arXiv subjects

F. Prada

Publications and source records attributed to F. Prada.

294 records · Page 17Linked to original sources

arXiv1999

The visible environment of gas-accreting galaxies

We studied the environment of a sample of galaxies in which the presence of polar rings or the presence of gas- and stars- counterrotation is observed. These galaxies are believed to have accreted this material, now in peculiar motion, from their environment. The variable considered here are the number of possible companions in the field, down to an apparent magnitude 22, their size, their concentration around the accreting galaxy, and a set of related parameters. A control sample of 'normal' galaxies has also been studied. From Kolgomorov-Smirnov tests of the considered variables, no significant differences have been found between the population of objects around the our accreting galaxies and the control sample. These results seems to give support to the models suggesting a long formation time for the acquisition process, starting from a diffuse gas instead of fagocitation of small satellite.

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arXiv1999

A Photometric System for Metallicity Mapping in Galaxies

A new photometric system suitable for deep, precise and quick metallicity mapping in galaxies is proposed. We find a linear correlation between our metallicity index and the Mg2 index for stellar, globular cluster, and early-type galaxy spectra, and model spectral energy distributions of the simple stellar populations.

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arXiv1999

Structural properties of spherical galaxies obeying the Sersic R^1/n law: a semi-analytical approach

By considering that the distribution of measured light along any galactocentric radius of an elliptical galaxy can be well represented by a R^{1/n} Sersic law, we propose in this paper a ``discrete ordenate'' method, which, for any value of n, allows an explicit expression for the luminous density, rho(r), to be found that can be numerically evaluated to any required precision. Once we have this semi-analytical expression for the spatial density, rho(r), the mass distribution, M(r), the potential, phi(r), and the velocity dispersions, sigma_s^2(r), in the space and in the observational plane, sigma_p^2(R), can be computed in a straightforward manner.

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arXiv1999

A counterrotating central component in NGC 5728

We present a detailed study of the stellar kinematics in the barred galaxy NGC 5728 based on I-band photometry and long-slit spectroscopic observations in the region of the near-IR Ca II triplet. The analysis of the stellar line-of-sight velocity distribution (LOSVD) has revealed, in the central regions of the bar, the presence of a cold (v/sigma~2.5) prograde $S$-shaped velocity component that coexists in the central 4 kpc with a fainter and hotter (v/sigma~0.5) counterrotating component. Beyond 4 kpc from the nucleus the LOSVD shows the stellar bar kinematics. The comparison of the radial surface brightness profile of the velocity components with that obtained from an I-band image shows that the counterrotating core follows a r^(1/4) profile, while the S-shaped component does not follows the flat bar surface brightness profile. Several possible scenarios accounting for such kinematic signatures found in the center of the bar in NGC 5728 are discussed.

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arXiv1996

A Counter-rotating Bulge in the Sb Galaxy NGC 7331

We have found that the bulge of the large, nearby Sb galaxy NGC 7331 rotates retrograde to its disk. Analysis of spectra in the region of the near-IR Ca II triplet along the major axis shows that, in the radial range between 5'' and ~20'', the line of sight velocity distribution of the absorption lines has two distinct peaks, and can be decomposed into a fast-rotating component with v/sigma > 3, and a slower rotating, retrograde component with v/sigma between 1 -- 1.5. The radial surface brightness profile of the counter-rotating component follows that of the bulge, obtained from a 2-dimensional bulge-disk decomposition of a near-infrared K-band image, while the fast rotating component follows the disk. At the radius where the disk starts to dominate the isophotes change from being considerably boxy to very disky. Although a number of spiral galaxies have been found that contain cold, couter-rotating disks, this is the first galaxy known to have a boxy, probably triaxial, fairly warm, counter-rotating component, which is dominating in the central regions. If it is a bar seen end-on, this bar has to be thicker than the disk. We find that NGC 7331, even though it is a fairly early-type spiral, does not have a conventional, co-rotating bulge. The fact that the inner component is retrograde makes us believe that it was formed from infalling material, in either stellar or gaseous form (e.g. Balcells & Quinn 1990). Another possibility however is that the structure has been there since the formation of the galaxy. In this case it will be a challenge to explain the large change in orientation of the angular momentum when going outward radially.

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arXiv1995

The Kinematics of the Ionized and Molecular Hydrogen in the Starburst Galaxy NGC 253

Near-infrared H_2 1-0 S(1) and Br_gamma velocity curves along the major axis of NGC 253 have revealed a central velocity gradient that is seven times steeper than that shown by the optical velocity curve. This is interpreted as an optical depth effect due to dust. Approximately 35 mag of visual extinction in the center is required to match the SW side of the optical velocity curve. The spatial variation of the ratio of these lines to the CO (J=1-0) line is compared among starburst galaxies NGC 253, M82, and NGC 4945 to investigate the excitation mechanism responsible for the H_2 1-0 S(1) line.

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