Spectroscopic Confusion: Its Impact on Current and Future Extragalactic HI Surveys

Abstract

We present a comprehensive model to predict the rate of spectroscopic confusion in HI surveys, and demonstrate good agreement with the observable confusion in existing surveys. Generically the action of confusion on the HI mass function was found to be a suppression of the number count of sources below the `knee', and an enhancement above it. This results in a bias, whereby the `knee' mass is increased and the faint end slope is steepened. For ALFALFA and HIPASS we find that the maximum impact this bias can have on the Schechter fit parameters is similar in magnitude to the published random errors. On the other hand, the impact of confusion on the HI mass functions of upcoming medium depth interferometric surveys, will be below the level of the random errors. In addition, we find that previous estimates of the number of detections for upcoming surveys with SKA-precursor telescopes may have been too optimistic, as the framework implemented here results in number counts between 60% and 75% of those previously predicted, while accurately reproducing the counts of existing surveys. Finally, we argue that any future single dish, wide area surveys of HI galaxies would be best suited to focus on deep observations of the local Universe (z < 0.05), as confusion may prevent them from being competitive with interferometric surveys at higher redshift, while their lower angular resolution allows their completeness to be more easily calibrated for nearby extended sources.

arXiv commentAccepted to MNRAS, 14 pages, 9 figures, 2 tables

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• Environmental dependence of the HI mass function in the ALFALFA 70% catalogue
• Outflows in Star-forming Galaxies: Stacking Analyses of Resolved Winds and the Relation to Their Hosts' Properties
• The AMIGA sample of isolated galaxies XIII. The HI content of an almost "nurture free" sample
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• The HI mass function of group galaxies in the ALFALFA survey
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• Large-scale motions and growth rate from forward-modelling Tully-Fisher peculiar velocities
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• Synthetic data products for future HI galaxy surveys: a tool for characterising source confusion in spectral line stacking experiments
• On the Uncertainties of Results Derived from HI Spectral Line Stacking Experiments
• The FAST Ultra-Deep Survey (FUDS): observational strategy, calibration and data reduction
• The ALFALFA HI velocity width function
• Interferometric Cubelet Stacking to Recover H\,\textsc{i} Emission from Distant Galaxies
• A Generalist, Automated ALFALFA Baryonic Tully-Fisher Relation
• The north-south asymmetry of the ALFALFA HI velocity width function
• The FAST Hundred-Deg${}^2$ HI Deep (HD${}^2$) Survey: Early Results from the Pilot Survey