We present a current catalog of 21?cm H I line sources extracted from the Arecibo Legacy Fast Arecibo L-band Feed Array (ALFALFA) survey over ~2800?deg2 of sky: the ?.40 catalog. Covering 40% of the final survey area, the ?.40 catalog contains 15,855 sources in the regions 07h30m < R.A. < 16h30m, +04? < decl.z < 0.25. A detailed analysis is presented of the completeness, width-dependent sensitivity function and bias inherent of the ?.40 catalog. The impact of survey selection, distance errors, current volume coverage, and local large-scale structure on the derivation of the H I mass function is assessed. While ?.40 does not yet provide a completely representative sampling of cosmological volume, derivations of the H I mass function using future data releases from ALFALFA will further improve both statistical and systematic uncertainties.
Available at: http://works.bepress.com/sarah_higdon/51/