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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents

ID: 742793.0, MPI für Astronomie / Publikationen_mpia
DDO 216-A1: A central globular cluster in a low-luminosity transition-type galaxy
Authors:Cole, A. A.; Weisz, D. R.; Skillman, E. D.; Leaman, R.; Williams, B. F.; Dolphin, A. E.; Johnson, L. C.; McConnachie, A. W.; Boylan-Kolchin, M.; Dalcanton, J.; Governato, F.; Madau, P.; Shen, S.; Vogelsberger, M.
Date of Publication (YYYY-MM-DD):2017
Title of Journal:The Astrophysical Journal
Issue / Number:1
Start Page:id. 54 (12 pp)
Audience:Not Specified
Abstract / Description:We confirm that the object DDO 216-A1 is a substantial globular cluster at the center of Local Group galaxy DDO 216 (the Pegasus dwarf irregular), using Hubble Space Telescope ACS imaging. By fitting isochrones, we find the cluster metallicity [M/H] = ‑1.6 ± 0.2, for reddening E(B–V) = 0.16 ± 0.02 the best-fit age is 12.3 ± 0.8 Gyr. There are ≈ 30 RR Lyrae variables in the cluster; the magnitude of the fundamental mode pulsators gives a distance modulus of 24.77 ± 0.08—identical to the host galaxy. The ratio of overtone to fundamental mode variables and their mean periods make DDO 216-A1 an Oosterhoff Type I cluster. We find a central surface brightness of 20.85 ± 0.17 F814W mag arcsec‑2, a half-light radius of 3\buildrel{\prime\prime}\over{.} 1 (13.4 pc), and an absolute magnitude M814 = ‑7.90 ± 0.16 (M/{M}ȯ ≈ 105). King models fit to the cluster give the core radius and concentration index, r c = 2\buildrel{\prime\prime}\over{.} 1 ± 0\buildrel{\prime\prime}\over{.} 9 and c = 1.24 ± 0.39. The cluster is an “extended” cluster somewhat typical of some dwarf galaxies and the outer halo of the Milky Way. The cluster is projected ≲30 pc south of the center of DDO 216, unusually central compared to most dwarf galaxy globular clusters. Analytical models of dynamical friction and tidal destruction suggest that it probably formed at a larger distance, up to ∼1 kpc, and migrated inward. DDO 216 has an unexceptional specific cluster frequency, S N = 10. DDO 216 is the lowest-luminosity Local Group galaxy to host a 105 {M}ȯ globular cluster and the only transition-type (dSph/dIrr) galaxy in the Local Group with a globular cluster. Based on observations made with the NASA/ESA Hubble Space Telesope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. These observations were obtained under program
Free Keywords:galaxies: dwarf; galaxies: individual: DDO 216; galaxies: star clusters: general; Local Group
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie
Identifiers:ISSN:0004-637X %R 10.3847/1538-4357/aa5df6
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