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If so, you may be looking for the "Gadget/Arepo Halo Comparison Project".

Astronomical Observing

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"The most beautiful thing we can experience is the mysterious. It is the source of all true art and all science. He to whom this emotion is a stranger, who can no longer pause to wonder and stand rapt in awe, is as good as dead: his eyes are closed."

-Albert Einstein


My name is Dylan Nelson. I am currently a postdoctoral fellow at the Max Planck Institute for Astrophysics (MPA) in Munich, Germany. Two years ago I completed my PhD in astrophysics at the Center for Astronomy (CfA) at Harvard University, working with Lars Hernquist. My interests include theoretical modeling of cosmological gas accretion, the circumgalactic medium, the baryon cycle, and energetic feedback processes, particularly in their connections to the formation and evolution of galaxies and galactic structure over cosmic time.

I study these problems through numerical simulations run with Arepo, a finite volume hydrodynamics code based on a moving unstructured mesh. I am a principal contributor to the IllustrisTNG Project, a next generation of cosmological magnetohydrodynamical simluations of galaxy and large-scale structure formation, and I am Co-PI of the TNG50 simulation. I also worked on the Illustris Simulation, the predecessor of TNG.

Herein you will find a further description of my research interests, more technical technical projects, some visualization and WebGL experiments, my CV, and contact information.

I am currently organizing the MPA Galaxy Group Meeting.




My main research projects to date fall into four main categories:

  1. The circumgalactic medium -- structure and origin, the impact of feedback, and observational signatures.
  2. Presenting the IllustrisTNG simulation project -- the next generation of magnetohydrodynamical cosmological simulations.
  3. Paper series: Zooming in on accretion -- idealized studies of hot halo gas, virial shocks, filaments, inflows and outflows.
  4. Tracing Cosmological gas accretion -- how do galaxies get their gas? Cold vs. hot mode accretion and the baryon cycle.

Below you can find some highlights and the relevant papers from each topic.

1. The circumgalactic medium

The abundance, distribution, and physical nature of highly ionized oxygen OVI, OVII, and OVIII in IllustrisTNG

[arXiv] We explore the abundance, spatial distribution, and physical properties of the OVI, OVII, and OVIII ions of oxygen in circumgalactic and intergalactic media (the CGM, IGM, and WHIM). We use the TNG100 and TNG300 large volume cosmological magneto-hydrodynamical simulations. Modeling the ionization states of simulated oxygen, we find good agreement with observations of the low-redshift OVI column density distribution function (CDDF), and present its evolution for all three ions from z=0 to z=4. Producing mock quasar absorption line spectral surveys, we show that the IllustrisTNG simulations are fully consistent with constraints on the OVI content of the CGM from COS-Halos and other low redshift observations, producing columns as high as observed.

We measure the total amount of mass and average column densities of each ion using hundreds of thousands of simulated galaxies spanning 1011 < Mhalo/Msun < 1015 corresponding to 109 < M*/Msun < 1012 in stellar mass. The stacked radial profiles of OVI around halos of different masses are computed in 3D number density as well as 2D projected column, decomposing into the 1-halo and 2-halo terms, the latter of which begins to dominate for Milky Way mass halos in the WHIM just beyond the virial radius.

Relating halo OVI to properties of the central galaxy, we find a correlation between the (g-r) color of a galaxy and the total amount of OVI in its CGM. In comparison to the COS-Halos finding, this leads to a dichotomy of columns around star-forming versus passive galaxies at fixed stellar (or halo) mass. We demonstrate that this correlation is a direct result of blackhole feedback associated with quenching, which also produces additional trends with other galaxy properties, and represents a causal consequence of galactic-scale baryonic feedback impacting the physical state of the circumgalactic medium.

2. The IllustrisTNG Simulation Project

First results from the IllustrisTNG simulations: the galaxy color bimodality

[arXiv] We introduce the first two simulations of the IllustrisTNG project, a next generation of cosmological magnetohydrodynamical simulations, focusing on the optical colors of galaxies. We explore TNG100, a rerun of the original Illustris box (~100 Mpc) and TNG300, which includes 2x25003 resolution elements in a volume twenty times larger (~300 Mpc); both are run using the new TNG model for galaxy formation.

Here we present first results on the galaxy color bimodality at low redshift. Accounting for the attenuation of stellar light by dust, we compare the simulated (g-r) colors of 109 < M*/Msun < 1012.5 galaxies to the observed distribution from the Sloan Digital Sky Survey (SDSS). We find a striking improvement with respect to the original Illustris simulation, as well as excellent quantitative agreement in comparison to the observations, with a sharp transition in median color from blue to red at a characteristic M* ~ 1010.5 Msun. Investigating the build-up of the color-mass plane and the formation of the red sequence, we demonstrate that the primary driver of galaxy color transition in the TNG model is supermassive blackhole feedback in its low-accretion state. Across the entire population we measure a median color transition timescale dt_green of ~1.6 Gyr, a value which drops for increasingly massive galaxies. We find signatures of the physical process of quenching: at fixed stellar mass, the color of a galaxy correlates with its SFR, age, metallicity, and gas fraction, as well as the magnetic properties of both its interstellar medium and extended gaseous halo. Finally, we measure the amount of stellar mass growth on the red sequence. Galaxies with M* > 1011 Msun which redden at z<1 accumulate on average ~25% of their final z=0 mass post-reddening; at the same time, ~18% of such massive galaxies acquire half or more of their final stellar mass while on the red sequence.

3. Zooming in on accretion

Zooming in on accretion - I. The structure of halo gas

[arXiv] [high-res PDF] We study the properties of gas in and around 10^12 Msun haloes at z=2 using a suite of high-resolution cosmological hydrodynamic 'zoom' simulations. We quantify the thermal and dynamical structure of these gaseous reservoirs in terms of their mean radial distributions and angular variability along different sightlines.

With each halo simulated at three levels of increasing resolution, the highest reaching a baryon mass resolution of ~10,000 solar masses, we study the interaction of filamentary inflow and the quasi-static hot halo atmosphere. We highlight the discrepancy between the spatial resolution available in the halo gas as opposed to within the galaxy itself. Stream morphologies become increasingly complex at higher resolution, with large coherent flows revealing density and temperature structure at progressively smaller scales.

Moreover, multiple gas components co-exist at the same radius within the halo, making radially averaged analyses misleading. This is particularly true where the hot, quasi-static, high entropy halo atmosphere interacts with cold, rapidly inflowing, low entropy accretion. We investigate the process of gas virialization and identify different regimes for the heating of gas as it accretes from the intergalactic medium. Haloes at this mass have a well-defined virial shock, associated with a sharp jump in temperature and entropy at ~1.25 rvir. The presence, radius, and radial width of this boundary feature, however, vary not only from halo to halo, but also as a function of angular direction, covering roughly ~85% of the 4π sphere.

Movies for each halo showing rotations at z=2 and time evolution. (Impatient? watch h0 on Vimeo)

4K resolution (3840x2160) versions: h0, h1, h2, h3, h4, h5, h6, h7. The following links are HD (1080p):

Zooming in on accretion - II. Cold Circumgalactic Gas Simulated with a super-Lagrangian Refinement Scheme

[paper soon] In this study we explore the complex multi-phase gas of the circumgalactic medium (CGM) surrounding galaxies. We propose and implement a novel, super-Lagrangian 'CGM zoom' scheme in the moving-mesh code AREPO, which focuses more resolution into the CGM and intentionally lowers resolution in the dense ISM.

We run three cosmological simulations of the same galaxy halo with increasingly comprehensive physical models, ultimately including a treatment of galactic-scale outflows as in the Illustris simulation. Our chosen halo has a total mass of ~1012 Msun at z~2, and we achieve a median gas mass (spatial) resolution of ~2,200 solar masses (~95 parsecs) in the CGM, six-hundred (fourteen) times better than in the Illustris-1 simulation, and higher than any cosmological simulation at this mass scale to date.

We explore the primary channel(s) of cold-phase CGM gas production in this regime. We find that winds substantially enhance the amount of cold gas in the halo, also evidenced in the covering fractions of HI and the equivalent widths of MgII out to large radii, in better agreement with observations than the case without galactic winds. Using a tracer particle analysis to follow the thermodynamic history of gas, we demonstrate how the majority of this cold, dense gas arises due to rapid cooling of the wind material interacting with the hot halo, and how large amounts of cold, ~104 K gas can be produced and persist in galactic halos with Tvir ~ 106 K.

4. Cosmological gas accretion

The impact of feedback on cosmological gas accretion

[arXiv] We investigate how the way galaxies acquire their gas across cosmic time in cosmological hydrodynamic simulations is modified by a comprehensive physical model for baryonic feedback processes. To do so, we compare two simulations -- with and without feedback -- both evolved with the moving mesh code AREPO. The feedback runs implement the full physics model of the Illustris simulation project, including star formation driven galactic winds and energetic feedback from supermassive blackholes. We explore:

  • (a) the accretion rate of material contributing to the net growth of galaxies and originating directly from the intergalactic medium, finding that feedback strongly suppresses the raw, as well as the net, inflow of this "smooth mode" gas at all redshifts, regardless of the temperature history of newly acquired gas.
  • (b) At the virial radius the temperature and radial flux of inflowing gas is largely unaffected at z=2. However, the spherical covering fraction of inflowing gas at 0.25 rvir decreases substantially, from more than 80% to less than 50%, while the rates of both inflow and outflow increase, indicative of recycling across this boundary.
  • (c) The fractional contribution of smooth accretion to the total accretion rate is lower in the simulation with feedback, by roughly a factor of two across all redshifts. Moreover, the smooth component of gas with a cold temperature history, is entirely suppressed in the feedback run at z<1.
  • (d) The amount of time taken by gas to cross from the virial radius to the galaxy -- the "halo transit time" -- increases in the presence of feedback by a factor of ~2-3, and is notably independent of halo mass. We discuss the implications of this invariance for models of hot halo gas cooling.

Moving mesh cosmology: Tracing cosmological gas accretion

[arXiv] We investigate the nature of gas accretion onto haloes and galaxies at z=2 using cosmological hydrodynamic simulations run with the moving mesh code AREPO. Implementing a Monte Carlo tracer particle scheme to determine the origin and thermodynamic history of accreting gas, we make quantitative comparisons to an otherwise identical simulation run with the smoothed particle hydrodynamics (SPH) code GADGET-3. Contrasting these two numerical approaches, we find significant physical differences in the thermodynamic history of accreted gas in massive haloes above 1010.5 solar masses. In agreement with previous work, GADGET simulations show a cold fraction near unity for galaxies forming in massive haloes, implying that only a small percentage of accreted gas heats to an appreciable fraction of the virial temperature during accretion. The same galaxies in AREPO show a much lower cold fraction, ‹20% in haloes of ~1011 solar masses. This results from a hot gas accretion rate which, at this same halo mass, is an order of magnitude larger than with GADGET, together with a cold accretion rate which is lower by a factor of two. These discrepancies increase for more massive systems, and we explain both trends in terms of numerical inaccuracies with the standard formulation of SPH.

We explore these differences by evaluating several ways of measuring a cold mode of accretion. As in previous work, the maximum past temperature of gas is compared to either a constant threshold value or some fraction of the virial temperature of each parent halo. We find that the relatively sharp transition from cold to hot mode dominated accretion at halo masses of ~1011, is a consequence of the constant temperature criterion, which can only separate virialised gas above some minimum halo mass.

Examining the spatial distribution of accreting gas, we find that the filamentary geometry of accreting gas near the virial radius is a common feature in massive haloes above 1011.5 solar masses. Gas filaments in GADGET, however, tend to remain collimated and flow coherently to small radii, or artificially fragment and form a large number of purely numerical "blobs". These same filamentary gas streams in AREPO show increased heating and disruption at 0.25-0.5 virial radii and contribute to the hot gas accretion rate in a manner distinct from classical cooling flows.

Spiral Structure (Masters Project)

This short video Compares two N-body (gravity only) simulations of a disk galaxy forming spiral arms due to the gravitational perturbations from massive "giant molecular clouds" (GMCs) which are represented as dots. The GMCs have a finite lifetime of 10Myr after which time they are reborn. On the left the formation is biased towards existing overdensities (i.e., GMCs are reborn within arms), while on the right the formation is unbiased (random). See D'Onghia et al. (2012) for more details.

Despite the several recognized methods for generating galactic spiral structure through interactions with external bodies, invoking a similar response in a secularly evolving galaxy is notably more difficult. Using high resolution (100 million particle) N-body simulations we model the evolution of an isolated stellar disk embedded in a Hernquist dark matter halo. We extend the work of D'Onghia et al. (2011) and consider the spiral structure arising from the gravitational influence of massive perturbers (e.g., giant molecular clouds) corotating in the stellar disk. Within a single rotation period we can develop a prominent, large-scale response in an initially smooth disk. This response represents the incoherent sum of small amplitude "wakes" generated by the swing amplifier acting locally in the neighborhood of each perturber. We systematically investigate this effect over a range of galaxy models.

By varying the critical wavelength with respect to axisymmetric instability, and requiring the disk to be everywhere stable by insuring Toomres Q>1, we explore the spectrum of spiral morphologies generated by the collective swing amplification mechanism. We make quantitative correlations between spiral structure and host galaxy and halo properties. We also predict the number of arms as a function of the strutural properties of the galaxy, and construct a classification catalog of arm morphologies to compare to spatially resolved observations of nearby galaxies. We measure radial variation of the spiral pattern speed using a modified Tremaine-Weinberg method, and find taht the pattern speed both decreases with radius and closely tracks the circular velocity of the disk, in excellent agreement with several recent observations. [Cefalu Poster] [ads]

The first four images link to movies showing the evolution of projected surface density for the LC-2, LC-4, LC-6, and LC-8 models (from left to right) from t=0 to 1 Gyr. The final movie is our barred galaxy control, which rotates with a constant pattern speed of ~45 km/s/kpc at 6 > 600 Myr. 150mb video file.

Undergraduate Research

MWA Correlator FoV Weighting (MIT Haystack)

Feasibility study of a correlator field of view weighting technique to address data volume and processing requirements of next generation radio telescope arrays (MWA and SKA), including mitigating the impact of excised frequency bands due to radio-frequency interference. [paper] [presentation]

Cloud Structure and the Origin of the IMF in rho-Ophiuchus (IfA Hawaii)

An in-depth, multi-wavelength comparison between the populations of dense, pre-stellar cores, and young, pre-main sequence stars in the rho-Ophiuchus region. We examined cloud structure and stellar content in order to probe the idea of a one-to-one mapping between core and stellar mass distributions.[paper] [presentation]

Weak Lensing Survey of Nearby SDSS Galaxy Clusters (Fermilab)

Investigation of galaxy clusters as probes of cosmology and the physics of structure formation. Cluster masses are derived through weak gravitational lensing measurements, using the Sloan Digital Sky Survey (SDSS) data. We presented weak lensing measurements of a sample of high-mass, low redshift (z < 0.1) clusters and found good agreement when compared with dynamical and X-ray estimates. [paper] [presentation]

LHC Tier2 Monitoring (INFN Roma)

Extension a monitoring/diagnostic system for the high-performance Tier2 grid designed for LHC data storage and analysis. Our implementation is a scalable, distributed system with a dynamic web-based interface provides status monitoring, diagnostic data visualization, and automatic fault notification and resolution. [presentation]


Some older writeups which occasionally get requested:

technical projects

Brief descriptions of some of the more technical projects I am working on.

IllustrisTNG Website and 3D Explorer

IllustrisTNG Website Logo

As part of the new TNG simulations, I have developed a public facing website for the project. Again, as a showcase for the collaboration, and in order to describe the motivation, its results and publications, visualizations and movies, and the future planned full data release. In addition to the now classic "Explorer2D", a new "Explorer3D" allows interactive nativation of the full subhalo/galaxy catalogs for all of the simulations using WebGL for browser-based 3D rendering. It is similarly coupled into the Data API, and users can select specific halos to then visualize additional information, e.g. the three dimensional distribution of satellites around massive clusters or merger trees through spacetime.

[See website for additional information.]

Illustris Simulation Website and Data Release

Illustris Website Logo

In support of the Illustris simulation project I developed the web presence for the collaboration, as a public showcase, its results, visuals/movies, and the full public data release. It acts as a platform for full download of the data, a comprehensive web-based API, and interactive data exploration and analysis. Current functionality allows dynamic queries over the data products (group catalogs) from the simulation, which are hosted in a relational database. This is coupled to a gigapixel-zoom interface in the Explorer, and a viewer for synthetic/mock stellar light images in the Observatory. Additional features tied into the API include data introspection and extraction from the full dataset (~300TB) hosted on a remote cluster, leveraging a Django-based backend and in-browser visualization of e.g. the merger trees of galaxies, using d3.js and three.js (WebGL). [Data Release Paper]

[See website for additional information.]

Arepo Visualization Toolkit (ArepoVTK)

ArepoVTK Logo

ArepoVTK is designed to produce high quality, presentation-ready visualizations of hydrodynamic simulations run with Arepo. It performs volumetric ray tracing in 3D through linearly reconstructed scalar and vector fields defined on an unstructured Voronoi tessellation of space. It also includes higher order spatial interpolation techniques such as natural neighbor interpolation. Time interpolation between discrete snapshots is currently under investigation. The framework supports multi-dimensional transfer functions to investigate fluid quantities, and explores novel visualization techniques for combining such a volume rendering approach with coincident point particle datasets (both luminous and dark).

[Website coming soon.]

Delaunay Triangulation using Parallel Incremental Extrapolation on GPUs

GPU Delaunay Logo

We develop a method for constructing the Delaunay triangulation of a point set which is massively parallel and designed for the many-core architecture of graphical processing units (GPUs). We implement a "parallel incremental extrapolation" algorithm on the plane (2D) under the general position assumption and measure promising speedup with respect to our naive serial implementation.

[See website for additional information.]

Monte Carlo Tracer Particles on a Moving Mesh

Tracers Logo

Tracing the origin and (thermo)dynamical history of accreting gas in Eulerian grid codes requires Lagrangian “tracer particles”. The typical approach, whereby massless particles are passively advected by interpolating the local fluid velocity field, is found to exhibit systematic bias in its ability to trace the mass flow. An alternative, probabilistic “Monte Carlo” method associates tracers with parent gas cells and exchanges them based on mass fluxes through each face. The Poisson noise inherent in this approach is minimized with the ALE moving mesh scheme but may be intractable for strictly Eulerian AMR codes.

[See Nelson et al. (2013) and Genel et al. (2013) for additional information.]

Front-Tracking Techniques for Multiphase Viscous Flow

Multiphase Flow Logo

We investigate the numerical simulation of multiphase fluid flow problems in two dimensions. In particular, we implement a front-tracking approach where a number of discrete points represent the free interface between two fluid phases. This boundary is advected in time, and at each timestep we calculate the surface curvature and include a model for surface tension effects. The Lagrangian surface is coupled to a fixed, Cartesian grid mapped to a square domain. The incompressible Navier Stokes equations are used to model continuum fluid flow of both phases, which have different densities and physical viscosities. We use the projection technique to split the second order time update into an advection-diffusion step following by a pressure correction step to enforce the divergence free constraint, while the spatial discretization uses the finite volume approach with staggered, rectangular control volumes for pressure and velocity. We investigate the numerical accuracy and convergence of the curvature calculation, area conservation of a high density drop surrounded by low density air, and the generation of spurious numerical velocities. The approach is then used to simulate the bounce of a water drop off of a rigid boundary. A proof of concept boundary merger algorithm is presented to handle the topological change of two colliding water drops, and extensions to more accurate numerical methods and physical models are discussed.

[See PDF Writeup and Matlab Code.]

[Also related: Continuous Galerkin Navier-Stokes in 2D Writeup.]


These experiments are almost all works in progress. Comments welcome!

Zooming in: the structure of halo gas

The distribution of gas (+ dark matter + stars) in and around a 10^12 Msun halo at z=2 simulated with a high-resolution cosmological hydrodynamic 'zoom'. This is h0L11, see the Research page for movies of the other seven halos. We show gas density, temperature, entropy, and radial velocity on the halo scale (circles are 1.0, 0.5, and 0.15 rvir). Also gas density and stellar density on small scales (circle is 0.15), and gas density and DM density on large scales (circles are 0.5 and 1.0 rvir). [1080p download] [4K download]

The Universe in Gas

"The Universe in Gas" shows a large volume of a simulated universe, 20 Mpc/h on a side, at redshift zero (the present time). Volume rendering highlights iso-surfaces of gas density, temperature, and their relation. Bright peaks in the density reveal galaxies, which are surrounded by their hot halo atmospheres, and interconnected with filaments arising from the large scale structure of the universe. This animation visualizes results from a numerical hydrodynamical simulation of a cosmological volume run with the moving mesh code AREPO. Included are the effects of gas (baryons), dark matter (not shown), as well as stars and black holes (also not shown) and their energetic feedback processes. Made with ArepoVTK. [1080p HD download]

Illustris: Hierarchical "Zoom" into a Galaxy

Continuous zoom-in from the scale of the entire simulation volume (~100 Mpc) to the scale of an individual spiral galaxy (~10 kpc), highlighting the diversity of structure across spatial scale, the large dynamic range of the simulation (10^6 per dimension), and the relationship between dark matter, gas, and stars. Made from images extracted from the interactive Illustris Explorer app. [1080p HD download]

Coffee Cup Problem (3D)

An impressive early animation made by V. Springel for the AREPO code was a 2D box within which a moving, curved solid boundary moves in a circular motion, meant to represent a spoon stirring a cup of coffee. We extend this to toy problem to 3D with an importer which creates an initial condition from any STL surface mesh - in this case, a spoon. Volume rendered with ArepoVTK, illuminating the spoon and highlighting density features due to mixing and the development of KH-like instabilities. [1080p HD download]

Gadget/Arepo Halo Comparison Project (v1)

We present a large catalog of several thousand halos extracted from cosmological simulations. Each is shown from three orthogonal views and with different rendering techniques - velocity field scatter plots, SPH kernel projection maps, and a large scale comparison with the dark matter field. A range of halo masses is rendered at each z=0,1,2,3 and individual halos are matched between the two simulations. [Visit Website]

Cosmological Gas Accretion Trajectories

This animation shows the trajectories of individual gas elements (on the left) and dark matter particles (on the right) which are bound to the same halo at redshift zero, evolving in time from redshift four.

Voronoi Meshing

When things go wrong...

ArepoVTK Development Gallery

A scrapbook of sorts of the ongoing development of ArepoVTK. Some extremely simple test meshes exploring different rendering techniques and approaches for transfer functions, as well as mesh visualization. Some galactic disks, face-on and edge-on. Some whole box and zoom-ins from cosmological hydro simulations.


These WebGL experiments are all works in progress and may frequently change. Any modern version of Firefox or Chrome should have no problem with these examples. Comments welcome!

Interactive Gadget/Arepo Halo Comparison Project (v2)

Gadget Arepo Halo Comparison WebGL App

The interactive Gadget/Arepo halo comparison project is a WebGL experiment that compares the gas distribution around two dark matter halos. Part of the Moving Mesh Cosmology simulations, one halo is taken from a cosmological simulation run with the well-known SPH code GADGET3. The other is a matched object run with the new moving mesh code AREPO. The experiment allows the user to manipulate the view, the fluid quantities which are displayed, and the rendering method employed. [Launch Now]

Tracing Cosmological Gas Accretion... Through Time

Galaxy Formation (Tracer Time Evolution) WebGL App

This second experiment visualizes the time evolution of tracer particles as they accrete into a galaxy at low redshift. Their trajectories relative to the evolving halo are animated, while the maximum temperature they obtain between each point is represented by a color mapping. Catmull-Rom splines interpolate between tracer positions at discrete snapshots. The evolving radius and virial temperature of the parent halo are represented by the changing virial sphere. In addition to viewing one instant at time, the radial mode also allows us to move all tracers to the same radius and investigate the time-collapsed geometry and thermal heating. [Launch Now]

Structure of 3D Voronoi Tesellations

Galaxy Formation (3D Voronoi Mesh) WebGL App

We implement the single-pass, shader-based wireframe rendering technique of Bærentzen et al. (2008) in WebGL (no geometry shaders), for the case of arbitrary polygonal faces. A Voronoi mesh is exported as its constituent faces, each having N vertices and requiring N+2 triangles in our approach. The edges and interiors of each face are simultaneously rendered by the fragment shader, using at each pixel the window space distance to the edge of the face. For large meshes, we can "illuminate" only a slab or a radial shell. The geometry can also be "exploded" by radially displacing each cell center. Note: The last two data sets (diego_disk and halo314) are extremely large (>2GB card required, e.g. GTX 670) and may make your browser unstable. With this technique we can render at most ~100k cells, corresponding to ~1mil faces and ~5mil triangles. Stereoscopic 3D support for side-by-side type systems (e.g. Oculus Rift, or see the CfA dual polarized projector setup). [Launch Now]

See also a rendered animation on Vimeo exploring the cosmological datasets and visualization options. [or download 800x800 or 1920x1080 versions]


Dylan Nelson :: Curriculum Vitae

Karl-Schwarzschild-Str. 1, 85741, Garching, Germany


  • Galaxy Formation and Evolution
  • Cosmological Gas Accretion, Circumgalactic Medium
  • Galactic Feedback, Baryon Cycle, Inflows and Outflows
  • Hydrodynamic/N-body Numerical Simulations, Methods, and Visualization Techniques


Max Planck Institute for Astrophysics (MPA), Munich, Germany

  • November 2015 - Present
  • Postdoctoral Fellow

Harvard University, Cambridge, MA

  • September 2009 - May 2015
  • Astrophysics PhD
  • Secondary Field: Computational Science and Engineering (CSE)

University of California Berkeley, Berkeley, CA - Graduated 2008

  • Triple Major: Physics, Astrophysics, and Mathematics
  • Member: National Society of Collegiate Scholars
  • Junior Member: American Astronomical Society
  • Honors Standing: September 2004 - May 2008

Montgomery High School, Santa Rosa, CA - Graduated 2004

  • International Baccalaureate (IB) Diploma
  • Member: California Scholarship Association


  • Harvard Institute for Applied Computational Science (IACS) Student Fellowship: 2014
  • National Science Foundation (NSF) Graduate Research Fellowship: 2009-2011 - Harvard
  • John P. Merrill Graduate Fellowship: 2009-2010 - Harvard
  • Pomerantz Physics Scholarship Recipient: 2007-08 - UC Berkeley
  • Dean's Honor List: Fall 2005 - UC Berkeley


  • Total: 47 refereed papers (of which 6 are first author, and 6 are second/third author).
  • 2257 total citations, 354 from first-author papers. [last updated: Dec 2017]


The abundance, distribution, and physical nature of highly ionized oxygen OVI, OVII, and OVIII in IllustrisTNG, MNRAS accepted. [ads] [arXiv]
Nelson, D., Kauffmann, G., Pillepich, A., Genel, S., Springel, V., Pakmor, R., Hernquist, L., Weinberger, R., Torrey, P., Vogelsberger, M., Marinacci, F. (2018)

First results from the IllustrisTNG simulations: the galaxy color bimodality, MNRAS. [ads] [arXiv]
Nelson, D., Pillepich, A., Springel, V., Weinberger, R., Hernquist, L., Pakmor, R., Genel, S., Torrey, P., Vogelsberger, M., Kauffmann, G., Marinacci, F., Naiman, J. (2017)

Zooming in on accretion - I. The structure of halo gas, MNRAS. [ads] [arXiv]
Nelson, D., Genel, S., Pillepich, A., Vogelsberger, M., Springel, V., Hernquist, L. (2016a)

The Illustris Simulation: Public Data Release, A&C. [ads] [arXiv]
Nelson, D., Pillepich, A., Genel, S., Vogelsberger, M., Springel, V., Torrey, P., Rodriguez-Gomez, V., Sijacki, D., Snyder, G., Griffen, B., Marinacci, F., Blecha, L., Sales, L., Xu, D., Hernquist, L. (2015b)

The impact of feedback on cosmological gas accretion, MNRAS. [ads] [arXiv]
Nelson, D., Genel, S., Vogelsberger, M., Sijacki, D., Springel, V., Torrey, P., Hernquist, L. (2015a).

Moving mesh cosmology: Tracing cosmological gas accretion, MNRAS. [ads] [arXiv]
Nelson, D., Vogelsberger, M., Genel, S., Sijacki, D., Keres, D., Springel, V., Hernquist, L. (2013).


The Size Evolution of Star-forming and Quenched Galaxies in the IllustrisTNG simulation, MNRAS. [ads] [arXiv]
Genel, S., Nelson, D., Pillepich, A., Springel, V., Pakmor, R., Weinberger, R., Hernquist, L., Naiman, J., Vogelsberger, M., Marinacci, F., Torrey, P. (2017)

First results from the IllustrisTNG simulations: the stellar mass content of groups and clusters of galaxies, MNRAS. [ads] [arXiv]
Pillepich, A., Nelson, D., Hernquist, L., Springel, V., Pakmor, R., Torrey, P., Weinberger, R., Genel, S., Naiman, J., Marinacci, F., Vogelsberger, M. (2017)

Simulating Galaxy Formation with the IllustrisTNG Model, MNRAS. [ads] [arXiv]
Pillepich, A., Springel, V., Nelson, D., Genel, S., Naiman, J., Pakmor, R., Hernquist, L., Torrey, P., Vogelsberger, M., Weinberger, R., Marinacci, F. (2017).

Clustering of MgII absorption line systems around massive galaxies: an important constraint on feedback processes in galaxy formation, MNRAS. [ads] [arXiv]
Kauffmann, G., Nelson, D., Menard, B., Zhu, G. (2017).

The morphology and kinematics of neutral hydrogen in the vicinity of z=0 galaxies with Milky Way masses -- a study with the Illustris simulation, MNRAS. [ads] [arXiv]
Kauffmann, G., Borthakur, S., Nelson, D. (2016).

Following the flow: tracer particles in astrophysical fluid simulations, MNRAS.
Genel, S., Vogelberger, M., Nelson, D., Sijacki, D., Springel, V., Hernquist, L. (2013). [ads] [arXiv]


The fraction of dark matter within galaxies from the IllustrisTNG simulations, MNRAS submitted. [ads] [arXiv]
Lovell, M., Pillepich, A., Genel, S., Nelson, D., Springel, V., Pakmor, R., Marinacci, F., Weinberger, R., Torrey, P., Vogelsberger, M., Hernquist, L. (2018)

Chemical pre-processing of cluster galaxies over the past 10 billion years in the IllustrisTNG simulations, MNRAS accepted. [ads] [arXiv]
Gupta, A., Yuan, T., Torrey, P., Vogelsberger, M., Martizzi, D., Tran, K., Kewley, L., Marinacci, F., Nelson, D., Pillepich, A., Hernquist, L., Genel, S., Springel, V. (2018)

Similar star formation rate and metallicity evolution timescales drive the fundamental metallicity relation, MNRAS accepted. [ads] [arXiv]
Torrey, P., Vogelsberger, M., Hernquist, L., McKinnon, R., Marinacci, F., Simcoe, R., Springel, V., Pillepich, A., Naiman, J., Pakmor, R., Weinberger, R., Nelson, D., Genel, S. (2018)

The evolution of the mass-metallicity relation in IllustrisTNG, MNRAS accepted. [ads] [arXiv]
Torrey, P., Vogelsberger, M., Marinacci, F., Pakmor, R., Springel, V., Nelson, D., Naiman, J., Pillepich, A., Genel, S., Weinberger, R., Hernquist, L. (2018)

A census of cool core galaxy clusters in IllustrisTNG, MNRAS submitted. [ads] [arXiv]
Barnes, D., Vogelsberger, M., Kannan, R., Marinacci, F., Weinberger, R., Springel, V., Torrey, P., Annalisa, P., Nelson, D., Pakmor, R., Naiman, J., Hernquist, L., McDonald, M. (2018)

Supermassive black holes and their feedback effects in the IllustrisTNG simulation, MNRAS. [ads] [arXiv]
Weinberger, R., Springel, S., Pakmor, R., Nelson, D., Genel, S., Pillepich, A., Vogelsberger, M., Marinacci, F., Naiman, J., Torrey, P., Hernquist, L. (2018)

Intra-cluster metal uniformity of galaxy clusters in IllustrisTNG, MNRAS. [ads] [arXiv]
Vogelsberger, M., Marinacci, F., Torrey, P., Genel, S., Springel, V., Weinberger, R., Pakmor, R., Hernquist, L., Naiman, J., Pillepich, A., Nelson, D. (2018)

First results from the IllustrisTNG simulations: matter and galaxy clustering, MNRAS. [ads] [arXiv]
Springel, V., Pakmor, R., Pillepich, A., Weinberger, R., Nelson, D., Hernquist, L., Vogelsberger, M., Genel, S., Torrey, P., Marinacci, F., Naiman, J. (2017)

First results from the IllustrisTNG simulations: radio haloes and magnetic fields, MNRAS submitted. [ads] [arXiv]
Marinacci, F., Vogelsberger, M., Pakmor, R., Torrey, P., Springel, V., Hernquist, L., Nelson, D., Weinberger, R., Pillepich, A., Naiman, J., Genel, S. (2017)

First results from the IllustrisTNG simulations: A tale of two elements - chemical evolution of magnesium and europium, MNRAS accepted. [ads] [arXiv]
Naiman, J., Pillepich, A., Springel, V., Ramirez-Ruiz, E., Torrey, P., Vogelsberger, M., Pakmor, R., Nelson, D., Marinacci, F., Hernquist, L., Weinberger, R., Genel, S. (2017)

Offsets between member galaxies and dark matter in clusters: a test with the Illustris simulation, MNRAS submitted. [ads] [arXiv]
Ng, K., Pillepich, A., Wittman, D., Dawson, W., Hernquist, L., Nelson, D. (2017).

Simulating galaxy formation with black hole driven thermal and kinetic feedback, MNRAS. [ads] [arXiv]
Weinberger, R., Springel, V., Hernquist, L., Pillepich, A., Marinacci, F., Pakmor, R., Nelson, D., Genel, S., Vogelsberger, M., Naiman, J., Torrey, P. (2017).

The inner structure of early-type galaxies in the Illustris simulation, MNRAS. [ads] [arXiv]
Xu, D., Springel, V., Sluse, D., Schneider, P., Sonnenfeld, A., Nelson, D., Vogelsberger, M., Hernquist, L. (2016).

The role of mergers and halo spin in shaping galaxy morphology, MNRAS. [ads] [arXiv]
Rodriguez-Gomez, V., Sales, L., V., Genel, S., Pillepich, A., Zjupa, J., Nelson, D., Griffen, B., Torrey, P., Snyder, G., Vogelsberger, M., Springel, V., Ma, C-P., Hernquist, L. (2016).

Shock finding on a moving-mesh: II. Hydrodynamics shocks in Illustris, MNRAS. [ads] [arXiv]
Schaal, K., Springel, V., Pakmor, R., Pfrommer, C., Nelson, D., Vogelsberger, M., Genel, S., Pillepich, A., Sijacki, D., Hernquist, L. (2016).

The stellar mass assembly of galaxies in the Illustris simulation, MNRAS. [ads] [arXiv]
Rodriguez-Gomez, V., Pillepich, A., Sales, L., V., Genel, S., Vogelsberger, M., Zhu, Q., Wellons, S., Nelson, D., Torrey, P., Springel, V., Ma, C-P., Hernquist, L. (2016).

On the Assembly of Dwarf Galaxies in Clusters and their Efficient Formation of Globular Clusters, MNRAS. [ads] [arXiv]
Mistani, P. A., Sales, L., Pillepich, A., Sanchez-Janssen, R., Vogelsberger, M., Nelson, D., Rodriguez-Gomez, V., Torrey, P., Hernquist, L. (2016).

Modeling Galactic Conformity with the Color-Halo Age Relation in the Illustris Simulation, MNRAS. [ads] [arXiv]
Bray, A., Pillepich, A., Sales, L., Zhu, E., Genel, S., Rodriguez-Gomez, V., Torrey, P., Nelson, D., Vogelsberger, M., Springel, V., Eisenstein, D., Hernquist, L. (2016).

Recoiling black holes: prospects for detection and implications of spin alignment, MNRAS. [ads] [arXiv]
Blecha, L., Sijacki, D., Kelley, L. Z., Torrey, P., Vogelsberger, M., Nelson, D., Springel, V., Snyder, G., Hernquist, L. (2016).

Lens galaxies in the Illustris simulation: power-law models and the bias of the Hubble constant from time-delays, MNRAS. [ads] [arXiv]
Xu, D., Sluse, D., Schneider, P., Springel, V., Vogelsberger, M., Nelson, D., Hernquist, L. (2016).

The diverse evolutionary paths of simulated high-z massive, compact galaxies to z = 0, MNRAS. [ads] [arXiv]
Wellons, S., Torrey, P., Ma, C-P., Rodriguez-Gomez, V., Pillepich, A., Nelson, D., Genel, S., Vogelsberger, M., Hernquist, L. (2016).

An analysis of the evolving comoving number density of galaxies in hydrodynamical simulations, MNRAS. [ads] [arXiv]
Torrey, P., Wellons, S., Machado, F., Griffen, B., Nelson, D., Rodriguez-Gomez, V., McKinnon, R., Pillepich, A., Ma, C-P., Vogelsberger, M., Springel, V., Hernquist, L. (2015).

Hydrogen Reionization in the Illustris Universe, MNRAS. [ads] [arXiv]
Bauer, A., Springel, V., Vogelsberger, M., Genel, S., Torrey, P., Sijacki, D., Nelson, D., Hernquist, L. (2015).

Galaxy Morphology and Star Formation in the Illustris Simulation at z=0, MNRAS. [ads] [arXiv]
Snyder, G., Torrey, P., Lotz, J., Genel, S., McBride, C., Vogelsberger, M., Pillepich, A., Nelson, D., Sales, L., Sijacki, D., Hernquist, L., Springel, V. (2015).

The merger rate of galaxies in the Illustris simulation, MNRAS. [ads] [arXiv]
Rodriguez-Gomez, V., Genel, S., Vogelsberger, M., Sijacki, D., Pillepich, A., Nelson, D., Torrey, P., Springel, V., Ma, C-P., Hernquist, L. (2015).

Formation of Massive, Compact Galaxies in the Illustris Simulation, MNRAS. [ads] [arXiv]
Wellons, S., Torrey, P., Ma, C-P., Hernquist, L., Vogelsberger, M., Kriek, M., van Dokkum, P., Nelson, E., Genel, S., Springel, V., Sijacki, D., Xu, D., Snyder, G., Nelson, D., Sales, L., Pillepich, A., Rodriguez-Gomez, V.

The Illustris simulation: Evolving population of black holes across cosmic time, MNRAS. [ads] [arXiv]
Sijacki, D., Vogelsberger, M., Genel, S., Springel, V., Torrey, P., Snyder, G., Nelson, D., Hernquist, L. (2014).

Star-forming galaxies and the star formation main sequence in the Illustris simulation, MNRAS.
Sparre, M., Hayward, C.C., Springel, V., Vogelsberger, M., Genel, S., Torrey, P., Nelson, D., Sijacki, D., Hernquist, L. (2015). [ads] [arXiv]

The colors of satellite galaxies in the Illustris Simulation, MNRAS Letters.
Sales, L., Vogelsberger, M., Genel, S., Torrey, P., Nelson, D., Rodriguez-Gomez, V., Wang, W., Pillepich, A., Sijacki, D., Springel, V., Hernquist, L. (2014). [ads] [arXiv]

Synthetic galaxy images and spectra from the Illustris simulation, MNRAS.
Torrey, P., Snyder, G., Vogelsberger, M., Hayward, C. C., Genel, S., Sijacki, D., Springel, V., Hernquist, L., Nelson, D., Kriek, M., Pillepich, A., Sales, L., McBride, C. (2014). [ads] [arXiv]

Halo Mass and Assembly History Exposed in the Faint Outskirts: the Stellar and Dark Matter Haloes of Illustris Galaxies, MNRAS.
Pillepich, A., Vogelsberger, M., Deason, A., Rodriguez-Gomez, V., Genel, S., Sales, L., Nelson, D., Torrey, P., Marinacci, F, Springel, V., Sijacki, D., Hernquist, L. (2014). [ads] [arXiv]

The Illustris Simulation: the evolution of galaxy populations across cosmic time, MNRAS.
Genel, S., Vogelsberger, M., Springel, V., Sijacki, S., Nelson, D., Snyder, G., Rodriguez-Gomez, V., Torrey, P., Hernquist, L. (2014). [ads] [arXiv]

Introducing the Illustris Project: Simulating the coevolution of dark and visible matter in the Universe, MNRAS.
Vogelsberger, M., Genel, S., Springel, V., Torrey, P., Sijacki, S., Xu, D., Snyder, G., Nelson, D., Hernquist, L. (2014). [ads] [arXiv]

Properties of galaxies reproduced by a hydrodynamic simulation, NATURE.
Vogelsberger, M., Genel, S., Springel, V., Torrey, P., Sijacki, S., Xu, D., Snyder, G., Bird, S., Nelson, D., Hernquist, L. (2014). [ads] [arXiv]

The Sloan Nearby Cluster Weak Lensing Survey, ApJ.
Kubo, J. M., Annis, J., Hardin, F. M., Kubik, D., Lawhorn, K., Lin, H., Nicklaus, L., Nelson, D., Reis, R. R., Seo, H-J., Soares-Santos, M., Stebbins, A., Yunker, T. (2009). [ads] [arXiv]


  • Santa Cruz Galaxy Formation Workshop (Aug 2018). Santa Cruz.
  • Circumgalactic Medium Workshop (July 2018). Northwestern.
  • Intergalactic Interconnections: 12th Marseille Cosmology Conference Series (July 2018). Marseille.
  • Summer Institute on the Philosophy of Cosmology, Lecturer (June 2018). Western Ontario.
  • Galactic Superwinds: Simons Symposium III (May 2018). Schloss Elmau.
  • Simulated Skies for Next-Generation Spectroscopic Surveys (Apr 2018). ESAC, Madrid.
  • Computational Galaxy Formation (Mar 2018). Schloss Ringberg.
  • BCCP Workshop: Modeling the Extragalactic Sky (Jan 2018). Berkeley.
  • Galaxy Evolution in Groups and Clusters at 'low' Redshift (Dec 2017). Schloss Ringberg.
  • Center for Computational Astrophysics: Lunch Talk (2 Nov 2017). NYC.
  • Flatiron Institute: Scientific Visualization (25 Oct 2017). NYC.
  • Frontiers of Astrophysical Modeling (22 Sep 2017). Leuven.
  • MIAPP: In & Out. What Rules the Galaxy Baryon Cycle? (July 2017). Garching.
  • What Matter(s) Around Galaxies (June 2017). Durham, UK.
  • Advances in Galaxy Evolution & Stellar Spectroscopy (June 2017). Schloss Ringberg.
  • Max Planck Institute for Astrophysics (MPIA) Konigstuhl KoCo Colloquim (9 June 2017). Heidelberg.
  • UC Berkeley Theoretical Astrophysics Center (TAC) Seminar (22 May 2017). Berkeley.
  • KITP: The Galaxy-Halo Connection (May 2017). Santa Barbara.
  • MPA Cosmology Seminar (30 May 2017). Garching.
  • Virgo Consortium Meeting (14 Dec 2016). Durham.
  • Haus der Astronomie Full-Dome Workshop (28 Sep 2016). Heidelberg.
  • Crossing the Rubicon: The fate of gas flows in galaxies (Sep 2016). Santarcangelo.
  • Computational Galaxy Formation Workshop (May 2016). Schloss Ringberg.
  • MPA Institute Seminar (7 March 2016). Garching.
  • Santa Cruz IMPS Winter Workshop (9 Feb 2016). Esalen Institute.
  • Virgo Consortium Meeting (14 Dec 2015). Leiden.
  • MPA-UWC (Univeristy of the Western Cape) Workshop (16 Nov 2015). Cape Town.
  • IGM@50: Is the IGM driving Star Formation? (8 June 2015). Abbazia di Spineto.
  • DARK Cosmology Centre Seminar (11 Feb 2015). Copenhagen.
  • Caltech Astronomy Tea Talk (15 Dec 2014). Pasadena.
  • UC Berkeley Theoretical Astrophysics Center (TAC) Seminar (24 Nov 2014). Berkeley.
  • "Arepofest-2" Workshop 2014 (Sep 2014). Boston.
  • Santa Cruz Galaxy Formation Workshop (Aug 2014). Santa Cruz.
  • Mind the Gap: from microphysics to large-scale structure in the universe (July 2013). Cambridge, UK.
  • Feeding, Feedback, and Fireworks: Our Cosmic Landscape (June 2013). Hamilton Island, Australia.
  • Institute for Theory and Computation (ITC) Luncheon (Nov 2012). Harvard University.


  • Computational Astrophysics: Physical Foundations and Numerical Techniques. International Max Planck Research School (IMPRS). Heidelberg, Germany. Sept, 2012.
  • AstroInformatics: International UC-High Performance Astrocomputing Center (HIPACC) Summer School. San Diego, CA. July, 2012.
  • XSEDE/PRACE Challenges in Computational Sciences: HPC Summer School. Dublin. June, 2012.
  • The Morphology and Pattern Speed of Spiral Structure. Nelson, D.R., D'Onghia, E., Hernquist, L. (2011). Advances in Computational Astrophysics Conference Proceeding, cefalu 2011. [ads]
  • Cloud Structure and the Origins of the Stellar Initial Mass Function in rho-Ophiuchus. Nelson, D., Swift, J. J., Williams, J. P. (2007). AAS Meeting 211, Austin, Session #89.12. [ads]
  • Effectiveness of the Correlator Field of View Weighting Technique in Source Attenuation. Nelson, D., Doeleman, S. S., Lonsdale, C. J., Oberoi, D., Cappallo, R. J. (2006). AAS Meeting 209, Seattle, Session #85.10. [ads]


Harvard University Teaching Fellow:

  • Astronomy 16 (Undergrad) - Stellar and Planetary Astronomy (Prof. D. Charbonneau)
  • Astronomy 17 (Undergrad) - Galactic and Extragalactic Astronomy (Prof. J. Lee)
  • Applied Mathematics 274 (Grad) - Computational Fluid Dynamics (Prof. D. Knezevic)
  • Computer Science 207 (Grad) - Systems Development for Computational Science (Prof. C. Cecka)