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Jeremy Webb

Assistant Professor
Department of Astronomy and Astrophysics
University of Toronto
jeremy.webb@utoronto.ca

Research

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Globular Clusters

Globular clusters are spherical collections of between 106 and 107 stars that are found in all types of galaxies. The Milky Way contains over 150 globular clusters, while some giant elliptical galaxies have been found to contain over 10,000. My research focuses on studying the dynamical evolution of globular clusters from birth to present day. More specifically, I am interested in the relationship between a globular cluster and the gravitational field of its host galaxy. What role does the host galaxy play in a cluster's evolution? Is the cluster's location and orbit within a galaxy a contributing factor? (Image Credit: apod.nasa.gov)

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Stellar Streams

As stars escape from a globular cluster, due to internal and external mechanisms, tidal tails begin to form. Once a cluster has fully dissolved, a long thin stellar stream of escaped of stars will continue along on the cluster's intitial orbit. Due to their length and the minimal amount of interaction between stars along a stream, streams are ideal for studying the gravitational field of their host galaxy. I am interested in how the properties of stellar streams depend on the initial host cluster and its orbit within the Milky Way. Understanding the details of how stellar streams form and evolve will allow for them to be used to trace out the distribution of dark matter in our own galaxy's halo and even search for evidence of dark matter substructure. (Image Credit: Carlberg 2018)

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Dark Matter Sub-Halos

The Cold Dark Matter framework predicts that galaxies consist of a large number of dark matter sub-halos. While the most massive sub-halos can be observed as satellite galaxies, lower mass sub-halos will likely have no luminous component to observe. Therefore astronomers are constantly searching for ways of indirectly determining that sub-halos exists in order to validate different cosmological theories and the nature of dark matter itself. I am interested in how sub-halos themselves evolve and interact with things like stellar streams and globular clusters. More specifically, do these interactions leave fingerprints of the properties of dark matter sub-halos? (Image Credit: Diemand et al. 2008)

Click here to view a recent talk I gave at the Canadian Institute for Theoretical Astrophysics

Click here to view a recent talk I gave for the Dunlap Institute's "Cosmos From Your Couch" Talk Series

Publications

Listed below is a complete list of my publications, as of November 2020. Click here to view my publications on NASA/ADS.:

Webb, J.J., Bovy, J. 2020, MNRAS, 499, 116

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High-Resolution Simulations of Dark Matter Subhalo Disruption in a Milky Way-like Tidal Field

Garrow, T., Webb, J.J., Bovy, J. 2020, MNRAS, 499, 804

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The effects of dwarf galaxies on the orbital evolution of galactic globular clusters

Cadelano, M., Dalessando, E., Webb, J.J., Vesperini, E., Lattanzio, D., Beccari, G. 2020, MNRAS, 499, 239

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Radial variation of the stellar mass functions in the globular clusters M15 and M30: clues of a non-standard IMF?

Price-Jones, N., Bovy, J., Webb, J.J., Prieto, C.A., Beaton, R., Brownstein, J.R., Cohen, R.E., Cunha, K., Donor, J., Frinchaboy, P.M., García-Hernández, D.A., Lane, R.R., Majewski, S.R., Nidever, D.L. 2020, MNRAS, 496, 5101

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Strong chemical tagging with APOGEE: 21 candidate star clusters that have dissolved across the Milky Way disc

Webb, J.J., Price-Jones, N., Bovy, J., Hunt, J.A.S, Portegies-Zwart, S., Mackereth, J.T., Leung, H.W. 2020, MNRAS, 494, 2268

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Searching for solar siblings in APOGEE and Gaia DR2 with N-body simulations

Starkman, N., Bovy, J., Webb, J.J. 2020, MNRAS, 493, 4978

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An extended Pal 5 stream in Gaia DR2

Hénault-Brunet, V., Bahramian, A., Côté, P., Eadie, G., Haggard, D., Harris, W.E., Heinke, C., Lamb, M., Pudritz, R., Roediger, J., Sills, A., Venn, K., Webb, J.J., Woods, T.E. 2019, Canadian Long Range Plan for Astronomy and Astrophysics White Papers, LRP2020

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Star Clusters Near and Far

Leaman, R., Ruiz-Lara, T., Cole, A.A., Beasley, M.A., Boecker, A., Fahrion, K., Bianchini, P., Falcon-Barroso, J., Webb, J.J., Sills, A., Mastrobuono-Battisti, A., Neumayer, N., 2019, MNRAS, 492, 5102

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There and Back Again: Globular cluster ejection, infall and the host dark matter halo of the Pegasus dwarf galaxy

Piatti, A.E, Webb, J.J., Carlberg, R.G. 2019, MNRAS, 489, 4367

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Characteristic radii of the Milky Way Globular Clusters

Webb, J.J., Bovy, J., Carlberg, R.G., Gieles, M. 2019, MNRAS, 488, 5748

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Modelling the Effects of Dark Matter Substructure on Globular Cluster Evolution with the Tidal Approximation

Webb, J.J., Leigh, N.W.C., Serrano, R., Bellovary, J., Ford, K.E.S., McKernan, B., Spera, M., Trani, A.A. 2019, MNRAS, 488, 3055

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The evolution of kicked stellar-mass black holes in star cluster environments - II. Rotating star clusters

Jindal, A., Webb, J.J. & Bovy,J. 2019, MNRAS, 487, 3693 arXiv:1903.11070

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The orbital anisotropy profiles of nearby globular clusters from Gaia Data Release 2

Webb, J.J., Reina-Campos, M. & Kruijssen, J.M.D. 2019, MNRAS, 486, 5879

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A systematic analysis of star cluster disruption by tidal shocks -- I. Controlled N-body simulations and a new theoretical model

Webb, J.J. & Bovy, J. 2019, MNRAS, 485, 5929

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Searching for the GD-1 Stream Progenitor in Gaia DR2 with Direct N-body Simulations

Kaderali, S., Hunt, J.A.S., Webb, J.J., Price-Jones, N., Carlberg, R. 2019, MNRAS Letters, 484, 114

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Rediscovering the Tidal Tails of NGC 288 with Gaia DR2

Hong, J., Patel, S.S., Vesperini, E., Webb, J.J.; Dalessandro, E. 2019, MNRAS, 483, 2592

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Spatial mixing of binary stars in multiple-population globular clusters

Fare, A., Webb, J.J. & Sills, A. 2018, MNRAS, 481, 3027

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The effect of stellar helium abundance on dynamics of multiple populations in globular clusters

Webb, J.J. & Vesperini, E. 2018, MNRAS, 479, 3708

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The Structural and Kinematic Evolution of Central Star Clusters in Dwarf Galaxies and Their Dependence on Dark Matter Halo Profiles

Vesperini, E., Hong, J., Webb, J.J., D'Antona, F., D'Ercole, A. 2018, MNRAS, 476, 2731

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Evolution of the stellar mass function in multiple-population globular clusters

Dalessandro, E., Cadelano, M., Vesperini, E., Salaris, M., Ferraro, F. R., Lanzoni, B., Raso, S., Hong, J., Webb, J.J., Zocchi, A. 2018, ApJ, 859, 15

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The Peculiar Radial Distribution of Multiple Populations in the Massive Globular Cluster M80s

Bianchini, P., Webb, J.J., Sills, A., Vesperini, E. 2018, MNRAS Letters, 475, 96

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Kinematic fingerprint of core-collapsed globular clusters

Webb, J.J., Leigh, N.W.C., Singh, A., Ford, K.E.S., McKernan, B., Bellovary, J. 2018, MNRAS, 474, 3835

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The evolution of kicked stellar-mass black holes in star cluster environments

Webb, J.J., Vesperini, E., Dalessandro, E., Beccari, G., Ferraro, F.R., Lanzoni, B. 2017, MNRAS, 471, 3845

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Modelling the observed stellar mass function and its radial variation in galactic globular clusters

Webb, J.J., Vesperini, E., Patel, S.S. 2017, MNRAS, 468, 92

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The early evolution of star clusters in compressive and extensive tidal fields

Webb, J.J. & Vesperini, E. 2017, MNRAS, 464, 1977

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On the link between energy equipartition and radial variation in the stellar mass function of star clusters

Webb, J.J. & Vesperini, E. 2016, MNRAS, 463, 2383

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Radial variation in the stellar mass functions of star clusters

Webb, J.J., Sills, A., Harris, W.E., Gómez, M., Paolillo, M., Woodley, K.A., Puzia, T.H. 2016, MNRAS, 460, 2129

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Globular cluster scale sizes in giant galaxies: orbital anisotropy and tidally underfilling clusters in M87, NGC 1399 and NGC 5128

Miholics, M., Webb, J.J., Sills, A. 2016, MNRAS, 456, 240

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The dynamical evolution of accreted star clusters in the Milky Way

Miholics, M., Webb, J.J., Sills, A. 2015, MNRAS, 454, 2166

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The dynamics of multiple populations in the globular cluster NGC 6362

Webb, J.J. & Leigh, N.W.C. 2015, MNRAS, 453, 3278

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Back to the future: estimating initial globular cluster masses from their present-day stellar mass functions

Leigh, N.W.C., Giersz, M., Marks, M., Webb, J.J., Hypki, A., Heinke, C.O., Kroupa, P., Sills, A. 2015, MNRAS, 446, 226

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The state of globular clusters at birth - II. Primordial binaries

Miholics, M., Webb, J.J., Sills, A. 2014, MNRAS, 445, 2872

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The size of star clusters accreted by the Milky Way

Webb, J.J., Sills, A., Harris, W.E., Hurley, J.R. 2014, MNRAS, 445, 1048

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The effects of orbital inclination on the scale size and evolution of tidally filling star clusters

Webb, J.J., Leigh, N.W.C., Sills, A., Harris, W.E., Hurley, J.R. 2014, MNRAS, 442, 1569

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The effect of orbital eccentricity on the dynamical evolution of star clusters

Leigh, N.W.C., Giersz, M., Webb, J.J., Hypki, A., De Marchi, G., Kroupa, P., Sills, A. 2013, MNRAS, 436, 3399

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The state of globular clusters at birth: emergence from the gas-embedded phase

Webb, J.J., Sills, A., Harris, W.E. 2013, ApJ, 779, 94

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Globular Cluster Scale Sizes in Giant Galaxies: The Case of M87 and the Role of Orbital Anisotropy and Tidal Filling

Webb, J.J., Harris, W.E., Sills, A., Hurley, J.R. 2013, ApJ, 764, 124

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The influence of orbital eccentricity on tidal radii of star clusters

Webb, J.J., Harris, W.E., Sills, A. 2012, ApJL, 759, 39

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The Size Difference between Red and Blue Globular Clusters is not due to Projection Effects

Webb, J.J., Sills, A., Harris, W.E. 2012, ApJ, 746, 93

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The Observational and Theoretical Tidal Radii of Globular Clusters in M87

Clustertools

clustertools is a Python package with tools for analysing star cluster simulations, although it can be applied to many N-body systems. The package is built around the StarCluster class, for which all functions are able to use or act on. clustertools can be used for unit and coordinate transformations, the calculation of key structural and kinematic parameters, analysis of the cluster’s orbit and tidal tails (with the help of galpy), and measuring common cluster properties like its mass function, density profile, and velocity dispersion profile (among others). The package contains methods for loading data from commonly used N-body codes (NBODY6, GYRFALCON, AMUSE) and generic snapshots. With the help of limepy , it is also possible to generate cluster datasets from a distribution function for immediate analysis. clustertools is developed on Github. Please go to https://github.com/webbjj/clustertools to report issues or contribute to the code.

Globular Cluster VR

For the July 2014 issue of Astronomy Magazine, Professor William E. Harris and I were asked to submit an article describing what life would be like if Earth was orbiting a star that lived within a globular cluster. For the article, we took dynamical simulations of globular clusters and placed our theoretical planet at various locations within the model. Not only were we able to determine what life would be like for astronomers on such a planet, but we used our simulations to generate images of what the night sky would look like for anyone living inside a globular cluster. Place your cursor over the images below to learn more:

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In the core of a globular cluster, the night sky would contain 130,000 stars visible to the naked eye and the brightest stars would be 100 times brighter than Venus. At night, the sky would be twenty times brighter than during a full moon.

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Near the half-light radius of the cluster, the brightest object in the sky would be the main body of the cluster. However, far from the cluster center one would be able to faintly see distant globular clusters as well as the bulge and disk of the host galaxy.

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In the outer regions of a globular cluster, you would still get a spectacular view when its center was in the night sky while still being able to perform astronomy at locations that faced away from the cluster at night.

More recently, with the help of UITS Research Technologies at Indiana University, we developed a 3D visualization of what the nighy sky would look like if you lived on such a planet. The visualization can be accessed here or by clicking on the screenshot below. The VR environment can be used with a mobile device aswell.

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