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Allow me to make some personal reflections: When I first decided to nominate Mayo for the Henry Norris Russell prize in 1997, letters in support of my nomination were received by Profesors L. Spitzer (Princeton University Observatory), H. vd Hulst, G. Miley and E. van Dishoeck (at Leiden), R.J. Allen (Baltimore), Bruce and Debbie Elmegreen (NY), D.A. Williams (University College London), P...
Astronomers have for decades referred to the Hubble Tuning Fork. We show that the actual originator of the Tuning Fork is that of Sir James Jeans. We next focus our attention on the duality of spiral structure and the temporal evolution of bars in our local Universe. Next, we present deep-IR observations of M33, which show gargantuan arcs of thermally pulsing asymptotic giant branch carbon stars;...
In March, David Block telephoned from Johannesburg with an interesting invita-tion to comment on the provenance of Hubble’s famous tuning fork galaxy classification diagram. Over the years he had often noticed that the diagram is not in Hubble’s definitive 1926 classification paper (Astrophysical Journal, 64, 321), and that it had only appeared in his semi-popular book “Realm of the Nebulae”, but...
In the current galaxy formation scenarios, two physical phenomena are invoked to build disk galaxies: hierarchical mergers and more quiescent external gas accretion, coming from intergalactic filaments. Although both are thought to play a role, their relative importance is not known precisely. Here we consider the constraints on these scenarios brought by the observation-deduced star formation history...
Bars serve as obvious funnels of gas towrard the cntral regions of galaxies, where the gas flow may then trigger activity. However, only a minority of bars is actively funnelling gas toward the nucleus and can thus be traced by dense, molecular gas. These objects offer an excellent laboratory for the study of changing gas properties, diagnosed by specific ratios between molecular lines. Ratios of...
I will review the basic properties of S0 galaxies in the local Universe in relation to both elliptical and spiral galaxies, their neighbours on the Hubble sequence, and also in relation to dwarf spheroidal (dSph) galaxies. This will include colours, luminosities, spectral features, information about the age and metallicity composition of their stellar populations and globular clusters, about their...
The properties of bars in S0 galaxies and early-type spirals is only beginning to be explored. This paper discusses some preliminary results on maximum relative gravitational bar torques and relative Fourier intensity amplitudes in SB0 and SB0/a galaxies and how these compare with similar quantities estimated for spirals.
NGC 2950 is a nearby and undisturbed SB0 galaxy hosting two nested stellar bars. We used the Tremaine-Weinberg method to measure the pattern speed of the primary bar. This also permitted us to establish that the two nested bars are rotating with different pattern speeds (at better than 99% confidence level). In particular, the rotation frequency of the secondary bar is higher than that of the primary...
In the first part of this article we show how observations of the chemical evo-lution of the Galaxy: G- and K—dwarf numbers as functions of metallicity, and abundances of the light elements, D, Li, Be and B, in both stars and the interstellar medium (ISM), lead to the conclusion that metal poor H I gas has been accreting to the Galactic disc during the whole of its lifetime, and is accreting today...
A multi-faceted approach is described to constrain the importance of bar-driven evolution in disk galaxies, with a special emphasis on bulge formation. N-body simulations of bars are compared to the stellar kinematics and near-infrared morphology of 30 edge-on spirals, most with a boxy bulge. The N-body simulations allow to construct stellar kinematic bar diagnostics for edge-on systems and to quantify...
I briefly discuss evidences for bar-driven gas fueling in the central regions of galaxies, focusing on scales down to about 10 pc. I thus mention the building of inner disks, and the link with resonances, as well as the corresponding kinematic signatures such as σ-drops and counter-rotating nuclear disks as probed via integral-field spectroscopy.
We present near-infrared K-band images of 15 galaxies. We have performed a Fourier analysis on the spiral structure of these galaxies in order to determine their pitch angles and dust-penetrated arm classes. We have also obtained rotation curve data for these galaxies and calculated their shear rates. We show that there is a correlation between pitch angle and shear rate and conclude that the main...
We detail the bar dissolution mechanisms Bars in spiral galaxies with a normal gas content are transient features, because of the effects of growing central mass concentrations, gravity torques, and decoupled nuclear bars. Their life-time is 1 to 4 Gyrs. As bars were already present several billions years ago, the ubiquity of bars in the Local universe requires that bars are reformed. The most efficient...
I use a method developed by Maciejewski & Sparke (2000) to find regular orbits that can support doubly barred galaxies. In such systems, double-frequency orbits play the same role as closed periodic orbits do in unchanging potentials. Orbits in double bars can be best studied through their maps. Here I use such maps in order to determine the fraction of the phase-space occupied by ordered motions...
Stars in the halo of M31 are enriched with heavy elements a factor of ten more than the Milky Way halo. Many M31 globular clusters show high metallicities and enhanced nitrogen abundance, as does the M31 nucleus and near-nuclear regions. The bulk of the nitrogen comes from mass-loss in intermediate-mass asymptotic giant branch stars, a fairly quiescent process incapable of driving enriched gas out...
There is considerable evidence that the circumnuclear regions of galaxies are intimately related to their host galaxies, most directly through their bars. There is also convincing evidence for relations between the properties of supermassive black holes in the nuclei of galaxies and those of their host galaxy. It is much less clear, however, how stellar (starburst) and non-stellar (AGN) activity in...
We present preliminary results from high resolution ~ 0.05”) adaptive optics observations of Cygnus A. The images show a biconical structure strongly suggestive of an obscuring torus around a quasar nucleus. A bright (K’ = 18.5) point source is found near the expected position of the nucleus. We interpret this source as the hot inner rim of the torus seen through the opening of the torus. Using high...
The results of bar-driven mass inflow are directly observable in high-resolution HST observations of their circumnuclear regions. These observations reveal a wealth of structures dominated by dust lanes, often with a spiral-like morphology, and recent star formation. Recent work has shown that some of these structures are correlated with the presence or absence of a bar. I extend this work with an...
Deep surface photometry in the near-infrared K’-band of ~100 spiral galaxies was obtained with SOFI at the 3.5m NTT, La Silla, and used to analyze nonaxisymmetric perturbations (e.g. bars and spiral structures) in disk galaxies. Synthetic rotation curves for the galaxies were constructed based on the axisymmetric light distribution in K and HI velocity width data. Bars were detected in 85%...
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