Towards a Global Metal Budget of the Universe: The missing link at Cosmic Noon
Saloni Deepak
Department of Physics and Astronomy
University of Notre Dame
The cosmic baryon cycle regulates the evolution of galaxies and connects larger scale structure formation to local galaxy properties. In this framework, metals act as tracer particles - their presence indicates the degree of interaction a parcel of gas has had with a galaxy. Globally, the distribution of metals (tracing the cosmic metal cycle) in various gas phases informs us of the dominant physics at any given epoch and environment. In this talk, I will present our results for the evolution of the global metal densities of various metal reservoirs and the uncertainties in these global estimates. This work revealed a crucial gap in CGM and IGM metallicity studies at z~1-2.4, also known as cosmic noon. Characterized by peaks in both the cosmic star formation rate density and AGN feedback, this is the most active epoch of metal production and redistribution. I will present results from our upcoming survey measuring metallicities of absorbers tracing the CGM and IGM of galaxies at cosmic noon, providing the first constraints to close this gap.
Tracing the diffuse neutral hydrogen (with 21 cm) around two nearby spiral galaxies
Mary Rickel
Department of Physics and Astronomy
University of Notre Dame
Nearly all galaxies in the Universe are forming new stars at a rate that would quickly exhaust their available star-forming gas supply (neutral hydrogen), suggesting a "missing" mass problem. However, neutral hydrogen is often primarily studied within the constraints of the disk and at higher column densities. This implies that a significant missing repository may be beyond the disk and/or at low column densities. With unprecedented sensitivity, we detected HI in the outer regions of nearby galaxies using radio observations from the Green Bank Telescope (GBT) and Westerbork Synthesis Radio Telescope (WSRT). Our findings uncover a substantial amount of gas in these outer regions, previously undetected due to prior sensitivity limitations published in Das et al. (2020) and Das, Rickel et al. (2024). I will present the results from a soon to be submitted paper highlighting the neutral hydrogen distributions along the off-axis of both galaxies. With the off-axis perspective, our results suggest an extended and co-rotating diffuse neutral hydrogen disk around both galaxies.