THE BARYONIC TULLY-FISHER RELATION OF GAS-RICH GALAXIES AS A TEST OF ΛCDM AND MOND

The baryonic Tully-Fisher relation (BTFR) is an empirical relation between baryonic mass and rotation velocity in disk galaxies. It provides tests of galaxy formation models in Lambda CDM and of alternative theories like modified Newtonian dynamics (MOND). Observations of gas-rich galaxies provide a measure of the slope and normalization of the BTFR that is more accurate (if less precise) than that provided by star-dominated spirals, as their masses are insensitive to the details of stellar population modeling. Recent independent data for such galaxies are consistent with M-b = AV(f)(4) with A = 47 +/- 6 M-circle dot km(-4) s(4). This is equivalent to MOND with a(0) = 1.3 +/- 0.3 angstrom s(-2). The scatter in the data is consistent with being due entirely to observational uncertainties. It is unclear why the physics of galaxy formation in Lambda CDM happens to pick out the relation predicted by MOND. We introduce a feedback efficacy parameter epsilon to relate halo properties to those of the galaxies they host. epsilon correlates with star formation rate and gas fraction in the sense that galaxies that have experienced the least star formation have been most impacted by feedback.