We present a (CO)-C-12 (2-1) mosaic map of the spiral galaxy NGC 6946 by combining data from the Submillimeter Array and the IRAM 30m telescope. We identify 390 giant molecular clouds (GMCs) from the nucleus to 4.5 kpc in the disk. GMCs in the inner 1 kpc are generally more luminous and turbulent, some of which have luminosities > 10(6)K. km. s(-1) pc(2) and velocity dispersions > 10. km s(-1). Large-scale bar-driven dynamics likely regulate GMC properties in the nuclear region. Similar to the MilkyWay and other disk galaxies, GMC mass function of NGC 6946 has a shallower slope (index > -2) in the inner region, and a steeper slope (index < -2) in the outer region. This difference in mass spectra may be indicative of different cloud formation pathways: gravitational instabilities might play a major role in the nuclear region, while cloud coalescence might be dominant in the outer disk. Finally, the NGC 6946 clouds are similar to those inM33 in terms of statistical properties, but they are generally less luminous and turbulent than the M51 clouds.

We present analytic models for the formation and evolution of tidal tails and related structures following single or multiple impulsive disturbances in galaxy collisions. Since the epicyclic approximation is not valid for large radial excursions, we use orbital equations of the form we call p-ellipses (a class of precessing ellipses). These have been shown to provide accurate representations of orbits in logarithmic and power-law halo potentials. In the simplest case of an impulsive collision yielding a purely tidal disturbance the resulting tidal tails have simple structure. Scalings for their maximum lengths and other characteristics as non-linear functions of the tidal amplitude and the exponent of the power-law potentials are described. The analytic model shows that azimuthal caustics (orbit crossing zones of high density also seen in numerical models) are produced generically in these tails at a fixed azimuth relative to the point of closest approach. Long tails, with high-order caustics at their base, and ocular waveforms are also produced at larger amplitudes. The analysis is then extended to non-linear disturbances and multiple encounters, which break the symmetries of purely tidal perturbations. The p-ellipse orbital solutions are similar to those in the linear tidal case. However, as the strength of the non-linear terms is varied the structure of the resulting forms varies from symmetric tails to one-armed plumes. Cases with two or more impulse disturbances are also considered as the simplest analytic models distinguishing between prograde and retrograde encounters. The model shows explicitly how tail growth differs in the two cases. In the prograde case a specific mechanism for the formation of tidal dwarf galaxies at the end of tails is suggested as a consequence of resonance effects in multiple or prolonged encounters. Qualitative comparisons to Arp Atlas systems suggest that the limiting analytic cases are realized in real systems. For example, we identify a few Arp systems which have multiple tidal strands meeting near the base of long tails. These may be swallowtail caustics, where dissipative gas streams are converging and triggering star formation. Ultraviolet and optical images reveal luminous knots of young stars at these 'hinge clump' locations.

As galáxias espirais continuam desafiando as teorias que buscam explicar como o universo se tornou o que observamos hoje. Em especial, no contexto hierárquico de formação de estruturas, é difícil entender como as galáxias podem ser tão parecidas entre si, obedecendo a relações de escala tão estritas, apesar de suas diferentes histórias evolutivas. A fim de esclarecer algumas dessas perguntas, o projeto GHASP observou 203 galáxias na linha H-alfa, através de interferometria Fabry-Perot, construindo uma base de dados homogênea e de alta qualidade para estudos cinemáticos do universo local. Neste trabalho, buscamos complementar os resultados consolidados do GHASP, apresentando um estudo fotométrico para 173 destas galáxias na banda Rc. Os dados, provenientes de observações no telescópio de 1,2m do Observatório de Haute-Provence ou do projeto SDSS, foram cuidadosamente tratados com ferramentas de redução IRAF adaptados para a automação dos processos. Através do ajuste de elipses sobre as galáxias, foram obtidos perfis de brilho calibrados e magnitudes totais para as galáxias da amostra. A decomposição da luz destes perfis foi estudada através de um modelo exponencial para o disco e uma função de Sérsic para o bojo. Os resultados da decomposição bojo-disco foram utilizados para o estudo de relações de escala e correlações entre os diversos parâmetros medidos. Algumas das mais significativas correlações são detalhadas, como a relação entre os parâmetros de escala de bojo e disco, que reforçam o cenário de evolução secular das galáxias disco. Finalmente, com o auxílio dos resultados cinemáticos da literatura, apresentamos, pela primeira vez, a relação Tully-Fisher para a amostra do GHASP, na banda Rc. / The spiral galaxies still challenge the theories that try to explain how the universe has turned into what we see today. In particular, in the context of the hierarchical structure formation, it is difficult to understand how galaxies can be so similar, obeying such strict scaling relations, in spite of their distinct evolutionary histories. In order to clarify some of these questions, the GHASP project has observed 203 galaxies in the H-alpha line, through Fabry-Perot interferometry, and has built a homogeneous and high quality database for kinematical studies in the local universe. In the present work, we seek to supplement the GHASP project results, presenting a photometric study for 173 of those galaxies in the Rc band. The data, taken with the 1.2m telescope at Haute-Provence Observatory or extracted from the SDSS database, was carefully treated with customized IRAF routines for the automation of most of the jobs. By fitting ellipses over the galaxies, calibrated surface brightness profiles and total magnitudes were obtained for galaxies in the sample. Then, galaxy light decomposition techniques were employed using an exponential model for the disk and a Sérsic function for the bulge. The results of the bulge-disk decomposition were used for the study of scaling relations and correlations among the several measured parameters. A few of the most significant correlations were described, such as the relation between bulge and disc scale lengths, reinforcing the galaxy-disk secular evolutionary scenario. Finally, with the aid of kinematic results from the literature, we present, for the first time, the Tully-Fisher relation for the GHASP sample, in the Rc-band.

As galáxias espirais continuam desafiando as teorias que buscam explicar como o universo se tornou o que observamos hoje. Em especial, no contexto hierárquico de formação de estruturas, é difícil entender como as galáxias podem ser tão parecidas entre si, obedecendo a relações de escala tão estritas, apesar de suas diferentes histórias evolutivas. A fim de esclarecer algumas dessas perguntas, o projeto GHASP observou 203 galáxias na linha H-alfa, através de interferometria Fabry-Perot, construindo uma base de dados homogênea e de alta qualidade para estudos cinemáticos do universo local. Neste trabalho, buscamos complementar os resultados consolidados do GHASP, apresentando um estudo fotométrico para 173 destas galáxias na banda Rc. Os dados, provenientes de observações no telescópio de 1,2m do Observatório de Haute-Provence ou do projeto SDSS, foram cuidadosamente tratados com ferramentas de redução IRAF adaptados para a automação dos processos. Através do ajuste de elipses sobre as galáxias, foram obtidos perfis de brilho calibrados e magnitudes totais para as galáxias da amostra. A decomposição da luz destes perfis foi estudada através de um modelo exponencial para o disco e uma função de Sérsic para o bojo. Os resultados da decomposição bojo-disco foram utilizados para o estudo de relações de escala e correlações entre os diversos parâmetros medidos. Algumas das mais significativas correlações são detalhadas, como a relação entre os parâmetros de escala de bojo e disco, que reforçam o cenário de evolução secular das galáxias disco. Finalmente, com o auxílio dos resultados cinemáticos da literatura, apresentamos, pela primeira vez, a relação Tully-Fisher para a amostra do GHASP, na banda Rc. / The spiral galaxies still challenge the theories that try to explain how the universe has turned into what we see today. In particular, in the context of the hierarchical structure formation, it is difficult to understand how galaxies can be so similar, obeying such strict scaling relations, in spite of their distinct evolutionary histories. In order to clarify some of these questions, the GHASP project has observed 203 galaxies in the H-alpha line, through Fabry-Perot interferometry, and has built a homogeneous and high quality database for kinematical studies in the local universe. In the present work, we seek to supplement the GHASP project results, presenting a photometric study for 173 of those galaxies in the Rc band. The data, taken with the 1.2m telescope at Haute-Provence Observatory or extracted from the SDSS database, was carefully treated with customized IRAF routines for the automation of most of the jobs. By fitting ellipses over the galaxies, calibrated surface brightness profiles and total magnitudes were obtained for galaxies in the sample. Then, galaxy light decomposition techniques were employed using an exponential model for the disk and a Sérsic function for the bulge. The results of the bulge-disk decomposition were used for the study of scaling relations and correlations among the several measured parameters. A few of the most significant correlations were described, such as the relation between bulge and disc scale lengths, reinforcing the galaxy-disk secular evolutionary scenario. Finally, with the aid of kinematic results from the literature, we present, for the first time, the Tully-Fisher relation for the GHASP sample, in the Rc-band.