We have observed 10 interacting galaxy pairs using the Fabry-Perot interferometer GH$alpha$FaS (Galaxy H$alpha$ Fabry-Perot system) on the $4.2rm{m}$ William Herschel Telescope (WHT) at the Observatorio del Roque de los Muchachos, La Palma. We presen
t here the H$alpha$ surface brightness, velocity and velocity dispersion maps for the 10 systems we have not previously observed using this technique, as well as the physical properties (sizes, H$alpha$ luminosities and velocity dispersion) of 1259 HII regions from the full sample. We also derive the physical properties of 1054 HII regions in a sample of 28 isolated galaxies observed with the same instrument in order to compare the two populations of HII regions. We find a population of the brightest HII regions for which the scaling relations, for example the relation between the H$alpha$ luminosity and the radius, are clearly distinct from the relations for the regions of lower luminosity. The regions in this bright population are more frequent in the interacting galaxies. We find that the turbulence, and also the star formation rate, are enhanced in the HII regions in the interacting galaxies. We have also extracted the H$alpha$ equivalent widths for the HII regions of both samples, and we have found that the distribution of HII region ages coincides for the two samples of galaxies. We suggest that the SFR enhancement is brought about by gas flows induced by the interactions, which give rise to gravitationally bound gas clouds which grow further by accretion from the flowing gas, producing conditions favourable to star formation.
We have combined observations of the Antennae galaxies from the radio interferometer ALMA (Atacama Large Millimeter/submillimeter Array) and from the optical interferometer GH$alpha$FaS (Galaxy H$alpha$ Fabry-Perot System). The two sets of observatio
ns have comparable angular and spectral resolutions, enabling us to identify 142 giant molecular clouds (GMCs) and 303 HII regions. We have measured, and compared, their basic physical properties (radius, velocity dispersion, luminosity). For the HII regions, we find two physical regimes, one for masses $>10^{5.4} mathrm{M_{odot}}$ of ionized gas, where the gas density increases with gas mass, the other for masses $<10^{5.4} mathrm{M_{odot}}$ of ionized gas, where the gas density decreases with gas mass. For the GMCs, we find, in contrast to previous studies in other galaxies over a generally lower mass range of clouds, that the gas surface density increases with the radius, hinting at two regimes for these clouds if we consider both sources of data. We also find that the GMC mass function has a break at $10^{6.7}mathrm{M_{odot}}$. Using the velocity dispersion measurements, we claim that the difference between the regimes is the nature of the dominant binding force. For the regions in the lower mass range, the dominant force is the external pressure, while in the higher mass range it is the internal gravity of the clouds. In the regime where gravity is dominant, the star formation rate, derived from the dust-corrected H$alpha$ luminosity, increases super-linearly with the velocity dispersion, and the gas density increases with the gas mass.
We have observed the Arp 270 system (NGC 3395 & NGC 3396) in H{alpha} emission using the GH{alpha}FaS Fabry-Perot spectrometer on the 4.2m William Herschel Telescope (La Palma). In NGC 3396, which is edge-on to us, we detect gas inflow towards the ce
ntre, and also axially confined opposed outflows, characteristic of galactic superwinds, and we go on to examine the possibility that there is a shrouded AGN in the nucleus. The combination of surface brightness, velocity and velocity dispersion information enabled us to measure the radii, FWHM, and the masses of 108 HII regions in both galaxies. We find two distinct modes of physical behaviour, for high and lower luminosity regions. We note that the most luminous regions show especially high values for their velocity dispersions and hypothesize that these occur because the higher luminosity regions form from higher mass, gravitationally bound clouds while those at lower luminosity HII regions form within molecular clouds of lower mass, which are pressure confined.
