R. E. de Souza

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.

On the lengths, colors, and ages of 18 face-on bars

Along with a brief analysis we present data obtained from BVRI and Ks images of a sample of 19 galaxies (18 barred and 1 unbarred), which will be further explored in a future paper. We measured the lengths and colors of the bars, created color maps, and estimated global color gradients. Applying a method developed in a companion paper, we could distinguish for seven galaxies in our sample those whose bars have been recently formed from the ones with already evolved bars. We estimated an average difference in the optical colors between young and evolved bars that may be translated to an age difference of the order of 10 Gyr, meaning that bars may be, at least in some cases, long-standing structures. Moreover, our results show that, on average, evolved bars are longer than young bars. This seems to indicate that, during its evolution, a bar grows longer by capturing stars from the disk, in agreement with recent numerical and analytical results. Although the statistical significance of these results is low, and further studies are needed to confirm them, we discuss the implications from our results on the possibility of bars being a recurrent phenomenon. We also present isophotal contours for all our images as well as radial profiles of relevant photometric and geometric parameters.

Near‐infrared surface photometry of a sample of barred galaxies

We have obtained deep J and K s images of a sample of nine barred galaxies in order to collect a reliable and homogeneous set of images to which N-body simulations of barred galaxies will be compared. The observations were performed using the new near-infrared camera available at the 2.1-m telescope of the Observatorio Astrofisico Guillermo Haro (OAGH) in Cananea, Sonora, Mexico. We present the results of surface photometry techniques applied to the observed images, as well as to the deprojected images. These results include radial profiles of surface brightness (elliptically averaged), colour, position angle, ellipticity and the b 4 Fourier component. In addition, we present isophotal maps, colour maps, surface brightness profiles along the bar major and minor axes, characteristic radial scalelengths and bar length estimates. We discuss how projection effects can influence these measurements and the uncertainties introduced by deprojecting galaxy images. We show that analytical expressions can be used to obtain reliable estimates of deprojected bar lengths, ellipticities and position angles directly from the observed images. These expressions are based on the assumption that the outer parts of the bar are vertically thin, as shown by theoretical work. The usefulness of our data in addressing issues on bar formation and evolution is also discussed. In particular, we present results showing a steep drop in the ellipticity profile, as expected for bar formation processes in which the dark matter halo plays a fundamental role. Furthermore, we show that the location of this drop is a good indicator of the end of the bar in strongly barred galaxies, as predicted by numerical models.

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.

Power-law stellar distributions

The density profiles and other quantities of physical interest for spherically symmetric systems are computed by assuming that a collisionless stellar gas may relax to the non-Gaussian power-law distribution suggested by the nonextensive kinetic theory. There are two different classes of solutions. The first class behaves like a subset of the polytropic Lane–Emden spheres, whereas the second one corresponds to a transition between two different potytropic indices. Unlike the isothermal Maxwellian sphere, the total mass and sizes of both classes are finite for a large range of the nonextensive q-parameter.

Detection of Galaxies with Gaia

Aims. Besides its major objective tuned to detecting the stellar galactic population, the Gaia mission experiment will also observe a large number of galaxies. In this work we intend to evaluate the number and the characteristics of the galaxies that will e ectively pass the on-board selection algorithm of Gaia. Methods. The detection of objects in Gaia will be performed in a section of the focal plane known as the Sky Mapper. Considering the Video Processing Algorithm criterion of detection and the known light profiles of disc and bulges galaxies, we assess the number and the type of extra-galactic objects that will be observed by Gaia. Results. We show that the stellar disc population of galaxies will be very di cult to observe. In contrast, the spheroidal component of elliptical galaxies and bulges having higher central surface brightness and steeper brightness profile will be easier to detect. We estimate that most of the 20 000 elliptical population of nearby galaxies inside the local region up to 170 Mpc are in a state to be observed by Gaia. A similar number of bulges could also be observed, although the low luminosity bulges should escape detection. About two thirds of the more distant objects up to 600 Mpc could also be detected, increasing the total sample to half a million objects including ellipticals and bulges. The angular size of the detected objects will never exceed 4.72 arcsec, which is the size of the largest transmitted windows. Conclusions. A heterogeneous population of elliptical galaxies and bulges will be observable by Gaia. This nearby Universe sample of galaxies should constitute a very rich and interesting sample for studying their structural properties and their distribution.

Chandrasekhar's Dynamical Friction and non-extensive statistics

The motion of a point like object of mass

Kinematic segregation of nearby disk stars from the Hipparcos database

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The redshift of twelve southern ring galaxies

passing through the background potential of massive collisionless particles (