Seminar: Metal Transport to the Gaseous Outskirts of Galaxies

Dr Jessica Werk 

UC Santa Cruz

HI in NGC2915 (shown in blue) over an optical image (shown in yellow). Credit: Prof Gerhardt Meurer (ICRAR).

Download the pdf poster.

Neutral hydrogen gas often extends far beyond the stellar component of galaxies in forms ranging from relatively quiescent extended disks to tidally stripped tails. Despite its ubiquity, knowledge of gas enrichment levels outside the stellar components of galaxies has remained somewhat limited.

In this talk, I will describe a search for outlying HII regions in the gaseous outskirts of extended, disturbed, and/or interacting gas-rich galaxies, and subsequent Gemini Telescope multi-slit spectroscopy from which I obtain the nebular oxygen abun- dances of numerous outlying and centrally-located HII regions.

Then, I will present oxygen abundance gradients out to 2.5 times the optical radius for 13 gas-rich galaxies that span a range of morphologies and masses. By analyzing the underlying stellar and neutral HI gas distributions in the vicinity of the HII regions, I attempt to identify the physical processes that could give rise to the observed metal distributions in galax- ies. These measurements, for the first time, convincingly show flat abundance gradients at large radii in a wide variety of systems, and have important implications on the efficiency of metal transport in galaxies, the star-formation history of outer-disk material, and the potential expulsion of metals into the intergalactic medium.