THE ARECIBO LEGACY FAST ALFA SURVEY. X. THE H I MASS FUNCTION AND {Omega}{sub H{sub i}} FROM THE 40% ALFALFA SURVEY
- Center for Radiophysics and Space Research, Space Sciences Building, Cornell University, Ithaca, NY 14853 (United States)
- Australian Astronomical Observatory, P.O. Box 296, Epping, NSW 1710 (Australia)
- Spitzer Science Center, California Institute of Technology, 1200 East California Boulevard, CA 91125 (United States)
The Arecibo Legacy Fast ALFA (ALFALFA) survey has completed source extraction for 40% of its total sky area, resulting in the largest sample of H I-selected galaxies to date. We measure the H I mass function from a sample of 10,119 galaxies with 6.2 < log (M{sub H{sub i}}/M{sub sun}) < 11.0 and with well-described mass errors that accurately reflect our knowledge of low-mass systems. We characterize the survey sensitivity and its dependence on profile velocity width, the effect of large-scale structure, and the impact of radio frequency interference in order to calculate the H I mass function with both the 1/V{sub max} and 2DSWML methods. We also assess a flux-limited sample to test the robustness of the methods applied to the full sample. These measurements are in excellent agreement with one another; the derived Schechter function parameters are {phi}{sub *} (h {sup 3}{sub 70} Mpc{sup -3} dex{sup -1}) = 4.8 {+-} 0.3 x 10{sup -3}, log (M{sub *}/M{sub sun}) + 2 log h{sub 70} = 9.96 {+-} 0.02, and {alpha} = -1.33 {+-} 0.02. We find {Omega}{sub H{sub i}}= 4.3 {+-} 0.3 x10{sup -4} h {sup -1}{sub 70}, 16% larger than the 2005 HIPASS result, and our Schechter function fit extrapolated to log (M{sub H{sub i}}/M{sub sun}) = 11.0 predicts an order of magnitude more galaxies than HIPASS. The larger values of {Omega}{sub H{sub i}} and of M{sub *} imply an upward adjustment for estimates of the detection rate of future large-scale H I line surveys with, e.g., the Square Kilometer Array. A comparison with simulated galaxies from the Millennium Run and a treatment of photoheating as a method of baryon removal from H I-selected halos indicate that the disagreement between dark matter mass functions and baryonic mass functions may soon be resolved.
- OSTI ID:
- 21471261
- Journal Information:
- Astrophysical Journal, Vol. 723, Issue 2; Other Information: DOI: 10.1088/0004-637X/723/2/1359; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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