The Arecibo Legacy Fast ALFA Survey. X. The H I Mass Function and Ω_H I from the 40% ALFALFA Survey
Abstract
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_H I/M_{⊙}) < 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 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* (h 3 70 Mpc-3 dex-1) = 4.8 ± 0.3 × 10-3, log (M */M sun) + 2 log h 70 = 9.96 ± 0.02, and α = -1.33 ± 0.02. We find Ω_H I = 4.3 ± 0.3 ×10-4 h -1 70, 16% larger than the 2005 HIPASS result, and our Schechter function fit extrapolated to log (M_H I/M_{⊙}) = 11.0 predicts an order of magnitude more galaxies than HIPASS. The larger values of Ω_H I and of M * 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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- November 2010
- DOI:
- 10.1088/0004-637X/723/2/1359
- arXiv:
- arXiv:1008.5107
- Bibcode:
- 2010ApJ...723.1359M
- Keywords:
-
- galaxies: distances and redshifts;
- galaxies: dwarf;
- galaxies: luminosity function;
- mass function;
- radio lines: galaxies;
- surveys;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- 21 pages, 13 figures, submitted to ApJ