Magellanic Bridge C (MB-C) is a metal-poor (∼1/5 Z⊙) low-density star-forming region located 59 kpc away in the Magellanic Bridge, offering a resolved view of the star formation process in conditions different to the Galaxy. From Atacama Large Millimetre Array CO (1-0) observations, we detect molecular clumps associated to candidate young stellar objects (YSOs), pre-main sequence (PMS) stars, and filamentary structure identified in far-infrared imaging. YSOs and PMS stars form in molecular gas having densities between 17–200 M⊙ pc−2, and have ages between ≲0.1–3 Myr. YSO candidates in MB -C have lower extinction than their Galactic counterparts. Otherwise, our results suggest that the properties and morphologies of molecular clumps, YSOs, and PMS stars in MB -C present no patent differences with respect to their Galactic counterparts, tentatively alluding that the bottleneck to forming stars in regions similar to MB-C is the conversion of atomic gas to molecular.
We present new deep near-infrared broad-and narrow-band imaging and low-resolution spectroscopy of the star formation region RCW 121 (IRAS 17149−3916) which we analyse in combination with Herschel (70, 160, 250, 350 and 500 µm) and Spitzer (3.6, 4.5, 5.8 and 8 µm) images. The near-infrared photometry reveals the presence of a stellar cluster of approximate size of 92 arcsec which is composed of at least 264 members, approximately 25 per cent of these showing excess emission at λ > 2.0 µm, indicative of circumstellar discs. Isochrones corresponding to ages 0.5-1.0 Myr and A V = 7.8 fit well the position of a large fraction of likely cluster members in the K s versus H − K s diagram. We find three massive star-forming cores located in the boundaries of an expanding H II region ionized by a central O-type star. From their far-infrared spectral energy distributions (SEDs) we derive masses and temperatures of the dense cores. When these young stellar objects (YSOs) have warm emission components, the 1.2-500 µm SEDs are fitted with Robitaille et al.'s star-disc-envelope model to obtain their physical parameters. The masses of the three YSOs are between 8 and 10 M . The youngest site (core I) is undetected at λ < 100 µm and is at the earliest evolutionary stage that can currently be detected. The other two cores (II and III) contain YSOs of similar masses and have near-infrared counterparts, which imply a more advanced evolutionary stage. The YSO at core II has been found to have associated a jet, with strong H 2 line emission, co-existing with an H 2 O maser source. RCW 121 is another example of multiple star formation being triggered by the expansion of a single H II region.
Aims. We investigated the possible cause–effect relation between the wiggling shape of two stellar jets, MHO 1502 and MHO 2147, and the potential binarity of the respective driving stars. Methods. We present high-angular-resolution H2 (2.122 μm) and K-band images obtained with the Gemini South Adaptive Optics Imager (GSAOI) and the Gemini Multi-conjugate Adaptive Optics System (GeMS). The profiles of the jets are depicted in detail by the H2 images. We used K-band data to search for potential close companions to the previously suggested exciting sources, and used archive data to investigate these sources and the environments in which the jets are located. We also applied a model to reproduce the wiggling profiles of the jets. Results. MHO 1502 is composed of a chain of knots delineating the wiggling jet, suggesting that the driving source emitted them in an intermittent manner. Our K-band image of the previously proposed exciting star, IRAC 18064, shows two sources separated by ~240 AU, hinting at its binarity. However, as IRAC 18064 is located off the jet axis at ~2064 AU, it is questionable as to whether this source is the true exciting star. Moreover, the orbital model centred on IRAC 18064 suggests a binary companion at a much greater distance (~2200 AU) than the nearby star (at ~240 AU). On the other hand, the orbital model centred on the axis provides the best fits. Nevertheless, the precession model centred on the axis cannot be discarded, despite having larger residuals and χ2. MHO 2147 displays an S-shaped gentle continuous emission in H2. We identify two other jets in the field of MHO 2147: a previously reported quasi-perpendicular jet, MHO 2148, and a third jet adjacent to MHO 2147. The model that best fits the morphology of the MHO 2147 jet and that of its adjacent jet is precession. The exciting source of MHO 2147 may be a triple system.
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