7.1.2 Infrared (H-Band) Relation
A significant improvement in the application of the TF relations occurred with the introduction of infrared H-band magnitudes (0 = 1.6 µm) by Aaronson et al. (1979). They realized that the infrared offered two distinct advantages over visible wavelengths: first, that the extinction at H is only 10% that in B, and second, that the infrared light is dominated by late-type giants. Thus, over the entire range of morphological types, the infrared is presumably a better tracer of the stellar mass than the B luminosity. Subsequent observations proved that the infrared Tully-Fisher relation (hereafter IRTF relation) has a significantly smaller dispersion than does the B-band relation, implying that uncertainties in the extinction corrections for the blue light (which were still rather crude at that time), and/or variations in mean stellar population, were significant. In a subsequent series of papers Aaronson et al. (1980) discussed the absolute calibration, while Mould et al. (1980) determined the distance to the Virgo Cluster, along with the corresponding value for H0. They restricted the sample of bright spirals to those with inclinations greater than 45° and with no morphological peculiarities, following Tully and Fisher (1977), and obtained a distance modulus for the Virgo Cluster of 30.98 ± 0.09 mag (internal errors only), with the updated Hyades distance.
Aaronson et al. (1980) used the IRTF relation to estimate distances to four clusters at about four times the Virgo distance. They found significantly larger values for H0 than they had found earlier for Virgo (i.e., 95 ± 4 km s-1 Mpc-1 versus 65 ± 4 from Virgo alone) and proposed that the larger value was representative of a global value, while the smaller value was the result of peculiar motion of the Local Group in the direction of the Virgo Cluster. This was consistent with the models for the peculiar velocities associated with the local mass distribution (e.g., Peebles 1976; Schechter 1980) and the dominant role of Virgo in the Local Supercluster (e.g., de Vaucouleurs 1953, 1956; Tully 1982). A more extensive analysis of the velocity field of the Local Supercluster by Aaronson et al. (1982) using distances estimated for a sample of ~ 300 galaxies via the IRTF relation produced convincing evidence of Virgocentric retardation or ``infall''. This model is now generally believed to be inadequate given recent observations implying larger scale peculiar motions (e.g., Aaronson et al. 1986, 1989; Dressler et al. 1987). A recent application of the IRTF to the problem of local peculiar velocities can be found in Han & Mould (1990). The ongoing effort of estimating large-scale peculiar velocities using the IRTF (e.g., Mould et al. 1991) is beyond the scope of this review.