Browsing by Author "Irwin, M"

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    A fork in the Sagittarius trailing debris
    (2017) Navarrete Silva, Camila Andrea; Belokurov, V; Koposov, S; Irwin, M; Catelan, Márcio; Duffau, S; Drake, A
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    A new Local Group galaxy in Cetus
    (1999) Whiting, AB; Hau, GKT; Irwin, M
    We report the discovery of a previously uncataloged Local Group galaxy in the constellation Cetus. Faintly visible on UKST survey plates, it has a smooth, diffuse appearance and appears to be a dwarf spheroidal of type dE3.5. A color-magnitude diagram in V, V-I shows a clear giant branch but no sign of recent star formation. From the position of the tip of the giant branch, we derive a reddening-corrected distance modulus of 24.45 +/- 0.15 and a metallicity of - 1.9 +/- 0.2. With an implied heliocentric distance of 775 +/- 50 kpc, and a corresponding Local Group barycentric distance of 615 kpc, the Cetus dwarf lies well within the boundaries of the Local Group, and although it currently lacks a radial velocity measurement, it is undoubtedly a member of the Local Group. The nearest Local Group galaxies are WLM and IC 1613 at angular separations of 7 degrees.3 and 16 degrees.3 and roughly 175 and 230 kpc total distance, respectively. Although the Cetus dwarf is unlikely to be directly associated with any other Local Group galaxy, it does lie in the general direction of the extension of the Local Group toward the Sculptor Group.
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    The southern dwarf hunt: Local Group dwarf candidates in the southern sky
    (2002) Whiting, AB; Hau, GKT; Irwin, M
    We present observations of 82 Local Group dwarf galaxy candidates, of which 62 were chosen visually from ESO-SRC survey plates of the southern sky (32 of which were not previously cataloged) and the rest suggested by various sources in the literature. Two are the Local Group galaxies Antlia and Cetus; nine are more distant galaxies, though still within a few megaparsecs; 45 are background galaxies; seven are planetary ( or other emission) nebulae; 15 are reflection or other Galactic nebulae; two are galaxy clusters; one is a Galactic star cluster; and one is a misidentified star. We conclude that there is no large population of faint Local Group dwarf galaxies of any familiar type awaiting discovery. We point out the danger of relying on a single type of data to reach conclusions about an object.