Building a 3D Map of Milky-Way Dust

Gregory Green, Edward Schlafly & Douglas Finkbeiner

Local Group Astrostatistics

University of Michigan, 2 June 2015

Why construct a 3D map of dust?

2D maps already exist

Schlegel, Finkbeiner & Davis (1998)

Limitations of (emission-based) 2D dust maps

  • Inadequate for objects in plane of Galaxy, and close-by objects
  • Systematics in modeling of dust emission, and conversion to extinction

Some possible uses of 3D dust maps

  • Extinction/reddening corrections in plane of Galaxy
  • Distances to objects of known reddening
  • Inference of Galactic structure: streams, spiral arms, disk scale heights, etc.
  • Different types of systematics than dust emission-based maps

What our map looks like...

Looking towards the Galactic anticenter

50 pc orbit about the Sun

Traveling through the Milky Way

Integrated Reddening:

Galactic anticenter

Integrated Reddening:

$50^{\circ} \leq \ell \leq 100^{\circ}$

Integrated Reddening:

Aquila South

How is the map constructed?

  • We have some idea of the what stars should look like
  • Stars are reddened by foreground dust
  • Each star therefore acts as a tracer of the dust column out to some point in space
  • By inferring reddening to hundreds of millions of stars across the sky, we can build up a 3D dust map


Assume all stars in one pixel trace the same reddening column

Model Parameters

$\hphantom{\mu_{k} ,\,} \Delta E_{j} ,$ $\ \ j = 1, \ldots , n_{\mathrm{bins}}$
$\mu_{k} ,\,$ $\delta_{k} ,\,$ $\Theta_{k} ,$ $\ \ k = 1, \ldots , n_{\mathrm{stars}}$
$$ \left. \vphantom{ \begin{align} \Delta E_{j} \\ \Theta_{k} \\ \Theta_{k} \end{align} } \right\} \Rightarrow \vec{m}_{k} $$

Website for project