Obtaining galaxy masses using stellar absorption and [O II] emission-line diagnostics in late-type galaxies

The [O II] lambda 3727 emission lines and absorption features from stellar Balmer and Ca H and K lines are the most accessible kinematic diagnostics i n galaxies at z similar to 1. We investigate the kinematics of 22 local lat e-type galaxies using these spectral features, and we compare the results w ith 21 fm neutral hydrogen spectra in order to assess the utility of each d iagnostic for measuring galaxy masses. In order to simulate data at high re dshift, where only one-dimensional velocity profiles are normally available , we study spatially integrated, as well as spatially resolved, spectra, Al though the studied galaxies span a wide range of morphological types, incli nations, and star formation rates, we find that the gaseous and stellar kin ematic tracers yield comparable kinematic line widths and systemic velociti es. The [O II] and H I line widths correlate most strongly, showing an intr insic dispersion of similar to 20 km s(-1), or similar to 10% for a typical galaxy with a kinematic width of 200 km s(-1) In a few extreme cases, the [O II] line widths underestimate the neutral hydrogen width by 50%. Reliabl e velocity widths can also be obtained from the stellar Balmer and Ca H and K absorption lines, even for some of the very late type galaxies that have strong emission lines. The intrinsic dispersion is less than or equal to 1 0% between the stellar absorption and H I line widths. We provide a prescri ption for using these strong stellar absorption and [O II] emission feature s to measure the kinematics, and thus masses, of galaxies in the distant un iverse.