Simulating HI spectral line stacking with the use of optical priors

Forthcoming deep HI surveys (e.g., LADUMA = Looking At the Distant Universe with the MeerKAT Array) will make extensive use of spectral line stacking, in order to achieve statistical detections of populations of galaxies that are too faint to be detected individually. Such stacking by definition requires previous measurements of optical redshifts, so that the appropriate spectral ranges from an HI data cube can be extracted, shifted, and averaged. However, it is also possible to consider using additional prior information from optical imaging (e.g., axis ratios) to “correct” an HI spectrum for inclination before including it in a stack. We have used archival spectra from the HI Parkes All-Sky Survey (HIPASS) to simulate the impact of using this type of information on spectral line stacking. Results include an exploration of how stacked profiles depend on galaxy size, redshift (within the narrow range probed by HIPASS), and the presence or absence of inclination “corrections.”

This work has been supported by National Science Foundation grants PHY-1560077 and AST-2050950.