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K.L. Masters, M.P. Haynes, R. Giovanelli (Cornell University)
In a \lambdaCDM universe there should exist a large number of low mass halos, more than are found in current observations. The extent of the over-prediction is not known since disagreements remain between observers over the number of low mass halos, with the most recent derivations of the HI mass function (HIMF) differing by an order of magnitude when extrapolated to HI masses 107 M\odot and lower. A potential problem with the measurement of the low mass end of the HIMF comes from the need to assign a distance to the galaxy. Low mass galaxies are seen only at distances where peculiar velocities can contribute a significant fraction of the recessional velocities. The error added to the distance by peculiar velocities has in the past been modelled by adding random Gaussian noise; however, velocity fields are coherent over the distances where low mass galaxies are seen, meaning that the errors could add up to a significant bias. Here we report on simulations of the effect of distance errors on derivations of the low mass slope of the HIMF based on density and velocity fields derived from the PSCz catalog. We consider various survey geometries and depths and compare the HIMFs measured when using the `real' distances, distances from a multi-attractor model, and distances derived from assuming pure Hubble flow. The effects are variable and dependent on the exact survey geometry, but we conclude that at least part of the discrepancy between the recent derivations of the HIMF can be accounted for by the different methods used by those authors to assign distances.
This work is partially funded by NSF grants AST-9900695 and AST-0307396.
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.