Speaker
Javier Zaragoza-Cardiel
(Instituto de Astrofísica de Canarias)
Description
We have used interacting galaxies to explore the properties of high luminosity star forming zones. With the GHaFaS Fabry-Perot spectrometer on the 4.2m William Herschel Telescope (La Palma) we have used Halpha emission to obtain complete 2D mapping in surface brightness, velocity, and velocity dispersion of 8 paris of interecting galaxies. The detailed kinematics reveal global features such as inflows towards the nuclei of some systems, and expanding superbubbles characteristic of galactic superwinds.
Combining the information in the three types of maps we have determined the radii, velocity dispersions, luminosities and then the masses of some 500 HII regions. We find two distinct parametric relations between mean density and mass for regions in the highest luminosity range and at lower luminosities. We note that the most luminous regions show especially high values for their
velocity dispersions, and use the evidence to support the hypothesis that these regions form from high mass molecular clouds which were originally gravitationally bound, while the lower luminosity regions formed within molecular clouds originally confined by external pressure. This is supported by the data of Wei et al. who detected, using CO observations in the Antennae, (which we have now confirmed using data from ALMA) two distinct sets of molecular clouds with a transition mass of $\sim 3 \times 10^6$ solar masses, a similar mass to the transition between the two regimes we find for the HII regions.
Our hypothesis is that the formation of the densest, most massive molecular clouds is favoured by galaxy-galaxy interaction. Within these clouds massive star formation occurs more readily than in lower mass pressure-confined clouds.
Author
Javier Zaragoza-Cardiel
(Instituto de Astrofísica de Canarias)