Estimating the Milky Way’s Mass via Hierarchical Bayes: A Blind Test on MUGS2 Simulated Galaxies

DIRAC Researcher, Gwendolyn Eadie, published a paper in the Astrophysical Journal.

Published on September 24, 2018.

Estimating the Milky Way’s Mass via Hierarchical Bayes: A Blind Test on MUGS2 Simulated Galaxies


In a series of three papers, Eadie et al. developed a hierarchical Bayesian method to estimate the Milky Way Galaxy’s mass given a physical model for the potential, a measurement model, and kinematic data of test particles such as globular clusters (GCs) or halo stars in the Galaxy’s halo. The Galaxy’s virial mass was found to have a 95% Bayesian credible region (c.r.) of (0.67, 1.09) × 1012 ${M}_{\odot }$. In the present study, we test the hierarchical Bayesian method against simulated galaxies created in the McMaster Unbiased Galaxy Simulations 2 (MUGS2), for which the true mass is known. We estimate the masses of MUGS2 galaxies using GC analogs from the simulations as tracers. The analysis, completed as a blind test, recovers the true M 200 of the MUGS2 galaxies within 95% Bayesian c.r. in 8 out of 18 cases. Of the 10 galaxy masses that were not recovered within the 95% c.r., a large subset have posterior distributions that occupy extreme ends of the parameter space allowed by the priors. A few incorrect mass estimates are explained by the exceptional evolution history of the galaxies. We also find evidence that the model cannot describe both the galaxies’ inner and outer structure simultaneously in some cases. After removing the GC analogs associated with the galactic disks, the true masses were found more reliably (13 out of 18 were predicted within the c.r.). Finally, we discuss how representative the GC analogs are of the real GC population in the Milky Way.



2018-09-28 DIRAC Astronomy Open-source Sprint

DIRAC Institute has the 1st Astronomy Open-source Sprint, Sep 28, 2018 at the University of Washington.

When: September 28, 2018 @ 1:00-4:30pm
Where: PAB, WRF Data Science Studio, 6th floor, Meeting Room
Maintainers of several projects (e.g. astropy, astroquery, astroplan, stingray, etc) have committed to attend the sprints and will help with getting started and other practicalities. 
Contributions can be of different types from issue triaging, implementing bug and documentation fixes to adding new features. Please bring your laptop, and if you have any issue in mind (otherwise there are also plenty to choose from e.g. here:  
Facilitated by Brigitta Sipocz.

2018-09-07 Seminar: Lia Sartori

When: September 7, 2018 @ 11:00am
Where: PAB, WRF Data Science Studio, 6th floor
Lia Sartori from the ETH Zürich Institute for Particle Physics and Astrophysics, will be discussing variability in active galactic nuclei. 
A study of active galactic nuclei variability on multiple timescales
Variability is ubiquitous in active galactic nuclei (AGN) and can be observed or inferred at all timescales, from hours to billions of years. In this talk I will first illustrate how spatially resolved optical spectroscopy, combined with high quality X-ray data, can be used to probe AGN variability on > 10^4 yr timescales. I will then present a compilation of variability measurements, covering many orders of magnitude both in time lags and variability amplitude, which provides an overview of the variabiltiy phenomena. This compilation includes ensemble studies, which characterise the mean variability among the AGN population, as well as measurements for single objects such as the changing look AGN, the Voorwerpjes galaxies, and our own Sagittarius A*. Finally, I will present a framework which allows us to test if and how variability in different AGN and at different timescales can be linked and explained based on the distribution of the Eddington ratio (ER) among the galaxy population. Specifically, we propose a forward modelling approach to simulate the evolution of AGN light curves with time based on the probability density function (PDF) and the power spectral density (PSD) of the ER distribution. At the end of the talk I will also discuss possible applications of our model, e.g. for understanding changing look AGN or planning future time domain surveys.

Collaborative, participant-driven learning works!



Science has become a big-data endeavor. But scientists are not universally adept in “data science” — the computing and statistical skillsets needed to handle, sort, analyze and draw conclusions from big data. The shortage of know-how in data science can hamper research, medicine and even private industry

A new paper led by Daniela Huppenkothen, Associate Director of DiRAC, was just published in the Proceedings of the National Academy of Sciences on how we can learn these skills by working collaboratively. With a team of researchers from the University of Washington, New York University and the University of California, Berkeley  she developed an interactive workshop in data science for researchers at multiple stages of their careers. The course format, called “hack week,” blends elements from both traditional lecture-style pedagogy with participant-driven projects. The most recent was a neuroscience-themed event held in July on the UW campus organized by Ariel Rokem, a data scientist with the UW eScience Institute. As the team reports in a their paper  published Aug. 20, participants rated the hack weeks as opportunities to learn about new concepts, foster new connections, share data openly, and develop skills and work on problems that will positively affect their day-to-day research lives.

Read more about this in the full UW press release



2018-08-03 Seminar: David van Dyk

When: August 3, 2018 @ 3:00 pm 
Where: PAB, WRF Data Science Studio, 6th floor

David A van Dyk, Statistics Section, Department of Mathematics, Imperial College London

Quantifying Discovery in Astro/Particle Physics: Frequentist and Bayesian Perspective

Statistical discovery questions in astrophysics and high-energy physics often involve mathematical subtleties that mean standard methods (e.g., chi-square) are inappropriate and can lead to misleading results. At the same time Bayesian and classical statistical techniques can lead researchers to differing conclusions. Moreover modern computational strategies are typically infeasible under extreme discovery criteria (4 sigma or more).  This talk explores the statistical challenges that arise in the quantification of discovery and suggests a strategy that combines Bayesian and classical statistical techniques to tackle these challenges.  

1st LSST Solar Systems Readiness Sprint

DIRAC Institute is hosting the 1st LSST Solar System Readiness Sprint, July 10-12, 2018 at the University of Washington. This is a LSST Solar System Science collaboration workshop to begin getting ready for LSST solar system science.

Happy Asteroid Day!

Live coverage is available here.

Astronauts, astronomers, scientists, students, teachers, and interested citizens around the world are coming together at this very moment to learn about and discuss asteroids.

Participate in the global conversation online right now
or at event near you today!

UW is participating in Asteroid Day, a global day of education to help protect Earth from potentially hazardous asteroid. The movie below shows how UW LSST and DIRAC’s astronomical software group is assisting that effort by making the LSST an unprecedented asteroid discovery machine.

Asteroid Day: University of Washington & LSST from Nikolina Horvat on Vimeo.


Visitors: Michael Hayden

June 27th-29th, 2018

I work on Galactic Archaeology, which is the study of the structure and evolution of the Milky Way. I did my PhD at New Mexico State University working with Jon Holtzman and Jo Bovy with the APOGEE survey, which is an SDSS3 and SDSS4 spectroscopic survey of several hundred thousand red giants across the Milky Way. I spent two years working in Nice at the Observatoire de la Cote d’Azur with the Gaia-ESO and AMBRE projects, which have spectroscopic observations of tens of thousands of stars throughout the Galaxy. 

Currently, I am an ASTRO 3D fellow working at the University of Sydney with the GALAH Survey. GALAH  is a large-scale spectroscopic survey of 500,000 stars throughout the Milky Way, and aims to measure chemical abundances for 30 different elements to map and chemically tag the stellar populations of the Galaxy. In my talk, “Chemical Cartography of the Milky Way”, I will discuss the chemodynamic properties of different stellar populations throughout the disk and how they vary with location.

I attached a figure of some preliminary results from the GALAH survey, showing how the chemical structure of the disk varies from the inner Galaxy to the edge of the disk.

Dr. Gwendolyn Eadie received the J.S. Plaskett Medal

Gwen Eadie

CASCA is pleased to announce Dr. Gwendolyn Eadie as the 2018 recipient of the J. S. Plaskett Medal.

Dr. Eadie completed her doctoral studies at McMaster University under the supervision of Dr. William Harris. In her thesis entitled “Lights in Dark Places: Inferring the Milky Way Mass Profile using Galactic Satellites and Hierarchical Bayes”, she developed a high-level statistical method to derive the mass and mass distribution within astrophysical systems. Mass is a fundamental variable driving the evolution of galaxies like our Milky Way, but it is notoriously difficult to measure due to the fact that it is dominated by the dark matter extending well beyond the visible starlight. This challenge is compounded by incomplete data on the positions and velocities of “tracer particles” such as stars, star clusters and dwarf satellites scattered through the galaxy’s halo. Dr. Eadie developed a powerful Bayesian formulation of the problem combined with Markov Chain Monte Carlo calculations of the relevant parameters in the problem and their probability distributions. Her formulation also included a hierarchical treatment of measurement uncertainties for each tracer. She used it to place a new constraint on the mass profile and total mass of the Milky Way, and it will be a very powerful tool in the exploitation of future very large datasets from the Gaia mission and the Large Synoptic Survey Telescope (LSST). .

CASCA congratulates Dr. Eadie on the receipt of the 2018 Plaskett medal for her groundbreaking work to shed light on the dark side of our Milky Way galaxy and other corners of the Universe.


Read full announcement here.

DiRAC Institute in B612 Press Release

Asteroid Institute Announces New Appointments

Dr. Sarah Greenstreet and Bryce Bolin named first senior research fellows.

SILICON VALLEY, CA/SEATTLE WASH. (May 17,2018) — The Asteroid Institute has announced new appointments in the field of planetary defense and asteroids. Dr. Sarah Greenstreet and Bryce Bolin have been selected to serve as the first Senior Research Fellows, under the direction of Dr. Ed Lu, Executive Director of the Asteroid Institute, three time NASA astronaut, former Google executive and co-founder of B612 Foundation. The fellows study the application of new technologies for the discovery, tracking and potential deflection of asteroids.

Read full article here.