The small scatter of the baryonic Tully-Fisher relation

Understand

In a LCDM cosmology, the baryonic Tully-Fisher relation (BTFR) is expected to show significant intrinsic scatter resulting from the mass-concentration relation of dark matter halos and the baryonic-to-halo mass ratio.

• We study the BTFR using a sample of 118 disc galaxies (spirals and irregulars) with data of the highest quality: extended HI rotation curves (tracing the outer velocity) and Spitzer photometry at 3.6 $\mu$m (tracing the stellar mass).
• Assuming that the stellar mass-to-light ratio (M*/L) is nearly constant at 3.6 $\mu$m, we find that the scatter, slope, and normalization of the BTFR systematically vary with the adopted M*/L.
• The observed scatter is minimized for M*/L > 0.5, corresponding to nearly maximal discs in high-surface-brightness galaxies and BTFR slopes close to ~4.