We present a photometric catalog of 45 massive star clusters in the nuclear starburst of M83 (NGC 5236), observed with the Hubble Space T elescope Wide Field Planetary Camera 2, in both broadband (F300W, F547M, and F814W) and narrowband (F656N and F487N) Ðlters. By comparing the photometry with theoretical population synthesis models, we estimate the age and mass of each cluster. We Ðnd that over 75% of the star clusters more massive than 2 ] 104 in the central 300 pc of M83 are M _ less than 10 Myr old. Among the clusters younger than 10 Myr and more massive than 5 ] 103 M _ , 70% are between 5 and 7 Myr old. We list an additional 330 objects that are detected in our F300W images but not in the shallower F547M and F814W images. The clusters are distributed throughout a semicircular annulus that identiÐes the active region in the galaxy core, between 50 and 130 pc from the optical center of M83. Clusters younger than 5 Myr are preferentially found along the northwestern end of the semicircular annulus, and the northwest region also corresponds to the highest equivalent widths of the Ha emission [EW(Ha)] values. The cluster ages are consistent with a burst of star formation that began Myr ago. However, the current data cannot exclude a longer duration of activity, because [10 the star clusters may dissolve on a D10 Myr timescale. We discuss both possible scenarios.

The small-and intermediate-scale structure and the fraction of the interstellar medium (ISM) ionized by nonradiative processes are investigated in a small sample of four local starburst galaxies, imaged with the Hubble Space Telescope (HST ) Wide Field Planetary Camera 2. The sample comprises three dwarf galaxies, NGC 3077, 4214, and 5253, and one giant spiral, NGC 5236 (M83). The galaxies span a range in metallicity ($0.2-2 Z ), luminosity (M B $ À17 to À20), and environment (isolated, interacting), enabling the investigation of nonradiative ionization processes in a variety of galactic conditions. For this purpose, the four galaxies were imaged in the lines of H (4861 Å ), [O iii] (5007 Å ), H (6563 Å ), and [S ii] (6717, 6731 Å ). This is a unique set of data, as very few galaxies (and only our four starbursts) have ever been imaged by HST in the relatively faint lines of H and [S ii]. The use of HST has allowed us to trace nonphotoionized gas in these galaxies on scales ranging from a few tens of parsecs to a few hundred parsecs and, thus, to provide a full budget for this ionized gas component. Using the ''maximum starburst line'' of Kewley et al. to discriminate between photoionized and nonphotoionized gas, we find that in all four galaxies non-photoionization processes are responsible for a small fraction of the total H emission, at the level of 3%-4%. Because the nonphotoionized gas is associated with low H surface brightness, it occupies between one-sixth and one-quarter of the total imaged area. The central starbursts yield enough mechanical energy to produce the nonphotoionized gas in the four galaxies, by means of shocks from massive star winds and supernova explosions. In particular, the starbursts in the three dwarf galaxies must deposit a significant fraction, 70%-100%, of their mechanical energy into the surrounding ISM, in order to account for the observed luminosity of the nonphotoionized gas. The morphology of the nonphotoionized regions is different in the dwarfs and the giant spiral. As already established in previous works, nonphotoionized gas in dwarfs is mainly associated with extended ''shells'' or filamentary regions, likely areas of supernova-driven expanding gas. In all three dwarfs, star formation has been an ongoing process for the last few times 10 7 yr to $10 8 yr; time-extended star formation episodes are a requirement to sustain the observed luminosity of the nonphotoionized gas. In the massive spiral, the nonphotoionized gas is concentrated in localized areas surrounded by active star formation, with no evidence of extended structures on the same (or smaller) spatial scales as the ''shells'' in the dwarfs. The two H cavities in NGC 5236 may be evolved regions within the starburst. This confirms the picture that starbursts remain confined events in massive galaxies, likely as a consequence of the deep potential well.

We present multicolor photometry of bright star cluster candidates in the nearby starburst galaxies NGC 3077 and NGC 5253, observed with the Hubble Space Telescope Wide Field and Planetary Camera 2 in both broadband (F300W, F547M and F814W) and narrowband (F487N and F656N) filters. By comparing the photometry with theoretical population synthesis models, we estimate the age and mass of each star cluster, which provides constraints on the recent star formation histories of the host galaxies. We compare the star cluster populations in these dwarf starburst galaxies to those of the nuclear starburst in the barred spiral M 83, and discuss implications for our understanding of the nature and evolution of starburst events.

This paper characterizes the actual science performance of the James Webb Space Telescope (JWST), as determined from the six month commissioning period. We summarize the performance of the spacecraft, telescope, science instruments, and ground system, with an emphasis on differences from pre-launch expectations. Commissioning has made clear that JWST is fully capable of achieving the discoveries for which it was built. Moreover, almost across the board, the science performance of JWST is better than expected; in most cases, JWST will go deeper faster than expected. The telescope and instrument suite have demonstrated the sensitivity, stability, image quality, and spectral range that are necessary to transform our understanding of the cosmos through observations spanning from near-earth asteroids to the most distant galaxies.

BackgroundWikipedia's health content is the most frequently visited resource for health information on the internet. While the literature provides strong evidence for its high usage, a comprehensive literature review of Wikipedia's role within the health context has not yet been reported. ObjectiveTo conduct a comprehensive review of peer-reviewed, published literature to learn what the existing body of literature says about Wikipedia as a health information resource and what publication trends exist, if any.Results 89 articles and conference proceedings were selected for inclusion in the review. Four categories of literature emerged: 1) studies that situate Wikipedia as a health information resource; 2) investigations into the quality of Wikipedia, 3) explorations of the utility of Wikipedia in education, and 4) studies that demonstrate the utility of Wikipedia in research. ConclusionThe literature positions Wikipedia as a prominent health information resource in various contexts for the public, patients, students, and practitioners seeking health information online. Wikipedia's health content is accessed frequently, and its pages regularly rank highly in Google search results. While Wikipedia itself is well into its second decade, the academic discourse around Wikipedia within the context of health is still young and the academic PLOS ONE | https://doi.