Foreground Data


Product Name
Reddening (E(B-V)) Map (Schlafly et al.)
Coord. System
Projection Type
HEALPix ring, res 9 (Nside=512)
7 to 14 arcmin
Original Data Source


Schlafly et al. (2014) derived a map of the dust reddening to 4.5 kpc from Pan-STARRS1 stellar photometry. The map covers almost the entire sky north of declination −30 degrees at a resolution of 7′ for |b| < 30 degrees or 14′ for |b| > 30 degrees, and is based on the estimated distances and reddenings to more than 500 million stars.

The reddening map is available as a binary FITS table, ordered according to the HEALPix scheme. Each record in the table has the following fields:

  • ebv
    estimated E(B-V) at 4.5 kpc; see below for information on the overall scale

  • err
    1 sigma formal uncertainty estimate, based on when chi^2 changes by 1

  • err2
    1 sigma formal uncertainty estimate, based on when chi^2 changes by 4

  • status
    integer indicating the status of the analysis of this pixel. The following values are possible

  • -999  no PS1 data in this pixel
    -2  analysis failed to converge in this pixel
    -1  interpolated value from adjacent pixels
    1  analysis converged

  • nstar
    number of PS1 stars used in the analysis (stars failing to fit the model are clipped)

  • nstar_tot
    number of PS1 stars with good photometry in the pixel

  • nside
    resolution (HEALPix nside) of the map in this pixel

Notes from Schlafly's web page:

The overall scaling of E(B-V) is somewhat subtle. We use measurements of the colors of stars in the PS1 bands, and infer E(B-V) in the context of a reddening vector that relates reddening E(B-V) to reddenings (and extinction) in the different bands. For this we adopt the coefficients of Schlafly & Finkbeiner (2011), who assume a Fitzpatrick (1999) reddening law, but additionally solve for an overall scaling which attempts to fix the overall reddening calibration of the Schlegel, Finkbeiner, and Davis (1998) map. By adopting the coefficients of Schlafly & Finkbeiner (2011), we are essentially putting our map on the same scale as Schlegel, Finkbeiner, and Davis (1998). This has the advantage that it means that the two maps can be directly compared, and that the coefficients of Schlafly & Finkbeiner (2011) can be directly used to convert from our E(B-V) estimates into other bands. It has the disadvantage that our E(B-V) values must be themselves converted to E(B-V), admittedly very confusingly.

More than 30 degrees from the Galactic plane, we use pixels with half the resolution of the lower Galactic latitude sky. To accomodate this in the FITS file, we fill in 4 identical records for each larger pixel, and mark those pixels as having a HEALPix nside of 256, as opposed to the usual 512.

We estimate that there is an additional 30 mmag systematic uncertainty in our data to due imperfections in our modeling of the Galaxy's stars; see the paper for details.

More details can be found in:

"A Map of Dust Reddening to 4.5 kpc from Pan-STARRS1", Schlafly, Green, Finkbeiner et al. 2014, ApJ, accepted, arXiv

Schlafly's web page

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