HI shells in the outer Milky Way

We present results of a method for an automatic search for HI shells in 3D data cubes and apply it to the Leiden-Dwingeloo HI survey of the northern Milky Way. In the 2nd Galactic quadrant, where identifications of structures are not substantially influenced by overlapping, we find nearly 300 structures. The Galactic distribution of shells has an exponential profile in the radial direction with a scale length of 3 kpc. In the z direction, one half of the shells are found at distances smaller than 500 pc. We also calculate the energies necessary to create the shells: there are several structures with energies greater than 10 E_SN but only one with an energy exceeding 100 E_SN. Their size distribution, corrected for distance effects, is approximated by a power-law with an index 2.1. Our identifications provide a lower limit to the filling factor of shells in the outer Milky Way: f_2D = 0.4 and f_3D = 0.05.Comment: accepted by A&A; 14 pages, 15 figures (3 multiple

HI shells in the Leiden/Argentina/Bonn HI survey

We analyse the all-sky Leiden/Argentina/Bonn HI survey, where we identify shells belonging to the Milky Way. We used an identification method based on the search of continuous regions of a low brightness temperature that are compatible with given properties of HI shells. We found 333 shells in the whole Galaxy. The size distribution of shells in the outer Galaxy is fitted by a power law with the coefficient of 2.6 corresponding to the index 1.8 in the distribution of energy sources. Their surface density decreases exponentially with a scale length of 2.8 kpc. The surface density of shells with radii >= 100 pc in the solar neighbourhood is around 4 per kpc^2 and the 2D porosity is approximately 0.7.Comment: 19 pages (incl. 10 pages appendix), 12 figures. Accepted for publication in A&

Is the dark matter halo of the Milky Way flattened?

We performed an extended analysis of the parameter space for the interaction of the Magellanic System with the Milky Way (MW). The varied parameters cover the phase space parameters, the masses, the structure, and the orientation of both Magellanic Clouds, as well as the flattening of the dark matter halo of the MW. The analysis was done by a specially adopted optimization code searching for the best match between numerical models and the detailed HI map of the Magellanic System by Bruens et al. (2005). The applied search algorithm is a genetic algorithm combined with a code based on the fast, but approximative restricted N-body method. By this, we were able to analyze more than 10^6 models, which makes this study one of the most extended ones for the Magellanic System. Here we focus on the flattening q of the axially symmetric MW dark matter halo potential, that is studied within the range 0.74<=q<=1.20. We show that creation of a trailing tail (Magellanic Stream) and a leading stream (Leading Arm) is quite a common feature of the Magellanic System-MW interaction, and such structures were modeled across the entire range of halo flattening values. However, important differences exist between the models, concerning density distribution and kinematics of HI, and also the dynamical evolution of the Magellanic System. Detailed analysis of the overall agreement between modeled and observed distribution of neutral hydrogen shows that the models assuming an oblate (q<1.0) dark matter halo of the Galaxy allow for better satisfaction of HI observations than models with other halo configurations.Comment: 19 pages, 20 figures, 2 appendices, accepted for publication in A&

Spheroids scaling relations over cosmic time

I report on recent measurements of two scaling relations of spheroids in the distant universe: the Fundamental Plane, and the relation between lensing velocity dispersion and stellar velocity dispersion. The joint analysis of the two scaling relations indicates that the most massive (above 10^11.5 solar masses) spheroids are consistent with no evolution since z~1 both in terms of star formation and internal structure. Furthermore their total mass density profile is on average well described by an isothermal sphere with no evidence for redshift evolution. At smaller masses the picture appears to be substantially different, as indicated by evidence for substantial recent star formation (as much as 20-40% of stellar mass formed since z~1), and by hints of a reduced dark matter content at smaller masses. A larger sample of lenses extending to velocity dispersions below 200 km/s, and to redshifts above >0.5 is needed to verify these trends.Comment: invited paper at the 235th IAU symposium Galaxy evolution across the Hubble Tim

The Conditions for Star Formation at Low Metallicity: Results from the LMC

We present our recent work on the conditions under which star formation occurs in a metal-poor environment, the Large Magellanic Cloud ([Fe/H] ~ -0.4). Water masers are used as beacons of the current star formation in HII regions. Comparing their location with the dust morphology imaged with the Spitzer Space Telescope, and additional Halpha imaging and groundbased near-infrared observations, we conclude that the LMC environment seems favourable to sequential star formation triggered by massive star feedback (Oliveira et al. 2006). Good examples of this are 30 Doradus and N 113. There are also HII regions, such as N 105A, where feedback may not be responsible for the current star formation although the nature of one young stellar object (YSO) suggests that feedback may soon start making an impact. The chemistry in one YSO hints at a stronger influence from irradiation effects in a metal-poor environment where shielding by dust is suppressed (van Loon 2005)Comment: in "Triggered Star Formation in a Turbulent ISM", IAU symposium, poster contribution; a better quality version of this manuscript can be found at http://www.astro.keele.ac.uk/~jacco/papers/proc.ps a full version of the poster can be found at http://www.astro.keele.ac.uk/~jacco/papers/IAUS237_LMC_2006.pd