870 micron continuum observations of the bubble-shaped nebula Gum 31

N. U. DURONEA; J. VASQUEZ; L. GÓMEZ; C. E. CAPPA

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Lugar: Paris; Año: 2015 vol. 582 p. 2 - 16

0004-6361

  % aims heading (mandatory)   { We are presenting here a study of the cold dust  in the close environs of the ring nebula Gum 31. We aim at deriving  the physical properties of the molecular gas and dust  associated with the nebula, and   investigating its correlation with the star formation in the region, that was probably  triggered by the expansion of the ionization front against its environment.    }% methods heading (mandatory)   {We make use of 870 $mu$m emission data obtained with the Large APEX Bolometer Camera (LABOCA) to map the dust emission. The 870 $mu$m emission provides an excellent probe of mass and density of dense molecular clouds.  The obtained LABOCA image was  compared to   archival infrared, radio continuum, and  optical images.} % results heading (mandatory)   {The 870 $mu$m emission follows the 8 $mu$m {em (Spitzer)}, 250 $mu$m, and 500 $mu$m  ({em Herschel}) emission distributions showing the classical morphology  of a two dimensional projection of a spherical shell. We use the  870 $mu$m and 250 $mu$m images to identify 60 dust clumps in the collected layers of molecular gas using the exttt{Gaussclumps} algorithm. The clumps have  effective deconvolved radii between 0.16 pc and 1.35 pc, masses between 70 msun and 2800 msun, and volume densities between  1.1 $imes$ 10$^3$ cm$^{-3}$  and $sim$ 2.04 $imes$ 10$^5$ cm$^{-3}$. The total mass of the clumps is $sim$ 37600 msun. The dust temperature of the clumps is in the range from 21 K to 32 K, while inside the hii region reaches $sim$ 40 K. The clump mass distribution for the sample is well-fitted by a power law  $d$N/$d$log($M$/M$_{odot}$) $propto$ $M^{-alpha}$, with  $alpha$ = 0.93 $pm$ 0.28.  The slope differs from those obtained for the stellar IMF in the solar neighborhood, suggesting that the clumps are not direct progenitors of single stars/protostars. The mass-radius relationship for the 41 clumps  detected in the 870 $mu$m emission shows that only 37$%$ of them  lie in or above the high-mass star formation threshold,  most of them having candidate YSOs projected inside their limits.  A comparison of the dynamical age of the hii region with the fragmentation time,   allowed us to conclude that the collect and collapse mechanism may be important for the star formation at the edge of Gum 31, although other  processes may also be acting.  The position of the identified young stellar objects in the region is also a strong indicator that the collect and collapse process is acting.