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Context. Clear identifications of Galactic young stellar clusters farther than a few kpc from the Sun are rare, despite the large number of candidate clusters. Aims. We aim to improve the selection of candidate clusters rich in massive stars with a multiwavelength analysis of photometric Galactic data that range from optical to mid-infrared wavelengths. Methods. We present a photometric and spectroscopic analysis of five candidate stellar clusters, which were selected as overdensities with bright stars (Ks < 7 mag) in GLIMPSE and 2MASS images. Results. A total of 48 infrared spectra were obtained. The combination of photometry and spectroscopy yielded six new red supergiant stars with masses from 10 M☉ to 15 M☉. Two red supergiants are located at Galactic coordinates (l, b) = (16.°7, -0.°63) and at a distance of about ∼3.9 kpc; four other red supergiants are members of a cluster at Galactic coordinates (l, b) = (49.°3, +0.°72) and at a distance of ∼7.0 kpc. Conclusions. Spectroscopic analysis of the brightest stars of detected overdensities and studies of interstellar extinction along their line of sights are fundamental to distinguish regions of low extinction from actual stellar clusters. The census of young star clusters containing red supergiants is incomplete; in the existing all-sky near-infrared surveys, they can be identified as overdensities of bright stars with infrared color-magnitude diagrams characterized by gaps. [ABSTRACT FROM AUTHOR]

The Magellanic Bridge is the nearest low-metallicity, tidally stripped environment, offering a unique high-resolution view of physical conditions in merging and forming galaxies. In this paper, we present an analysis of candidate massive young stellar objects (YSOs), i.e., in situ, current massive star formation (MSF) in the Bridge using Spitzer mid-IR and complementary optical and near-IR photometry. While we definitely find YSOs in the Bridge, the most massive are ∼10 M☼, ≪45 M☼ found in the LMC. The intensity of MSF in the Bridge also appears to be decreasing, as the most massive YSOs are less massive than those formed in the past. To investigate environmental effects on MSF, we have compared properties of massive YSOs in the Bridge to those in the LMC. First, YSOs in the Bridge are apparently less embedded than in the LMC: 81% of Bridge YSOs show optical counterparts, compared to only 56% of LMC sources with the same range of mass, circumstellar dust mass, and line-of-sight extinction. Circumstellar envelopes are evidently more porous or clumpy in the Bridge's low-metallicity environment. Second, we have used whole samples of YSOs in the LMC and the Bridge to estimate the probability of finding YSOs at a given H I column density, N(H I). We found that the LMC has ∼3 × higher probability than the Bridge for N(H I) >12 × 1020 cm–2, but the trend reverses at lower N(H I). Investigating whether this lower efficiency relative to H I is due to less efficient molecular cloud formation or to less efficient cloud collapse, or to both, will require sensitive molecular gas observations. [ABSTRACT FROM AUTHOR]