1 v 1 2 5 A pr 1 99 6 The Milky Way , The Local Galaxies & the IR Tully - Fisher Relation

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) & L (3.5 μm) band maps and published Cepheid distances, we construct Tully-Fisher diagrams for the nearby galaxies. The measured dispersions in these luminosity-linewidth diagrams are remarkably small: σJ = 0.09 magnitudes, σK = 0.13 magnitudes, and σL = 0.20 magnitudes. These dispersions include contributions from both the intrinsic Tully-Fisher 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 Tully-Fisher diagram of σJ ≤ 0.35 and σK ≤ 0.45. We determine Milky Way’s luminosity and place it in the Tully-Fisher 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 = 8.5kpc and Θ0 = 220km/s), the Milky Way lies within 1.5σ of the TF relations. We can use the TF relation and the Cepheid distances to nearby bright galaxies to constrain R0 and Θ0: − log (R0/8.5kpc) + 1.63 log (Θ0/220km/s) = 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 Tully-Fisher relation to determine the Hubble Constant directly: H0 = 66± 12 km/s/Mpc. We have also tested the Tully-Fisher relation at longer wavelengths, where the emission is dominated by dust. We find no evidence for a Tully Fisher relation at wavelengths beyond 10μm. The tight correlation seen in L band suggests that stellar emission dominates over the 3.3 μm PAH emission. Subject headings: Galaxy: fundamental parameters Galaxy: general galaxies: distances and redshifts COBE data sets were developed by the NASA Goddard Space Flight Center under the guidance of the COBE Science Working Group and were provided by the NSSDC.