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We present a comparison of low-J¹³CO and CS observations of four different regions in the LMC—the quiescent Molecular Ridge, 30 Doradus, N159, and N113, all at a resolution of ∼3 pc. The regions 30 Dor, N159, and N113 are actively forming massive stars, while the Molecular Ridge is forming almost no massive stars, despite its large reservoir of molecular gas and proximity to N159 and 30 Dor. We segment the emission from each region into hierarchical structures using dendrograms and analyze the sizes, masses, and line widths of these structures. We find that the Ridge has significantly lower kinetic energy at a given size scale and also lower surface densities than the other regions, resulting in higher virial parameters. This suggests that the Ridge is not forming massive stars as actively as the other regions because it has less dense gas and not because collapse is suppressed by excess kinetic energy. We also find that these physical conditions and energy balance vary significantly within the Ridge and that this variation appears only weakly correlated with distance from sites of massive-star formation such as R136 in 30 Dor, which is ∼1 kpc away. These variations also show only a weak correlation with local star formation activity within the clouds.

 

Abstract The properties of young massive clusters (YMCs) are key to understanding the star formation mechanism in starburst systems, especially mergers. We present Atacama Large Millimeter/submillimeter Array high-resolution (∼10 pc) continuum (100 and 345 GHz) data of YMCs in the overlap region of the Antennae galaxy. We identify six sources in the overlap region, including two sources that lie in the same giant molecular cloud (GMC). These YMCs correspond well with radio sources in lower-resolution continuum (100 and 220 GHz) images at GMC scales (∼60 pc). We find most of these YMCs are bound clusters through virial analysis. We estimate their ages to be ∼1 Myr and that they are either embedded or just beginning to emerge from their parent cloud. We also compare each radio source with a Pa β source, and find they have consistent total ionizing photon numbers, which indicates they are tracing the same physical source. By comparing the free–free emission at ∼10 pc scale and ∼60 pc scale, we find that ∼50% of the free–free emission in GMCs actually comes from these YMCs. This indicates that roughly half of the stars in massive GMCs are formed in bound clusters. We further explore the mass correlation between YMCs and GMCs in the Antennae and find it generally agrees with the predictions of the star cluster simulations. The most massive YMC has a stellar mass that is 1%–5% of its host GMC mass. 

ABSTRACT We use the angular two-point correlation function (TPCF) to investigate the hierarchical distribution of young star clusters in 12 local (3–18 Mpc) star-forming galaxies using star cluster catalogs obtained with the Hubble Space Telescope (HST) as part of the Treasury Program Legacy ExtraGalactic UV Survey. The sample spans a range of different morphological types, allowing us to infer how the physical properties of the galaxy affect the spatial distribution of the clusters. We also prepare a range of physically motivated toy models to compare with and interpret the observed features in the TPCFs. We find that, conforming to earlier studies, young clusters ($T \lesssim 10\, \mathrm{Myr}$) have power-law TPCFs that are characteristic of fractal distributions with a fractal dimension D2, and this scale-free nature extends out to a maximum scale lcorr beyond which the distribution becomes Poissonian. However, lcorr, and D2 vary significantly across the sample, and are correlated with a number of host galaxy physical properties, suggesting that there are physical differences in the underlying star cluster distributions. We also find that hierarchical structuring weakens with age, evidenced by flatter TPCFs for older clusters ($T \gtrsim 10\, \mathrm{Myr}$), that eventually converges to the residual correlation expected from a completely random large-scale radial distribution of clusters in the galaxy in $\sim 100 \, \mathrm{Myr}$. Our study demonstrates that the hierarchical distribution of star clusters evolves with age, and is strongly dependent on the properties of the host galaxy environment. 

Abstract Using recently acquired Hubble Space Telescope NIR observations ( J , Pa β , and H bands) of the nearby galaxy NGC 1313, we investigate the timescales required by a young star cluster to emerge from its natal cloud. We search for extincted star clusters, potentially embedded in their natal cloud as either (1) compact sources in regions with high H α /Pa β extinctions or (2) compact H ii regions that appear as point-like sources in the Pa β emission map. The NUV–optical–NIR photometry of the candidate clusters is used to derive their ages, masses, and extinctions via a least- χ 2 spectral energy distribution broad- and narrowband fitting process. The 100 clusters in the final samples have masses in the range and moderate extinctions, E ( B − V ) ≲ 1.0 mag. Focusing on the young clusters (0–6 Myr), we derive a weak correlation between extinction and age of the clusters. Almost half of the clusters have low extinctions, E ( B − V ) < 0.25 mag, already at very young ages (≤3 Myr), suggesting that dust is quickly removed from clusters. A stronger correlation is found between the morphology of the nebular emission (compact, partial or absent, both in H α and Pa β ) and cluster age. Relative fractions of clusters associated with a specific nebular morphology are used to estimate the typical timescales for clearing the natal gas cloud, resulting in between 3 and 5 Myr, ∼1 Myr older than what was estimated from NUV–optical-based cluster studies. This difference hints at a bias for optical-only-based studies, which James Webb Space Telescope will address in the coming years.