Explore the vast range of titles available.

There is now evidence that some aspects of compact star cluster formation and destruction are quasi-universal in nature, and some aspects depend on environment. But what do we mean by these terms, environmental and universal? Is one the dominant influence? How can things be both universal and environmentally dependent? In this contribution we first provide a brief historical overview, then examine evidence for both universality and environmental dependences, and finish by examining a new approach that both demonstrates the degree to which cluster mass functions are universal (i.e., to a level of roughly 0.2 in the Log over three orders of magnitude when normalizing by the star formation rate), and enables a method for quantifying 2nd-order environmental effects.

We report on the development of a framework for understanding the demographics of star cluster systems. The model incorporates a universal initial power-law mass function, selected formation histories, selected disruption laws, and a convolution with common artifacts and selection effects found in observational data. An important component of our model is the use of a ‘two-stage’ disruption process, with a very high ‘infant mortality’ rate for the clusters with ages less than ≈10 8  yr (i.e., roughly 80 to 90% are lost each factor of ten in time, τ , independent of mass), and two-body relaxation, which becomes the dominant disruption mechanism at older ages, preferentially removing the lower-mass clusters. Stars from the dissolved clusters form the field population, and hence the galaxies themselves. We also report on efforts to distinguish stars from clusters in the Antennae galaxies, allowing us to show that the power-law luminosity function for star clusters extends roughly three magnitudes fainter than previously demonstrated, contrary to reports that there is a turnover. Finally, we briefly show that, while triggered star formation in several regions of the Antennae is relatively mild (i.e., producing roughly 10% as many stars as in the previous generation), in some regions there can be an amplification of a factor of four or more.

The availability of high spatial resolution molecular gas observations from ALMA, and similar resolution observations in the radio continuum using the VLA, is providing the opportunity to make comparisons with specific features seen in optical observations more directly than in the past. Using our ALMA observations of the Antennae galaxies as a springboard, we have compared the locations of small-scale CO (3−2) features with a variety of multi-wavelength observations, in particular optical and near-infrared imaging using both broad (UBVI) and narrow-band data (Hα and Paβ) taken with the HST, and radio (3.6 cm) continuum observations taken with the VLA. This comparison leads to the development of an evolutionary classification system which provides a framework for studying the sequence of star cluster formation and evolution, from diffuse Giant Molecular Clouds (GMCs), to proto, embedded, emerging, young, and intermediate/old star clusters. Using this evolutionary framework, we estimate the maximum age range of clusters formed in a single GMC is approximately 10 Myr. This suggests that the molecular gas is removed over this timescale, resulting in the cessation of star formation and the destruction of the GMC within a radius of about 200 pc.

We present narrow band, continuum subtracted H α , [S ii ], H β , [O iii ] and [O ii ] data taken with the Wide Field Camera 3 on the Hubble Space Telescope in the nearby dwarf starburst galaxy NGC 4214. From these images, we identify seventeen new planetary nebula candidates, and seven supernova remnant candidates. We use the observed emission line luminosity function of the planetary nebulae to establish a new velocity-independent distance to NGC 4214. We conclude that the PNLF technique gives a reddening independent distance to NGC 4214 of 3.19±0.36 Mpc, and that our current best-estimate of the distance to this galaxy ids 2.98±0.13 Mpc.

We are using NVO tools to obtain a large (N≃100), uniform (SDSS images, cross checked with HST images; analyzed using WESIX) database of super star clusters in nearby star-forming galaxies in order to address two fundamental astronomical questions: (i) Is the initial luminosity function of star clusters universal?; and (ii) What fraction of super star clusters is ‘missing’ in optical studies (i.e., are hidden by dust)?

The Space Telescope Science Institute (STScI), in collaboration with the European Coordinating Facility (ECF), and the Canadian Astronomy Data Centre (CADC), is studying the development of an enhanced archive for the Hubble Space TelescopeHST), with the goal of improving the scientific value of the data. The primary enhancements would be:

Observations of young star clusters in a variety of galaxies have been used to constrain basic properties related to star-formation, such as the fraction of stars found in clusters (Gam) and the shape of the cluster mass function. However, the results can depend heavily on the reliability of the cluster age-dating process and other assumptions. One of the biggest challenges for successful age-dating lies in breaking the age-reddening degeneracy, where older, dust-free clusters and young, reddened clusters can have similar broad-band colors. While this degeneracy affects cluster populations in all galaxies, it is particularly challenging in dusty, extreme star-forming environments systems. We study the cluster demographics in the luminous infrared galaxy NGC1614 using Hubble imaging taken in 8 optical-NIR passbands. For age-dating, we adopt a spectral energy distribution fitting process that limits the maximum allowed reddening by region, and includes Ha photometry directly. We find that without these assumptions, essentially all clusters in the dust-free UV-bright arm which should have ages 50-250Myr are incorrectly assigned ages younger than 10Myr. We find this method greatly reduces the number of clusters in the youngest (tau<10Myrs) age bin and shows a fairly uniform distribution of massive clusters, the most massive being few10^7M. A maximum likelihood fit shows that the cluster mass function is well fitted by a power-law with an index -1.8, with no statistically significant high-mass cutoff. We calculate the fraction of stars born in clusters to be Gam1-10=22.4+_5.7%. The fraction of stars in clusters decreases quickly over time, with Gam10-100= 4.5+_1.1% and Gam100-400=1.7+_0.4%, suggesting that clusters dissolve rapidly over the first ~0.5Gyr. The decreasing fraction of stars in clusters is consistent with the declining shape observed for the cluster age distribution.

We present new catalogs of likely globular clusters (GCs) in 17 nearby spiral galaxies studied as part of the PHANGS-HST Treasury Survey. The galaxies were imaged in five broad-band filters from the near-ultraviolet through the \\(I\\) band. PHANGS-HST has produced catalogs of stellar clusters of all ages by selecting extended sources (from multiple concentration index measurements) followed by morphological classification (centrally concentrated and symmetric or asymmetric, multiple peaks, contaminant) by visually examining the V-band image and separately by a machine-learning algorithm which classified larger samples to reach fainter limits. From both cluster catalogs, we select an initial list of candidate GCs to have \\(B-V \\geq 0.5\\) and \\(V-I \\geq 0.73\\)~mag, then remove likely contaminants (including reddened young clusters, background galaxies misclassified by the neural network, and chance superpositions/blends of stars) after a careful visual inspection. We find that \\(\\approx86\\) % of the color-selected candidates classified as spherically symmetric, and \\(\\approx68\\) of those classified as centrally concentrated but asymmetric are likely to be GCs. The luminosity functions of the GC candidates in 2 of our 17 galaxies, NGC 628 and NGC 3627, are atypical, and continue to rise at least 1~mag fainter than the expected turnover near \\(M_V \\sim -7.4\\). These faint candidate GCs have more extended spatial distributions than their bright counterparts, and may reside in the disk rather than the bulge/halo, similar to faint GCs previously discovered in M101. These faint clusters may be somewhat younger since the age-metallicity degeneracy makes it difficult to determine precise cluster ages from integrated colors once they reach \\(\\approx1\\)~Gyr.

We present narrow band, continuum subtracted H alpha , [S ii], H beta , [O iii] and [O ii] data taken with the Wide Field Camera 3 on the Hubble Space Telescope in the nearby dwarf starburst galaxy NGC4214. From these images, we identify seventeen new planetary nebula candidates, and seven supernova remnant candidates. We use the observed emission line luminosity function of the planetary nebulae to establish a new velocity-independent distance to NGC4214. We conclude that the PNLF technique gives a reddening independent distance to NGC4214 of 3.19 plus or minus 0.36Mpc, and that our current best-estimate of the distance to this galaxy ids 2.98 plus or minus 0.13Mpc.

Currently available star cluster catalogues from HST imaging of nearby galaxies heavily rely on visual inspection and classification of candidate clusters. The time-consuming nature of this process has limited the production of reliable catalogues and thus also post-observation analysis. To address this problem, deep transfer learning has recently been used to create neural network models which accurately classify star cluster morphologies at production scale for nearby spiral galaxies (D < 20 Mpc). Here, we use HST UV-optical imaging of over 20,000 sources in 23 galaxies from the Physics at High Angular Resolution in Nearby GalaxieS (PHANGS) survey to train and evaluate two new sets of models: i) distance-dependent models, based on cluster candidates binned by galaxy distance (9-12 Mpc, 14-18 Mpc, 18-24 Mpc), and ii) distance-independent models, based on the combined sample of candidates from all galaxies. We find that the overall accuracy of both sets of models is comparable to previous automated star cluster classification studies (~60-80 per cent) and show improvement by a factor of two in classifying asymmetric and multi-peaked clusters from PHANGS-HST. Somewhat surprisingly, while we observe a weak negative correlation between model accuracy and galactic distance, we find that training separate models for the three distance bins does not significantly improve classification accuracy. We also evaluate model accuracy as a function of cluster properties such as brightness, colour, and SED-fit age. Based on the success of these experiments, our models will provide classifications for the full set of PHANGS-HST candidate clusters (N ~ 200,000) for public release.