Abstract
Abstract In deep near-infrared imaging of the low-metallicity ([O/H] = −0.7 dex) H ii region Sh 2-127 (S127) with Subaru/MOIRCS, we detected two young clusters with 413 members (S127A) in a slightly extended H ii region and another with 338 members (S127B) in a compact H ii region. The limiting magnitude was K = 21.3 mag (10σ), corresponding to a mass detection limit of ∼0.2 . These clusters are an order of magnitude larger than previously studied young low-metallicity clusters and larger than the majority of solar neighborhood young clusters. Fits to the K-band luminosity functions indicate very young cluster ages of 0.5 Myr for S127A and 0.1–0.5 Myr for S127B, consistent with the large extinction (up to A V ≃ 20 mag) from thick molecular clouds and the presence of a compact H ii region and class I source candidates, and suggest that the initial mass function (IMF) of the low-metallicity clusters is indistinguishable from typical solar neighborhood IMFs. Disk fractions of 28% ± 3% for S127A and 40% ± 4% for S127B are significantly lower than those of similarly aged solar neighborhood clusters (∼50%–60%). The disk fraction for S127B is higher than those of previously studied low-metallicity clusters (<30%), probably due to S127B’s age. This suggests that a large fraction of very young stars in low-metallicity environments have disks, but the disks are lost on a very short timescale. These results are consistent with our previous studies of low-metallicity star-forming regions, suggesting that a solar neighborhood IMF and low disk fraction are typical characteristics for low-metallicity regions, regardless of cluster scales.
Highlights
Considering that the only elements in existence at the beginning of our universe were H and He, and that the present chemical composition of the universe is the result of metal pollution due to elemental synthesis inside stars and the influence of supernovae explosions, exploring the physical processes involved with star formation under different metallicity environments is of great interest
The peak coordinates are α2000 = 21h28m43.9s, δ2000 = +54◦37′21′′ and α2000 = 21h28m40.2s, δ2000 = +54◦36′29′′ with an accuracy of ∼10′′. Both stellar enhancement peaks are located very close to the peaks of the NRAO VLA Sky Survey (NVSS) radio sources, shown with blue diamonds, and the distributions of the clusters are consistent with the distribution of H II regions observed by Rudolph et al (1996) for both S127A and S127B (Section 2.2)
The resultant distribution for the control field shows a peak of AV = 1–3 mag, and the number count decreases with larger AV, whereas that for the cluster region shows a peak at the much larger extinction of AV ∼ 3–7 and 3–4 mag for the S127A and S127B clusters, respectively, and they continue up to AV ∼ 20 mag
Summary
Considering that the only elements in existence at the beginning of our universe were H and He (and an insignificant amount of Li), and that the present chemical composition of the universe is the result of metal pollution due to elemental synthesis inside stars and the influence of supernovae explosions, exploring the physical processes involved with star formation under different metallicity environments is of great interest. To see the full details of the star formation processes, it is necessary to make spatially resolved observations down to the substellar mass regime (∼0.1 M⊙) This enables us to compare results obtained for low-metallicity environments with those in the solar neighborhood on the same basis. This paper is one in a series of papers in which we present deep NIR imaging observations of low-metallicity young clusters in the Galaxy and analysis of those images These clusters were selected using the following: i) the Sharpless catalog (a list of Hα-selected bright H II regions; Sharpless 1959), ii) the region associated with clusters having a significant number of cluster members, and iii) an oxygen metallicity [O/H] ≤ −0.5 dex, assuming a solar abundance of 12 + log (O/H) = 8.73 (Asplund et al 2009).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
