Astrophys. J., 675, 443-453 (2008/March-1)
Star formation in the extreme outer galaxy: Digel Cloud 2 clusters.
YASUI C., KOBAYASHI N., TOKUNAGA A.T., TERADA H. and SAITO M.
Abstract (from CDS):
We obtained deep near-infrared (NIR) images of two embedded clusters at the northern and southern CO peaks of Cloud 2, which is one of the most distant star-forming regions in the extreme outer Galaxy, at the Galactic radius (Rg) of ∼19 kpc. We detected cluster members with a mass detection limit of <0.1 M☉, which is well into the substellar regime (K∼21 mag, 5 σ). These high-quality data enable a comparison of EOG values to those in the solar neighborhood on the same basis for the first time. We first constructed the NIR color-color diagram in the Mauna Kea Observatory (MKO) filter system and also for the low-metallicity environment, since the metallicity in the EOG is much lower than it is in the solar neighborhood. The estimated stellar density suggests that ``isolated-type'' star formation is ongoing in Cloud 2-N, while ``cluster-type'' star formation is ongoing in Cloud 2-S. Despite this different star formation mode, other characteristics of the two clusters are almost identical: (1) the K-band luminosity functions (KLFs) of the two clusters are quite similar, as are the estimated IMFs and ages (∼0.5-1 Myr) from the KLF fitting; (2) the estimated star formation efficiencies (SFEs) for both clusters are typical compared to those of embedded clusters in the solar neighborhood. The similarity of two independent clusters with a large separation (∼25 pc) strongly suggests that their star formation activities were triggered by the same mechanism, probably a supernova remnant (GSH 138-01-94), as suggested in our earlier works.
Infrared: Stars - ISM: Clouds - open clusters and associations: individual (Digel Cloud 2 (read: [YKT2006b] Cloud2-N, [YKT2006b] Cloud2-S)) - Stars: Formation - Stars: Luminosity Function, Mass Function - Stars: Pre-Main-Sequence - ISM: Supernova Remnants
Fig.2: [YKT2006b] Cloud2-W (No. S).
Digel Cloud 2 = [DDT94] Cloud 2
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