The bright radio source, GLEAM J091734–001243 was previously selected as a candidate ultra-high redshift (z > 5) radio galaxy due to its compact radio size and optical faintness.

Seymour et al. have just published new HST observations revealing a redshift of 3.00. The extended component of the [OII]λ3727 spectral line detected with HST is co-spatial with one of two components seen at 2.3 GHz in high resolution (60 × 20 milli-arcsecond) Long Baseline Array data, reminiscent of the alignments seen in local compact radio galaxies. Modelling of the radio jet demonstrates that this is a young (~50,000 yr old), but powerful compact steep spectrum radio source. The team infer that the line emission is directly caused by shocks from the jet and that this radio source is one of the youngest and most powerful known.

The figure above shows an inverted greyscale combined HST image overlaid with the resolved [OII]λ3727 emission of the host (green contours) and the 2.3 GHz LBA data (red contours with the restoring beam in the lower left). The extended [OII]λ3727 and the two components of the LBA data are aligned, although the alignment with the unrelated nearby source to the southwest is serendipitous.