The Milky Way , The Local Galaxies & the IR

Using the near infrared uxes of local galaxies derived from Cosmic Background Explorer (COBE)/Diiuse Infrared Background Experiment (DIRBE) 1 J(1.25 m) K (2.2 m) & L (3.5 m) 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: J = 0:09 magnitudes, K = 0:13 magnitudes, and L = 0:20 magnitudes. These dispersions include contributions from the intrinsic Tully-Fisher relation scatter and the errors in estimated galaxy distances, uxes, inclination angles, extinction corrections, and circular speeds. For the J and K bands, Monte Carlo simulations give a 95% conndence interval upper limit on the true scatter in the Tully-Fisher diagram of J 0:35 and K 0:45. We determine Milky Way's luminosity and place it in the Tully-Fisher diagram by tting 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 R 0 = 8:5kpc and 0 = 220km=s), the Milky Way lies within 1:5 of the TF relations. We can use the TF relation and the Cepheid distances to nearby bright galaxies to constrain R 0 and 0 : 1:63 log ((0 =220km=s) ? log (R 0 =8:5kpc) = 0:08 0:03. Alternatively, we can x 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: H 0 = 72 12 km/s/Mpc. We have also tested the Tully-Fisher relation at longer wavelengths, where the emission is dominated by dust. We nd no evidence for a Tully Fisher relation at wavelengths beyond 10m. The tight correlation seen in L band suggests that stellar emission dominates over the 3.3 m PAH emission.