The Outer Halo of Centaurus A

Sarah Bird (University of Turku)

The very earliest stars in giant galaxies – the most metal-poor halo stars and globular clusters – may have formed before the onset of hierarchical merging, within small pregalactic dwarfs that populated the large-scale dark-matter potential well. Today, these relic stars should be found in a sparse and extremely extended “outermost-halo” component. Finding clear traces of this component in other giant galaxies, and deconvolving it from the more obvious and metal-rich spheroid component generated later by mergers, has been extraordinarily difficult. Now, striking new evidence discovered in M 31 and NGC 3379 suggests that the metal-poor outermost halo can be isolated at very large radii, R > 12Reff. We now have a new deep imaging study with ESO VLT of the nearest giant elliptical and merger remnant, Centaurus A, to search for this extended remnant of the galaxy’s earliest history.

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