Nearby Groups Research Articles

Gas and stellar dynamics in Stephan’s Quintet

In nearby compact galaxy groups we can study the complex processes of galaxy interactions at high resolution and obtain a window into a time in the history of the Universe when the galaxies were closely spaced and the intergalactic medium was awash with gas. Stephan’s Quintet is a nearby compact galaxy group and a perfect laboratory for studying the process of galaxy evolution through galaxy harassment and interaction. By analysing the kinematics of Stephan’s Quintet we aim to provide an increased understanding of the group, the history of the interactions, their cause and effect, and the details regarding the physical processes occurring as galaxies interact. Ionised gas and stellar kinematics have been studied using data from the Large Binocular Telescope, while the molecular gas kinematics have been obtained from CO observations using the IRAM 30m telescope. Large areas of the group have been mapped and analysed. We obtain a total ionised gas mass in the regions chosen for closer analysis of 20.1 ± 0.2 ⋅ 1010 M⊙ and a total H2 gas mass of 21 ± 2 ⋅ 109 M⊙ in the observed area (spectra integrated over the velocity range covering Stephan’s Quintet), while the star-forming clouds show an impressive complexity, with gas congregations at multiple velocities at many locations throughout the group. We map the large-scale nuclear wind in NGC7319 and its decoupled gas and stellar disk. With our high resolution data we can, for the first time, reveal the Seyfert 1 nature of NGC7319 and fit the narrow-line region and broad-line region of the Hα line. While the 12CO (1 − 0) map shows significant emission in the area in or near NGC7319, the bridge, and the star-forming ridge, the 12CO (2 − 1) emission shows a prevalence to the star-forming ridge, an area south of the NGC7318 pair, and shows an extension towards NGC7317 – connecting NGC7317 to the centre of the group, indicating a previous interaction. NGC7317 may also be a prime candidate for studies of the process of galaxy harassment. Furthermore, we connect the kinematical structures in Stephan’s Quintet to the history of the group and the ongoing interaction with NGC7318B. Through our extensive observations of Stephan’s Quintet we trace and present the kinematics and evolution of the complex processes and structures occurring in this nearby interactive group.

The unusually high dark matter concentration of the galaxy group NGC 1600

ABSTRACT We investigate the properties of the dark matter (DM) halo surrounding the nearby galaxy group NGC 1600. Through the use of deep (252 ks) Chandra observations and 64.3 ks of XMM–Newton observations, we construct surface brightness profiles in multiple energy bands in order to perform hydrostatic equilibrium analysis of the hot plasma within NGC 1600. Regardless of the DM model profile assumed, we measure a halo concentration (c200) that is an extreme, positive outlier of the ΛCDM c200–M200 relation. For a typical NFW DM profile, we measure c200 = 26.7 ± 1.4 and M200 = (2.0 ± 0.2) × 1013 M⊙; assuming a similar halo mass, the average concentration expected is c200 = 6 − 7 for the theoretical ΛCDM c–M relation. Such a high concentration is similar to that of well-known fossil groups MRK 1216 and NGC 6482. While NGC 1600 exhibits some properties of a fossil group, it fails to meet the X-ray luminosity threshold of LX > 5 × 1041 erg s−1. Whether or not it is considered a fossil group, the high concentration value makes it part of a select group of galaxy groups.

Low‐Coordinated CoNC on Oxygenated Graphene for Efficient Electrocatalytic H2O2 Production

AbstractElectrochemical H2O2 production through the 2‐electron oxygen reduction reaction (ORR) is a promising alternative to the energy‐intensive anthraquinone process. Herein, by simultaneously regulating the coordination number of the atomically dispersed cobalt sites and the nearby oxygen functional groups via a one‐step microwave thermal shock, a highly selective and active CoNC electrocatalyst for H2O2 electrosynthesis that exhibits a high H2O2 selectivity (91.3%), outstanding mass activity (44.4 A g−1 at 0.65 V), and large kinetic current density (11.3 mA cm−2 at 0.65 V) in 0.1 m KOH is obtained. In strong contrast to the typical CoN4 moieties for the 4‐electron ORR, the present CoNC catalyst possesses a low‐coordinated CoN2 configuration and abundant epoxide groups, which work in synergy for promoting the 2‐electron ORR, as demonstrated by a series of control experiments and theoretical simulations. This study may provide an effective avenue to modulating the composition and structure of electrocatalysts at the atomic scale, leading to the development of new electrocatalysts with unprecedented reactivity.

The Resolved Sunyaev–Zel’dovich Profiles of Nearby Galaxy Groups

Abstract Many of the baryons in galaxy groups are thought to have been driven out to large distances (≳R 500) by feedback, but there are few constraining observations of this extended gas. This work presents the resolved Sunyaev–Zel’dovich (SZ) profiles for a stacked sample of 10 nearby galaxy groups within the mass range log 10 ( M 500 [ M ⊙ ] ) = 13.6 – 13.9 . We measured the SZ profiles using the publicly available y-map from the Planck Collaboration as well as our own y-maps constructed from more recent versions of Planck data. The y-map extracted from the latest data release yielded a significant SZ detection out to 3 R 500. In addition, the stacked profile from these data was consistent with simulations that included AGN feedback. Our best-fit model using the latest Planck data suggested a baryon fraction ≈5.6% within R 500. This is significantly lower than the cosmic value of ≈16%, supporting the idea that baryons have been driven to large radii by AGN feedback. Lastly, we discovered a significant (∼3σ) “bump” feature near ∼2 R 500 that is most likely the signature of internal accretion shocks.

AT 2019qyl in NGC 300: Internal Collisions in the Early Outflow from a Very Fast Nova in a Symbiotic Binary* †

Abstract Nova eruptions, thermonuclear explosions on the surfaces of white dwarfs (WDs), are now recognized to be among the most common shock-powered astrophysical transients. We present the early discovery and rapid ultraviolet (UV), optical, and infrared (IR) temporal development of AT 2019qyl, a recent nova in the nearby Sculptor Group galaxy NGC 300. The light curve shows a rapid rise lasting ≲1 day, reaching a peak absolute magnitude of M V = −9.2 mag and a very fast decline, fading by 2 mag over 3.5 days. A steep dropoff in the light curves after 71 days and the rapid decline timescale suggest a low-mass ejection from a massive WD with M WD ≳ 1.2 M ⊙. We present an unprecedented view of the early spectroscopic evolution of such an event. Three spectra prior to the peak reveal a complex, multicomponent outflow giving rise to internal collisions and shocks in the ejecta of an He/N-class nova. We identify a coincident IR-variable counterpart in the extensive preeruption coverage of the transient location and infer the presence of a symbiotic progenitor system with an O-rich asymptotic-giant-branch donor star, as well as evidence for an earlier UV-bright outburst in 2014. We suggest that AT 2019qyl is analogous to the subset of Galactic recurrent novae with red-giant companions such as RS Oph and other embedded nova systems like V407 Cyg. Our observations provide new evidence that internal shocks between multiple, distinct outflow components likely contribute to the generation of the shock-powered emission from such systems.

Hidden Historical Habitat-Linked Population Divergence and Contemporary Gene Flow of a Deep-Sea Patellogastropod Limpet

Hydrothermal vents and hydrocarbon seeps in the deep ocean are rare oases fueled by chemosynthesis. Biological communities inhabiting these ecosystems are often distributed in widely separated habitats, raising intriguing questions on how these organisms achieve connectivity and whether habitat types facilitate intraspecific divergence. The deep-sea patellogastropod limpet Bathyacmaea nipponica that colonizes both vents and seeps across ∼2,400 km in the Northwest Pacific is a feasible model to answer these questions. We analyzed 123 individuals from four vents and three seeps using a comprehensive method incorporating population genomics and physical ocean modeling. Genome survey sequencing and genotyping-by-sequencing resulted in 9,838 single-nucleotide polymorphisms for population genomic analyses. Genetic divergence and demographic analyses revealed four habitat-linked (i.e., three seep and one vent) genetic groups, with the vent genetic group established via the opportunistic invasion of a few limpet larvae from a nearby seep genetic group. TreeMix analysis uncovered three historical seep-to-vent migration events. ADMIXTURE and divMigrate analyses elucidated weak contemporary gene flow from a seep genetic group to the vent genetic group. Physical ocean modeling underlined the potential roles of seafloor topography and ocean currents in shaping the genetic connectivity, contemporary migration, and local hybridization of these deep-sea limpets. Our study highlighted the power of integrating genomic and oceanographic approaches in deciphering the demography and diversification of deep-sea organisms. Given the increasing anthropogenic activities (e.g., mining and gas hydrate extraction) affecting the deep ocean, our results have implications for the conservation of deep-sea biodiversity and establishment of marine protected areas.

Dissecting the Strong-lensing Galaxy Cluster MS 0440.5+0204. II. New Optical Spectroscopic Observations in a Wider Area and Cluster Dynamical State

Abstract We present an optical study of the strong-lensing galaxy cluster MS 0440.5+0204 at z = 0.19593, based on CFHT/MegaCam g′, r′ photometry and GMOS/Gemini and CFHT/MOS/SIS spectroscopy in a broader area than previous works. We have determined new spectroscopic redshifts for the most prominent gravitational arcs surrounding the central galaxy in the cluster. The new redshifts and the information provided by the photometric catalog allow us to perform a detailed weak- and strong-lensing mass reconstruction of the cluster. The large number of member galaxies and the area covered by our observations allow us to estimate more accurately the velocity dispersion and mass of the cluster and to examine in detail the nature of the cluster and surrounding structures. The dynamical mass is in good agreement with the mass inferred from the lensing analysis and X-ray estimates. About 68% of the galaxies are located in the inner ≲0.86 h 70 − 1 Mpc region of the cluster. The galaxy redshift distribution in the inner region of the cluster shows a complex structure with at least three substructures along the line of sight. Other substructures are also identified in the galaxy density map and in the weak-lensing mass map. The member galaxies in the northeast overdensity are distributed in a filament between the clusters MS 0440.5+0204 and ZwCL 0441.1+0211, suggesting that these two structures might be connected. MS 0440.5+0204 appears to be dynamically active, with a cluster core that is likely experiencing a merging process, and with other nearby groups at projected distances of ≲1 h 70 − 1 Mpc that could be being accreted by the cluster.

A high occurrence of nuclear star clusters in faint Coma galaxies, and the roles of mass and environment

ABSTRACT We use deep high-resolution Hubble Space Telescope (HST)/Advanced Camera for Surveys (ACS) imaging of two fields in the core of the Coma Cluster to investigate the occurrence of nuclear star clusters (NSCs) in quiescent dwarf galaxies as faint as MI = −10 mag. We employ a hierarchical Bayesian logistic regression framework to model the faint end of the nucleation fraction (fn) as a function of both galaxy luminosity and environment. We find that fn is remarkably high in Coma: at MI ≈ −13 mag half of the cluster dwarfs still host prominent NSCs. Comparison with dwarf systems in nearby clusters and groups shows that, within the uncertainties, the rate at which the probability of nucleation varies with galaxy luminosity is nearly universal. On the other hand, the fraction of nucleated galaxies at fixed luminosity does exhibit an environmental dependence. More massive environments feature higher nucleation fractions and fainter values of the half-nucleation luminosity, which roughly scales with host halo virial mass as $L_{I,f_{\mathrm{ n}50}} \propto \mathcal {M}_{200}^{-0.2}$. Our results reinforce the role of galaxy luminosity/mass as a major driver of the efficiency of NSC formation and also indicate a clear secondary dependence on the environment, hence paving the way to more refined theoretical models.

A Number of nearby Moving Groups May Be Fragments of Dissolving Open Clusters

Abstract We propose that 14 co-moving groups of stars uncovered by Kounkel & Covey may be related to known nearby moving groups and bridge those and nearby open clusters with similar ages and space velocities. This indicates that known nearby moving groups may be spatially much more extended than previously thought, and some of them might be parts of tidal tails around the cores of known open clusters, reminiscent of those recently found around the Hyades and a handful of other nearby clusters. For example, we find that both the nearby Carina and Columba associations may be linked to Theia 208 from Kounkel & Covey and together form parts of a large tidal tail around the Platais 8 open cluster. The AB Doradus moving group and Theia 301 may form a trailing tidal tail behind the Pleiades open cluster, with hints of a possible leading tidal tail in Theia 369. Similarly, we find that IC 2391 and its tidal tails identified by Meingast et al. may be extended by the nearby Argus association and are possibly further extended by Theia 115. The nearby Octans and Octans-Near associations, as well as Theia 94 and 95, may form a large tidal tail leading the poorly studied Platais 5 open cluster candidate. While a preliminary analysis of Gaia color–magnitude sequences hint that these structures are plausibly related, more observational evidence is still required to corroborate their consistent ages and space velocities. These observations may change our current understanding of nearby moving groups and the different pathways through which they can form. While some moving groups may have formed loosely in extended star formation events with rich spatial structure, others may in fact correspond to the tidal tails of nearby open clusters.

Do cultural districts spur urban revitalization: Evidence from Louisiana

In the past two decades, cultural districts have become a popular instrument to encourage urban revitalization. Districts typically receive support such as grants, investments, or tax credits and, in this sense, are a variation of place-based economic development policies. In this paper, we examine the effect of state-designated cultural districts on transaction-level residential real estate prices in the metropolitan region of Lafayette, Louisiana. Using a difference-in-differences identification strategy that adjusts for staggered treatment timing, we find that residential properties within districts sell for 7% more after certification relative to nearby comparison group properties. The results are robust to extreme sale prices, alternative samples, and recently developed randomization inference techniques. Our results add to the literature showing that place-based policies can spur economic revitalization if they are carefully targeted toward amenities that residents value.

Optical counterparts of ULXs in two dwarf galaxies: NGC 4861 and NGC 4449

ABSTRACT We present the results of a search for optical candidates of ultraluminous X-ray sources (ULXs) in two dwarf galaxies, NGC 4861 and NGC 4449, using Hubble Space Telescope (HST) archival data. With precise astrometry, we confirm that NGC 4861 X1 is associated with an H ii complex and we conclude that NGC 4861 X2 resides in a young star group of mass 400 ± 80 M⊙. We also find that NGC 4449 X7 is associated with three optical candidates within an error radius of 0.2 arcsec at the 90 ${{\ \rm per\ cent}}$ confidence level. Absolute magnitudes (Mv) of these candidates are determined as −5.0 and −4.1. The age and mass values for the three candidates are estimated as 40–50 Myr and ∼8 M⊙, respectively, using stellar evolutionary tracks. The locations of optical candidates suggest a possible association with a nearby group of stars. In addition, we analysed previously unused archival data of XMM–Newton, Chandra, and Swift where the sources were detected. Although the X-ray spectral data do not allow us to discriminate between physical models, long-term data at hand are consistent with the sources being in luminous hard states.

The conspecific avoidance strategies of adult female-calf humpback whales

Abstract During migration, humpback whale (Megaptera novaeangliae) adult females and their calves use acoustic calling to help maintain contact. The signals produced by these pairs, however, may unintentionally attract nearby breeding males, which can result in interactions that have negative physical and physiological effects on the calf. Therefore, maternal females must choose the vocal and/or behavioral strategy that most effectively balances intra-pair communication with male avoidance. Here, we analyzed differences in adult female-calf vocal activity and movement behavior according to the presence of, and distance to, singing whales and other groups likely to contain males. The results of this study found that these pairs make only minimal changes to their vocal behavior in response to nearby males, suggesting that they have instead evolved calls that are naturally difficult to detect (i.e., produced at significantly lower rates and acoustic levels than other whale groups, resulting in a restricted active space). In addition, they maintain spatial separation from nearby groups by moving to shallower, inshore waters, increasing their proportion of time spent near the surface, and favoring a direct migratory course. This combination of cryptic strategies balances avoidance of unwanted conspecific interaction with the necessity of continued contact between maternal female humpback whales and their calves.

Rhodium Single‐Atom Catalysts on Titania for Reverse Water Gas Shift Reaction Explored by First Principles Mechanistic Analysis and Compared to Nanoclusters

AbstractThe thermocatalytic reduction of CO2 by H2 often proceeds via two competing reaction mechanisms – the reverse water gas shift reaction (rWGSR, CO2+H2⇌CO+H2O) and methanation (CO2+4H2⇌CH4+2H2O). Atomically dispersed Rh1 catalysts on TiO2 show high selectivity toward the rWGSR compared with larger Rh nanoclusters, but the origin of this size‐dependent selectivity has not been fully explained. Here we report density functional theory (DFT) calculations and microkinetic simulations that clarify the Rh1 active sites and rWGSR pathway on anatase TiO2(101), as well as the high rWGSR selectivity of Rh1 compared with supported Rhx (x=2–8 atoms) nanoclusters. DFT‐computed formation energies, vibrational frequency analysis, and microkinetic modeling suggest three plausible active sites: Rh1 on titania (Rh1/TiO2(101)), Rh1 with a nearby hydroxyl group (Rh1OH/TiO2(101)), and Rh1 near an oxygen vacancy at a three‐fold coordinated site (Rh1 near O3cvac). Predicted turnover frequencies and apparent activation barriers for Rh1 indicate a faster reaction involving CO2 dissociation assisted by a support oxygen vacancy via Rh1 near O3cvac, as well as slower reactions involving Rh1OH/TiO2(101) or Rh1/TiO2(101) through a COOH intermediate. These Rh1 sites are selective toward CO rather than CH4 because of the weak adsorption of CO, large barrier for C−O bond dissociation, and the lack of nearby metal sites for H2 dissociation, in contrast to Rhx nanoclusters, including Rh2 dimers.

Dystonia in children

Dystonia is a motor disorder characterized by sustained muscle contractions producing twisting, repetitive, and patterned movements or abnormal postures. Dystonia is among the most commonly observed motor disorders in clinical practice in children. Unlike dystonia in adults that typically remains focal or spreads only to nearby muscle groups, childhood dystonia often generalizes. Classification of dystonia has direct implications for narrowing down the differential diagnosis, choosing the diagnostic work-up, predicting the prognosis, and choosing treatment options. The etiology of pediatric dystonia is quite heterogeneous. The etiological classification distinguishes primary dystonia with no identifiable exogenous cause or evidence of neurodegeneration and secondary syndromes. Dystonia can be secondary to any pathological process that affects the basal ganglia. The treatment options of childhood dystonia include several oral pharmaceutical agents, botulinum toxin injections, and deep brain stimulation therapy. Botulinum toxin treatment is the first choice treatment for most types of focal dystonia. In children it is less used because dystonic forms are mainly generalized, but it might also be helpful in controlling the most disabling symptoms of segmental or generalized dystonia. Long-term electrical stimulation of the globus pallidum internum is now established as an effective treatment for various types of movement disorders including dystonia. However, this method has not yet found its application in Russia due to the difficulty of implementation and the lack of patient routing. To increase the effectiveness of complex therapy of dystonia in children, new pathogenetic methods of treatment of common forms of primary dystonia and dystonic syndromes in the structure of degenerative diseases of the central nervous system are needed, as well as the development of optimal algorithms for the diagnosis and treatment of these patients.

Ultrahigh Hydrogen Uptake in an Interpenetrated Zn 4 O-Based Metal–Organic Framework

As a highly promising candidate for hydrogen storage, crucial to vehicles powered by fuel cells, metal–organic frameworks (MOFs) have attracted the attention of chemists in recent decades. H2 uptak...

The Hawaii Infrared Parallax Program. V. New T-dwarf Members and Candidate Members of Nearby Young Moving Groups

Abstract We present a search for new planetary-mass members of nearby young moving groups (YMGs) using astrometry for 694 T and Y dwarfs, including 447 objects with parallaxes, mostly produced by recent large parallax programs from UKIRT and Spitzer. Using the BANYAN Σ and LACEwING algorithms, we identify 30 new candidate YMG members, with spectral types of T0–T9 and distances of 10–43 pc. Some candidates have unusually red colors and/or faint absolute magnitudes compared to field dwarfs with similar spectral types, providing supporting evidence for their youth, including four early-T dwarfs. We establish one of these, the variable T1.5 dwarf 2MASS J21392676+0220226, as a new planetary-mass member ( M Jup) of the Carina-Near group (200 ± 50 Myr) based on its full six-dimensional kinematics, including a new parallax measurement from CFHT. The high-amplitude variability of this object is suggestive of a young age, given the coexistence of variability and youth seen in previously known YMG T dwarfs. Our four latest-type (T8–T9) YMG candidates, WISE J031624.35+430709.1, ULAS J130217.21+130851.2, WISEPC J225540.74–311841.8, and WISE J233226.49–432510.6, if confirmed, will be the first free-floating planets (≈2–6 M Jup) whose ages and luminosities are compatible with both hot-start and cold-start evolutionary models, and thus overlap with the properties of the directly imaged planet 51 Eri b. Several of our early/mid-T candidates have peculiar near-infrared spectra, indicative of heterogenous photospheres or unresolved binarity. Radial velocity measurements needed for final membership assessment for most of our candidates await upcoming 20–30 m class telescopes. In addition, we compile all 15 known T7–Y1 benchmarks and derive a homogeneous set of their effective temperatures, surface gravities, radii, and masses.

Improved distance estimation with node selection localization and particle swarm optimization for obstacle-aware wireless sensor networks

Sensor-node localization is among the greatest concerns in the field of wireless sensor networks. Range-based localization techniques generally outperform range-free techniques, particularly in terms of their accuracy. Range-based localization techniques depend on a popular distance estimation method, which requires conversion from a received signal strength indicator to distances. In a case where sensor nodes are in an area with obstacles, direct communication between certain pairs of nodes is impracticable; the data must be relayed over multihop (or detour) routes. One promising approach to improve the accuracy of sensor-node distance estimation is to segment (or cluster) sensor nodes to a restricted set of anchor nodes whose estimated distances to unknown nodes are not on a detour route. Some certain topologies can decrease the localization precision; e.g., when each group’s node density is low, large empty spaces (or gaps) might affect the localization precision. If an unknown node is close to another group, using only anchor nodes within its own group could reduce the estimation precision. When anchor nodes within the same group lie along a straight line, the approximation of the unknown-node location could be misinterpreted. Thus, to enhance the localization precision, we make use of anchor nodes in other nearby groups to estimate the locations of unknown nodes. We also apply particle swarm optimization (PSO) with an improved fitness function to estimate the locations of unknown nodes. The localization performance is intensively evaluated in obstacle-prone scenarios. The simulation results show that the proposed scheme achieves higher accuracy than recent state-of-the-art PSO-based methods.

Probing within the Bondi radius of the ultramassive black hole in NGC 1600

ABSTRACT We present deep (250 ks) Chandra observations of the nearby galaxy group NGC 1600, which has at its centre an ultramassive black hole (17 ± 1.5 billion M⊙). The exceptionally large mass of the black hole coupled with its low redshift makes it one of only a handful of black holes for which spatially resolved temperature and density profiles can be obtained within the Bondi radius with the high spatial resolution of Chandra. We analysed the hot gas properties within the Bondi accretion radius R$_{\mbox{B}}=1.2\!-\!1.7\:\mathrm{ arcsec}= 0.38\!-\!0.54 \,{\mbox{kpc}}$. Within a ∼3 kpc radius, we find two temperature components with statistical significance. Both the single-temperature and two-temperature models show only a very slight rise in temperature towards the centre, and are consistent with being flat. This is in contrast with the expectation from Bondi accretion for a temperature profile which increases towards the centre, and appears to indicate that the dynamics of the gas are not being determined by the central black hole. The density profile follows a relatively shallow ρ ∝ r−[0.61 ± 0.13] relationship within the Bondi radius, which suggests that the true accretion rate on to the black hole may be lower than the classical Bondi accretion rate.

Application of clustering algorithm to wide stellar pairs for unsupervised search of parts of disrupting clusters

Abstract We introduce the application of the clustering algorithm to the preliminary compiled list of probable wide pairs of co-moving stars. The main aim of such development is a possibility of unsupervised blind search of coeval loose stellar structures over significant regions in space. Using Gaia EDR3 data, we investigated the application of the method to nearby region hosting recently discovered loose structures – tidal tails of Coma Ber star cluster and a nearby stellar group named Group X. We compare the results of straightforward clustering of stellar data with results of using our method with varying parameters. We then compare the results of our method to the recent results of the two groups of authors who independently discovered the discussed structures. We find parameters allowing the method to find the full scope of distributed stellar groups without preliminary knowledge of their characteristics. It decreases the risk of false positive clustering and improves the ability to discover loose stellar groups, in comparison with the application of clustering algorithm to the individual stars. Further we obtain a refined dataset of probable members of both stellar groups and independently obtain their ages (700 ± 70 Myr and 450 ± 100 Myr) and space velocities ((U,V,W) = (8.63 ± 0.13, 6.63 ± 0.20, 6.65 ± 0.95) km/s for Coma Ber star cluster, and (U,V,W) = (7.70 ± 0.12, 3.27 ± 0.45, 5.69 ± 0.80) km/s for Group X). Our results are in very good agreement with those of previous investigators.

Autonomous Social Distancing in Urban Environments Using a Quadruped Robot

Corona Virus Disease 2019 (COVID-19) pandemic has become a global challenge faced by people all over the world. Social distancing has been proved to be an effective practice to reduce the spread of COVID-19. Against this backdrop, we propose that the surveillance robots can not only monitor but also promote social distancing. Robots can be flexibly deployed and they can take precautionary actions to remind people of practicing social distancing. In this paper, we introduce a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">fully autonomous</i> surveillance robot based on a quadruped platform that can promote social distancing in complex urban environments. Specifically, to achieve autonomy, we mount multiple cameras and a three dimensional light detection and ranging sensor (3D LiDAR) on the legged robot. The robot then uses an onboard real-time social distancing detection system to track nearby pedestrian groups. Next, the robot uses a crowd-aware navigation algorithm to move freely in highly dynamic scenarios. The robot finally uses a crowd-aware routing algorithm to effectively promote social distancing by using human-friendly verbal cues to send suggestions to over-crowded pedestrians. We demonstrate and validate that our robot can be operated autonomously by conducting several experiments in various urban scenarios.