Category Archives: News

New Paper: The AGORA High-Resolution Galaxy Simulations Comparison Project

Today, we have posted our flagship paper on the AGORA galaxy formation simulation comparison project. I’m extremely happy to be a part of this collaboration to further understand the differences between astrophysical simulation codes. This paper outlines the philosophy behind the project and serves as a platform for independent scientific projects, which we have covered in this paper in the Appendix. This is just the start of the papers that will come out of this project, which we will discuss in an upcoming AGORA workshop next week in Santa Cruz.

New paper: Enzo method paper

I’m a little late announcing the Enzo method paper, but we have finally finished writing the method paper that is 15 years in the making. Nevertheless, I hope this paper provides our users with a theoretical basis of the inner workings of Enzo. It accompanies the v2.3 release of Enzo, which includes a new MHD implementation, PPM implementation in CUDA, and an updated Haardt & Madau (2012) ultraviolet background. There are also many other bugfixes.

Publishing Simulation Data

The Georgia Tech Library, specifically Elizabeth Rolando, has been helping me publish some of my simulation data on a “Dataverse” on theastrodata.org. Another possible service is figshare (Tip to Britton!). Considering that the full simulation dataset is over 2TB, this would be unwieldy for the front-end interface without some high-speed transfer program, like GlobusOnline. However, a mesh between a Dataverse and GlobusOnline could be a solution in the future to share full simulation data!

In the end, I have uploaded the metadata and reduced data from the “radiation pressure” simulation from our 2012 paper to my Dataverse.  The reduced data set consists of the following items from ~60 outputs. Continue reading Publishing Simulation Data

New paper: The remnants of the first stars

There is building evidence that the first stars are not as massive as previously thought and that they are merely typical massive stars on the order of tens of solar masses instead of behemoths up to 300 solar masses.  Furthermore, a non-negligible fraction of this population form in binary systems. These stellar systems can leave behind stellar-mass black holes, chemically enriched regions from their supernovae, and X-ray binaries if the companion star overflows onto the black hole during its giant phase. All of this depends on the initial mass function of the first stars, which is highly uncertain at the moment, but luckily it’s an active area of research!

To determine the evolution and impact of these remnants, we must know where they migrate after their progenitor star dies.  This week, Hao Xu, Michael Norman at UCSD and I submitted a paper that focuses on exactly this point. Continue reading New paper: The remnants of the first stars

Building the Visualization Lab I: 3D Projection System

I have helped in setting up visualization labs previously in grad school, but I was not involved in choosing the equipment and the details of its construction. Building a visualization lab from the ground up was a totally new experience for me. By posting my experiences, I hope that this series helps people who want to build a similar outfit.

Continue reading Building the Visualization Lab I: 3D Projection System

Optimized Multi-Frequency Spectra

Last week, we submitted a paper titled “Optimized Multi-Frequency Spectra for Applications in Radiative Feedback and Cosmological Reionization” to the Astrophysical Journal.  You can find it on arXiv.  Here we investigate the impact of varying energy discretizations in radiation transport schemes.  Mono-chromatic approximations can underestimate the amount of partial ionization at large radii because all of the ionizing photons are absorbed at some characteristic radius.  This is especially true for X-rays, which have large mean free paths.

With a multi-frequency approach, the solution converges with 4 or more frequency bins. For example with a 10^5 K blackbody source, the temperature of an HII region at r = 8 kpc is underestimated by a factor of 20 if a mono-chromatic spectrum is used.  However it is unclear the best technique on how to choose these frequencies.  In this work, we developed a Monte Carlo scheme to determine optimal frequency values for such radiation calculations.  In the paper, we give optimal discretizations for a 10^5 K blackbody and power law spectrum for 1-4 bins.  The code that employs this method will be released when the paper is accepted.