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Register a new userDiscovery of two embedded clusters with WISE in the high Galactic latitude cloud HRK 81.4-77.8
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Denilso da Silva Camargo
Publication date
2015
fields
Physics
and research's language is
English
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Molecular clouds at very high latitude ($b>60^{circ}$) 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 $ell=81.11^{circ}$ and $b=-77.84^{circ}$ is an $sim2$ Myr embedded cluster (EC) located at a distance from the Sun of $d_{odot}=5.09pm0.47$ kpc. Adopting the distance of the Sun to the Galactic centre $R_{odot}=7.2$ kpc we derive for Camargo 439 a Galactocentric distance of $R_{GC}=8.70pm0.26$ kpc and a vertical distance from the plane of $-4.97pm0.46$ kpc. Camargo 438 at $ell=79.66^{circ}$ and $b=-78.86^{circ}$ 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 $sim8.7$ kpc and $sim5.0$ 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 this ECs are the most distant known embedded clusters from the plane and both cloud and clusters are probably falling ballistically from the halo onto the Galactic disc, or performing a flyby.
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Careful analyses of photometric and star count data available for the nine putative young clusters identified by Camargo et al. (2015, 2016) at high Galactic latitudes reveal that none of the groups contain early-type stars, and most are not significant density enhancements above field level. 2MASS colours for stars in the groups match those of unreddened late-type dwarfs and giants, as expected for contamination by (mostly) thin disk objects. A simulation of one such field using only typical high latitude foreground stars yields a colour-magnitude diagram that is very similar to those constructed by Camargo et al. (2015, 2016) as evidence for their young groups as well as the means of deriving their reddenings and distances. Although some of the fields are coincident with clusters of galaxies, one must conclude that there is no evidence that the putative clusters are extremely young stellar groups.
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