The ALFALFA HI velocity width function

Abstract

We make the most precise determination to date of the number density of extragalactic 21-cm radio sources as a function of their spectral line widths - the HI velocity width function (HIWF) - based on 21827 sources from the final 7000 deg${}^2$ data release of the Arecibo Legacy Fast ALFA (ALFALFA) survey. The number density of sources as a function of their neutral hydrogen masses - the HI mass function (HIMF) - has previously been reported to have a significantly different low-mass slope and 'knee mass' in the two sky regions surveyed during ALFALFA. In contrast with this, we find that the shape of the HIWF in the same two sky regions is remarkably similar, consistent with being identical within the confidence intervals implied by the data (but the overall normalisation differs). The spatial uniformity of the HIWF implies that it is likely a stable tracer of the mass function of dark matter haloes, in spite of the environmental processes to which the measured variation in the HIMF are attributed, at least for galaxies containing enough neutral hydrogen to be detected. This insensitivity of the HIWF to galaxy formation and evolution can be exploited to turn it into a powerful constraint on cosmological models as future surveys yield increasingly precise measurements. We also report on the possible influence of a previously overlooked systematic error affecting the HIWF, which may plausibly see its low-velocity slope steepen by $\sim$40 per cent in analyses of future, deeper surveys. Finally, we provide an updated estimate of the ALFALFA completeness limit.

13 pages, 4 figures, 1 table, +appendices. MNRAS, accepted version

References in corpus (15)

• The Tidal Evolution of Local Group Dwarf Spheroidals
• Is there a "too big to fail" problem in the field?
• Bent by baryons: the low mass galaxy-halo relation
• The velocity function in the local environment from LCDM and LWDM constrained simulations
• The Arecibo Legacy Fast ALFA Survey: IV. Strategies for Signal Identification and Survey Catalog Reliability
• Expanded haloes, abundance matching and too-big-to-fail in the Local Group
• NIHAO X: Reconciling the local galaxy velocity function with Cold Dark Matter via mock HI observations
• The ALFALFA-SDSS Galaxy Catalog
• Detailed HI kinematics of Tully-Fisher calibrator galaxies
• The HI Mass Function and Velocity Width Function of Void Galaxies in the Arecibo Legacy Fast ALFA Survey
• Spectroscopic Confusion: Its Impact on Current and Future Extragalactic HI Surveys
• The halo mass function of late-type galaxies from HI kinematics
• HI Global Scaling Relations in the WISE-WHISP Survey
• Surveying the Local Supercluster Plane
• Star Formation in Nearby Dwarf Galaxies

Cited by in corpus (7)

• Observational constraints on stellar feedback in dwarf galaxies
• The Tiered Radio Extragalactic Continuum (T-RECS) simulation II: HI emission and continuum-HI cross-correlation
• The FAST Ultra-Deep Survey (FUDS): observational strategy, calibration and data reduction
• The HI Mass Function of the Local Universe: Combining Measurements from HIPASS, ALFALFA and FASHI
• Modeling Post-Reionization HI Distributions in Fuzzy Dark Matter Cosmologies Using Conditional Normalizing Flows
• FAST Ultra-Deep Survey (FUDS): Data Release for FUDS0
• The north-south asymmetry of the ALFALFA HI velocity width function