Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21341903c&link_type=abstract
American Astronomical Society, AAS Meeting #213, #419.03; Bulletin of the American Astronomical Society, Vol. 41, p.234
Astronomy and Astrophysics
Astronomy
Scientific paper
We present new optical and HI spectral line imaging of the extremely optically compact dwarf galaxy ADBS 113845+2008. This peculiar object was discovered in the Arecibo Dual Beam Survey; subsequent optical imaging revealed one of the most compact stellar distributions known in any galaxy to date (optical scale length 0.6 kpc). MMT spectra show emission lines characteristic of a "post-starburst" galaxy with sub-solar nebular abundance. In stark contrast to the compact stellar body, the neutral gas is very extended; HI is detected to more than 20 kpc (>25 optical scale lengths), making this one of the most dramatic examples known of a large HI cloud associated with a compact optical system. The optical body is located near the center of a broken ring of HI that is 15 kpc in diameter; column densities peak in this structure at the 3.5x1020/cm2 level. At the center of this ring, in a region of comparatively low HI column density, we find ongoing star formation traced by Hα emission. To explain these enigmatic properties, we examine simplistic "inside-out" and "outside-in" evolutionary scenarios. "Feedback" from concentrated star formation is not capable of producing the ring structure; we posit that this is a rare system where the large HI disk is evolving in quiescent isolation. Stochastic effects have initiated and sustained star formation only in the very innermost region of the disk. In a global sense, this system is exceedingly inefficient at converting neutral gas into stars. We sample the rotation curve to the point of turn over; this indirectly constrains the size of the dark matter halo of the galaxy, which outweighs the luminous component (stars + gas) by at least a factor of 10.
Cannon John M.
Rosenberg Jessica L.
Salzer John Joseph
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