arXiv subjects

David Thompson

Publications and source records attributed to David Thompson.

At least 19 recordsLinked to original sources

arXiv2026

Detection of a triple nucleus in the Wolf-Rayet composite Sy 2 galaxy NGC 6764

We report adaptive-optics Ks-band imaging of the composite Seyfert 2 and Wolf-Rayet galaxy NGC 6764 (D = 32 Mpc), obtained with LUCI/SOUL at the Large Binocular Telescope. The nucleus resolves into three compact sources with pairwise projected separations of 0.07-0.20 arcsec, corresponding to 11.0-30.9 pc. All three have indistinguishable H, Ks, H2, and Br-gamma colours, so photometry alone cannot separate accretion from star formation. The system is consistent with a Seyfert nucleus and two star-forming regions, but a dual or triple AGN cannot be excluded. In the latter case, the separations would be two orders of magnitude smaller than in any confirmed or candidate AGN triplet reported to date. Diffraction-limited near-infrared integral-field spectroscopy is required to establish the nature of each component.

astro-ph.GA↗

arXiv2024

Generative AI Is Not Ready for Clinical Use in Patient Education for Lower Back Pain Patients, Even With Retrieval-Augmented Generation

Low back pain (LBP) is a leading cause of disability globally. Following the onset of LBP and subsequent treatment, adequate patient education is crucial for improving functionality and long-term outcomes. Despite advancements in patient education strategies, significant gaps persist in delivering personalized, evidence-based information to patients with LBP. Recent advancements in large language models (LLMs) and generative artificial intelligence (GenAI) have demonstrated the potential to enhance patient education. However, their application and efficacy in delivering educational content to patients with LBP remain underexplored and warrant further investigation. In this study, we introduce a novel approach utilizing LLMs with Retrieval-Augmented Generation (RAG) and few-shot learning to generate tailored educational materials for patients with LBP. Physical therapists manually evaluated our model responses for redundancy, accuracy, and completeness using a Likert scale. In addition, the readability of the generated education materials is assessed using the Flesch Reading Ease score. The findings demonstrate that RAG-based LLMs outperform traditional LLMs, providing more accurate, complete, and readable patient education materials with less redundancy. Having said that, our analysis reveals that the generated materials are not yet ready for use in clinical practice. This study underscores the potential of AI-driven models utilizing RAG to improve patient education for LBP; however, significant challenges remain in ensuring the clinical relevance and granularity of content generated by these models.

cs.AI↗

arXiv2024

The instrumentation program at the Large Binocular Telescope Observatory in 2024

The Large Binocular Telescope, with its expansive collecting area, angular resolving power, and advanced optical design, provides a robust platform for development and operation of advanced instrumentation for astronomical research. The LBT currently hosts a mature suite of instruments for spectroscopy and imaging at optical through mid-infrared wavelengths, supported by sophisticated adaptive optics systems. This contribution summarizes the current state of instrumentation, including upgrades to existing instruments and commissioning of second generation instruments now in progress. The LBT is soliciting proposals for next generation instrument concepts, with participation open to consortium members and others interested in participation in the Observatory.

astro-ph.IM↗

arXiv2024

On the feasibility of a component-based approach to predict aerodynamic noise from high-speed train bogies

At speeds above 300 km/h, aerodynamic noise becomes a significant source of railway noise. In a high-speed train, the bogie area is one of the most important aerodynamic noise sources. To predict aerodynamic noise, semi-empirical component-based models are attractive as they allow fast and cheap calculations compared with numerical methods. Such component-based models have been previously applied successfully to predict the aerodynamic noise from train pantographs which consist of various cylinders. In this work, the feasibility is evaluated of applying them to the aerodynamic noise from bogies, which consist of various bluff bodies. To this end, noise measurements were carried out in an anechoic wind tunnel for different flow speeds using simple shapes representing various idealised components of a bogie. These results have been used to adjust the empirical constants of the component-based prediction model to enable its application to the bogie case. In addition, the noise from a 1:10 scale simplified bogie mock-up was measured and used for comparison with the prediction model. The results show good agreement between measurements and predictions for the bogie alone. When the bogie is located between two ramps approximating a simplified bogie cavity the noise is underpredicted at low frequencies. This is attributed to the noise from the cavity which is not included in the model.

physics.flu-dyn↗

arXiv2023

Comparison of numerical software for predicting the performance of a horizontal axis tidal turbine

For tidal energy to become an alternative energy resource to fossil fuels then there needs to be confidence in the predicted performance of horizontal axis tidal turbine devices. A number of computational fluids dynamics packages are now available to assist in the design and testing of new devices. The work in this paper describes a comparative study as a scoping exercise between two widely used packages, OpenFOAM and ANSYS CFX. The numerical simulations were run using the same geometry, mesh and turbulence model on both software. The results were compared to experimental testing conducted at INSEAN. The setup for each model is detailed. Differences were noted in the running and setup of the models as well as within the time history of the results. Overall both CFX and OpenFOAM were shown to give good predictions for the performance coefficients compared to the experimental testing with the data averaged over several complete rotations and well when compared to each other.

physics.flu-dyn↗

arXiv2021

Lunar-like silicate material forms the Earth quasisatellite (469219) 2016 HO3 Kamo`oalewa

Little is known about Earth quasi-satellites, a class of near-Earth small solar system bodies that orbit the sun but remain close to the Earth, because they are faint and difficult to observe. Here we use the Large Binocular Telescope (LBT) and the Lowell Discovery Telescope (LDT) to conduct a comprehensive physical characterization of quasi-satellite (469219) Kamo`oalewa and assess its affinity with other groups of near-Earth objects. We find that (469219) Kamo`oalewa rotates with a period of 28.3 (+1.8/-1.3) minutes and displays a reddened reflectance spectrum from 0.4-2.2 microns. This spectrum is indicative of a silicate-based composition, but with reddening beyond what is typically seen amongst asteroids in the inner solar system. We compare the spectrum to those of several material analogs and conclude that the best match is with lunar-like silicates. This interpretation implies extensive space weathering and raises the prospect that Kamo`oalewa could comprise lunar material.

astro-ph.EP↗

arXiv2019

Supermassive black holes at high redshifts

MeV blazars are the most luminous persistent sources in the Universe and emit most of their energy in the MeV band. These objects display very large jet powers and accretion luminosities and are known to host black holes with a mass often exceeding $10^9 M_{\odot}$. An MeV survey, performed by a new generation MeV telescope which will bridge the entire energy and sensitivity gap between the current generation of hard X-ray and gamma-ray instruments, will detect $>$1000 MeV blazars up to a redshift of $z=5-6$. Here we show that this would allow us: 1) to probe the formation and growth mechanisms of supermassive black holes at high redshifts, 2) to pinpoint the location of the emission region in powerful blazars, 3) to determine how accretion and black hole spin interplay to power the jet.

astro-ph.HE↗

arXiv2018

The Discovery of a Gravitationally Lensed Quasar at z = 6.51

Strong gravitational lensing provides a powerful probe of the physical properties of quasars and their host galaxies. A high fraction of the most luminous high-redshift quasars was predicted to be lensed due to magnification bias. However, no multiple imaged quasar was found at z>5 in previous surveys. We report the discovery of J043947.08+163415.7, a strongly lensed quasar at z=6.51, the first such object detected at the epoch of reionization, and the brightest quasar yet known at z>5. High-resolution HST imaging reveals a multiple imaged system with a maximum image separation theta ~ 0.2", best explained by a model of three quasar images lensed by a low luminosity galaxy at z~0.7, with a magnification factor of ~50. The existence of this source suggests that a significant population of strongly lensed, high redshift quasars could have been missed by previous surveys, as standard color selection techniques would fail when the quasar color is contaminated by the lensing galaxy.

astro-ph.GA↗

arXiv2016

Current Status of the Facility Instrumentation Suite at The Large Binocular Telescope Observatory

We review the current status of the facility instrumentation for the Large Binocular Telescope (LBT). The LBT has 2x 8.4m primary mirrors on a single mount with an effective collecting area of 11.8m or 23m when interferometrically combined. The facility instruments are: 1) the Large Binocular Cameras (LBCs), each with a 23'x25' field of view (FOV). The blue and red optimized optical LBCs are mounted at the prime focus of the left and right primary mirrors, respectively. The filter suite of the two LBCs covers 0.3-1.1{\mu}m, including the new TiO (0.78{\mu}m) and CN (0.82{\mu}m) filters; 2) the Multi-Object Double Spectrograph (MODS), two identical optical spectrographs each mounted at a straight through f/15 Gregorian mount. MODS-1 & -2 can do imaging with Sloan filters and medium resolution (R~2000) spectroscopy, each with 24 interchangeable masks (multi-object or longslit) over a 6'x6' FOV. Each MODS is capable of blue (0.32-0.6{\mu}m) and red (0.5-1.05{\mu}m) wavelength only coverage or, using a dichroic, 0.32-1.05{\mu}m coverage; and 3) the two LBT Utility Camera in the Infrared instruments (LUCIs), each mounted at a bent-front Gregorian f/15 port. LUCI-1 & 2 are designed for seeing-limited (4'x4'FOV) and AO (0.5'x0.5' FOV) imaging & spectroscopy over 0.95-2.5{\mu}m with spectroscopic resolutions of R~400-11000, including 32 interchangeable cryogenically cooled masks. All facility instruments are on the LBT and, for the first time, have been on-sky for science. We also report on the first science use of "mixed-mode" (differently paired instruments). While both primary mirrors reside on a single fixed mount, they are capable of operating independently within a defined "co-pointing" limit. This provides users with the additional capability to independently dither each mirror or center observations on two different sets of spatial coordinates within this limit. (ABRIDGED)

astro-ph.IM↗

arXiv2015

An ultra-luminous quasar with a twelve-billion-solar-mass black hole at redshift 6.30

So far, roughly 40 quasars with redshifts greater than z=6 have been discovered. Each quasar contains a black hole with a mass of about one billion solar masses ($10^9 M_\odot$). The existence of such black holes when the Universe was less than 1 billion years old presents substantial challenges to theories of the formation and growth of black holes and the coevolution of black holes and galaxies. Here we report the discovery of an ultra-luminous quasar, SDSS J010013.02+280225.8, at redshift z=6.30. It has an optical and near-infrared luminosity a few times greater than those of previously known z>6 quasars. On the basis of the deep absorption trough on the blue side of the Ly $\alpha$ emission line in the spectrum, we estimate the proper size of the ionized proximity zone associated with the quasar to be 26 million light years, larger than found with other z>6.1 quasars with lower luminosities. We estimate (on the basis of a near-infrared spectrum) that the black hole has a mass of $\sim 1.2 \times 10^{10} M_\odot$, which is consistent with the $1.3 \times 10^{10} M_\odot$ derived by assuming an Eddington-limited accretion rate.

astro-ph.GA↗

arXiv2011

Keck Deep Fields. IV. Luminosity Dependent Clustering and Galaxy Downsizing in UV-Selected Galaxies at z=4, 3, and 2

We investigate the luminosity dependent clustering of rest-frame UV selected galaxies at z~4, 3, 2.2, and 1.7 in the Keck Deep Fields (KDFs), which are complete to R = 27 and cover 169 arcmin^2. We find that at z~4 and 3, UV-bright galaxies cluster more strongly than UV-faint ones, but at z~2.2 and 1.7, the UV-bright galaxies are no longer the most strongly clustered. We derive mass estimates for objects in our sample by comparing our measurements to the predicted clustering of dark matter haloes in the Millennium Simulation. From these estimates, we infer relationships between halo mass and star formation rate (SFR), and find that the most massive dark matter haloes in our sample host galaxies with high SFRs (M_1700 < -20, or > 50 M_sun/yr) at z~3 and 4, moderate SFRs (-20<M_1700<-19, or ~20 M_sun/yr) at z~2.2, and lower SFRs (-19<M_1700<-18, or ~2 M_sun/yr) at z~1.7. We believe our measurements may provide a new line of evidence for galaxy downsizing by extending that concept from stellar to halo mass. We also find that the objects with blue UV colors in our sample are much more strongly clustered than those with red UV colors, and we propose that this may be due to the presence of the 2175A dust absorption bump in more massive halos, which contain the older stellar populations and dust needed to produce the feature. The relatively small area covered by the survey means that the absolute values of the correlation lengths and halo masses we derive are heavily dependent on the "integral constraint" correction, but the uniformly deep coverage across a large redshift interval allows us to detect several important trends that are independent of this correction.

astro-ph.CO↗

arXiv2010

Isoperimetric problems in sectors with density

We consider the isoperimetric problem in planar sectors with density $r^{p}$, and with density $a>1$ inside the unit disk and $1$ outside. We characterize solutions as a function of sector angle. We also solve the isoperimetric problem in $\mathbb{R}^{n}$ with density $r^{p},\; p<0$.

math.DG↗

arXiv2010

LBT/LUCIFER Observations of the z~2 Lensed Galaxy J0900+2234

We present rest-frame optical images and spectra of the gravitationally lensed, star-forming galaxy J0900+2234 (z=2.03). The observations were performed with the newly commissioned LUCIFER1 near-infrared instrument mounted on the Large Binocular Telescope (LBT). We fit lens models to the rest-frame optical images and find the galaxy has an intrinsic effective radius of 7.4 kpc with a lens magnification factor of about 5 for the A and B components. We also discovered a new arc belonging to another lensed high-z source galaxy, which makes this lens system a potential double Einstein ring system. Using the high S/N rest-frame optical spectra covering H+K band, we detected Hbeta, OIII, Halpha, NII and SII emission lines. Detailed physical properties of this high-z galaxy were derived. The extinction towards the ionized HII regions (E_g(B-V)) is computed from the flux ratio of Halpha and Hbeta and appears to be much higher than that towards stellar continuum (E_s(B-V)), derived from the optical and NIR broad band photometry fitting. The metallicity was estimated using N2 and O3N2 indices. It is in the range of 1/5-1/3 solar abundance, which is much lower than the typical z~2 star-forming galaxies. From the flux ratio of SII 6717 and 6732, we found that the electron number density of the HII regions in the high-z galaxy were >1000 cm^-3, consistent with other z~2 galaxies but much higher than that in local HII regions. The star-formation rate was estimated via the Halpha luminosity, after correction for the lens magnification, to be about 365\pm69 Msun/yr. Combining the FWHM of Halpha emission lines and the half-light radius, we found the dynamical mass of the lensed galaxy is 5.8\pm0.9x10^10 Msun. The gas mass is 5.1\pm1.1x10^10~Msun from the H\alpha flux surface density by using global Kennicutt-Schmidt Law, indicating a very high gas fraction of 0.79\pm0.19 in J0900+2234.

astro-ph.CO↗

arXiv2008

An Exploratory Search for z~6 Quasars in the UKIDSS Early Data Release

We conducted an exploratory search for quasars at z~ 6 - 8, using the Early Data Release from United Kingdom Infrared Deep Sky survey (UKIDSS) cross-matched to panoramic optical imagery. High redshift quasar candidates are chosen using multi-color selection in i,z,Y,J,H and K bands. After removal of apparent instrumental artifacts, our candidate list consisted of 34 objects. We further refined this list with deeper imaging in the optical for ten of our candidates. Twenty-five candidates were followed up spectroscopically in the near-infrared and in the optical. We confirmed twenty-five of our spectra as very low-mass main-sequence stars or brown dwarfs, which were indeed expected as the main contaminants of this exploratory search. The lack of quasar detection is not surprising: the estimated probability of finding a single z>6 quasar down to the limit of UKIDSS in the 27.3 square degrees of the EDR is <5%. We find that the most important limiting factor in this work is the depth of the available optical data. Experience gained in this pilot project can help refine high-redshift quasar selection criteria for subsequent UKIDSS data releases.

astro-ph↗

arXiv2007

A deep Large Binocular Telescope view of the Canes Venatici I dwarf galaxy

We present the first deep color-magnitude diagram of the Canes Venatici I (CVnI) dwarf galaxy from observations with the wide field Large Binocular Camera on the Large Binocular Telescope. Reaching down to the main-sequence turnoff of the oldest stars, it reveals a dichotomy in the stellar populations of CVnI: it harbors an old (> 10 Gyr), metal-poor ([Fe/H] ~ -2.0) and spatially extended population along with a much younger (~ 1.4-2.0 Gyr), 0.5 dex more metal-rich, and spatially more concentrated population. These young stars are also offset by 64_{-20}^{+40} pc to the East of the galaxy center. The data suggest that this young population, which represent ~ 3-5 % of the stellar mass of the galaxy within its half-light radius, should be identified with the kinematically cold stellar component found by Ibata et al. (2006). CVnI therefore follows the behavior of the other remote MW dwarf spheroidals which all contain intermediate age and/or young populations: a complex star formation history is possible in extremely low-mass galaxies.

astro-ph↗

arXiv2006

The Long Faint Tail of the High-Redshift Galaxy Population

We study the properties of very faint, sub-L* Lyman break galaxies at z~2-5 - thus far a largely neglected but numerically and energetically very important population. We find that the LBG luminosity function undergoes luminosity-dependent evolution: the number of luminous galaxies remains constant while the number of faint ones grows with time. The total UV luminosity density increases with cosmic time from at least z~5 until reaching a peak or a plateau around z~2 - behaviour that is governed by the sub-L* galaxies in the LF's "faint tail". Using broadband SED fitting we find a nearly-linear relationship between SFR and galaxy stellar mass at z~2. A typical L* LBG at z~2 shows a stellar mass of ~10^10M_sun, remarkably similar to the bimodality mass at low redshift. This similarity suggests that the mechanisms responsible for the galaxy bimodality at low-z may have also been at play at z~2.

astro-ph↗

arXiv2006

G515, Revisited. I. Stellar Populations And Evidence Of Nuclear Activity In A Luminous "E+A" Galaxy

We present multiwavelength observations of the very luminous "E+A" galaxy known as G515 (J152426.55+080906.7), including deep K_s imaging, spatially resolved H-alpha spectroscopy, and radio observations. The data, together with detailed spectral synthesis of the galaxy's integrated stellar population, show that G515 is a ~1 Gyr old post-merger, post-starburst galaxy. We detect no Balmer line emission in the galaxy, although there is a small amount of [NII]6548,6583A emission. The galaxy's H I mass has a 2-sigma upper limit of 1.0 * 10^9 solar masses. IRAS detections in the 60-micron and 100-micron bands indicate a far infrared luminosity of ~5.8 * 10^10 solar luminosities. A small amount (~3 mJy) of radio continuum flux, which appears to be variable, has been detected. The data suggest that G515 may have once been an ultraluminous infrared galaxy, and may harbor a weak, dust-obscured active nucleus.

astro-ph↗

arXiv2006

Keck Deep Fields. III. Luminosity-dependent Evolution of the Ultraviolet Luminosity and Star Formation Rate Densities at z~4, 3, and 2

We use the Keck Deep Fields UGRI catalog of z~4, 3, and 2 UV-selected galaxies to study the evolution of the rest-frame 1700A luminosity density at high redshift. The ability to reliably constrain the contribution of faint galaxies is critical and our data do so as they reach to M*+2 even at z~4 and deeper still at lower redshifts. We find that the luminosity density at high redshift is dominated by the hitherto poorly studied galaxies fainter than L*, and, indeed, the the bulk of the UV light in the high-z Universe comes from galaxies in the luminosity range L=0.1-1L*. It is these faint galaxies that govern the behavior of the total UV luminosity density. Overall, there is a gradual rise in luminosity density starting at z~4 or earlier, followed by a shallow peak or a plateau within z~3--1, and then followed by the well-know plunge at lower redshifts. Within this total picture, luminosity density in sub-L* galaxies evolves more rapidly at high redshift, z>~2, than that in more luminous objects. However, this is reversed at lower redshifts, z<~1, a reversal that is reminiscent of galaxy downsizing. Within the context of the models commonly used in the observational literature, there seemingly aren't enough faint or bright LBGs to maintain ionization of intergalactic gas even as late as z~4. This is particularly true at earlier epochs and even more so if the faint-end evolutionary trends we observe at z~3 and 4 continue to higher redshifts. Apparently the Universe must be easier to reionize than some recent studies have assumed. Nevertheless, sub-L* galaxies do dominate the total UV luminosity density at z>~2 and this dominance further highlights the need for follow-up studies that will teach us more about these very numerous but thus far largely unexplored systems.

astro-ph↗