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 color--magnitude diagram that is optimised 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 (turnoff point at $r_0\sim$ 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 $(u-g{)}_0$, $(g-r{)}_0$ color--color 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${}^{\circ }$ (2.5 kpc), with a width of 112 pc. The narrow width suggests a globular cluster progenitor.

9 pages, 7 figures, accepted to MNRAS

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