Identifying RR Lyrae Variable Stars in Six Years of the Dark Energy Survey

Stringer, K. M.; Drlica-Wagner, A.; Macri, L.; Martínez-Vázquez, C. E.; Vivas, A. K.; Ferguson, P.; Pace, A. B.; Walker, A. R.; Neilsen, E.; Tavangar, K.; Wester, W.; Abbott, T. M. C.; Aguena, M.; Allam, S.; Bacon, D.; Bechtol, K.; Bertin, E.; Brooks, D.; Burke, D. L.; Carnero Rosell, A.; Carrasco Kind, M.; Carretero, J.; Costanzi, M.; Crocce, M.; da Costa, L. N.; Pereira, M. E. S.; De Vicente, J.; Desai, S.; Diehl, H. T.; Doel, P.; Ferrero, I.; García-Bellido, J.; Gaztanaga, E.; Gerdes, D. W.; Gruen, D.; Gruendl, R. A.; Gschwend, J.; Gutierrez, G.; Hinton, S. R.; Hollowood, D. L.; Honscheid, K.; Hoyle, B.; James, D. J.; Kuehn, K.; Kuropatkin, N.; Li, T. S.; Maia, M. A. G.; Marshall, J. L.; Menanteau, F.; Miquel, R.; Morgan, R.; Ogando, R. L. C.; Palmese, A.; Paz-Chinchón, F.; Plazas, A. A.; Roodman, A.; Sanchez, E.; Schubnell, M.; Serrano, S.; Sevilla-Noarbe, I.; Smith, M.; Soares-Santos, M.; Suchyta, E.; Tarle, G.; Thomas, D.; To, C.; Varga, T. N.; Wilkinson, R. D.; Zhang, Y.; DES Collaboration
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The Astrophysical Journal

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We present a search for RR Lyrae stars using the full six-year data set from the Dark Energy Survey covering ∼5000 deg2 of the southern sky. Using a multistage multivariate classification and light-curve template-fitting scheme, we identify RR Lyrae candidates with a median of 35 observations per candidate. We detect 6971 RR Lyrae candidates out to ∼335 kpc, and we estimate that our sample is >70% complete at ∼150 kpc. We find excellent agreement with other wide-area RR Lyrae catalogs and RR Lyrae studies targeting the Magellanic Clouds and other Milky Way satellite galaxies. We fit the smooth stellar halo density profile using a broken-power-law model with fixed halo flattening (q = 0.7), and we find strong evidence for a break at ${R}_{0}={32.1}_{-0.9}^{+1.1}\,\mathrm{kpc}$ with an inner slope of ${n}_{1}=-{2.54}_{-0.09}^{+0.09}$ and an outer slope of ${n}_{2}=-{5.42}_{-0.14}^{+0.13}$ . We use our catalog to perform a search for Milky Way satellite galaxies with large sizes and low luminosities. Using a set of simulated satellite galaxies, we find that our RR Lyrae-based search is more sensitive than those using resolved stellar populations in the regime of large (rh ≳ 500 pc), low-surface-brightness dwarf galaxies. A blind search for large, diffuse satellites yields three candidate substructures. The first can be confidently associated with the dwarf galaxy Eridanus II. The second has a distance and proper motion similar to the ultrafaint dwarf galaxy Tucana II but is separated by ∼5 deg. The third is close in projection to the globular cluster NGC 1851 but is ∼10 kpc more distant and appears to differ in proper motion.
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