BoRG CoI Benne Holwerda (Leiden University) took advantage of the random pointings nature of BoRG to investigate the distribution of cool stars (primarily M dwarfs) in the Milky Way. The work has been accepted for publication in the Astrophysical Journal and is available on arXiv.

The distribution of BoRG lines of sight in galactic coordinates is shown here:

borg_cool_stars

Each colored point corresponds to a different WFC3 BoRG pointing, with size proportional to the surface density of dwarfs. Two intriguing conclusions of the study are:

  1. There is a North-South asymmetry, with North fields showing a ~2$$\sigma$$ evidence of overdensity, despite the fact that the sun is above the galactic plane. The work confirms and strengthens the asymmetry previously noted on just two lines of  sight of GOODS north vs. south.
  2. We clearly detect the Sagittarius Stream as an overdensity of dwarf stars (star point in the figure).

The work by Benne demonstrates the legacy value of BoRG imaging beyond its key contributions on galaxy formation during the epoch of reionization, and complements studies of the Milky Way structure by tracing stars that are much fainter than those that Gaia will observe (BoRG identifies stars to about $$m_{AB}$$~24 in the H band).