Obtaining Galaxy Masses Using Stellar Absorption and [O [CSC]ii[/CSC]] Emission-Line Diagnostics in Late-Type Galaxies

Abstract

The [O II] λ3727 emission lines and absorption features from stellar Balmer and Ca H and K lines are the most accessible kinematic diagnostics in galaxies at z ∼ 1. We investigate the kinematics of 22 local late-type galaxies using these spectral features, and we compare the results with 21 cm neutral hydrogen spectra in order to assess the utility of each diagnostic for measuring galaxy masses. In order to simulate data at high redshift, where only one-dimensional velocity profiles are normally available, we study spatially integrated, as well as spatially resolved, spectra. Although the studied galaxies span a wide range of morphological types, inclinations, and star formation rates, we find that the gaseous and stellar kinematic tracers yield comparable kinematic line widths and systemic velocities. The [O II] and H I line widths correlate most strongly, showing an intrinsic dispersion of ∼20 km s-1, or ∼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%. Reliable 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 ≤10% between the stellar absorption and H I line widths. We provide a prescription for using these strong stellar absorption and [O II] emission features to measure the kinematics, and thus masses, of galaxies in the distant universe.