The milky way, local galaxies, and the infrared tully-fisher relation

Using the near-infrared fluxes of local galaxies derived from Cosmic Background Explorer (COBE)/ Diffuse Infrared Background Experiment (DIRBE)⁵ J- (1.25 μm) K- (2.2 μm), and L-band (3.5 μm) maps and published Cepheid distances, we construct Tully-Fisher (TF) diagrams for nearby galaxies. The measured dispersions in these luminosity-line width diagrams are remarkably small : σ_J = 0.09 mag, σ_K = 0.13 mag, and σ_L = 0.20 mag. These dispersions include contributions from the intrinsic TF relation scatter and the errors in estimated galaxy distances, fluxes, inclination angles, extinction corrections, and circular speeds. For the J and K bands, Monte Carlo simulations give a 95% confidence interval upper limit on the true scatter in the TF diagram of σ_J ≤ 0.35 and σ_K ≤ 0.45. We determine the Milky Way's luminosity and place it in the TF diagram by fitting a bar plus exponential disk model of the Milky Way to the all-sky DIRBE maps. For " standard " values of its size and circular speed (Sun-Galactic center distance R₀ = 8.5 kpc and ₀ = 220 km s^-1), the Milky Way lies within 1.5 σ of the TF relations. We can use the TF relation and the Cepheid distances to nearby bright galaxies to constrain R₀ and ₀: 1.63 log (₀/220 km s^-1) - log (R₀/8.5 kpc) = 0.08 ±0.03. Alternatively, we can fix the parameters of the Galaxy to their standard values, ignore the Cepheid zero point, and use the TF relation to determine the Hubble constant directly: H₀ = 72 ±12 km s^-1 Mpc^-1. We have also tested the TF relation at longer wavelengths, where the emission is dominated by dust. We find no evidence for a TF relation at wavelengths beyond 10 μm. The tight correlation seen in the L band suggests that stellar emission dominates over the 3.3 μm polycyclic aromatic hydrocarbon emission.