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J. K. Werk, M. E. Putman (University of Michigan), G. R. Meurer (Johns Hopkins University), E. V. Ryan-Weber (University of Cambridge), SINGG Team
Star formation traditionally proceeds within high density, kinematically active regions of galaxy disks. Here, we find evidence for star formation in the low density halos of galaxies at projected distances up to 30 kpc from the galaxy disk. 68 small, isolated emission-line objects, (Emission Line Dots, ELDots) derived from 98 images (of target galaxies with recessional velocities between 500 and 4000 km/s) in the NOAO Survey for Ionization in Neutral Gas Galaxies (SINGG) compose our sample of candidates for isolated star-forming regions. ELDots are located at least twice the {\mu}R = 25 mag arcsec-2 isophotal radius from the apparent host galaxy and appear as high equivalent width, unresolved objects in continuum-subtracted H{\alpha} images. We present the spectroscopic follow-up of approximately half of our sample of ELDots, assessing what fraction represents star formation in the low density environment of the SINGG galaxy halos and what fraction represents higher-redshift background objects. Previous follow-up work has found ~1/4 of the ELDots are indeed \ion{H}{2} regions tidally bound to a host SINGG galaxy, located in the far outskirts of the galaxy's halo. These confirmed objects represent an atypical mode of star formation in the low-density environment of the outer halos of galaxies. The number of confirmed sources also has a direct impact on our understanding of the enrichment and ionization source of the intergalactic medium (IGM), the trigger of star formation for the first stars formed in the universe, and potential contributors to intracluster light (ICL). We expect to nearly complete the spectroscopic confirmation for our sample by April of 2006.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.