A NEW CATATALOGUE OF H I SUPERSHELL CANDIDATES IN THE OUTER PART OF THE MILKY WAY

LAURA SUAD; CAIAFA CESAR F.; MARCELO ARNAL; SILVINA CICHOWOLSKI

Florianopolis

Conferencia; XIV Latin American Regional IAU Meeting (LARIM 2013); 2013

The interstellar medium, when viewed in the neutral hydrogen (HI) line emission, reveals a complex structure that is evidenced by the presence of inhomogeneities like shells, supershells, arcs, cavities and loops. In particular HI supershells are minima in the galactic HI emission distribution surrounded completely, or partially, by walls of enhanced HI emission. Supershells are believed to be created, most likely, by the action of the powerful stellar winds of massive stars and their subsequent explosion as supernova. Nevertheless, other mechanisms like gamma-ray bursts or high velocity cloud infall have been proposed for those shells whose kinetic energy is about 10^53-54 erg. In this work we present a new catalogue of HI supershell candidates in the outer part of the Galaxy. Several catalogues of shells and/or supershells have been made using either a visual inspection (Heiles 1979, 1984; McClure-Griffiths et. al 2002) or automatic algorithms (Ehlerov & Palous 2005, 2013; Daigle et al. 2007). In this new catalogue we have used a combination of both visual and automatic identification procedures. One of the main features of our algorithm has to do with the fact that it is able to recognize structures even when they are not completely surrounded by walls of HI emission. In this respect it is quite different from the automatic detection algorithms used up to now by other researchers. We used the Leiden-Argentine-Bonn survey (Kalberla et al. 2005). The catalogue corees most of the second and third galactic quadrants, except for a region 30o wide centered at 180o (90o < l < 165o and 195o < l < 270o; −50o < b < 50o). We have considered as supershell candidates those structures satisfying the following criteria: I) a linear diameter larger than 200 pc, II) an angular diameter larger than 2o, and III) a velocity extent of at least 6.5k s−1. A total of 575 supershells have been catalogued. Only 55% of them are completely surrounded by walls of enhanced HI emission. In this work we also analyze the main statistical parameters of the supershell candidates. From the OB associations and open clusters catalogues we have looked for correlations between these objects and the supershells. Finally, we have compared our catalogue with the ones made by other authors.