* Astronomy

Blobrana · L

RE: ADBS 113845+2008

Blobrana · L

A U.S. astronomer says he discovered a galaxy in which gas is distributed over a much larger area than researchers expected to find.
Macalester College Professor John Cannon said the "giant disk" dwarf galaxy he discovered has the largest size difference between stars and gas of any known galaxy. That finding, he said, is important for furthering the understanding of how galaxies form and how they remain stable over time.

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Blobrana · L

A U.S. astronomer says he discovered a galaxy in which gas is distributed over a much larger area than researchers expected to find.
Macalester College Professor John Cannon said the "giant disk" dwarf galaxy he discovered has the largest size difference between stars and gas of any known galaxy. That finding, he said, is important for furthering the understanding of how galaxies form and how they remain stable over time.

Read more

Blobrana · L

Title: Quiescent Isolation: The Extremely Extended HI Halo of the Optically Compact Dwarf Galaxy ADBS 113845+2008
Authors: John M. Cannon, John J. Salzer, Jessica L. Rosenberg,

We present new optical imaging and spectroscopy and H i spectral line imaging of the dwarf galaxy ADBS 113845+2008 (hereafter ADBS 1138). This metal-poor (Z -30% Z/dot), "post-starburst" system has one of the most compact stellar distributions known in any galaxy to date (B-band exponential scale length =0.57 kpc). In stark contrast to the compact stellar component, the neutral gas is extremely extended; H i is detected to a radial distance of - 25 kpc at the 10^19 cm^-2 level (>- 44 B-band scale lengths). Comparing to measurements of similar "giant disk" dwarf galaxies in the literature, ADBS 1138 has the largest known H i-to-optical size ratio. The stellar component is located near the center of a broken ring of H i that is - 15 kpc in diameter; column densities peak in this structure at the - 3.5 x 10^20 cm^-2 level. At the center of this ring, in a region of comparatively low H i column density, we find ongoing star formation traced by H emission. We sample the rotation curve to the point of turn over; this constrains the size of the dark matter halo of the galaxy, which outweighs the luminous component (stars + gas) by at least a factor of 15. To explain these enigmatic properties, we examine "inside-out" and "outside-in" evolutionary scenarios. Calculations of star formation energetics indicate that "feedback" from concentrated star formation is not capable of producing the ring structure; we posit that this is a system where the large H i disk is evolving in quiescent isolation. In a global sense, this system is exceedingly inefficient at converting neutral gas into stars.

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