• Acute pulmonary embolism in a child with ANCA-negative Idiopathic Pulmonary Capillaritis

  Asseri, Ali A; Zeng, Yi; Daines, Cori L; Univ Arizona, Dept Pediat (SAUDI MED J, 2019-06)

  Diffuse alveolar hemorrhage is an uncommon and often fatal condition in children that is characterized by distinct histopathological etiologies. Herein, we discuss the case of an 11-year-old girl who presented with acute worsening of hypoxia and left-sided chest pain. The patient had lung biopsy-proven idiopathic pulmonary capillaritis and was being treated with prednisolone every alternate day, azathioprine, and hydroxychloroquine. A contrast-computed tomography (CT) scan of the chest showed an acute left lower-lobe pulmonary embolism. Negative results were obtained on a test for thrombophilia. In children, pulmonary embolism with anti-neutrophil cytoplasmic antibody-negative idiopathic pulmonary capillaritis is a rare clinical condition. The exact cause of thrombus formation in this case is unknown; however, obesity, immobility, and chronic systemic corticosteroid therapy probably played a role.
• General theory of inflammation: patient self-administration of hydrocortisone safely achieves superior control of hydrocortisone-responding disorders by matching dosage with symptom intensity

  Irwin, John B.; Baldwin, A. L.; Stenberg, Virgil, I; Univ Arizona, Sch Med, Dept Physiol (Dove Medical Press Ltd, 2019-06)

  Objective: To determine if patient self-administration of hydrocortisone will safely achieve superior symptom control for all hydrocortisone-responding disorders as it does for Addison's disease and rheumatoid arthritis. Methods: Two thousand four hundred and twenty-eight participants with hydrocortisone-responding disorders were brought to a minimum symptom state using daily administered hydrocortisone tablets in a 24-week, open study. Thereafter, participants used 5-day, low-dose hydrocortisone regimens to quench subsequent disorder exacerbations (flares) to maintain the minimum symptom state. Stressors such as emotional traumas, infections, allergies, and injuries were minimized to reduce disorder intensity, hydrocortisone consumption, and participant discomfort. Results: Two thousand fifteen participants, 601 with fibromyalgia, 579 with osteoarthritis, 246 with rheumatoid arthritis, 226 with undifferentiated arthritis, 75 with back pain, 51 with Parkinson's disease, 44 with polymyalgia rheumatica, 25 with neuropathy, 25 with chronic fatigue syndrome, 25 with dementia, 21 with migraine headache, 19 with multiple sclerosis, and 78 with other disorders completed the 24-week study to achieve a composite average symptom improvement of 76% with equal response rates. The participants averaged ingesting 12 mg of hydrocortisone per day. No significant adverse reactions were observed. Conclusions: Patient self-administration of hydrocortisone safely achieves superior symptom control for 38 hydrocortisone-responding disorders at equal rates and symptom improvements to confirm and amplify an earlier double-blind study finding on rheumatoid arthritis. These results are consistent with the body having an inflammation control system and chronic inflammation being a disorder unto itself with differing symptoms sets dependent on its location.
• Estimating the annual distribution of monarch butterflies in Canada over 16 years using citizen science data

  Flockhart, D. T. Tyler; Larrivee, Maxim; Prudic, Kathleen L.; Norris, D. Ryan; Univ Arizona, Dept Entomol (CANADIAN SCIENCE PUBLISHING, NRC RESEARCH PRESS, 2019-06-21)

  Monarch butterflies (Danaus plexippus, Linnaeus, 1758) are comprised of two migratory populations separated by the Rocky Mountains and are renowned for their long-distance movements among the United States, Canada, and Mexico. Both populations have declined over several decades across North America prompting all three countries to evaluate conservation efforts. Monitoring monarch distribution and abundance is a necessary aspect of ongoing management in Canada where they are a species at risk. We used presence-only data from two citizen science data sets to estimate the annual breeding distribution of monarch butterflies in Canada between 2000 and 2015. Monarch breeding distribution in Canada varied widely among years owing to natural variation, and when considering the upper 95% of the probability of occurrence, the annual mean breeding distribution in Canada was 484 943 km(2) (min: 173 449 km(2); max: 1 425 835 km(2)). The area of occurrence was approximately an order of magnitude larger in eastern Canada than in western Canada. Habitat restoration for monarch butterflies in Canada should prioritize productive habitats in southern Ontario where monarchs occur annually and, therefore, likely contribute most to the long-term viability of monarchs in eastern North America. Overall, our assessment sets the geographic context to develop successful management strategies for monarchs in Canada.
• High-power, continuous-wave, scalable, single-frequency 852nm laser source for 213nm generation

  Kaneda, Yushi; Tago, Tsuyoshi; Sasa, Toshiaki; Sasaura, Masahiro; Nakao, Hiroaki; Hirohashi, Junji; Furukawa, Yasunori; Univ Arizona, Coll Opt Sci (SPIE-INT SOC OPTICAL ENGINEERING, 2019-03-04)

  We developed a high-power, continuous-wave (CW), single-frequency 852nm laser source, for the purpose of fourth harmonic generation at 213nm. Our approach is the doubly resonant sum-frequency mixing (DRSFM) with two fiber sources. An in-house single-frequency master oscillator at 1907nm is amplified by an in-house clad-pumped amplifier to 5W, and a commercial single-frequency master oscillator at 1540nm is amplified by a commercial amplifier to 10W. The two beams are combined via a dichroic mirror to a single beam before incident on a dual-wavelength resonator, consisting of one set of dual-wavelength mirrors. The external resonator is locked to the 1907nm laser frequency, and the frequency of the 1540nm is locked to the resonator, realizing double-resonance. With a periodically-poled stoichiometric lithium tantalate in the resonator, the sum-frequency at 852nm is efficiently generated. All 3 waves are in the same polarization (e-ray), allowing the effective use of Brewster-cut device, eliminating reflection loss for all wavelengths without any antireflection coatings. With 4.6W at 1907nm and 7.7W at 1540nm incident onto the resonator, 5.2W at 852nm was generated, representing the efficiency of greater than 40%. The experimental result indicates our current setup will be more efficient with higher input powers at 1907nm. With both fiber sources at 1540nm and 1907nm being scalable in output power, the output at 852nm is also scalable. By the forth harmonic of 852nm, 0.456 W CW 213nm was generated.
• Generation of broad spectral components from midwave infrared ultrashort pulse laser propagation through ZnSe and ZnS

  Werner, Kevin; Tripepi, Michael; Schweinsberg, Aaron; Hastings, Michael; Vanderhoef, Laura; Wolfe, Christopher; Ensley, Trenton; Wilmer, Brian; Kolesik, Miroslav; Moloney, Jerome; et al. (SPIE-INT SOC OPTICAL ENGINEERING, 2019-03-04)

  We investigate the nonlinear optical properties of ZnSe and ZnS using ultrashort (pulse duration approximately 200 fs) midwave infrared laser pulses between 3 and 4 mu m. Multiple harmonic generation in both materials was observed, as well as significant spectral modification of the fundamental pulse. Simulations using a nonlinear polarization model enhanced with ionization compared favorably with experimental data. Random quasi phase matching in the materials is the likely generator of the observed harmonics.
• Influence of microscopic many-body scattering on multi-wavelength VECSEL lasing

  Kilen, Isak R.; Hader, Jörg; Koch, Stephan W.; Moloney, Jerome V.; Univ Arizona, Dept Math; Univ Arizona, Coll Opt Sci (SPIE-INT SOC OPTICAL ENGINEERING, 2019-03-04)

  Non-equilibrium multi-wavelength operation of vertical external-cavity surface-emitting lasers (VECSELs) is investigated numerically using a coupled system of Maxwell semiconductor Bloch equations. The propagation of the electromagnetic field is modeled using Maxwell's equations, and the semiconductor Bloch equations simulate the optically active quantum wells. Microscopic many-body carrier-carrier and carrier-phonon scattering are treated at the level of second Born-Markov approximation, polarization dephasing with a characteristic rate, and carrier screening with the static Lindhard formula. At first, an initialization scheme is constructed to study multi-wavelength operation in a time-resolved VECSEL. Intracavity dual-wavelength THz stabilization is examined using longitudinal modes and an intracavity etalon. In the latter, anti-correlated noise is observed for THz generation and investigated.
• Safety and efficacy of ex vivo expanded CD34 stem cells in murine and primate models

  Zhang, Yu; Shen, Bin; Guan, Xin; Qin, Meng; Ren, Zhihua; Ma, Yupo; Dai, Wei; Ding, Xinxin; Jiang, Yongping; Univ Arizona, Coll Pharm, Dept Pharmacol & Toxicol (BMC, 2019-06-13)

  Background: Hematopoietic stem cell (HSC) transplantation has been widely applied to the treatment of malignant blood diseases. However, limited number of functional HSCs hinders successful transplantation. The purpose of our current study is to develop a new and cost-efficient medium formulation that could greatly enhance the expansion of HSCs while retaining their long-term repopulation and hematopoietic properties for effective clinical transplantation. Methods: Enriched human CD34(+) cells and mobilized nonhuman primate peripheral blood CD34(+) cells were expanded with a new, cost-efficient expansion medium formulation, named hematopoietic expansion medium (HEM), consisting of various cytokines and nutritional supplements. The long-term repopulation potential and hematologic-lineage differentiation ability of expanded human cells were studied in the non-obese diabetic/severe combined immunodeficiency mouse model. Furthermore, the efficacy and safety studies were performed by autologous transplantation of expanded primate cells in the nonhuman primate model. Results: HEM could effectively expand human CD34(+) cells by up to 129 fold within 9 days. Expanded HSCs retained long-term repopulation potential and hematologic-lineage differentiation ability, as indicated by (1) maintenance (over unexpanded HSCs) of immunophenotypes of CD38(-)CD90(+)CD45RA(-)CD49f(+) in CD34(+) cells after expansion; (2) significant presence of multiple human hematopoietic lineages in mouse peripheral blood and bone marrow following primary transplantation; (3) enrichment (over unexpanded HSCs) in SCID-repopulating cell frequency measured by limiting dilution analysis; and (4) preservation of both myeloid and lymphoid potential among human leukocytes from mouse bone marrow in week 24 after primary transplantation or secondary transplantation. Moreover, the results of autologous transplantation in nonhuman primates demonstrated that HEM-expanded CD34(+) cells could enhance hematological recovery after myelo-suppression. All primates transplanted with the expanded autologous CD34(+) cells survived for over 18 months without any noticeable abnormalities. Conclusions: Together, these findings demonstrate promising potential for the utility of HEM to improve expansion of HSCs for clinical application.
• Mental health in elite athletes: International Olympic Committee consensus statement (2019)

  Reardon, Claudia L; Hainline, Brian; Aron, Cindy Miller; Baron, David; Baum, Antonia L; Bindra, Abhinav; Budgett, Richard; Campriani, Niccolo; Castaldelli-Maia, João Mauricio; Currie, Alan; et al. (BMJ PUBLISHING GROUP, 2019-06)

  Mental health symptoms and disorders are common among elite athletes, may have sport related manifestations within this population and impair performance. Mental health cannot be separated from physical health, as evidenced by mental health symptoms and disorders increasing the risk of physical injury and delaying subsequent recovery. There are no evidence or consensus based guidelines for diagnosis and management of mental health symptoms and disorders in elite athletes. Diagnosis must differentiate character traits particular to elite athletes from psychosocial maladaptations. Management strategies should address all contributors to mental health symptoms and consider biopsychosocial factors relevant to athletes to maximise benefit and minimise harm. Management must involve both treatment of affected individual athletes and optimising environments in which all elite athletes train and compete. To advance a more standardised, evidence based approach to mental health symptoms and disorders in elite athletes, an International Olympic Committee Consensus Work Group critically evaluated the current state of science and provided recommendations.
• On the Meaning of Fermi’s paradox

  DeVito, Carl L.; Univ Arizona, Dept Math (Elsevier BV, 2019-02)

  One of the few pieces of hard data that we have in connection with SETI is embodied in Fermi’s famous question, often stated simply as: Where is everyone? Our purpose here is to show that this “paradox” is telling us something about the number of communicating societies in the galaxy and the rate at which such societies “grow”. Our analysis is based on a mathematical technique that is of fundamental importance in a number of areas of physics.
• VECSEL-based frequency comb in the MIR

  Rockmore, Robert; Laurain, Alexandre; Moloney, Jerome V.; Jones, R. Jason; Univ Arizona, Coll Opt Sci (SPIE-INT SOC OPTICAL ENGINEERING, 2019-03-04)

  The mid-infrared (MIR) region above 3 microns is of great interest for spectroscopic applications. Because it is difficult to produce modelocked laser sources that emit natively in this region, difference frequency generation (DFG) is a popular method to produce mid-IR output using more traditional laser oscillators. Previous examples include fiber based DFG sources and OPOs, which are typically limited to repetition rates on the order of tens to hundreds of MHz. VECSELs allow access to higher repetition rates, while the use of highly nonlinear waveguides enables the requisite spectral broadening despite the lower pulse energy. In this work we present a VECSEL-based frequency comb that uses DFG to produce output in the 3-4 micron range. This system is based on a modelocked VECSEL emitting at a 1030 nm wavelength with a 1.6 GHz repetition rate. A Yb fiber amplification system is used to increase the power to over lOW and compress the pulses to sub-90 fs. Coherent spectral broadening out to 1560 nm is achieved with a nonlinear waveguide. By combining the 1030 nm and 1560 nm beams in a PPLN DFG crystal, 290 mW of mid IR output between 3.0 and 3.5 microns is produced. Since the DFG light is produced by two wavelengths from the same oscillator, the carrier envelope offset frequency is cancelled, producing an offset free comb requiring stabilization of only a single degree of freedom. We characterize this VECSEL based frequency comb and discuss the advantages it provides for spectroscopic applications.
• Information and Communication in Organizations

  Deimen, Inga; Szalay, Dezso; Univ Arizona, Eller Coll Management (American Economic Association, 2019-05)

  We study a constrained information design problem in an organization. A designer chooses the information structure. A sender with preferences different from the decision-maker observes and processes the information before he communicates with the decision-maker. Information shapes conflicts within the organization: the optimal information structure essentially eliminates conflicts and serves as a substitute to the allocation of decision-making authority in the organization.
• Modeling and experimental investigation of transverse mode dynamics in VECSEL

  Laurain, Alexandre; Hader, Jörg; Moloney, Jerome V.; Univ Arizona, Coll Opt Sci (SPIE-INT SOC OPTICAL ENGINEERING, 2019-03-04)

  We present a new method to simulate the formation of transverse modes in VECSELs. An expression for the gain as a function of carrier density and temperature is derived from a simulation of the structure reflectivity, while the field propagation in the cavity is computed with the Huygens-Fresnel integral. A rate equation model is employed to calculate the field and gain dynamics over numerous round-trips. The optimal mode size for single mode operation for a given pump shape is calculated and compared to experimental results. The effect of pump geometry, thermal lensing and structure design will be discussed.
• Evaluating narrative operative reports for endoscopic sinus surgery in a residency training program

  Wheeler, Shannon C; Miglani, Amar; Deep, Nicholas L; Girardo, Marlene E; Hinni, Michael; Lal, Devyani; Univ Arizona, Coll Med Phoenix (WILEY, 2019-06)

  Objective: The narrative operative report (NR) bears testimony to critical elements of patient care. Residents' NRs also provide insights into their comprehension of the procedure. NR documentation is an informal element of surgical residency training but data regarding quality of such training are scant. We aim to evaluate the NR within a residency training program. Methods: The quality of NRs for endoscopic sinus surgery (ESS) was evaluated through a retrospective analysis of 90 NRs for ESS. Thirty-four elements that the attending surgeon regards as "critical" variables, or quality indicators (QIs), that should be documented, were studied to evaluate quality. A "performance metric (PM)," defined as the average percent of QIs dictated/total word count, was determined. Subgroup analysis by the level of training was additionally performed. Results: Surgical indications, procedural steps, and immediate postoperative findings were accurately documented in 71%, 84%, and 82% of patients, respectively. The attending surgeon had the highest proportion of included key elements (89% +/- 6.2%) followed by junior residents (87% +/- 5.7%) and then senior residents (80% +/- 14%) (P = .008). The attending surgeon also demonstrated the highest PM, followed by senior and then junior residents (P < .0001). Conclusions: The quality of NRs was found to be high overall, but not "perfect" for either the attending or trainee surgeon. The PM among residents was expectedly lower than the attending surgeon. We propose that a synoptic reporting system that ensures inclusion of key elements may be helpful in training residents (and attendings) in creating comprehensive and efficient NRs. Level of Evidence: 3
• Lower Back Injuries in National Collegiate Athletic Association Football Players: A 5-Season Epidemiological Study

  Makovicka, Justin L; Patel, Karan A; Deckey, David G; Hassebrock, Jeffrey D; Chung, Andrew S; Tummala, Sailesh V; Hydrick, Thomas C; Gulbrandsen, Matthew; Hartigan, David E; Chhabra, Anikar; et al. (SAGE PUBLICATIONS INC, 2019-06-18)

  Background: Low back injuries are common in collegiate football players and can frequently lead to persistent pain, reinjuries, and time lost from participation. Purpose: To describe the epidemiology of back injuries in National Collegiate Athletic Association (NCAA) football players during the 2009/2010 through 2013/2014 academic years utilizing the NCAA Injury Surveillance Program (ISP) database. Study Design: Descriptive epidemiology study. Methods: A convenience sample of NCAA varsity football teams was utilized to determine the rates and patterns of back injuries as well as to generate national injury estimates. The rates and distribution of back injuries were identified within the context of mechanism of injury, injury chronicity, and time lost from sport. Injury rates were calculated as the number of injuries divided by the total number of athlete-exposures (AEs). Incidence rate ratios were calculated to compare the rates of injury between season, event type, mechanism of injury, injury chronicity, and time lost from sport. Results: Nationally, there were 267 low back injuries reported in the database. These were used to estimate 7076 back injuries over the 5-year period, approximately 82% of which were new injuries. The injuries occurred at a rate of 2.70 per 10,000 AEs. Overall, injuries were 3.12 times more likely to occur in competitions than in practices. Athletes were 4.67 times more likely to sustain a back injury during the preseason compared with the postseason but were 1.41 times more likely to sustain a low back injury during the preseason compared with the regular season. Both contact and noncontact were reported equally as the mechanism of injury (37.8% and 38.3%, respectively), and unspecified low back pain was the most common injury (64.2%). Only 1.6% of patients required surgery for their injury, and the majority of athletes (59.6%) returned to play within 24 hours. Conclusion: There was a relatively high rate of lumbar back injuries at the collegiate level (2.70/10,000 AEs), the majority of which were new injuries. About 18% of reported injuries were reinjuries. Although very few required surgery, a careful examination and work-up should be conducted to evaluate each injury. Regimented physical therapy and reconditioning programs are recommended to avert reinjuries.
• Interplay between intermittency and dissipation in collisionless plasma turbulence

  Mallet, Alfred; Klein, Kristopher G.; Chandran, Benjamin D. G.; Grošelj, Daniel; Hoppock, Ian W.; Bowen, Trevor A.; Salem, Chadi S.; Bale, Stuart D.; Univ Arizona, Lunar & Planetary Lab (CAMBRIDGE UNIV PRESS, 2019-06-14)

  We study the damping of collisionless Alfvenic turbulence in a strongly magnetised plasma by two mechanisms: stochastic heating (whose efficiency depends on the local turbulence amplitude delta z(lambda)) and linear Landau damping (whose efficiency is independent of delta z(lambda)), describing in detail how they affect and are affected by intermittency. The overall efficiency of linear Landau damping is not affected by intermittency in critically balanced turbulence, while stochastic heating is much more efficient in the presence of intermittent turbulence. Moreover, stochastic heating leads to a drop in the scale-dependent kurtosis over a narrow range of scales around the ion gyroscale.
• Clustering Regression Wavelet Analysis for Lossless Compression of Hyperspectral Imagery

  Ahanonu, Eze; Marcellin, Michael; Bilgin, Ali; Univ Arizona, Dept Elect & Comp Engn; Univ Arizona, Dept Biomed Engn (IEEE, 2019)

  Recently, Regression Wavelet Analysis (RWA) was proposed as a method for lossless compression of hyperspectral images. In RWA, a linear regression is performed after a spectral wavelet transform to generate predictors which estimate the detail coefficients from approximation coefficients at each scale of the spectral wavelet transform. In this work, we propose Clustering Regression Wavelet Analysis (RWA-C), an extension of the original ‘Restricted’ RWA model which may be used to improve compression performance while maintaining component scalability. We demonstrate that clustering may be used to group pixels with similar spectral profiles, these clusters may then be more efficiently processed to improve RWA prediction performance while only requiring a modest increase side-information.
• Strong Preferential Ion Heating is Limited to within the Solar Alfvén Surface

  Kasper, Justin C.; Klein, Kristopher G.; Univ Arizona, Lunar & Planetary Lab (IOP PUBLISHING LTD, 2019-06-01)

  The decay of the solar wind helium-to-hydrogen temperature ratio due to Coulomb thermalization can be used to measure how far from the Sun strong preferential ion heating occurs. Previous work has shown that a zone of preferential ion heating, resulting in mass-proportional temperatures, extends about 20-40 R-circle dot from the Sun on average. Here we look at the motion of the outer boundary of this zone with time and compare it to other physically meaningful distances. We report that the boundary moves in lockstep with the Alfven point over the solar cycle, contracting and expanding with solar activity with a correlation coefficient of better than 0.95 and with an rms difference of 4.23 R-circle dot. Strong preferential ion heating is apparently predominately active below the Alfven surface. To definitively identify the underlying preferential heating mechanisms, it will be necessary to make in situ measurements of the local plasma conditions below the Alfven surface. We predict that the Parker Solar Probe (PSP) will be the first spacecraft to directly observe this heating in action, but only a couple of years after launch as activity increases, the zone expands, and PSP's perihelion drops.
• The Western Bulge of 162173 Ryugu Formed as a Result of a Rotationally Driven Deformation Process

  Hirabayashi, Masatoshi; Tatsumi, Eri; Miyamoto, Hideaki; Komatsu, Goro; Sugita, Seiji; Watanabe, Sei-ichiro; Scheeres, Daniel J.; Barnouin, Olivier S.; Michel, Patrick; Honda, Chikatoshi; et al. (IOP PUBLISHING LTD, 2019-03-26)

  162173 Ryugu, the target of Hayabusa2, has a round shape with an equatorial ridge, which is known as a spinning top shape. A strong centrifugal force is a likely contributor to Ryugu's top-shaped features. Observations by the Optical Navigation Camera on board Hayabusa2 show a unique longitudinal variation in geomorphology; the western side of this asteroid, later called the western bulge, has a smooth surface and a sharp equatorial ridge, compared to the other side. Here, we propose a structural deformation process that generated the western bulge. Applying the mission-derived shape model, we employ a finite element model technique to analyze the locations that experience structural failure within the present shape. Assuming that materials are uniformly distributed, our model shows the longitudinal variation in structurally failed regions when the spin period is shorter than similar to 3.75 hr. Ryugu is structurally intact in the subsurface region of the western bulge while other regions are sensitive to structural failure. We infer that this variation is indicative of the deformation process that occurred in the past, and the western bulge is more relaxed structurally than the other region. Our analysis also shows that this deformation process might occur at a spin period between similar to 3.5 and similar to 3.0 hr, providing the cohesive strength ranging between similar to 4 and similar to 10 Pa.
• The Unexpected Spectrum of the Innermost Ejecta of the Red Hypergiant VY CMa

  Humphreys, Roberta M.; Ziurys, L. M.; Bernal, J. J.; Gordon, Michael S.; Helton, L. Andrew; Ishibashi, Kazunori; Jones, Terry J.; Richards, A. M. S.; Vlemmings, Wouter; Univ Arizona, Dept Astron; et al. (IOP PUBLISHING LTD, 2019-04-03)

  Hubble Space Telescope/STIS spectra of the small clumps and filaments closest to the central star in VY CMa reveal that the very strong K I emission and TiO and VO molecular emission, long thought to form in a dusty circumstellar shell, actually originate in a few small clumps hundreds of au from the star. The K I lines are 10-20 times stronger in these nearest ejecta than on the star. The observations also confirm VO as a circumstellar molecule. In this Letter we discuss the spectra of the features, their motions and ages, and the identification of the molecular emission. The strength of the atomic and molecular features in the small clumps present an astrophysical problem for the excitation process. We show that the clumps must have a nearly clear line of sight to the star's radiation.
• The Proper-motion Field along the Magellanic Bridge: A New Probe of the LMC–SMC Interaction

  Zivick, Paul; Kallivayalil, Nitya; Besla, Gurtina; Sohn, Sangmo Tony; van der Marel, Roeland P.; Del Pino, Andrés; Linden, Sean T.; Fritz, Tobias K.; Anderson, J.; Univ Arizona, Steward Observ (IOP PUBLISHING LTD, 2019-03-26)

  We present the first detailed kinematic analysis of the proper motions (PMs) of stars in the Magellanic Bridge, from both the Gaia Data Release 2 catalog and from Hubble Space Telescope (HST) Advanced Camera for Surveys data. For the Gaia data, we identify and select two populations of stars in the Bridge region, young main-sequence (MS) and red giant stars. The spatial locations of the stars are compared against the known H I gas structure, finding a correlation between the MS stars and the H I gas. In the HST fields our signal comes mainly from an older MS and turnoff population, and the PM baselines range between similar to 4 and 13 yr. The PMs of these different populations are found to be consistent with each other, as well as across the two telescopes. When the absolute motion of the Small Magellanic Cloud is subtracted out, the residual Bridge motions display a general pattern of pointing away from the Small Magellanic Cloud toward the Large Magellanic Cloud. We compare in detail the kinematics of the stellar samples against numerical simulations of the interactions between the Small and Large Magellanic Clouds, and find general agreement between the kinematics of the observed populations and a simulation in which the Clouds have undergone a recent direct collision.

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