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Abstract

In an effort to improve our understanding of galaxy evolution, we study how stellar evolution in the form of feedback affects dwarf galaxies. Our galaxy sample consists of the 82 galaxies in the Survey of HI in Extremely Low-mass Dwarfs (SHIELD) program. These galaxies were selected from the Arecibo Legacy Fast ALFA (ALFALFA) survey, an unbiased extragalactic neutral hydrogen (HI) survey. The motivation for this project is to make progress in understanding the life cycle of galaxies, to catch strong feedback in action, and to investigate the frequency of these events. Our goal is to identify and study dwarf galaxies that show an offset between their gaseous and stellar distributions. We evaluate the overlap of total intensity HI maps, which come from observations made with the Very Large Array (VLA), onto infrared and optical images, which come from observations made with the Spitzer Space Telescope and the DESI Legacy Imaging Survey respectively, to quantitatively and qualitatively characterize this offset. We have classified 11 galaxies out of the sample of 82 as “offset”, all displaying a visible physical separation between the center of the HI distribution and the stellar distribution as well as additional characteristics indicative of disturbed gas. Seven additional galaxies were classified as “possibly offset” due to gas which is shown to be disturbed, but not necessarily offset from the stellar component. An environmental analysis of the galaxies using ALFALFA and SDSS survey data shows that some of the galaxies identified as offset or possibly offset were also identified as isolated, indicating that an internal mechanism, such as feedback, may cause the HI gas to be offset rather than an external mechanism. Additionally, the relative lack of Hα from star formation indicates recent (and possibly temporary) quenching of star formation.

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