The Brightest of Reionizing Galaxies Survey is a large Hubble Space Telescope Program focused on finding rare and bright galaxy candidates at redshift z~8-10, that is when the Universe was about 500 to 650 million years old. We use Hubble’s Wide Field Camera 3, which is highly efficient in the near-infrared bands (Y, J, H) that are needed to identify these very distant galaxies. The near-infrared filters are complemented by deep optical imaging.


BoRG is a pure-parallel survey. This means that the data are acquired while Hubble is pointing for primary spectroscopic observations (typically distant QSOs or extrasolar planets).

BoRG was originally designed in Cycle 17 (GO 11700) to search for z~8 sources and continued with observations in Cycle 19 (GO 12572) and Cycle 20 (GO 12905), augmented by assimilation of other parallel imaging in the Hubble archive (see Bradley et al. 2012 and Schmidt et al. 2014 for the list of pointings and associated programs). Currently, we are boldly moving to Hubble’s detection frontier at z~9-10, and the BoRG Cycle22 observations (GO 13767) are optimized for identifying J-band dropouts that is galaxies observed when the Universe was about 500 Myr old.

We are releasing all science images through the Mikulski Archive for Space Telescopes.

BoRG Cool Stars

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:


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).

BoRG@Keck: Witnessing reionization in progress

BoRG CoI Tommaso Treu led a spectroscopic follow-up of 13 BoRG z~8 galaxies to search for Ly-$$\alpha$$ emission. The results have been published in the Astrophysical Journal.

The lack of Ly-$$\alpha$$ detection to a faint flux (median sensitivity of 25$$\mathring{A}$$ at 5$$\sigma$$) sets very interesting constraints on the evolution of the Ly-$$\alpha$$ equivalent width distribution, which is most naturally interpreted as evidence of an increase in the neutral gas content at z>6: