A 3D Map of Dust from Pan-STARRS 1 Photometry

Gregory Green, Edward Schlafly & Douglas Finkbeiner

European Week of Astronomy & Space Science

La Laguna, Tenerife, 25 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:

Three Quarters of the Sky

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

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

The Data

  • Multi-band photometry of ~800 million stars
  • Pan-STARRS 1 grizy photometry
  • 2MASS JHKs photometry

Source Density across the Sky

Source Density across the Sky

Source Density across the Sky

Sources per Band

Bands per Source

Comparison with 2D Maps

3D Map Projected to 2D

Residuals with Schlegel, Finkbeiner & Davis (1998)

Residuals with Planck $\tau_{353 \mathrm{GHz}}$ Dust Map

Aquila South

Schlegel, Finkbeiner & Davis (1998)

Aquila South

3D Dust Map at 8 kpc

Aquila South


Aquila South

Residuals (stretched)

Website for project