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We present an algorithm that mitigates the effects of charge migration due to the \"brighter-fatter effect'' (BFE) that occurs for highly illuminated stars in the Teledyne HAWAII-2RG detectors used in the NIRCam, NIRISS, and NIRSpec science instruments aboard the James Webb Space Telescope (JWST). The impact of this effect is most significant for photometry and spectrophotometry of bright stars in data for which the point spread function (PSF) is undersampled, which is the case for several observing modes of the NIRISS instrument. The main impact of the BFE to NIRISS data is incorrect count rate determinations for pixels in the central regions of PSFs of bright stars due to jump detections that are caused by charge migration from peak pixels to surrounding pixels. The effect is especially significant for bright compact sources in resampled, distortion-free images produced by the drizzle algorithm: quantitatively, apparent flux losses of \\(>\\) 50% can occur in such images due to the BFE. We describe the algorithm of the \"charge_migration'' mitigation step that has been implemented in version 10.0 of the operational JWST calibration pipeline as of Dec 5, 2023. We illustrate the impact of this step in terms of the resulting improvements of the precision of imaging photometry of point sources. The algorithm renders the effects of the BFE on photometry and surface brightness measurements to stay within 1%.

We report on the final two days of a multiwavelength campaign of Sgr A* observing in the radio, submillimeter, infrared, and X-ray bands in July 2019. Sgr A* was remarkably active, showing multiple flaring events across the electromagnetic spectrum. We detect a transient \\(\\sim35\\)-minute periodicity feature in Spitzer Space Telescope light curves on 21 July 2019. Time-delayed emission was detected in ALMA light curves, suggesting a hotspot within the accretion flow on a stable orbit. On the same night, we observe a decreased flux in the submillimeter light curve following an X-ray flare detected by the Chandra X-ray Observatory and model the feature with an adiabatically expanding synchrotron hotspot occulting the accretion flow. The event is produced by a plasma \\(0.55~R_{\\text{S}}\\) in radius with an electron spectrum \\(p=2.84\\). It is threaded by a \\(\\sim130\\) Gauss magnetic field and expands at \\(0.6\\%\\) the speed of light. Finally, we reveal an unambiguous flare in the infrared, submillimeter, and radio, demonstrating that the variable emission is intrinsically linked. We jointly fit the radio and submillimeter light curves using an adiabatically expanding synchrotron hotspot and find it is produced by a plasma with an electron spectrum \\(p=0.59\\), \\(187\\) Gauss magnetic field, and radius \\(0.47~R_{\\text{S}}\\) that expands at \\(0.029c\\). In both cases, the uncertainty in the appropriate lower and upper electron energy bounds may inflate the derived equipartition field strengths by a factor of 2 or more. Our results confirm that both synchrotron- and adiabatic-cooling processes are involved in the variable emission's evolution at submillimeter and infrared wavelengths.

In a cold and stable space environment, the James Webb Space Telescope (JWST or \"Webb\") reaches unprecedented sensitivities at wavelengths beyond 2 microns, serving most fields of astrophysics. It also extends the parameter space of high-contrast imaging in the near and mid-infrared. Launched in late 2021, JWST underwent a six month commissioning period. In this contribution we focus on the NIRCam Coronagraphy mode which was declared \"science ready\" on July 10 2022, the last of the 17 JWST observing modes. Essentially, this mode will allow to detect fainter/redder/colder (less massive for a given age) self-luminous exoplanets as well as other faint astrophysical signal in the vicinity of any bright object (stars or galaxies). Here we describe some of the steps and hurdles the commissioning team went through to achieve excellent performances. Specifically, we focus on the Coronagraphic Suppression Verification activity. We were able to produce firm detections at 3.35\\(\\mu\\)m of the white dwarf companion HD 114174 B which is at a separation of \\(\\simeq\\) 0.5\" and a contrast of \\(\\simeq\\) 10 magnitudes (\\(10^{4}\\) fainter than the K\\(\\sim\\)5.3 mag host star). We compare these first on-sky images with our latest, most informed and realistic end-to-end simulations through the same pipeline. Additionally we provide information on how we succeeded with the target acquisition with all five NIRCam focal plane masks and their four corresponding wedged Lyot stops.

The effects of galaxy-galaxy collisions on star formation are investigated for a large, morphologically selected sample of strongly interacting disk-type galaxies. Current star formation rates, stellar contents, and spatial distributions of star forming sites are explored on both global and nuclear scales via narrow-band imaging and spectrophotometry. Measurements of total H(alpha) fluxes reveal an average increase in global star formation rates of about a factor of 2.5 over isolated spiral galaxies. Alternatively, an analysis of far-infrared luminosities shows that the interacting galaxies have anomalously high L(IR)/L(H(alpha)) ratios, and this leads to L(IR)-derived global star formation rates that, on average, are a factor of 6 higher than in isolated spiral galaxies. Quantitative analyses of the spatial distribution of star forming sites suggests that the majority of enhanced star formation activity is concentrated near the nuclei of the interacting galaxies. No correlation is found between global star formation rates and either HI gas content or optical luminosity. The nuclei of the interacting galaxies exhibit a wide range in star formation rates, but have significantly higher overall levels of both H(alpha) emission-line equivalent width and luminosity than samples of isolated spiral galaxies. However, a surprisingly large fraction ((TURN)30%) of the nuclei are characterized by stellar absorption spectra reminiscent of old, elliptical galaxy-like stellar populations. The implications of this work are four-fold. First, the disk regions of galaxies are not strongly affected (in terms of star formation) as a result of an interaction with a close companion. Second, when interaction-induced activity does occur, it is primarily seen as an enhancement in the star formation rate in and around the nuclear regions of a galaxy. Third, exotic forms of nuclear activity, such as Seyferts, are not optically detectable in this sample of interacting galaxies. Fourth, while the observations agree in general with theoretical models, no explanations exist for (1) those galaxies that have not experienced any significant levels of star formation activity for a length of time comparable to the dynamical timescale for interactions, and (2) the overall lack of Seyfert and LINER nuclei in the sample.

We have obtained spectrophotometry for central regions of five interacting systems of galaxies chosen from the Arp Atlas of Peculiar Galaxies. The data are analyzed to derive star-formation rates for different epochs in the galaxies' histories. Oxygen abundances are estimated from emission-line ratios, and stellar population mixes are determined via spectral synthesis modeling. All systems have near-solar oxygen abundances. We find only one system, Arp 299, to be definitely undergoing a burst of star formation, while the remaining systems are found to be characterized by nearly constant rates of star formation and are not obviously different from noninteracting disk galaxies.

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 (Ys), 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 square arcmin 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\\simeq 26.0-27.0 mag (5-{\\sigma}) for point sources, and AB\\simeq 25.5-26.5 mag for compact galaxies. In this paper, we describe: a) the scientific rationale, and the data taking plus reduction procedures of the panchromatic 10-band ERS mosaics; b) the procedure of generating object catalogs across the 10 different ERS filters, and the specific star-galaxy separation techniques used; and c) 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\\simeq 25-26 mag from the UV to the near-IR, respectively.

A sample of 19 low redshift (0.03\\(<\\)z\\(<\\)0.07) very luminous infrared galaxy (VLIRG: \\(10^{11}L_\\odot< \\) L[8-1000 \\(\\mu\\)m] \\( < 10^{12} L_\\odot\\)) systems (30 galaxies) has been imaged in \\(B\\), \\(V\\), and \\(I\\). These objects cover a luminosity range that is key to linking the most luminous infrared galaxies with the population of galaxies at large. We have obtained photometry for all of these VLIRG systems, the individual galaxies (when detached), and their nuclei, and the relative behavior of these classes has been studied in optical color-magnitude diagrams. The photometric properties of the sample are also compared with previously studied samples of ULIRGs. The mean observed photometric properties of VLIRG and ULIRG samples, considered as a whole, are indistinguishable at optical wavelengths. This suggests that not only ULIRG, but also the more numerous population of VLIRGs, have similar rest-frame optical photometric properties as the submillimeter galaxies (SMG), reinforcing the connection between low-{\\it z} LIRGs -- high-{\\it z} SMGs. When the nuclei of the {\\it young} and {\\it old} interacting systems are considered separately, some differences between the VLIRG and the ULIRG samples are found. In particular, the old VLIRGs are less luminous and redder than old ULIRG systems. If confirmed with larger samples, this behavior suggests that the late-stage evolution is different for VLIRGs and ULIRGs. Specifically, as suggested from spectroscopic data, the present photometric observations support the idea that the activity during the late phases of VLIRG evolution is dominated by starbursts, while a higher proportion of ULIRGs could evolve into a QSO type of object.

We have obtained CO(1-0) observations for a sample of 37 interacting galaxy systems, chosen from a parent sample of optically-selected interacting galaxies. The sample observed here spans a large range of interaction strengths and star formation rates (SFR). Using the standard CO-to-H2 conversion factor we find that the interacting galaxies are, on average, marginally more rich in molecular gas than a comparison sample of isolated spiral galaxies, having mean H2/LB and H2/HI ratios 20-40% higher than isolated spirals. The interacting galaxies also have a mean LIR/MH2 ratio that is a factor of ~1.3 higher than the isolated galaxies. There is a strong correlation between relative H2 content and SFRs, indicating that the level of interaction-induced star formation activity is very dependent upon the the available gas supply. Some galaxies, however, have moderate amounts of H2 but much lower than normal SFRs. Therefore molecular gas is a necessary, but not sufficient, prerequisite for star formation. There is also a strong correlation between interaction strength and both SFR and relative H2 content. If the increase in H2 content is real, there must be a substantial conversion of HI to H2 gas taking place in the strongest interacting systems. At least some portion of this apparent increase, however, could be due to non-standard CO-to-H2 conversion factors. A reduction in the conversion factor by amounts consistent with that applicable to ultraluminous infrared galaxies would completely account for the systematic increase in derived H2 content as a function of interaction strength. Such a change could not, however, account for the total range of relative H2 content as a function of SFR. Therefore the correlation between molecular gas content and star formation rate must be real.