The Milky Way, Local Galaxies, and the Infrared Tully‐Fisher Relation

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Abstract
Using the near-infrared fluxes of local galaxies derived from Cosmic Background Explorer (COBE)/ Diffuse Infrared Background Experiment (DIRBE)* 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: σJ = 0.09 mag, σK = 0.13 mag, and σL = 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 σJ ≤ 0.35 and σK ≤ 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 Θ0 = 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 Θ: 1.63 log (Θ0/220 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.
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