Discovery of Distant RR Lyrae Stars in the Milky Way Using DECam

作者：Medina Gustavo E^*; Munoz Ricardo R; Katherina Vivas A; Carlin Jeffrey L; Forster Francisco; Martinez Jorge; Galbany Lluis; Gonzalez Gaitan Santiago; Hamuy Mario; de Jaeger Thomas; Carlos Maureira Juan; San Martin Jaime

来源：Astrophysical Journal, 2018, 855(1): 43.

DOI：10.3847/1538-4357/aaad02

• Galaxy: halo
• Galaxy: stellar content
• Galaxy: structure
• stars: variables: RR Lyrae

We report the discovery of distant RR Lyrae stars, including the most distant known in the Milky Way, using data taken in the g-band with the Dark Energy Camera as part of the High cadence Transient Survey (HiTS; 2014 campaign). We detect a total of 173 RR Lyrae stars over a similar to 120 deg(2) area, including both known RR Lyrae and new detections. The heliocentric distances d(H) of the full sample range from 9 to > 200 kpc, with 18 of them beyond 90 kpc. We identify three sub-groups of RR Lyrae as members of known systems: the Sextans dwarf spheroidal galaxy, for which we report 46 new discoveries, and the ultra-faint dwarf galaxies Leo IV and Leo V. Following an MCMC methodology, we fit spherical and ellipsoidal profiles of the form rho(R) similar to R-n to the radial density distribution of RR Lyrae in the Galactic halo. The best fit corresponds to the spherical case, for which we obtain a simple power-law index of n = 4.17(-0.20)(+0.18), consistent with recent studies made with samples covering shorter distances. The pulsational properties of the outermost RR Lyrae in the sample (d(H) > 90 kpc) differ from the ones in the halo population at closer distances. The distribution of the stars in a period-amplitude diagram suggest they belong to Oosterhoff-intermediate or Oosterhoff II groups, similar to what is found in the ultra-faint dwarf satellites around the Milky Way. The new distant stars discovered represent an important addition to the few existing tracers of the Milky Way potential in the outer halo.

• 出版日期2018-3-1