Discovery of two embedded clusters with WISE in the high Galactic latitude cloud HRK 81.4-77.8

作者：Camargo D^*; Bica E; Bonatto C; Salerno G

来源：Monthly Notices of the Royal Astronomical Society, 2015, 448(2): 1930-1936.

DOI：10.1093/mnras/stv092

• ISM: clouds
• ISM: kinematics and dynamics
• open clusters and associations: general

Molecular clouds at very high latitude (b > 60 degrees) away from the Galactic plane are rare and in general are expected to be non-star-forming. However, we report the discovery of two embedded clusters (Camargo 438 and Camargo 439) within the high-latitude molecular cloud HRK 81.4-77.8 using WISE. Camargo 439 with Galactic coordinates l = 81.degrees 11 and b = -77.degrees 84 is an similar to 2 Myr embedded cluster (EC) located at a distance from the Sun of d(circle dot) = 5.09 +/- 0.47 kpc. Adopting the distance of the Sun to the Galactic Centre R-circle dot = 7.2 kpc, we derive for Camargo 439 a Galactocentric distance of R-GC = 8.70 +/- 0.26 kpc and a vertical distance from the plane of -4.97 +/- 0.46 kpc. Camargo 438 at l = 79.degrees 66 and b = -78.degrees 86 presents similar values. The derived parameters for these two ECs put HRK 81.4-77.8 in the halo at a distance from the Galactic Centre of similar to 8.7 kpc and similar to 5.0 kpc from the disc. Star clusters provide the only direct means to determine the high-latitude molecular cloud distances. The present study shows that the molecular cloud HRK 81.4-77.8 is currently forming stars, apparently an unprecedented event detected so far among high-latitude clouds. We carried out a preliminary orbit analysis. It shows that these ECs are the most distant known ECs from the plane and both cloud and clusters are probably falling ballistically from the halo on to the Galactic disc, or performing a flyby.

• 出版日期2015-4-1