Gas kinematics in FIRE simulated galaxies compared to spatially unresolved HI observations

Kareem El-Badry, Jeremy Bradford, Eliot Quataert, Marla Geha, Michael Boylan-Kolchin, Daniel R. Weisz, Andrew Wetzel, Philip F. Hopkins, T. K. Chan, Alex Fitts, Dušan Kereš, Claude André Faucher-Giguère

Research output: Contribution to journalArticlepeer-review

41 Scopus citations


The shape of a galaxy's spatially unresolved, globally integrated 21-cm emission line depends on its internal gas kinematics: galaxies with rotationally supported gas discs produce double-horned profiles with steep wings, while galaxies with dispersion-supported gas produce Gaussian-like profiles with sloped wings. Using mock observations of simulated galaxies from the FIRE project, we show that one can therefore constrain a galaxy's gas kinematics from its unresolved 21-cm line profile. In particular, we find that the kurtosis of the 21-cm line increases with decreasing V/σ and that this trend is robust across a wide range of masses, signal-to-noise ratios, and inclinations. We then quantify the shapes of 21-cm line profiles from a morphologically unbiased sample of ~2000 low-redshift, HI-detected galaxies with Mstar = 107-11M and compare to the simulated galaxies. At Mstar ≳ 1010M, both the observed and simulated galaxies produce double-horned profiles with low kurtosis and steep wings, consistent with rotationally supported discs. Both the observed and simulated line profiles become more Gaussian like (higher kurtosis and less-steep wings) at lower masses, indicating increased dispersion support. However, the simulated galaxies transition from rotational to dispersion support more strongly: at Mstar = 108-10M, most of the simulations produce more Gaussian-like profiles than typical observed galaxies with similar mass, indicating that gas in the low-mass simulated galaxies is, on average, overly dispersion supported. Most of the lower-mass-simulated galaxies also have somewhat lower gas fractions than the median of the observed population. The simulations nevertheless reproduce the observed line-width baryonic Tully-Fisher relation, which is insensitive to rotational versus dispersion support.

Original languageEnglish (US)
Pages (from-to)1536-1548
Number of pages13
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
StatePublished - Jun 21 2018
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Galaxies: Dwarf
  • Galaxies: Irregular
  • Galaxies: Kinematics and dynamics


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