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Session 115 - Star Clusters & Dwarf Galaxies.
Oral session, Saturday, January 10

[115.03] The Completely Transparent Galaxy UGC 12695

K. O'Neil, G. D. Bothun (U. Oregon), C. D. Impey (Steward Obs.)

Utilizing the F814W and F300W filters, short exposure Hubble Space Telescope Wide Field Planetary Camera-2 images were taken of UGC 12695, a low surface brightness disk galaxy. UGC 12695 has an unusual morphology, consisting of a Y-shaped nucleus surrounded by a faint spiral arm with a number of bright H II regions interspersed throughout the galaxy. Surface photometry indicates the majority of recent star formation in this galaxy occurred in these very localized regions, most of which have a radius of R_T_814\:\leq 2". The uneven distribution of stellar age combined with the galaxy's overall extremely blue color and low metallicity indicates UGC 12695 is a galaxy still in the throes of formation.

The WFPC-2 image has revealed that part of the structural peculiarities of this galaxy arise because a number of background galaxies are showing through both the outer nucleus and spiral arms of UGC 12695. Surface photometry was done on these galaxies through the F814W (I-band) filter, showing them to be fairly small (\alpha\: < 1.8") disk galaxies with total magnitudes ranging from 19.6 through 24.2, and central surface brightnesses between 20.2 mag/arcsec^2\:\leq\:\mu(0)\:\leq\:23.1\:mag/arcsec^2, all through the in the F814 band. When possible, the U, B, V, and I colors of these galaxies were found using ground-based images, which show the galaxies to be fairly red. Coupled with their small angular size, we estimate their redshifts to be z \geq 0.5. The discovery of multiple distant galaxies seen through the body of UGC 12695 immediately demonstrates it to be highly transparent. Even though its total luminosity is similar to a typical Sc galaxy, it clearly evolved in a way that did not produce significant disk opacity. Spectroscopy of these background galaxies, through the transparent disk of UGC 12695, may help to clarify its chemical evolution and current heavy element content.

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Program listing for Saturday