We present high-resolution Hα rotation curves for a sample of 15 dwarf and low surface brightness galaxies. From these, we derive limits on the slopes of the central mass distributions, using both a direct inversion of the rotation curves as well as detailed mass models. Assuming the density distributions of dark matter halos follow a power-law at small radii, ρ(r) ∝ r −α , we find inner slopes in the range 0 < ∼ α < ∼ 1 for most galaxies. Thus, even with the relatively high spatial resolution of the Hα rotation curves presented here the inner slopes are poorly constrained. In general, halos with constant density cores (α = 0) provide somewhat better fits, but the majority of our galaxies (∼ 75 percent) are also consistent with α = 1, as long as the R-band stellar massto-light ratios are smaller than about 2. Halos with α = 1.5, however, are ruled out in virtually every case. In order to investigate the robustness of these results we discuss and model several possible causes of systematic errors including non-circular motions, galaxy inclination, slit width, seeing, and slit alignment errors. Taking the associated uncertainties into account, we conclude that even for the ∼ 25 percent of the cases where α = 1 seems inconsistent with the rotation curves, we cannot rule out cusp slopes this steep. Inclusion of literature samples similar to the one presented here leads to the same conclusion when the possibility of systematic errors is taken into account. In the ongoing debate on whether the rotation curves of dwarf and low surface brightness galaxies are consistent with predictions for a cold dark matter universe, we argue that our sample and the literature samples discussed in this paper provide insufficient evidence to rule out halos with α = 1. At the same time, we note that none of the galaxies in these samples require halos with steep cusps, as most are equally well or better explained by halos with constant density cores.

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We compare optical and near-infrared colors of disks and bulges in a diameter-limited sample of inclined, bright, nearby, early-type spirals. Color profiles along wedge apertures at 15 o from the major axis and on the minor axis on the side of the galaxy opposite to the dust lane are used to assign nominal colors for the inner disks (at 2 scale length) and for the bulges (∼ 0.5 r ef f ), respectively. We estimate that the effects of dust reddening and the cross-talk between the colors of the two components is negligible. We find that color differences (bulge -disk) are very small: ∆(U − R) = 0.126 ± 0.165, ∆(R − K) = 0.078 ± 0.165. Disks tend to be bluer by an amount three times smaller than that reported by Bothun & Gregg B84 (1990) for S0's. Color variations from galaxy to galaxy are much larger than color differences between disk and bulge in each galaxy. Probably, the underlying old population of disks and bulges is much more similar than the population paradigm would lead us to believe. Implied age differences, assuming identical metallicities, are less than 30%.

Context. Satellite accretion events have been invoked for mimicking the internal secular evolutionary processes of bulge growth. However, N-body simulations of satellite accretions have paid little attention to the evolution of bulge photometric parameters, to the processes driving this evolution, and to the consistency of this evolution with observations. Aims. We want to investigate whether satellite accretions indeed drive the growth of bulges, and whether they are consistent with global scaling relations of bulges and discs. Methods. We perform N-body models of the accretion of satellites onto disc galaxies. A Tully-Fisher (M ∝ V α TF rot ) scaling between primary and satellite ensures that density ratios, critical to the outcome of the accretion, are realistic. We carry out a full structural, kinematic and dynamical analysis of the evolution of the bulge mass, bulge central concentration, and bulge-to-disc scaling relations. Results. The remnants of the accretion have bulge-disc structure. Both the bulge-to-disc ratio (B/D) and the Sérsic index (n) of the remnant bulge increase as a result of the accretion, with moderate final bulge Sérsic indices: n = 1.0 to 1.9. Bulge growth occurs no matter the fate of the secondary, which fully disrupts for α TF = 3 and partially survives to the remnant center for α TF = 3.5 or 4. Global structural parameters evolve following trends similar to observations. We show that the dominant mechanism for bulge growth is the inward flow of material from the disc to the bulge region during the satellite decay.Conclusions. The models confirm that the growth of the bulge out of disc material, a central ingredient of secular evolution models, may be triggered externally through satellite accretion.

We use Hubble Space Telescope (HST) near-infrared imaging to explore the shapes of the surface brightness profiles of bulges of S0-Sbc galaxies at high resolution. Modeling extends to the outer bulge via bulge-disk decompositions of combined HST-ground-based profiles. Compact, central unresolved components similar to those reported by others are found in ∼84% of the sample. We also detect a moderate frequency (∼34%) of nuclear components with exponential profiles that may be disks or bars. Adopting the Sérsic functional form 1/n r for the bulge, none of the bulges have an behavior; derived Sérsic shape indices are. For 1/4 r AnS p 1.7 ‫ע‬ 0.7 the same sample, fits to near-infrared ground-based profiles yield Sérsic indices up to. The high n of n p 4-6 ground-based profiles are the result of nuclear point sources blending with the extended light of the bulge because of seeing. The low Sérsic indices are not expected from violent relaxation in mergers.