Monica Relano

Ionized gas kinematics and massive star formation in NGC 1530

We present emission line mapping of the strongly barred galaxy NGC 1530 obtained using Fabry-Perot interferom- etry in Hα, at significantly enhanced angular resolution compared with previously published studies. The main point of the work is to examine in detail the non-circular components of the velocity field of the gas, presumably induced by the strongly non-axisymmetric gravitational potential of the bar. To do this we first derive a model rotation curve making minimum assump- tions about kinematic symmetry, and go on to measure the non-circular component of the full radial velocity field. This clearly reveals the streaming motions associated with the spiral density wave producing the arms, and the quasi-elliptical motions with speeds of order 100 km s −1 aligned with the bar. It also shows in some detail how these flows swing in towards and around the nucleus as they cross a circumnuclear resonance, from the dominant x1 orbits outside the resonance to x2 orbits within it. Comparing cross-sections of this residual velocity map along and across the bar with the surface brightness map in Hα indicates a systematic offset between regions of high non-circular velocity and massive star formation. To investigate further we produce maps of velocity gradient along and across the bar. These illustrate very nicely the shear compression of the gas, revealed by the location of the dust lanes along loci of maximum velocity gradient perpendicular to the bar. They also show clearly how shear, seen in our data as velocity gradient perpendicular to the flow, acts to inhibit massive star formation, whereas shocks, seen as strong velocity gradients along the flow vector, act to enhance it. Although the inhibiting effect of gas shear flow on star formation has long been predicted, this is the clearest observational illustration so far of the effect, thanks to the strong shock-induced counterflow system in the bar. It is also the clearest evidence that dust picks out shock-induced inflow along bars. These observations should be of considerable interest to those modelling massive star formation in general.

The internal dynamical equilibrium of H II regions: A statistical study

We present an analysis of the integrated Hα emission line profiles for the H uf769uf769 region population of the spiral galaxies NGC 1530, NGC 6951 and NGC 3359. We show that ∼70% of the line profiles show two or three Gaussian components. The relations between the luminosity (log LHα) and non-thermal line width (log σnt )f or the Huf769uf769 regions of the three galaxies are studied and compared with the relation found taken all the H uf769uf769 regions of the three galaxies as a single distribution. In all of these distributions we find a lower envelope in log σnt. A clearer envelope in σnt is found when only those H uf769uf769 regions with σnt >σ s(13 km s −1 ) are considered, where σs is a canonical estimate of the sound speed in the interestellar medium. The linear fit for the envelope is log LHα = (36.8 ± 0.7) + (2.0 ± 0.5) log σnt where the Hα luminosity of the region is taken directly from a photometric H uf769uf769 region catalogue. When the Hα luminosity used instead is that fraction of the H uf769uf769 region luminosity, corresponding to the principal velocity component, i.e. to the turbulent non-expanding contribution, the linear fit is log LHα = (36.8 ± 0.6) + (2.0 ± 0.5) log σnt, i.e. unchanged but slightly tighter. The masses of the H uf769uf769 regions on the envelope using the virial theorem and the mass estimates from the Hα luminosity are comparable, which offers evidence that the H uf769uf769 regions on the envelope are virialized systems, while the remaining regions, the majority, are not in virial equilibrium.

Propagation of ionizing radiation in Hii regions: The effects of optically thick density fluctuations

The accepted explanation of the observed dichotomy of two orders of magnitude between in situ measurements of electron density in Hii regions, derived from emission line ratios, and average measurements based on integrated emission measure, is the inhomogeneity of the ionized medium. This is expressed as a filling factor, the volume ratio of dense to tenuous gas, measured with values of order 10 −3 . Implicit in the filling factor model as normally used, is the assumption that the clumps of dense gas are optically thin to ionizing radiat ion. Here we explore implications of assuming the contrary: that the clumps are optically thick. A first consequence is the pre sence within Hii regions of a major fraction of neutral hydrogen. We estimate the mean H ◦ /H + ratio for a population of Hii regions in the spiral galaxy NGC 1530 to be the order of 10, and support this inference using dynamical arguments. The optically thick clumpy models allow a significant fraction of the photons generated by the ionizing stars to escape from their Hii region. We show, by comparing model predictions with observations, that these models give an account at least as good as, and probably better than that of conventional models, of the radial s urface brightness distribution and of selected spectral line diag nostics for physical conditions within Hii regions. These models explain how an Hii region can appear, from its line ratios, to be ionization bou nded, yet permit a major fraction of its ionizing photons to escape.

Expansive components in H II regions

We study the presence of low intensity high velocity components, which we have termed wing features in the integrated Hα emission line profiles of the H uf769uf769 region populations of the spiral barred galaxies NGC 1530, NGC 3359 and NGC 6951. We find that more than a third of the H uf769uf769 region line profiles in each galaxy show these components. The highest fraction is obtained in the galaxy whose line profiles show the best S:N, which suggests that wing features of this type may well exist in most, if not all, H uf769uf769 region line profiles. Applying selection criteria to the wing features, we obtain a sample of H uf769uf769 regions with clearly defined high velocity components in their profiles. Deconvolution of a representative sample of the line profiles eliminates any doubt that the wing features could possibly be due to instrumental effects. We present an analysis of the high velocity low intensity features fitting them with Gaussian functions; the emission measures, central velocities and velocity dispersions for the red and blue features take similar values. We interpret the features as signatures of expanding shells inside the H uf769uf769 regions. Up to a shell radius of Rshell ∼ 0.2 Rreg, the stellar winds from the central ionizing stars appear to satisfy the energy and momentum requirements for the formation and driving the shell. Several examples of the most luminous H uf769uf769 regions show that the shells appear to have larger radii; in these cases additional mechanisms may well be needed to explain the kinetic energies and momenta of the shells.

Four-fermion contact terms in charged current processes and large extra dimensions

We study the bounds that can be obtained on four-fermion contact terms from the experimental data for

Fabry-Perot observations of the ionized gas in the spiral galaxy NGC 6951

{e}^{+}stackrel{ensuremath{rightarrow}}{p}overline{ensuremath{nu}}X

Circumnuclear Star-forming Regions in barred Galaxies

obtained at DESY HERA and

Gas Flows, Star Formation and Galaxy Evolution

poverline{p}ensuremath{rightarrow}{e}^{ifmmodepmelsetextpmfi{}}

Why we need to measure turbulent magnetic fields in HII regions

measured at the Fermilab Tevatron. We compare these bounds with the ones available in the literature. Finally, we apply these results to study the compactification radius in theories with large extra dimensions and we obtain the bound

High Resolution Velocity Fields in the Strongly Barred Galaxy NGC 1530

{M}_{c}g~3.3 mathrm{TeV}.