D. A. Gadotti

BUDDA: A New Two-dimensional Bulge/Disk Decomposition Code for Detailed Structural Analysis of Galaxies*

We present BUDDA (Bulge/Disk Decomposition Analysis), a new code devoted to perform a two-dimensional bulge/disk decomposition directly from the images of galaxies. The bulge component is fitted with a generalized Sersic profile, whereas disks have an exponential profile. No other components are included. Bars and other substructures, like lenses, rings, inner bars, and inner disks, are studied with the residual images obtained through the subtraction of bulges and disks from the original images. This means that a detailed structural analysis of galaxies may be performed with a small number of parameters, and substructures may be directly studied with no a priori assumptions. As has been already shown by several studies, two-dimensional fitting is much more reliable than one-dimensional profile fitting. Moreover, our code has been thoroughly tested with artificial data, and we demonstrate it to be an accurate tool for determining structural parameters of galaxies. We also show that our code is useful in various kinds of studies, including galaxies of, e.g., different morphological types, and inclinations, which also may be observed at different spatial resolutions. Thus, the code has a broader range of potential applications than most of the previous codes, which are developed to tackle specific problems. To illustrate its usefulness, we present the results obtained with a sample of 51 mostly early-type galaxies (but covering the whole Hubble sequence). These results show some of the applications in which the code may be used: the determination of parameters for fundamental plane and structural studies, quantitative morphological classification of galaxies, and the identification and study of hidden substructures. We have determined the structural parameters of the galaxies in our sample and found many examples of hidden inner disks in ellipticals, secondary bars, nuclear rings and dust lanes in lenticulars and spirals, and also wrong morphological classification cases. We now make BUDDA generally available to the astronomical community.

The Vertical Stellar Kinematics in Face-On Barred Galaxies: Estimating the Ages of Bars

In order to perform a detailed study of the stellar kinematics in the vertical axis of bars, we obtained high signal-to-noise spectra along the major and minor axes of the bars in a sample of 14 face-on galaxies and used them to determine the line-of-sight stellar velocity distribution, parameterized as a Gauss-Hermite series. With these data, we developed a diagnostic tool that allows one to distinguish between recently formed and evolved bars, as well as to estimate their ages, assuming that bars form in vertically thin disks that are recognizable by low values for the vertical velocity dispersion σz. Through N-body realizations of bar unstable disk galaxies we were also able to check the timescales involved in the processes that give bars an important vertical structure. We show that σz in evolved bars is roughly 100 km s-1, which translates to a height scale of about 1.4 kpc, giving support to scenarios in which bulges form through disk material. Furthermore, the bars in our numerical simulations have values for σz generally smaller than 50 km s-1, even after evolving for 2 Gyr, suggesting that a slow process is responsible for making bars as vertically thick as we observe. We verify theoretically that the Spitzer-Schwarzschild mechanism is quantitatively able to explain these observations if we assume that giant molecular clouds are twice as concentrated along the bar as in the rest of the disk.

NGC 4608 AND NGC 5701: BARRED GALAXIES WITHOUT DISKS?

We have performed for the first time in the literature a two-dimensional structural analysis on the barred lenticular and face-on galaxies NGC 4608 and NGC 5701. The results indicate that either these galaxies have never had large disks or their disks were almost completely destroyed by their strong bars because of secular evolution processes. We discuss these surprising conclusions, checking for signs of secular evolution, considering bar-forming instabilities, and suggesting, based on N-body simulations, a new mechanism to form bars in spheroids, which includes nonspherical halos. Quantitative predictions from our new mechanism are compared with those from other recent models for bar formation and evolution.

On the Formation and Evolution of Stellar Bars in Galaxies

We have done a detailed study on the structural and kinematical properties of lenticular and early- and late-type spiral galaxies with bars, aiming to explore the formation and evolution processes of stellar bars in galaxies, and their implications on the global formation and evolution of galaxies. Using spectra obtained along the major and minor axes of the bars in a sample of 14 galaxies, we have determined the stellar velocity distribution in the bars vertical axis. With these data, it was possible to develop a diagnostic tool that allows one to estimate the ages of bars. Through realistic N-body simulations, we have studied the necessary conditions to the formation of bars in galaxies, as well as the time scale involved in the processes which give bars an important vertical structure. Finally, using optical and near-infrared imaging, we have performed a detailed galaxy structural analysis. Among the main results obtained, we point out: (i) there are vertically thin and thick bars and this difference is caused by a difference in the ages of the bars; (ii) the bar thickening process, as we have determined, is slow (5-10 Gyr); (iii) the current scenario for bar formation is not able to explain naturally the existence of bars in galaxies which are kinematically hot and have prominent bulges; (iv) we suggest a new mechanism for bar formation in galaxies, which can account for the serious drawbacks confronted in the current scenario; (v) bulges in lenticular and in spiral galaxies are, at least partially, formed through the secular evolutionary processes in bars; (vi) during its evolution, a bar grows stronger by capturing stars from the disk, which becomes fainter, in agreement with recent numerical and analytical results. [Abridged]

A new challenge: Bar formation and secular evolution in lenticular galaxies

Departamento de Astronomia, Instituto de Astronomia, Geof´isica e CiˆenciasAtmosf´ericas, Universidade de S˜ao Paulo — Rua do Mat˜ao, 1226 – Cid. Univers.CEP 05508-900, S˜ao Paulo – SP, BrasilAbstract. To further enhance our understanding on the formation and evolutionof bars in lenticular (S0) galaxies, we are undertaking a detailed photometric andspectroscopic study on a sample of 22 objects. Here we report the results of a 2Dstructural analysis on two barred face–on S0’s, which indicate that presently thesegalaxies do not possess disks. We discuss two possibilities to explain these surprisingresults, namely strong secular evolution and bar formation without disks.Keywords: galaxies: evolution, galaxies: structure, methods: N-body simulations