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Extended, soft X-ray emission from the halo of a very large disk galaxy has been detected out to r~20-40 kpc. The luminosity and surface brightness distribution is in very good agreement with predictions by recent, cosmological galaxy formation models. Predictions of Ly-alpha emission, associated with ``cold'' accretion of filamentary gas onto galaxies, are presented. In particular these predictions are compared to the properties of a recently detected Ly-alpha ``blob'', which shows no obvious continuum counter-part in any of 12 broad-bands, from X-rays (Chandra) to infrared (Spitzer). Finally, the predicted evolution of the Tully-Fisher relation, going from z=0 to 1, is discussed in relation to recent observations.

We present an updated estimate of the surface density and surface brightness in B,V,I of the local Galactic disc, based on a model for the "Solar cylinder" calibrated to reproduce Hipparcos and Tycho star counts. We discuss the mass-to-light ratio of the local stellar disc and infer the global luminosity of the Milky Way, which results underluminous with respect to the Tully-Fisher relation.

Two ways of possibly solving the angular momentum problem plaguing cold dark matter (CDM)ab initiosimulations of disk galaxy formation are discussed: 1) Stellar feedback processes and 2) Warm dark matter (WDM) rather than CDM

The major advantage of studying galaxies in the near infrared (NIR), is the minimization of dust extinction. The NIR is the region of the stellar emission spectrum which is least affected by both dust emission and extinction. Dust emission becomes more of a factor at longer wavelengths while dust extinction is more significant at shorter ones. The other important advantage of a NIR study is that it probes the bulk of the stellar mass in the galaxies. Since Tully-Fisher (T-F) is a relationship between a galaxy’s total stellar content and its rotation speed, minimizing the biases in the measurement of the bulk of the stellar emission provides a significant advantage.

The influence of the virgocentric model in the study of Malmquist bias in TF relation is investigated from field galaxies and Virgo cluster.

The observed scatter in the H-band Tully-Fisher relation is O.45 — O.5 O mag (Aaronson and Mould 1983, Aaronson et al. 1986). In order to yield more reliable information concerning the local form of the velocity-distance relation, it is desirable to obtain relative distances to galaxies that are accurate to 1O%. The present scatter in the Tully-Fisher relation thus needs to be reduced by a factor of 2. In this contribution, we report on the sources of scatter in the Tully-Fisher relation and elaborate on a possible scheme which yields a scatter of only O.25 mag.

We discuss the possibilities of using the velocity width integrated luminosity relation for spiral galaxies at cosmologically interesting redshifts. Our estimates and discussion show that questions of cosmological nature can be usefully addressed by use of optical lines such as Hα, when observed as integrated profiles on a 16-m ground-based telescope such as ESO’s VLT.

Among existing secondary distance indicators, the IR Tully-Fisher relation is probably the most reliable available for measuring the far flung Hubble flow. Absolute calibration of the method, however, remains highly uncertain owing to the poor state of nearby galaxy distances. A coordinated ground-based and space attack on this problem, primarily involving Cepheids, holds out great promise for a measurement of the Hubble constant good to ten percent.

Numerous attempts have been made to calibrate the Tully-Fisher relation (between absolute magnitude and total HI linewidth) and to apply it in different wavebands since it is one of the most powerful extragalactic distance indicators. For a recent review and a recalibration using blue magnitudes see Richter and Huchtmeier (1984).

When the Bottinelli et al. version of the Tully-Fisher relation is applied to derive distances, and when the observed parameters are used to predict the Malmquist bias at a given distance, the observed variation of the Hubble ratio as a function of kinematic distance is about 2.5 times the predicted variation.