A 3D extinction map of the Northern Galactic Plane based on IPHAS photometry

In Sale et al (2014) we present a 3D extinction map of the entire Northern Galactic Plane (|b| < 5°) based on H-MEAD, an algorithm previously described in Sale (2012), and IPHAS DR2 photometry.

There are two main products available for download: the 3D extinction map itself and a catalogue of stellar parameters for the ~38 million stars employed to build the map. They can be downloaded from this page. In addition, both products will be available for download from the CDS.

The extinction map is presented in two forms. First, we publish the posterior expectations of mean extinction and differential extinction for every voxel in the map. These expectations are accompanied by measurements of the half-widths of 68.3 per cent credible intervals centred on the expectation for both mean extinction and differential extinction. In addition we also make available 20 samples from the posterior distribution on the mean extinction.

The posterior expectations and uncertainties are available in one large file (107MB) covering the entire sky, in this form the maximum reliable distance is indicated in the seventh column. The README accompanying this file contains column definitions.

Alternatively the same data are available with one file per sightline. These files detail the Galactic longitude and latitudes covered in the file header. The individual files are organised into archives covering 10° wide strips of the Glactic plane. In this format the final column flags whether a voxel is considered 'trustworthy' or not, i.e. if it is within or beyond the maximum reliable distance for the sightline. The limits of the voxel in Galactic longitude and latitude are given in the file header. Column definitions for these files follow after download details.

We also make available 20 samples from the posterior distribution on mean extinction. For many purposes this might be a more useful representation of the posterior than that given by the expectation and halfwidth of the credible interval. We provide one file for each sightline, where the filename gives the Galactic longitude and latitude at the centre of the line of sight. The first column of each file gives the midpoint distance of a voxel, whilst the subsequent columns each give a value sampled from the posterior on mean extinction. The samples were all taken from the same set of iterations in the MCMC chain and so each column is itself a sample from the posterior on the entire distance extinction relationship.

There is one file for each sightline. These files detail the Galactic longitude and latitudes covered in the file header. The individual files are organised into archives covering 10° wide strips of the Glactic plane.

In adition to estimating the three dimensional distribution of extinction, H-MEAD also infers the fundamental parameters of stars in the catalogue employed.

By publishing only expectations and one dimensional standard deviations we are passing on only a relatively crude depiction of the posterior probability distribution. Consequently features such as multimodality of the posterior and covariance between parameters will not be apparent. Additionally, the calculation of the stellar parameters has been subject to both a set of priors and a survey selection function, both of which have heavily shaped the results obtained. Any further analysis of these data will also be inevitably subject to these same priors and selection function. In light of these factors, we caution the reader that care must be taken not to over-interpret or mistake patterns which appear in this catalogue. These data are provided in the spirit that they may be a useful resource for gaining insight into the origin of features in the extinction map.

We provide one file that contains the entire catalogue (1.5GB).

We also split the catalogue up into files corresponding to each sightline analysed. These files detail the Galactic longitude and latitudes covered in the file header. The individual files are organised into archives covering 10° wide strips of the Glactic plane.