The ISM-METALS group has played a leading role in two collaborations, bringing expertise on understanding the metallicities measured within new optical spectroscopic datasets. With a focus on the Milky Way and Large and Small Magellanic Clouds (LMC, SMC), the Sloan Digital Sky Survey (SDSS) Local Volume Mapper (LVM) project is carrying out an optical integral field unit (IFU) survey that resolves the internal structures of HII regions at 1-10 pc resolution. With a focus on more distant galaxies, the PHANGS (Physics at High Angular resolution in Nearby GalaxieS) collaboration has surveyed 42 nearby galaxies with the optical IFU instrument MUSE on the Very Large Telescope, isolating tens of thousands of individual HII regions at 100 pc scales. The ISM-METALS project overcomes limitation of past projects by bridging the high resolution HII region studies in LVM with large, statistical integrated HII region studies in PHANGS. In support of our scientific analysis, we are also contributing to the refinement of the data calibration and reduction pipelines associated with these two projects.
Using the more distant sample of HII regions, we have characterized the temperatures of different ions, finding that the N+ emission lines provide remarkably robust constraints on the temperature within the full volume of ionized gas. Leveraging this insight, we have determined precise radial metallicity gradients for PHANGS galaxies, finding very low scatter that is indicative of a systematically well-mixed ISM. Within one particular, peculiar galaxy located in a low-density void environment, we have used metallicity constraints for the N/O abundances relative to O/H to present chemodynamic evidence of ongoing pristine gas accretion. This insight links internal and external processes that balance to regulate galaxy growth.
We have also published the first scientific analysis from the LVM dataset. We constructed the largest IFU map made (to date) of the Milky Way and providing insights into the physical conditions of well-known nebulae within the Orion constellation, including the Horsehead Nebula and Flame Nebula. In addition, we supported projects analyzing the ionization structure of the Rosette Nebula, characterizing collisionless shocks in a Galactic supernova remnant, and identifying ionized helium emission associated with extreme Wolf-Rayet stars in the SMC. A total area of 3000 square degrees have now been observed by the LVM, an unprecedented dataset.
