is a collection of $m$ connected line segments specified as the linear interpolation of a list of points $\{p_0, p_1, \ldots, p_m\}$. These curves may be obtained by sampling points from an oriented curve in $\mathbb{R}^n$. In applications it can be useful for this sample of points to be close to \textit{equilateral}, with equal distance between consecutive points. We present a computationally efficient method for respacing the points of a polygonal curve and show that iteration of this method converges to an equilateral polygonal curve.

math.NA↗

arXiv2020

Powderday: Dust Radiative Transfer for Galaxy Simulations

We present Powderday, a flexible, fast, open-source dust radiative transfer package designed to interface with galaxy formation simulations. Powderday builds on FSPS population synthesis models, Hyperion dust radiative transfer, and employs yt to interface between different software packages. We include our stellar population synthesis modeling on the fly, which allows for significant run-time flexibility in the assumed stellar physics. We include a model for nebular line emission that can employ either precomputed Cloudy lookup tables (for efficiency), or direct photoionization calculations for all young stars (for flexibility). The dust content follows either observationally-motivated prescriptions, direct modeling from galaxy formation simulations, or a novel approach that includes the dust content via learning-based algorithms from the SIMBA cosmological galaxy formation simulation. AGN can additionally be included via a range of prescriptions. The output of these models are broadband SEDs, as well as filter-convolved images. Powderday is designed to eliminate last-mile efforts by researchers that employ different hydrodynamic galaxy formation models, and seamlessly interfaces with GIZMO, AREPO, GASOLINE, CHANGA, and ENZO. We demonstrate the capabilities of the code via three applications: a model for the star formation rate (SFR) - infrared luminosity relation in galaxies (including the impact of AGN); the impact of circumstellar dust around AGB stars on the mid-infrared emission from galaxy SEDs; and the impact of galaxy inclination angle on dust attenuation laws.

astro-ph.GA↗

arXiv2018

The Robustness of Cosmological Hydrodynamic Simulation Predictions to Changes in Numerics and Cooling Physics

We test and improve the numerical schemes in our smoothed particle hydrodynamics (SPH) code for cosmological simulations, including the pressure-entropy formulation (PESPH), a time-dependent artificial viscosity, a refined timestep criterion, and metal-line cooling that accounts for photoionisation in the presence of a recently refined Haardt \& Madau (2012) model of the ionising background. The PESPH algorithm effectively removes the artificial surface tension present in the traditional SPH formulation, and in our test simulations it produces better qualitative agreement with mesh-code results for Kelvin-Helmholtz instability and cold cloud disruption. Using a set of cosmological simulations, we examine many of the quantities we have studied in previous work. Results for galaxy stellar and HI mass functions, star formation histories, galaxy scaling relations, and statistics of the Ly$\alpha$ forest are robust to the changes in numerics and microphysics. As in our previous simulations, cold gas accretion dominates the growth of high-redshift galaxies and of low mass galaxies at low redshift, and recycling of winds dominates the growth of massive galaxies at low redshift. However, the PESPH simulation removes spurious cold clumps seen in our earlier simulations, and the accretion rate of hot gas increases by up to an order of magnitude at some redshifts. The new numerical model also influences the distribution of metals among gas phases, leading to considerable differences in the statistics of some metal absorption lines, most notably NeVIII.

astro-ph.GA↗

arXiv2018

Identifying Mergers Using Quantitative Morphologies in Zoom Simulations of High-Redshift Galaxies

Non-parametric morphology measures are a powerful tool for identifying galaxy mergers at low redshifts. We employ cosmological zoom simulations using Gizmo with the Mufasa feedback scheme, post-processed using 3D dust radiative transfer into mock observations, to study whether common morphological measures Gini G, M20, concentration C, and asymmetry A are effective at identifying major galaxy mergers at z ~ 2 - 4, i.e. "Cosmic Noon". Our zoom suite covers galaxies with 10^8.6 < M_* < 10^11 M_sun at z ~ 2, and broadly reproduces key global galaxy observations. Our primary result is that these morphological measures are unable to robustly pick out galaxies currently undergoing mergers during Cosmic Noon, typically performing no better than a random guess. This improves only marginally if we consider whether galaxies have undergone a merger within the last Gyr. When also considering minor mergers, galaxies display no trend of moving towards the merger regime with increasing merger ratio. From z = 4 -> 2, galaxies move from the non-merger towards the merger regime in all statistics, but this is primarily an effect of mass: Above a given noise level, higher mass galaxies display a more complex outer morphology induced by their clustered environment. We conclude that during Cosmic Noon, these morphological statistics are of limited value in identifying galaxy mergers.

astro-ph.GA↗

arXiv2017

Baseline Metal Enrichment from Population III Star Formation in Cosmological Volume Simulations

We utilize the hydrodynamic and N-body code {\small GIZMO} coupled with our newly developed sub-grid Population~III (Pop~III) Legacy model, designed specifically for cosmological volume simulations, to study the baseline metal enrichment from Pop~III star formation at $z>7$. In this idealized numerical experiment, we only consider Pop~III star formation. We find that our model Pop~III star formation rate density (SFRD), which peaks at $\sim 10^{-3}\ {\rm M_\odot yr^{-1} Mpc^{-1}}$ near $z\sim10$, agrees well with previous numerical studies and is consistent with the observed estimates for Pop~II SFRDs. The mean Pop~III metallicity rises smoothly from $z=25-7$, but does not reach the critical metallicity value, $Z_{\rm crit}=10^{-4}\ Z_\odot$, required for the Pop~III to Pop~II transition in star formation mode until $z\simeq7$. This suggests that, while individual halos can suppress in-situ Pop~III star formation, the external enrichment is insufficient to globally terminate Pop~III star formation. The maximum enrichment from Pop~III star formation in star forming dark matter halos is $Z\sim10^{-2}\ Z_\odot$, whereas the minimum found in externally enriched haloes is $Z\gtrsim10^{-7}\ Z_\odot$. Finally, mock observations of our simulated IGM enriched with Pop~III metals produce equivalent widths similar to observations of an extremely metal poor damped Lyman alpha (DLA) system at $z=7.04$, which is thought to be enriched by Pop~III star formation only.

astro-ph.GA↗

arXiv2017

The IRX-Beta Dust Attenuation Relation in Cosmological Galaxy Formation Simulations

We utilise a series of high-resolution cosmological zoom simulations of galaxy formation to investigate the relationship between the ultraviolet (UV) slope, beta, and the ratio of the infrared luminosity to UV luminosity (IRX) in the spectral energy distributions (SEDs) of galaxies. We employ dust radiative transfer calculations in which the SEDs of the stars in galaxies propagate through the dusty interstellar medium. Our main goals are to understand the origin of, and scatter in the IRX-beta relation; to assess the efficacy of simplified stellar population synthesis screen models in capturing the essential physics in the IRX-beta relation; and to understand systematic deviations from the canonical local IRX-beta relations in particular populations of high-redshift galaxies. Our main results follow. Galaxies that have young stellar populations with relatively cospatial UV and IR emitting regions and a Milky Way-like extinction curve fall on or near the standard Meurer relation. This behaviour is well captured by simplified screen models. Scatter in the IRX-beta relation is dominated by three major effects: (i) older stellar populations drive galaxies below the relations defined for local starbursts due to a reddening of their intrinsic UV SEDs; (ii) complex geometries in high-z heavily star forming galaxies drive galaxies toward blue UV slopes owing to optically thin UV sightlines; (iii) shallow extinction curves drive galaxies downward in the IRX-beta plane due to lowered NUV/FUV extinction ratios. We use these features of the UV slopes of galaxies to derive a fitting relation that reasonably collapses the scatter back toward the canonical local relation. Finally, we use these results to develop an understanding for the location of two particularly enigmatic populations of galaxies in the IRX-beta plane: z~2-4 dusty star forming galaxies, and z>5 star forming galaxies.

astro-ph.GA↗

arXiv2016

The AGORA High-Resolution Galaxy Simulations Comparison Project. II: Isolated Disk Test

Using an isolated Milky Way-mass galaxy simulation, we compare results from 9 state-of-the-art gravito-hydrodynamics codes widely used in the numerical community. We utilize the infrastructure we have built for the AGORA High-resolution Galaxy Simulations Comparison Project. This includes the common disk initial conditions, common physics models (e.g., radiative cooling and UV background by the standardized package Grackle) and common analysis toolkit yt, all of which are publicly available. Subgrid physics models such as Jeans pressure floor, star formation, supernova feedback energy, and metal production are carefully constrained across code platforms. With numerical accuracy that resolves the disk scale height, we find that the codes overall agree well with one another in many dimensions including: gas and stellar surface densities, rotation curves, velocity dispersions, density and temperature distribution functions, disk vertical heights, stellar clumps, star formation rates, and Kennicutt-Schmidt relations. Quantities such as velocity dispersions are very robust (agreement within a few tens of percent at all radii) while measures like newly-formed stellar clump mass functions show more significant variation (difference by up to a factor of ~3). Systematic differences exist, for example, between mesh-based and particle-based codes in the low density region, and between more diffusive and less diffusive schemes in the high density tail of the density distribution. Yet intrinsic code differences are generally small compared to the variations in numerical implementations of the common subgrid physics such as supernova feedback. Our experiment reassures that, if adequately designed in accordance with our proposed common parameters, results of a modern high-resolution galaxy formation simulation are more sensitive to input physics than to intrinsic differences in numerical schemes.

astro-ph.GA↗

arXiv2015

The Formation of Submillimetre-Bright Galaxies from Gas Infall over a Billion Years

Submillimetre-luminous galaxies at high-redshift are the most luminous, heavily star-forming galaxies in the Universe, and are characterised by prodigious emission in the far-infrared at 850 microns (S850 > 5 mJy). They reside in halos ~ 10^13Msun, have low gas fractions compared to main sequence disks at a comparable redshift, trace complex environments, and are not easily observable at optical wavelengths. Their physical origin remains unclear. Simulations have been able to form galaxies with the requisite luminosities, but have otherwise been unable to simultaneously match the stellar masses, star formation rates, gas fractions and environments. Here we report a cosmological hydrodynamic galaxy formation simulation that is able to form a submillimetre galaxy which simultaneously satisfies the broad range of observed physical constraints. We find that groups of galaxies residing in massive dark matter halos have rising star formation histories that peak at collective rates ~ 500-1000 Msun/yr at z=2-3, by which time the interstellar medium is sufficiently enriched with metals that the region may be observed as a submillimetre-selected system. The intense star formation rates are fueled in part by a reservoir gas supply enabled by stellar feedback at earlier times, not through major mergers. With a duty cycle of nearly a gigayear, our simulations show that the submillimetre-luminous phase of high-z galaxies is a drawn out one that is associated with significant mass buildup in early Universe proto-clusters, and that many submillimetre-luminous galaxies are actually composed of numerous unresolved components (for which there is some observational evidence).

astro-ph.GA↗

arXiv2015

Identifying mergers using non-parametric morphological classification at high redshifts

We investigate the time evolution of non-parametric morphological quantities and their relationship to major mergers between $4\geq z \geq 2$ in high-resolution cosmological zoom simulations of disk galaxies that implement kinetic wind feedback, $H_2$-based star formation, and minimal ISM pressurisation. We show that the resulting galaxies broadly match basic observed physical properties of $z\sim 2$ objects. We measure the galaxies' concentrations ($C$), asymmetries ($A$), and $Gini$ ($G$) and $M_{20}$ coefficients, and correlate these with major merger events identified from the mass growth history. We find that high values of asymmetry provide the best indicator for identifying major mergers of $>1:4$ mass ratio within our sample, with $Gini$-$M_{20}\,$ merger classification only as effective for face-on systems and much less effective for edge-on or randomly-oriented galaxies. The canonical asymmetry cut of $A\geq0.35$, however, is only able to correctly identify major mergers $\sim 10\%$ of the time, while a higher cut of $A\geq 0.8$ more efficiently picks out mergers at this epoch. We further examine the temporal correlation between morphological statistics and mergers, and show that for randomly-oriented galaxies, half the galaxies with $A\geq0.8$ undergo a merger within $\pm0.2\,{\rm Gyr}$, whereas $Gini$-$M_{20}\,$ identification only identifies about a third correctly. The fraction improves further using $A\geq 1.5$, but about the half the mergers are missed by this stringent cut.

astro-ph.GA↗

arXiv2015

Simulator of Galaxy Millimeter/Submillimeter Emission (SIGAME): The [CII]-SFR Relationship of Massive z=2 Main Sequence Galaxies

We present S\'IGAME simulations of the [CII]157.7$\mu$ fine structure line emission from cosmological smoothed particle hydrodynamics (SPH) simulations of seven main sequence galaxies at z=2. Using sub-grid physics prescriptions the gas in our simulations is modeled as a multi-phased interstellar medium (ISM) comprised of molecular gas residing in giant molecular clouds, an atomic gas phase associated with photo-dissociation regions (PDRs) at the cloud surfaces, and a diffuse, ionized gas phase. Adopting logotropic cloud density profiles and accounting for heating by the local FUV radiation field and cosmic rays by scaling both with local star formation rate (SFR) volume density, we calculate the [CII] emission using a photon escape probability formalism. The [CII] emission peaks in the central $\lesssim$1 kpc of our galaxies as do the SFR radial profiles, with most [CII] ($\gtrsim$70%) originating in the molecular gas phase, whereas further out ($\gtrsim$2 kpc), the atomic/PDR gas dominates ($\gtrsim$90%) the [CII] emission, no longer tracing on-going star formation. Throughout, the ionized gas contribution is negligible ($\lesssim$3%). The [CII] luminosity vs. SFR ([CII]-SFR) relationship, integrated as well as spatially resolved (on scales of 1 kpc), delineated by our simulated galaxies is in good agreement with the corresponding relations observed locally and at high redshifts. In our simulations, the molecular gas dominates the [CII] budget at SFR$\gtrsim$20 M$_{\odot}$yr$^{-1}$ (SFR density $\gtrsim$0.5 M$_{\odot}$yr$^{-1}$kpc$^{-2}$), while atomic/PDR gas takes over at lower SFRs, suggesting a picture in which [CII] predominantly traces the molecular gas in high-density/pressure regions where star formation is on-going, and otherwise reveals the atomic/PDR gas phase.

astro-ph.GA↗

arXiv2014

The rise and fall of a challenger: the Bullet Cluster in $\Lambda$ Cold Dark Matter simulations

The Bullet Cluster has provided some of the best evidence for the $\Lambda$ cold dark matter ($\Lambda\rm{CDM}$) model via direct empirical proof of the existence of collisionless dark matter, while posing a serious challenge owing to the unusually high inferred pairwise velocities of its progenitor clusters. Here we investigate the probability of finding such a high-velocity pair in large-volume N-body simulations, particularly focusing on differences between halo finding algorithms. We find that algorithms that do not account for the kinematics of infalling groups yield vastly different statistics and probabilities. When employing the ROCKSTAR halo finder that considers particle velocities, we find numerous Bullet-like pair candidates that closely match not only the high pairwise velocity, but also the mass, mass ratio, separation distance, and collision angle of the initial conditions that have been shown to produce the Bullet Cluster in non-cosmological hydrodynamic simulations. The probability of finding a high pairwise velocity pair among haloes with $M_{\rm halo}\geq10^{14} M_{\odot}$ is $4.6\times 10^{-4}$ using ROCKSTAR, while it is $\approx 34\times$ lower using a friends-of-friends (FOF) based approach as in previous studies. This is because the typical spatial extent of Bullet progenitors is such that FOF tends to group them into a single halo despite clearly distinct kinematics. Further requiring an appropriately high average mass among the two progenitors, we find the comoving number density of potential Bullet-like candidates to be on the order of $\approx10^{-10} \,{\rm Mpc}^{-3}$. Our findings suggest that $\Lambda\rm{CDM}$ straightforwardly produces massive, high relative velocity halo pairs analogous to Bullet Cluster progenitors, and hence the Bullet Cluster does not present a challenge to the $\Lambda\rm{CDM}$ model.

astro-ph.CO↗

arXiv2014

An Unstable Change of Rings for Morava E-Theory

The Bousfield-Kan (or unstable Adams) spectral sequence can be constructed for various homology theories such as Brown-Peterson homology theory BP, Johnson-Wilson theory $E(n)$, or Morava $E$-theory $E_n$. For nice spaces the $E_2$-term is given by Ext in a category of unstable comodules. We establish an unstable Morava change of rings isomorphism between $\text{Ext}_{\mathcal{U}_{\Gamma_B}}(B,M)$ and $\text{Ext}_{\mathcal{U}_{E_{n*}E_n}/I_{n}}(E_{n*}/I_{n},E_{n*}\otimes_{BP_*} M)$ where $(B,\Gamma_B)$ denotes the Hopf Algebroid $(v_n^{-1}BP_*/I_{n}, v_n^{-1}BP_*BP/I_{n} )$. We show that the latter groups can be interpreted as $\text{Ext}$ in the category of continuous modules over the profinite monoid of endomorphisms of the Honda formal group law. By comparing this with the cohomology of the Morava stabilizer group we obtain an unstable Morava vanishing theorem when $p-1 \nmid n$.

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