The edge of the young galactic disc

GIOVANNI CARRARO; RUBEN A. VÁZQUEZ; EDGARDO COSTA; GABRIEL PERREN; ANDRÉ MOITINHO

ASTROPHYSICAL JOURNAL

IOP PUBLISHING LTD

Lugar: Londres; Año: 2010 vol. 718 p. 683 - 694

0004-637X

In this work we report and discuss the detection of two distant diffuse stel-lar groups in the third Galactic quadrant. They are composed of young stars,with spectral types ranging from late O to late B, and lie at galactocentric dis-tances between 15 and 20 kpc. These groups are located in the area of twocataloged open clusters (VdB-Hagen 04 and Ruprecht 30), projected towards theVela-Puppis constellations, and within the core of the Canis Major over-density.Their reddening and distance has been estimated analyzing their color-color andcolor-magnitude diagrams, derived from deep UBV photometry. The existenceof young star aggregates at such extreme distances from the Galactic center chal-lenges the commonly accepted scenario in which the Galactic disc has a sharpcut-off at about 14 kpc from the Galactic center, and indicates that it extendsto much greater distances (as also supported by recent detection of CO molecu-lar complexes well beyond this distance). While the groups we find in the areaof Ruprecht 30 are compatible with the Orion and Norma-Cygnus spiral arms,respectively, the distant group we identify in the region of VdB-Hagen 4 lies inthe external regions of the Norma-Cygnus arm, at a galactocentric distance (20kpc) where no young stars had been detected so far in the optical.