A Comparison between P[CLC]a[/CLC]α and Hα Emission: The Relation between Mean H [CSC]ii[/CSC] Region Reddening, Local Gas Density, and Metallicity

We present detailed studies of a z = 2.12 submillimeter galaxy, ALESS67.1, using sub-arcsecond resolution ALMA, adaptive optics-aided VLT/SINFONI, and Hubble Space Telescope (HST)/CANDELS data to investigate the kinematics and spatial distributions of dust emission (870 μm continuum), 12CO(J = 3–2), strong optical emission lines, and visible stars. Dynamical modeling of the optical emission lines suggests that ALESS67.1 is not a pure rotating disk but a merger, consistent with the apparent tidal features revealed in the HST imaging. Our sub-arcsecond resolution data set allows us to measure half-light radii for all the tracers, and we find a factor of 4–6 smaller sizes in dust continuum compared to all the other tracers, including 12CO; also, ultraviolet (UV) and Hα emission are significantly offset from the dust continuum. The spatial mismatch between the UV continuum and the cold dust and gas reservoir supports the explanation that geometrical effects are responsible for the offset of the dusty galaxy on the IRX–β diagram. Using a dynamical method we derive an , consistent with other submillimeter galaxies (SMGs) that also have resolved CO and dust measurements. Assuming a single value we also derive resolved gas and star formation rate surface densities, and find that the core region of the galaxy ( kpc) follows the trend of mergers on the Schmidt–Kennicutt relationship, whereas the outskirts ( kpc) lie on the locus of normal star-forming galaxies, suggesting different star formation efficiencies within one galaxy. Our results caution against using single size or morphology for different tracers of the star formation activity and gas content of galaxies, and therefore argue the need to use spatially resolved, multi-wavelength observations to interpret the properties of SMGs, and perhaps even for galaxies in general.

We present a hierarchical Bayesian pipeline, BP3M, that measures positions, parallaxes, and proper motions (PMs) for cross-matched sources between Hubble Space Telescope (HST) images and Gaia—even for sparse fields (N * < 10 per image)—expanding from the recent GaiaHub tool. This technique uses Gaia-measured astrometry as priors to predict the locations of sources in HST images, and is therefore able to put the HST images onto a global reference frame without the use of background galaxies/QSOs. Testing our publicly available code in the Fornax and Draco dwarf spheroidal galaxies, we measure PMs that are a median of 8–13 times more precise than Gaia DR3 alone for 20.5 < G < 21 mag. We are able to explore the effect of observation strategies on BP3M astrometry using synthetic data, finding an optimal strategy to improve parallax and position precision at no cost to the PM uncertainty. Using 1619 HST images in the sparse COSMOS field (median nine Gaia sources per HST image), we measure BP3M PMs for 2640 unique sources in the 16 < G < 21.5 mag range, 25% of which have no Gaia PMs; the median BP3M PM uncertainty for 20.25 < G < 20.75 mag sources is 0.44 mas yr−1 compared to 1.03 mas yr−1 from Gaia, while the median BP3M PM uncertainty for sources without Gaia-measured PMs (20.75 < G < 21.5 mag) is 1.16 mas yr−1. The statistics that underpin the BP3M pipeline are a generalized way of combining position measurements from different images, epochs, and telescopes, which allows information to be shared between surveys and archives to achieve higher astrometric precision than that from each catalog alone.

Accurate and precise measurements of the Hubble constant are critical for testing our current standard cosmological model and revealing possibly new physics. With Hubble Space Telescope (HST) imaging, each strong gravitational lens system with measured time delays can allow one to determine the Hubble constant with an uncertainty of $\sim 7\%$. Since HST will not last forever, we explore adaptive-optics (AO) imaging as an alternative that can provide higher angular resolution than HST imaging but has a less stable point spread function (PSF) due to atmospheric distortion. To make AO imaging useful for time-delay-lens cosmography, we develop a method to extract the unknown PSF directly from the imaging of strongly lensed quasars. In a blind test with two mock data sets created with different PSFs, we are able to recover the important cosmological parameters (time-delay distance, external shear, lens mass profile slope, and total Einstein radius). Our analysis of the Keck AO image of the strong lens system RXJ1131-1231 shows that the important parameters for cosmography agree with those based on HST imaging and modeling within 1-$\sigma$ uncertainties. Most importantly, the constraint on the model time-delay distance by using AO imaging with $0.045"$resolution is tighter by $\sim 50\%$ than the constraint of time-delay distance by using HST imaging with $0.09"$when a power-law mass distribution for the lens system is adopted. Our PSF reconstruction technique is generic and applicable to data sets that have multiple nearby point sources, enabling scientific studies that require high-precision models of the PSF.

We present the results of a campaign to obtain an accurate registration of Hubble Space Telescope (HST) and MERLIN images of NGC 1068, the prototypical Seyfert 2 galaxy. The final registration is accurate to 100 mas. A strong anticorrelation between radio and optical emission is revealed; in particular, the radio jet lies on a region of relatively low optical emission and is surrounded by line-emitting clouds. A major exception is the brightest narrow-line region (NLR) knot, cloud B, which lies, at least in projection, along the radio jet. These results can be understood as due to the interaction between the jet and the surrounding medium: in this scenario, the outflowing plasma is sweeping and heating the interstellar gas. As a result of this interaction and compression, the line emission is highly enhanced along the edges of the radio jet. It therefore appears that the morphology of the NLR of NGC 1068 is dominated by the presence of a radio outflow, as already revealed by HST observations of several Seyfert galaxies with extended radio emission. The optical peak seen in the HST images is located at α = 02h42m40711, δ = -00°00'4781 (J2000, FK5), with an error of 80 mas. The hidden nucleus, as determined by HST imaging polarimetry, falls at α = 02h42m40710, δ = -00°00'4811 (J2000, FK5). It is offset toward the south (i.e., along the radio axis) with respect to the two southernmost radio components and, in particular, by 170 mas from the inverted spectrum radio component, S1. This does not rule out that S1 is indeed the radio core but suggests that the nucleus of NGC 1068 might be radio silent, or its emission absorbed at radio wavelengths also. There are several contributions to the final accuracy of the optical-to-radio registration. A significant decrease of the astrometric error budget has to wait for substantial improvements, like those expected from the radio-optical link in the forthcoming HIPPARCOS catalog.

We present Hubble Space Telescope (HST) imaging data and CFHT Near IR ground-based images for the final sample of 56 candidate galaxy-scale lenses uncovered in the CFHT Legacy Survey as part of the Strong Lensing in the Legacy Survey (SL2S) project. The new images are used to perform lens modeling, measure surface photometry, and estimate stellar masses of the deflector early-type galaxies. Lens modeling is performed on the HST images (or CFHT when HST is not available) by fitting the spatially extended light distribution of the lensed features assuming a singular isothermal ellipsoid mass profile and by reconstructing the intrinsic source light distribution on a pixelized grid. Based on the analysis of systematic uncertainties and comparison with inference based on different methods we estimate that our Einstein Radii are accurate to \sim3%. HST imaging provides a much higher success rate in confirming gravitational lenses and measuring their Einstein radii than CFHT imaging does. Lens modeling with ground-based images however, when successful, yields Einstein radius measurements that are competitive with spaced-based images. Information from the lens models is used together with spectroscopic information from the companion paper IV to classify the systems, resulting in a final sample of 39 confirmed (grade-A) lenses and 17 promising candidates. The redshifts of the main deflector span a range 0.3<zd< 0.8, providing an excellent sample for the study of the cosmic evolution of the mass distribution of early-type galaxies over the second half of the history of the Universe.

Automated arc detection methods are needed to scan the ongoing and next-generation wide-field imaging surveys, which are expected to contain thousands of strong lensing systems. Arc finders are also required for a quantitative comparison between predictions and observations of arc abundance. Several algorithms have been proposed to this end, but machine learning methods have remained as a relatively unexplored step in the arc finding process. In this work we introduce a new arc finder based on pattern recognition, which uses a set of morphological measurements derived from the Mediatrix Filamentation Method as entries to an Artificial Neural Network (ANN). We show a full example of the application of the arc finder, first training and validating the ANN on simulated arcs and then applying the code on four Hubble Space Telescope (HST) images of strong lensing systems. The simulated arcs use simple prescriptions for the lens and the source, while mimicking HST observational conditions. We also consider a sample of objects from HST images with no arcs in the training of the ANN classification. We use the training and validation process to determine a suitable set of ANN configurations, including the combination of inputs from the Mediatrix method, so as to maximize the completeness while keeping the false positives low. In the simulations the method was able to achieve a completeness of about 90% with respect to the arcs that are input to the ANN after a preselection. However, this completeness drops to $\sim$ 70% on the HST images. The false detections are of the order of 3% of the objects detected in these images. The combination of Mediatrix measurements with an ANN is a promising tool for the pattern recognition phase of arc finding. More realistic simulations and a larger set of real systems are needed for a better training and assessment of the efficiency of the method.

We investigate the X-ray and near-infrared emission properties of a sample of pre-main-sequence (PMS) stellar systems in the Orion Nebula Cluster (ONC) that display evidence for circumstellar disks (proplyds) and optical jets in Hubble Space Telescope (HST) imaging. Our study uses X-ray data acquired during Chandra Orion Ultradeep Program (COUP) observations, as well as complementary optical and near-infrared data recently acquired with HST and the Very Large Telescope (VLT), respectively. Approximately 70% of ~140 proplyds were detected as X-ray sources in the 838 ks COUP observation of the ONC, including ~25% of proplyds that do not display central stars in HST imaging. In near-infrared imaging, the detection rate of proplyd central stars is >90%. Many proplyds display near-infrared excesses, suggesting disk accretion is ongoing onto the central, PMS stars. About 50% of circumstellar disks that are detected in absorption in HST imaging contain X-ray sources. For these sources, we find that X-ray absorbing column and apparent disk inclination are well correlated, providing insight into the disk scale heights and metal abundances of UV- and X-ray-irradiated protoplanetary disks. Approximately 2/3 of the ~30 proplyds and PMS stars exhibiting jets in Hubble images have COUP X-ray counterparts. These jet sources display some of the largest near-infrared excesses among the proplyds, suggesting that the origin of the jets is closely related to ongoing, PMS stellar accretion. One morphologically complex jet source, d181-825, displays a double-peaked X-ray spectral energy distribution with a prominent soft component that is indicative of strong shocks in the jet collimation region. A handful of similar objects also display X-ray spectra that are suggestive of shocks near the jet source. These results support models in which circumstellar disks collimate and/or launch jets from young stellar objects and, furthermore, demonstrate that star-disk-jet interactions may contribute to PMS X-ray emission.

In support of the NASA Deep Space 1 (DS1) mission to comet 19P/Borrelly, we obtained Hubble Space Telescope (HST) images and ultraviolet (UV) spectra of the comet near the time of the DS1 flyby in 2001 September. The HST data provide context information on 19P/Borrelly's circumnuclear dust environment, the rotational period and rotational phase of its nucleus, the H2O and CS2 production rates, the dust production rate, the dust reflectivity in the visible and mid-UV, and the time variability of these quantities around the time of the DS1 encounter. We derive average values of Q = (3.0 ± 0.6) × 1028 molecules s-1, [CS2/H2O] = (1.0 ± 0.3) × 10-3, and Qdust ≈ 240 kg s-1. The corresponding dust-to-gas mass ratio is 0.24, but this is only a rough estimate because the dust production rate is uncertain by about an order of magnitude. The dust continuum was strongly reddened between 2400 and 3200 Å, and the Afρ value of 745 ± 15 cm near 6500 Å was ∼2.5 times larger than the value near 2900 Å. The observed coma morphology consisted of a strong jet centered ∼6° from the projected solar vector, one broad fan centered ∼23° from the sunward direction, and another broad fan centered ∼18° from the antisunward direction. The light curve of the optical continuum, as measured in target acquisition images, has an amplitude of ∼40% in a square aperture that subtends 160 km at the comet; the rotational period could not be independently derived from the HST images but is consistent with the value of ∼26 hr derived from HST observations in 1994 and ground-based images in 2000. The new HST data reveal a prominent offset in the emission peak of neutral gas molecules, and therefore in the peak column densities of gas in the coma, relative to the position of the cometary nucleus, which may be related to the offset in ion densities observed in situ by the DS1 Plasma Experiment for Planetary Exploration (PEPE) plasma spectrometer.

The globular cluster (GC) system of our Galaxy contains four planetary nebulae (PNe): K 648 (or Ps 1) in M15, IRAS 18333-2357 in M22, JaFu 1 in Pal 6, and JaFu 2 in NGC 6441. Because single-star evolution at the low stellar mass of present-epoch GCs was considered incapable of producing visible PNe, their origin presented a puzzle. We imaged the PN JaFu 1 with the Hubble Space Telescope (HST) to obtain photometry of its central star (CS) and high-resolution morphological information. We imaged IRAS 18333-2357 with better depth and resolution, and we analyzed its archival HST spectra to constrain its CS temperature and luminosity. All PNe in Galactic GCs now have quality HST data, allowing us to improve CS mass estimates. We find reasonably consistent masses between 0.53 and 0.58 M ⊙ for all four objects, though estimates vary when adopting different stellar evolutionary calculations. The CS mass of IRAS 18333-2357, though, depends strongly on its temperature, which remains elusive due to reddening uncertainties. For all four objects, we consider their CS and nebula masses, their morphologies, and other incongruities to assess the likelihood that these objects formed from binary stars. Although generally limited by uncertainties (∼0.02 M ⊙) in post-AGB tracks and core mass versus luminosity relations, the high-mass CS in K 648 indicates a binary origin. The CS of JaFu 1 exhibits compact, bright [O iii] and Hα emission, like EGB 6, suggesting a binary companion or disk. Evidence is weaker for a binary origin of JaFu 2.

Coordinated 1996 HST and IRTF Imaging of Neptune and Triton: I. Observations, Navigation, and Differential Deconvolution

We present Hubble Space Telescope (HST) narrow-passband H? and [S II] images and broadband continuum images of the region around an extremely luminous optical and X-ray supernova remnant complex in the spiral galaxy NGC 6946. These images, obtained with the PC1 CCD of the Wide Field Planetary Camera 2, show a circular, limb-brightened shell of diameter 035 [9 d/(5.1 Mpc) pc] superposed on the edge of a larger, lower surface brightness elliptical shell (14 ? 08, or 34 pc ? 20 pc). The HST images allow us to see that the [S II]?:?H? ratio remains high across both shells, indicating that both are collisionally heated. A brightening of the H? and [S II] line emission arises on the eastern side of the smaller shell, where it is apparently interacting with the western edge of the larger shell. Our HST V image includes the nebula's strong [O III] ?5007 emission in the blue wing of the filter, providing a glimpse at the [O III] nebular morphology. The smaller shell looks similar, but the extended structure looks sharper than in H? and [S II] images, reminiscent of a cavity wall. The HST and ground-based continuum images show the brightest members of the underlying and adjacent stellar population, indicating the presence of massive OB stars in and near the region. A new optical ground-based spectrum confirms that the [N II]?:?H? ratio is enhanced in the region, consistent with mass loss from massive stars. These data show an average ([S II] ??6716, 6731)?:?H? ratio across both shells of ~1 and a mean electron density of ~400 cm-3, indicating preshock densities of order 10 cm-3. We interpret this nebular morphology and supporting information as an indication of multiple supernova explosions in relatively close temporal and spatial proximity. We discuss possible scenarios for this complex region and the reasons for its extreme luminosity.

High-resolution (07 to 08) Hα images of the Hickson Compact Group 31 (HCG 31) obtained with the WIYN telescope are used in conjunction with broadband optical images from the Hubble Space Telescope (HST) to examine the star formation history and properties of the component galaxies. The high spatial resolution of the WIYN telescope has allowed us to identify a large number of starburst regions from their Hα emission, which traces the recent star birth activity. The HST images of galaxies E and F reveal more detail within the starburst regions in which we have identified numerous super star clusters (SSCs). Photometry of these starburst regions and SSCs in the Hα and optical images indicates that there has been a substantial amount of star formation throughout HGC 31 over the past 10 Myr. The Hα equivalent widths suggest activity within the group as recently as a few megayears ago. There is evidence that galaxy F, the youngest member of the group, is possibly undergoing its initial episode of star formation, as no underlying stellar population has yet been detected.

view Abstract Citations (74) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Hubble Space Telescope Observations of Giant Arcs: High-Resolution Imaging of Distant Field Galaxies Smail, Ian ; Dressler, Alan ; Kneib, Jean-Paul ; Ellis, Richard S. ; Couch, Warrick J. ; Sharples, Ray M. ; Oemler, Augustus, Jr. Abstract We present Hubble Space Telescope (HST) imaging of eight spectroscopically confirmed giant arcs, pairs, and arclets. These objects have all been studied extensively from the ground, and we demonstrate the unique advantages of HST imaging in the study of such features by a critical comparison of our data with the previous observations. In particular, we present new estimates of the core radii of two clusters (Cl 0024+16, A370) determined from lensed features that are identifiable in our HST images. Although our HST observations include both pre- and postrefurbishment images, the depth of the exposures guarantees that the majority of the arcs are detected with diffraction-limited resolution. A number of the objects in our sample are multiply imaged, and we illustrate the ease of identification of such features when working at high resolution. We discuss the morphological and size information on these distant field galaxies in the light of HST studies of lower redshift samples. We suggest that the dominant population of star-forming galaxies at z ~ 1 is a factor of 1.5-2 times smaller in size than the equivalent population in the local field. This implies either a considerable evolution in the sizes of star-forming galaxies within the last ~10 Gyr or a shift in the relative space densities of massive and dwarf star-forming systems over the same timescale. Publication: The Astrophysical Journal Pub Date: October 1996 DOI: 10.1086/177799 arXiv: arXiv:astro-ph/9503063 Bibcode: 1996ApJ...469..508S Keywords: GALAXIES: CLUSTERS: GENERAL; GALAXIES: PHOTOMETRY; COSMOLOGY: GRAVITATIONAL LENSING; Astrophysics E-Print: 9 pages (no figures), uuencoded, compressed Postscript. Postscript text, tables and figures (803 Kb) available via anonymous ftp in at ftp://ociw.edu//pub/irs/pub/hstarcs.tar.Z full text sources arXiv | ADS | data products SIMBAD (54) NED (11) MAST (1) ESA (1)

Saturn’s zonal wind profile at cloud level has been measured at different epochs since the first spacecraft visits from Voyager 1 and 2 in 1980-81 [1-2]. Saturn’s wind measurements available in the literature include zonal wind profiles obtained from HST before Cassini, from 1996 to 2002 [3], Cassini ISS images and VIMS data from 2004 to 2017 [4-6], and zonal wind profiles from Hubble Space Telescope (HST) images in 2015 [7] and 2018-2020 [8]. In most latitudes, there is a very close agreement among those zonal wind profiles. However, the equatorial region, between the planetographic latitudes of 10ºN and 10ºS, presents a complex vertical structure and significant variability [e.g. 7]. In this work, we track and characterize several discrete features in Saturn’s atmosphere and measure the zonal winds along four years from 2021 to 2024. We used ground-based images from amateur observers (available in the PVOL database and similarly to refs. [9-10]) to track individual meteorological systems, and HST images obtained by the OPAL program [8] to obtain zonal wind profiles. The ground-based images have lower spatial resolution than HST, but the tracked features are followed over long timescales, reducing uncertainty in wind speed measurements. HST images in different filters were used to retrieve zonal wind profiles by correlating pairs of images taken one planetary rotation apart. The results in filters F631N and F763M show an intensification and strong variability in the equatorial jet when compared to Cassini measurements. In the methane absorbing bands (FQ727N and FQ889N) we also observed changes with respect to previous measurements. Given Saturn’s yearly illumination cycle due to its tilt and ring shadows, images from 2021 to 2024 provide the first measurements of the southern hemisphere since the end of the Cassini mission. REFERENCES:[1] Sromovsky et al. Journal of Geophysical Research (1983). [2] Sánchez-Lavega et al. Saturn’s Zonal Winds at Cloud Level, Icarus (2000). [3] Sánchez-Lavega et al. Nature (2003). [4] García-Melendo et al. Geophys. Res. Lett. (2010). [5] García-Melendo et al. Icarus (2011). [6] Studwell eta l. Geophys. Res. Lett. (2018). [7] Sánchez-Lavega et al. Nature Communications (2016). [8] Simon et al. Planet. Sci. Journal (2021). [9] Sánchez-Lavega et al. Nature Comm. (2019). [10] Hueso et al. Icarus (2020).

We present Hubble Space Telescope (HST) imaging, a Very Large Array (VLA) radio map (4.74 GHz), optical high-resolution (echelle) spectroscopy and UBV photoelectric photometry of the symbiotic star CH Cyg obtained during its 1998–2000 active phase. The HST imaging, taken during eclipse, shows the central stars are embedded in a nebula extending to 620 ± 150 au for a distance of 270 ± 66 pc. The inner nebula is strongly influenced by the onset of activity and associated outflow in 1998. The surface brightness contours of the contemporaneous radio VLA observation agree well with HST images. Photometric observations of the broad 1999 U-minimum suggest that it is due to the eclipse of the active hot component by the giant on the long-period (14.5 yr) outer orbit. We also find that the onset of the 1998 and the 1992 active periods occur at the same orbital phase of the inner binary. Spectroscopic observations reveal two types of outflow from the active star: a high-velocity (>1200 km s−1) hot star wind sporadically alternating with a more massive outflow indicated by P-Cygni-like profiles. We present evidence connecting the extended nebulosity with the high-velocity shocked outflow, and hence the activity in the central binary.