The different baryonic Tully-Fisher relations at low masses.
We compare the Baryonic Tully-Fisher relation (BTFR) of simulations and observations of galaxies ranging from dwarfs to spirals, using various measures of rotational velocityVrot. We explore the BTFR when measuringVrotat the flat part of the rotation curve,Vflat, at the extent of H i gas,Vlast, and using 20 per cent (W20) and 50 per cent (W50) of the width of H i line profiles. We also compare with the maximum circular velocity of the parent halo, [Formula: see text], within dark matter only simulations. The different BTFRs increasingly diverge as galaxy mass decreases. UsingVlastone obtains a power law over four orders of magnitude in baryonic mass, with slope similar to the observed BTFR. MeasuringVflatgives similar results asVlastwhen galaxies with rising rotation curves are excluded. However, higher rotation velocities would be found for low-mass galaxies if the cold gas extended far enough forVrotto reach a maximum.W20gives a similar slope asVlastbut with slightly lower values ofVrotfor low-mass galaxies, although this may depend on the extent of the gas in your galaxy sample.W50bends away from these other relations towards low velocities at low masses. By contrast, [Formula: see text] bends towards high velocities for low-mass galaxies, as cold gas does not extend out to the radius at which haloes reach [Formula: see text]. Our study highlights the need for careful comparisons between observations and models: one needs to be consistent about the particular method of measuringVrot, and precise about the radius at which velocities are measured.
Departamento de Física Teórica, Universidad Autónoma de Madrid, E-28049 Cantoblanco, Madrid, Spain; Astro-UAM, UAM, Unidad Asociada CSIC, E-28049, Madrid, Spain.
Chris B
CB
Brook
Departamento de Física Teórica, Universidad Autónoma de Madrid, E-28049 Cantoblanco, Madrid, Spain.
Isabel
I
Santos-Santos
Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany.
Greg
G
Stinson
cosmology: theory; dark matter; galaxies: evolution