The baryonic Tully–Fisher relation for different velocity definitions and implications for galaxy angular momentum

Abstract

We study the baryonic Tully-Fisher relation (BTFR) at z=0 using 153 galaxies\nfrom the SPARC sample. We consider different definitions of the characteristic\nvelocity from HI and H-alpha rotation curves, as well as HI line-widths from\nsingle-dish observations. We reach the following results: (1) The tightest BTFR\nis given by the mean velocity along the flat part of the rotation curve. The\northogonal intrinsic scatter is extremely small (6%) and the best-fit slope is\n3.85+/-0.09, but systematic uncertainties may drive the slope from 3.5 to 4.0.\nOther velocity definitions lead to BTFRs with systematically higher scatters\nand shallower slopes. (2) We provide statistical relations to infer the flat\nrotation velocity from HI line-widths or less extended rotation curves (like\nH-alpha and CO data). These can be useful to study the BTFR from large HI\nsurveys or the BTFR at high redshifts. (3) The BTFR is more fundamental than\nthe relation between angular momentum and galaxy mass (the Fall relation). The\nFall relation has about 7 times more scatter than the BTFR, which is merely\ndriven by the scatter in the mass-size relation of galaxies. The BTFR is\nalready the "fundamental plane" of galaxy discs: no value is added with a\nradial variable as a third parameter.\n