Deep Near-Infrared Imaging af an Embedded Cluster in the Extreme Outer Galaxy: Census of Supernovae Triggered Star Formation

Abstract

While conducting a near-infrared (NIR) survey of ``Digel Clouds'', which are thought to be located in the extreme outer Galaxy (EOG), Kobayashi & Tokunaga found star formation activity in ``Cloud 2'', a giant molecular cloud at the Galactic radius of ~ 20 kpc. Additional infrared imaging showed two embedded young clusters at the densest regions of the molecular cloud. Because the molecular cloud is located in the vicinity of a supernova remnant (SNR) HI shell, GSH 138-01-94, it was suggested that the star formation activity in Cloud 2 was triggered by this expanding HI shell. We obtained deep J (1.25 um), H (1.65 um) and K (2.2 um) images of one of the embedded clusters in Cloud 2 with high spatial resolution (FWHM ~0".3) and high sensitivity (K ~ 20 mag, 10 sigma). We identified 52 cluster members. The estimated stellar density (~ 10 pc^{-2}) suggests that the cluster is a T-association. This is the deepest NIR imaging of an embedded cluster in the EOG. The observed K-band luminosity function (KLF) suggests that the underlying initial mass function (IMF) of the cluster down to the detection limit of ~ 0.1 M_sun is not significantly different from the typical IMFs in the field and in the near-by star clusters. The overall characteristics of this cluster appears to be similar to those of other embedded clusters in the far outer Galaxy. The estimated age of the cluster from the KLF, which is less than 1 Myr, is consistent with the view that the star formation was triggered by the HI shell whose age was estimated at 4.3 Myr (Stil & Irwin). The 3-dimensional geometry of SNR shell, molecular cloud and the embedded cluster, which is inferred from our data, as well as the cluster age strongly suggest that the star formation in Cloud 2 was triggered by the SNR shell.

arXiv comment19pages, 8 figures, 1 table, accepted to ApJ. Full paper (pdf) with high resolution figures available at http://www.ioa.s.u-tokyo.ac.jp/~ck_yasui/papers/Cloud2N_1.pdf

References in corpus (8)

• Embedded Clusters in Molecular Clouds
• The Initial Mass Function of Stars: Evidence for Uniformity in Variable Systems
• Evolutionary models for low-mass stars and brown dwarfs: uncertainties and limits at very young ages
• The Mauna Kea Observatories Near-Infrared Filter Set. II. Specifications for a New JHKL'M' Filter Set for Infrared Astronomy
• The Luminosity & Mass Function of the Trapezium Cluster: From B stars to the Deuterium Burning Limit
• Modeling the Near-Infrared Luminosity Functions of Young Stellar Clusters
• Discovery of Young Stellar Objects at the Edge of the Optical Disk of Our Galaxy
• GSH 138-01-94, an old supernova remnant in the far outer Galaxy

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