A Search for Boron in Damped Ly{\alpha} Systems

Abstract

We present the first systematic study of boron beyond the Local Group. This analysis is performed on a sample of 30 damped Ly{\alpha} systems (DLAs) with strong metal-lines, which are expected to trace the interstellar medium of high z galaxies. We report on two boron detections at > 3{\sigma} significance; one new detection and one confirmation. The ratios of B/O and, for the first time, B/S are compared with previous stellar and interstellar measurements in the Milky Way and Small Magellanic Cloud. The novel comparison with sulphur, which tracks oxygen's abundance, alleviates the uncertainty associated with stellar oxygen measurements. For both detections, the inferred B/S ratio is in excess of the prediction of primary boron production from spallation processes. Possible sources of contamination are discussed, as well as physical effects that could impact the observed ratios. However taken at face value, the implication of these measurements suggest potentially higher cosmic ray fluxes in DLAs. The prospects for future boron detections in other high redshift DLAs to confirm our results is also discussed.Comment: Accepted for publication in MNRAS, 19 pages, 10 figure