We present a spatially resolved near-UV/optical study, using the Wide Field Camera 3 (WFC3) on board the Hubble Space Telescope, of NGC 4150, a sub-L-*, early-type galaxy (ETG) of around 6 x 10(9) M-circle dot, which has been observed as part of the WFC3 Early-Release Science Programme. Previous work indicates that this galaxy has a large reservoir of molecular hydrogen gas, exhibits a kinematically decoupled core (a likely indication of recent merging) and strong, central H beta absorption (indicative of young stars). While relatively uninspiring in its optical image, the core of NGC 4150 shows ubiquitous near-UV emission and remarkable dusty substructure. Our analysis shows this galaxy to lie in the near-UV green valley, and its pixel-by-pixel photometry exhibits a narrow range of near-UV/optical colors that are similar to those of nearby E+A (post-starburst) galaxies and lie between those of M83 (an actively star-forming spiral) and the local quiescent ETG population. We parameterize the properties of the recent star formation (RSF; age, mass fraction, metallicity, and internal dust content) in the NGC 4150 pixels by comparing the observed near-UV/optical photometry to stellar models. The typical age of the RSF is around 0.9 Gyr, consistent with the similarity of the near-UV colors to post-starburst systems, while the morphological structure of the young component supports the proposed merger scenario. The typical RSF metallicity, representative of the metallicity of the gas fuelling star formation, is similar to 0.3-0.5 Z(circle dot). Assuming that this galaxy is a merger and that the gas is sourced mainly from the infalling companion, these metallicities plausibly indicate the gas-phase metallicity (GPM) of the accreted satellite. Comparison to the local mass-GPM relation suggests (crudely) that the mass of the accreted system is similar to 3 x 10(8) M-circle dot, making NGC 4150 a 1: 20 minor merger. A summation of the pixel RSF mass fractions indicates that the RSF contributes similar to 2%-3% of the stellar mass. This work reaffirms our hypothesis that minor mergers play a significant role in the evolution of ETGs at late epochs.

Stable isotopes record the evolution of planetary systems, beginning with stars coalescing from molecular clouds, followed by the nucleosynthesis of elements in stars, and proceeding to the accretion and differentiation of planets. Current stable isotope measurements range in scale from isotopic mapping of the Milky Way Galaxy with spectrographs on telescopes to the analysis of stardust with ion probes.

We use new WFC3 observations of the nearby grand-design spiral galaxy M83 to develop two independent methods for estimating the ages of young star clusters. The first method uses the physical extent and morphology of H alpha emission to estimate the ages of clusters younger than tau approximate to 10 Myr. It is based on the simple premise that the gas in very young (tau < a few Myr) clusters is largely coincident with the cluster stars, is in a small, ring-like structure surrounding the stars in slightly older clusters since massive star winds and supernovae have had time to push out the natal gas (e.g., tau approximate to 5 Myr), and is in a larger ring-like bubble for still older clusters (i.e., approximate to 5-10 Myr). If no H alpha is associated with a cluster it is generally older than approximate to 10 Myr. The second method is based on an observed relation between pixel-to-pixel flux variations within clusters and their ages. This method relies on the fact that the brightest individual stars in a cluster are most prominent at ages around 10 Myr, and fall below the detection limit (i.e., M-V < -3.5) for ages older than about 100 Myr. Older clusters therefore have a smoother appearance and smaller pixel-to-pixel variations. The youngest clusters also have lower flux variations, hence the relationship is double valued. This degeneracy in age can be broken using other age indicators such as H alpha morphology. These two methods are the basis for a new morphological classification system which can be used to estimate the ages of star clusters based on their appearance. We compare previous age estimates of clusters in M83 determined from fitting UBVIH alpha measurements using predictions from stellar evolutionary models with our new morphological categories and find good agreement, at the approximate to 95% level. The scatter within categories is approximate to 0.1 dex in log tau for young clusters (< 10 Myr) and approximate to 0.5 dex for older (> 10 Myr) clusters. A by-product of this study is the identification of 22 "single-star" H II regions in M83, with central stars having ages approximate to 4 Myr.

We used near-infrared data obtained with the Wide Field Camera 3 on the Hubble Space Telescope to identify objects having the colors of brown dwarfs (BDs) in the field of the massive galactic cluster NGC 3603. These are identified through a combination of narrow-and medium-band filters which span the J and H bands and are particularly sensitive to the presence of the 1.3-1.5 mu m H2O molecular band unique to BDs. We provide a calibration of the relationship between effective temperature and color for both field stars and BDs. This photometric method provides effective temperatures for BDs to an accuracy of +/-350K relative to spectroscopic techniques. This accuracy is shown to be not significantly affected by either stellar surface gravity or uncertainties in the interstellar extinction. We identify nine objects having effective temperatures between 1700 and 2200 K, typical of BDs, observed J-band magnitudes in the range 19.5-21.5, and that are strongly clustered toward the luminous core of NGC 3603. However, if these are located at the distance of the cluster, they are far too luminous to be normal BDs. We argue that it is unlikely that these objects are either artifacts of our data set, normal field BDs/M-type giants, or extragalactic contaminants and, therefore, might represent a new class of stars having the effective temperatures of BDs but with luminosities of more massive stars. We explore the interesting scenario in which these objects would be normal stars that have recently tidally ingested a hot Jupiter, the remnants of which are providing a short-lived extended photosphere to the central star. In this case, we would expect them to show the signature of fast rotation.

We investigate the ionization structure of the nebular gas in M83 using the line diagnostic diagram, [O III](5007 angstrom)/H beta versus [S II](6716 angstrom+6731 angstrom)/H alpha, with the newly available narrowband images from the Wide Field Camera 3 (WFC3) of the Hubble Space Telescope (HST). We produce the diagnostic diagram on a pixel-by-pixel (0 ''.2 x 0 ''.2) basis and compare it with several photo- and shock-ionization models. We select four regions from the center to the outer spiral arm and compare them in the diagnostic diagram. For the photoionized gas, we observe a gradual increase of the log ([O III]/H beta) ratios from the center to the spiral arm, consistent with the metallicity gradient, as the H II regions go from super-solar abundance to roughly solar abundance from the center out. Using the diagnostic diagram, we separate the photoionized from the shock-ionized component of the gas. We find that the shock-ionized H alpha emission ranges from similar to 2% to about 15%-33% of the total, depending on the separation criteria used. An interesting feature in the diagnostic diagram is a horizontal distribution around log ([O III]/H beta) approximate to 0. This feature is well fit by a shock-ionization model with 2.0 Z(circle dot) metallicity and shock velocities in the range of 250350 km s(-1). A low-velocity shock component, <200 km s(-1), is also detected and is spatially located at the boundary between the outer ring and the spiral arm. The low-velocity shock component can be due to (1) supernova remnants located nearby, (2) dynamical interaction between the outer ring and the spiral arm, and (3) abnormal line ratios from extreme local dust extinction. The current data do not enable us to distinguish among those three possible interpretations. Our main conclusion is that, even at the HST resolution, the shocked gas represents a small fraction of the total ionized gas emission at less than 33% of the total. However, it accounts for virtually all of the mechanical energy produced by the central starburst in M83.

We describe the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) Early Release Science (ERS) observations in the Great Observatories Origins Deep Survey (GOODS) South field. The new WFC3 ERS data provide calibrated, drizzled mosaics in the UV filters F225W, F275W, and F336W, as well as in the near-IR filters F098M (Y-s), F125W (J), and F160W (H) with 1-2 HST orbits per filter. Together with the existing HST Advanced Camera for Surveys (ACS) GOODS-South mosaics in the BViz filters, these panchromatic 10-band ERS data cover 40-50 arcmin(2) at 0.2-1.7 mu m in wavelength at 0 ''.07-0 ''.15 FWHM resolution and 0 ''.090 Multidrizzled pixels to depths of AB similar or equal to 26.0-27.0 mag (5 sigma) for point sources, and AB similar or equal to 25.5-26.5 mag for compact galaxies. In this paper, we describe (1) the scientific rationale, and the data taking plus reduction procedures of the panchromatic 10-band ERS mosaics, (2) the procedure of generating object catalogs across the 10 different ERS filters, and the specific star-galaxy separation techniques used, and (3) the reliability and completeness of the object catalogs from the WFC3 ERS mosaics. The excellent 0 ''.07-0 ''.15 FWHM resolution of HST/WFC3 and ACS makes star-galaxy separation straightforward over a factor of 10 in wavelength to AB similar or equal to 25-26 mag from the UV to the near-IR, respectively. Our main results are: (1) proper motion of faint ERS stars is detected over 6 years at 3.06 +/- 0.66 mas year(-1) (4.6 sigma), consistent with Galactic structure models; (2) both the Galactic star counts and the galaxy counts show mild but significant trends of decreasing count slopes from the mid-UV to the near-IR over a factor of 10 in wavelength; (3) combining the 10-band ERS counts with the panchromatic Galaxy and Mass Assembly survey counts at the bright end (10 mag less than or similar to AB less than or similar to 20 mag) and the Hubble Ultra Deep Field counts in the BVizY(s)JH filters at the faint end (24 mag less than or similar to AB less than or similar to 30 mag) yields galaxy counts that are well measured over the entire flux range 10 mag less than or similar to AB less than or similar to 30 mag for 0.2-2 mu m in wavelength; (4) simple luminosity+density evolution models can fit the galaxy counts over this entire flux range. However, no single model can explain the counts over this entire flux range in all 10 filters simultaneously. More sophisticated models of galaxy assembly are needed to reproduce the overall constraints provided by the current panchromatic galaxy counts for 10 mag less than or similar to AB less than or similar to 30 mag over a factor of 10 in wavelength.

We present the highest redshift detections of resolved Ly alpha emission, using Hubble Space Telescope (HST)/Advanced Camera for Surveys F658N narrowband-imaging data taken in parallel with the Wide Field Camera 3 Early Release Science program in the GOODS Chandra Deep Field-South. We detect Ly alpha emission from three spectroscopically confirmed z = 4.4 Ly alpha emitting galaxies (LAEs), more than doubling the sample of LAEs with resolved Ly alpha emission. Comparing the light distribution between the rest-frame ultraviolet continuum and narrowband images, we investigate the escape of Ly alpha photons at high redshift. While our data do not support a positional offset between the Ly alpha and rest-frame ultraviolet (UV) continuum emission, the half-light radius in one out of the three galaxies is significantly (> 1 sigma) larger in Ly alpha than in the rest-frame UV continuum. Stacking the three LAEs in both the narrowband and UV continuum images, we find that the Ly alpha light appears larger than the rest-frame UV at 4.2 sigma significance. This Ly alpha flux detected with HST is a factor of 4-10 less than observed in similar filters from the ground. These results together imply that the Ly alpha emission is not strictly confined to its indigenous star-forming regions. Rather, for at least one object the Ly alpha emission is more extended, with the missing HST flux possibly existing in a diffuse outer halo. This suggests that the radiative transfer of Ly alpha photons in high-redshift LAEs is complicated, with the interstellar-medium geometry and/or outflows playing a significant role in galaxies at these redshifts.

Using observations obtained with the Wide-Field Camera 3 on board the Hubble Space Telescope, we have studied the properties of the stellar populations in the central regions of 30 Dor in the Large Magellanic Cloud. The observations clearly reveal the presence of considerable differential extinction across the field. We characterize and quantify this effect using young massive main-sequence stars to derive a statistical reddening correction for most objects in the field. We then search for pre-main-sequence (PMS) stars by looking for objects with a strong (>4 sigma) H alpha excess emission and find about 1150 of them over the entire field. Comparison of their location in the Hertzsprung-Russell diagram with theoretical PMS evolutionary tracks for the appropriate metallicity reveals that about one-third of these objects are younger than similar to 4 Myr, compatible with the age of the massive stars in the central ionizing cluster R 136, whereas the rest have ages up to similar to 30 Myr, with a median age of similar to 12 Myr. This indicates that star formation has proceeded over an extended period of time, although we cannot discriminate between an extended episode and a series of short and frequent bursts that are not resolved in time. While the younger PMS population preferentially occupies the central regions of the cluster, older PMS objects are more uniformly distributed across the field and are remarkably few at the very center of the cluster. We attribute this latter effect to photo-evaporation of the older circumstellar disks caused by the massive ionizing members of R 136.

In the first of a series of forthcoming publications, we present a panchromatic catalog of 102 visually selected early-type galaxies (ETGs) from observations in the Early Release Science (ERS) program with the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) of the Great Observatories Origins Deep Survey-South (GOODS-S) field. Our ETGs span a large redshift range, 0.35 less than or similar to z less than or similar to 1.5, with each redshift spectroscopically confirmed by previous published surveys of the ERS field. We combine our measured WFC3 ERS and Advanced Camera for Surveys (ACS) GOODS-S photometry to gain continuous sensitivity from the rest-frame far-UV to near-IR emission for each ETG. The superior spatial resolution of the HST over this panchromatic baseline allows us to classify the ETGs by their small-scale internal structures, as well as their local environment. By fitting stellar population spectral templates to the broadband photometry of the ETGs, we determine that the average masses of the ETGs are comparable to the characteristic stellar mass of massive galaxies, 10(11) < M-*[M-circle dot]< 10(12). By transforming the observed photometry into the Galaxy Evolution Explorer FUV and NUV, Johnson V, and Sloan Digital Sky Survey g' and r' bandpasses we identify a noteworthy diversity in the rest-frame UV-optical colors and find the mean rest-frame (FUV-V) = 3.5 and (NUV-V) = 3.3, with 1 sigma standard deviations similar or equal to 1.0. The blue rest-frame UV-optical colors observed for most of the ETGs are evidence for star formation during the preceding gigayear, but no systems exhibit UV-optical photometry consistent with major recent (less than or similar to 50 Myr) starbursts. Future publications which address the diversity of stellar populations likely to be present in these ETGs, and the potential mechanisms by which recent star formation episodes are activated, are discussed.

We present the size evolution of passively evolving galaxies at z similar to 2 identified in Wide-Field Camera 3 imaging from the Early Release Science program. Our sample was constructed using an analog to the passive BzK galaxy selection criterion, which isolates galaxies with little or no ongoing star formation at z greater than or similar to 1.5. We identify 30 galaxies in similar to 40 arcmin(2) to H < 25 mag. By fitting the 10-band Hubble Space Telescope photometry from 0.22 mu m less than or similar to lambda(obs) less than or similar to 1.6 mu m with stellar population synthesis models, we simultaneously determine photometric redshift, stellar mass, and a bevy of other population parameters. Based on the six galaxies with published spectroscopic redshifts, we estimate a typical redshift uncertainty of similar to 0.033(1+z). We determine effective radii from Sersic profile fits to the H-band image using an empirical point-spread function. By supplementing our data with published samples, we propose a mass-dependent size evolution model for passively evolving galaxies, where the most massive galaxies (M-* similar to 10(11) M-circle dot) undergo the strongest evolution from z similar to 2 to the present. Parameterizing the size evolution as (1+z)(-alpha), we find a tentative scaling of alpha approximate to (-0.6 +/- 0.7) + (0.9 +/- 0.4) log(M-*/10(9) M-circle dot), where the relatively large uncertainties reflect the poor sampling in stellar mass due to the low numbers of high-redshift systems. We discuss the implications of this result for the redshift evolution of the M-*-R-e relation for red galaxies.