Discovery of new dwarf galaxy near the isolated spiral galaxy NGC 6503

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We report the discovery of a new dwarf galaxy (NGC 6503-d1) during the Subaru extended ultraviolet disk survey. It is a likely companion of the spiral galaxy NGC 6503. The resolved images, in the B, V, R, i, and H alpha bands, show an irregular appearance due to bright stars with underlying, smooth and unresolved stellar emission. It is classified as the transition type (dwarf irregular (dIrr)/dwarf spheroidal (dSph)) between the dIrr and dSph types. Its structural properties are similar to those of the dwarfs in the Local Group, with an absolute magnitude M-V similar to -10.5, half-light radius r(e) similar to 400 pc, and central surface brightness mu(0,V) similar to 25.2. Despite the low stellar surface brightness environment, one H II region was detected, though its H alpha luminosity is low, indicating an absence of any appreciable O-stars at the current epoch. The presence of multiple stellar populations is indicated by the color-magnitude diagram of similar to 300 bright resolved stars and the total colors of the dwarf, with the majority of its total stellar mass similar to 4 x 10(6) M-circle dot in an old stellar population.
© 2015. The American Astronomical Society. All rights reserved. This research used data collected with the Subaru Telescope operated by the National Astronomical Observatory of Japan and with the GALEX operated for NASA by the Caltech under NASA contract NAS5-98034, and used the NASA/IPAC Extragalactic Database (NED) operated by the Jet Propulsion Laboratory, Caltech, under contract with NASA. We thank an anonymous referee for constructive comments, Fumiaki Nakata for help in observations, Eric Greisen for HI data, and the Pan-STARRS1 Surveys collaboration for the photometric catalog. This research is supported by NASA through grant NNX14AF74G. J.K. also acknowledges support from the NSF (AST-1211680).
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