A cold stellar stream in Pegasus

Abstract

We report the serendipitous discovery of a stellar stream in the constellation Pegasus in the south Galactic hemisphere. The stellar stream was detected using the SDSS Data Release 14 by means of a matched filter in the colour-magnitude diagram that is optimized for a stellar population that is 8 Gyr old with [Fe/H] = -0.46 dex, and located at heliocentric distance of 18 kpc. The candidate stream is faint (turn-off point at r₀ ∼ 19.6), sparse and barely visible in SDSS photometry. It is also detected in the (shallower) Pan-STARRs data. The residual stellar density in the (u - g)₀, (g - r)₀ colour-colour diagram gives the same estimate for the age and [Fe/H] of this stellar population. The stream is located at a Galactic coordinates (l, b) = (79.4°, -24.6°) and extends over 9° (2.5 kpc), with a width of 112 pc. The narrow width suggests a globular cluster progenitor.