NGC 1705: The missing link between blue compact dwarf and dwarf elliptical galaxies?
ABSTRACT We report results of a detailed study of the nearby blue compact dwarf galaxy NGC 1705. There are two stellar populations in NGC 1705: an underlying population around a Gyr old or older, and a young population of fairly continuous star formation for the last 250 Myr. An off-centre nucleus, which is probably a young (10 Myr old), massive (106
) globular cluster, is part of this young population. The H morphology and emission line kinematics are consistent with an expulsive flow triggered by the formation of the nucleus. We show that NGC 1705 is losing ionized material in this galactic wind with neutral material probably entrained in the flow. This flow may lead to total removal of the ISM. The evolutionary fate of NGC 1705 is uncertain but the most likely outcome is rapid evolution into a nucleated dwarf elliptical galaxy.
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ABSTRACT: Using images from a charge-coupled device survey with the Wide Field Camera on the Isaac Newton Telescope, we performed B- and I-band photometry on 156 Virgo cluster dwarf elliptical (dE) galaxies, 25 candidate new cluster dwarfs, and nine candidate field dwarfs. Galaxies were modelled with Sérsic profiles, using both 1D χ2 and 2D cross-correlation methods, with nuclei modelled as point sources. The intensity profiles of 50 galaxies previously classified as dE, dE?, or ? are more accurately fitted if a nucleus is included, and this results in the majority of dwarfs now being classified as nucleated dwarf ellipticals (dE,N). Some faint galaxies with B magnitudes of 18–21 have particularly large relative nuclei, while a small number have apparent central dimmings. For cluster dE,N galaxies the nucleus magnitude is correlated with the magnitude of the host galaxy. The profile parameters of dE and dE,N galaxies are not significantly different, and there is no evident discontinuity in relative nucleus size between non-nucleated and nucleated dwarfs, suggesting that they may form a continuum. Nuclei are on average redder than their underlying galaxies, though a spread of relative colours was found, and two-fifths of nuclei are bluer. Formation mechanisms of nuclei are discussed: at least some appear to have formed in an already existing non-nucleated galaxy, though others may have formed simultaneously with their galaxies and subsequently evolved within them.Monthly Notices of the Royal Astronomical Society 01/2005; · 5.52 Impact Factor