Measuring the H I mass function below the detection threshold
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Date
2019-10-30
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Publisher
Oxford University Press
Abstract
We present a Bayesian stacking technique to directly measure the H I mass function (HIMF)
and its evolution with redshift using galaxies formally below the nominal detection threshold.
We generate galaxy samples over several sky areas given an assumed HIMF described by a
Schechter function and simulate the H I emission lines with different levels of background
noise to test the technique. We use MULTINEST to constrain the parameters of the HIMF in
a broad redshift bin, demonstrating that the HIMF can be accurately reconstructed, using
the simulated spectral cube far below the H I mass limit determined by the 5σ flux-density
limit, i.e. down to MH I = 107.5 M over the redshift range 0 <z< 0.55 for this particular
simulation, with a noise level similar to that expected for the MIGHTEE survey. We also
find that the constraints on the parameters of the Schechter function, φ , M , and α can be
reliably fit, becoming tighter as the background noise decreases as expected, although the
constraints on the redshift evolution are not significantly affected. All the parameters become
better constrained as the survey area increases. In summary, we provide an optimal method
for estimating the H I mass at cosmological distances that allows us to constrain the HIMF
below the detection threshold in forthcoming H I surveys. This study is a first step towards the
measurement of the HIMF at high (z > 0.1) redshifts.
Description
Keywords
methods: statistical, galaxies: mass function, radio lines: galaxies
Citation
Jarvis, M et al. 2020. Measuring the H I mass function below the detection threshold. Monthly Notices of the Royal Astronomical Society. 491(1):1227-1242