We present optical long-slit rotation curves (RCs) for 304 northern Sb-Sc UGC galaxies originally selected for Tully-Fisher (TF) applications. 20% of the galaxies were observed twice or more, allowing for a proper determination of systematic errors. Various measures of maximum rotational velocity to be used as input in the TF relation are tested on the basis of their repeatability, minimization of TF scatter, and match with 21cm linewidths. The best measure of TF velocity, v2.2, is given at the location of peak rotational velocity of a pure exponential disk. Optical TF calibrations yield internal scatter comparable to, if not smaller than, the best calibrations based on single-dish 21cm radio linewidths. Even though resolved HI RCs are more extended than their optical counterpart, a tight match between optical and radio linewidths exists since the bulk of the HI surface density is enclosed within the optical radius. We model the 304 RCs presented here and a sample of 958 curves from Mathewson etal. (1992) with various fitting functions. An arctan function provides an adequate simple fit (not accounting for non-circular motions and spiral arms). More elaborate, empirical models may yield a better match at the expense of strong covariances. We caution against physical or "universal" parameterizations for TF applications. (abridged)Comment: 39 pages, 19 eps figures, 7 tables, 3 appendices. To be published in AJ (Dec. 97 issue). Appendix A is 55 pages long; only the first 3 pages are shown. The appendices and 3 tables were abridged and will be fully released in the AAS CD-ROM Serie

We use observed rotation velocity-luminosity (V L) and size-luminosity (RL) relations to single out a specific scenario for disk galaxy formation in the ΛCDM cosmology. Our model involves four independent log-normal random variables: dark-halo concentration c, disk spin λ gal , disk mass fraction m gal , and stellar mass-to-light ratio Υ I . A simultaneous match of the V L and RL zero points with adiabatic contraction requires low-c halos, but this model has V 2.2 ∼ 1.8V vir (where V 2.2 and V vir are the circular velocity at 2.2 disk scale lengths and the virial radius, respectively) which will be unable to match the luminosity function (LF). Similarly models without adiabatic contraction but standard c also predict high values of V 2.2 /V vir . Models in which disk formation induces an expansion rather than the commonly assumed contraction of the dark-matter halos have V 2.2 ∼ 1.2V vir which allows a simultaneous fit of the LF. This may result from non-spherical, clumpy gas accretion, where dynamical friction transfers energy from the gas to the dark matter. This model requires low λ gal and m gal values, contrary to naive expectations. However, the low λ gal is consistent with the notion that disk galaxies predominantly survive in halos with a quiet merger history, while a low m gal is also indicated by galaxy-galaxy lensing. The smaller than expected scatter in the RL relation, and the lack of correlation between the residuals of the V L and RL relations, respectively, imply that the scatter in λ gal and in c need to be smaller than predicted for ΛCDM halos, again consistent with the idea that disk galaxies preferentially reside in halos with a quiet merger history.

A robust analysis of galaxy structural parameters, based on the modeling of bulge and disk brightnesses in the BVRH bandpasses, is presented for 121 face-on and moderately inclined late-type spirals. Each surface brightness (SB) profile is decomposed into a sum of a generalized Sérsic bulge and an exponential disk. The reliability and limitations of our bulge-to-disk (B/D) decompositions are tested with extensive simulations of galaxy brightness profiles (one-dimensional) and images (two-dimensional). We have used repeat observations to test the consistency of our decompositions. The average systematic model errors are d20% and d5% for the bulge and disk components, respectively. The final set of galaxy parameters is studied for variations and correlations in the context of profile type differences and wavelength dependencies. Galaxy types are divided into three classes according to their SB profile shapes: Freeman type I, type II, and a third '' transition '' class for galaxies whose profiles change from type II in the optical to type I in the infrared. Roughly 43%, 44%, and 13% of type I, type II, and transition galaxies, respectively, comprise our sample. Only type I galaxies, with their fully exponential disks, are adequately modeled by our two-component decompositions, and our main results focus on these profiles. We discuss possible interpretations of Freeman type II profiles. The Sérsic bulge shape parameter for nearby type I late-type spirals shows a range between n ¼ 0:1 and 2, but, on average, the underlying surface density profile for the bulge and disk of these galaxies is adequately described by a double-exponential distribution. The distribution of disk scale lengths shows a decreasing trend with increasing wavelength, consistent with a higher concentration of old stars or dust (or both) in the central regions relative to the outer disk. We confirm a coupling between the bulge and disk with a scale length ratio hr e =hi ¼ 0:22 AE 0:09, or hh bulge =h disk i ¼ 0:13 AE 0:06 for late-type spirals, in agreement with recent N-body simulations of disk formation. This ratio increases from $0.20 for late-type spirals to $0.24 for earlier types. These observations are consistent with bulges of late-type spiral galaxies being more deeply embedded in their host disk than earlier type bulges. Bulges and disks can thus preserve a nearly constant r e /h but show a great range of SB for any given effective radius. The similar scaling relations for early-and late-type spirals suggest comparable formation and/or evolution scenarios for disk galaxies of all Hubble types. In the spirit of Courteau, de Jong, & Broeils but using our new, more extensive database, we interpret this result as further evidence for regulated bulge formation by redistribution of disk material to the galaxy center, in agreement with models of secular evolution of the disk.