Hubble Space Telescope WFPC2 Images Research Articles

The Globular Cluster Systems of Five Nearby Spiral Galaxies: New Insights fromHubble Space TelescopeImaging

We use available multifilter Hubble Space Telescope (HST) WFPC2 imaging of five (M81, M83, NGC 6946, M101, and M51) low inclination, nearby spiral galaxies to study ancient star cluster populations. M81 globular clusters (GC) have an intrinsic color distribution which is very similar to those in the Milky Way and M31, with ~40% of the clusters having colors expected for a metal-rich population. On the other hand, the GC system in M51 appears almost exclusively blue and metal poor. This lack of metal-rich GCs associated with the M51 bulge indicates that the bulge formation history of this Sbc galaxy may have differed significantly from that of our own. Ancient clusters in M101, and possibly in NGC 6946, appear to have luminosity distributions which continue to rise to our detection limit (M_V ~ -6.0), well beyond the expected turnover (M_V ~ -7.4) in the luminosity function. This is reminiscent of the situation in M33, a Local Group galaxy of similar Hubble type. The faint ancient cluster candidates in M101 and NGC 6946 have colors and radii similar to their more luminous counterparts, and we suggest that these are either intermediate age (3-9 Gyr) disk clusters or the low mass end of the original GC population. If the faint, excess GC candidates are excluded, we find that the specific frequency (S_N) of ancient clusters formed in later-type spirals is roughly constant, with S_N=0.5 +- 0.2. By combining the results of this study with literature values for other systems, we find that the total GC specific frequencies in spirals appear to correlate best with Hubble type and bulge/total ratio, rather than with galaxy luminosity or galaxy mass (abridged).

PV Cephei: Young Star Caught Speeding?

Three independent lines of evidence imply that the young star PV Cep is moving at roughly 20 km s-1 through the interstellar medium. The first and strongest suggestion of motion comes from the geometry of the Herbig-Haro (HH) knots in the giant HH flow associated with PV Cep. Bisectors of lines drawn between pairs of knots at nearly equal distances from PV Cep imply an east-west motion of the source, and a plasmon model fitted to the knot positions gives a good fit of 22 km s-1 motion for the star. The second bit of damning evidence comes from a redshifted trail of molecular gas pointing in the same east-west direction implied by the HH knot geometry. The third exhibit we offer in accusing PV Cep of speeding involves the apparent tilt in the high-velocity molecular jet now emanating from the star. This tilt is best explained if the true, current jet direction is north-south, as it is in Hubble Space Telescope WFPC2 images, and the star is moving, again at roughly 20 km s-1. Tracing the motion of PV Cep backward in time to the nearest cluster from which it might have been ejected, we find that it is very likely to have been thrown out of the massive star-forming cluster NGC 7023, more than 10 pc away. PV Cep and NGC 7023 are at similar distances, and the backward trace of PV Cep's motion is astonishingly well aligned with a dark, previously unexplained rift in NGC 7023. We propose that PV Cep was ejected, at a speed large enough to escape NGC 7023, at least 100,000 yr ago but that it did not enter the molecular cloud in which it now finds itself until more like 35,000 yr ago. Our calculations show that the currently observable molecular outflow associated with PV Cep is about 10,000 yr old, so the flow has had plenty of time to form while in its current molecular cloud. However, the question of what PV Cep was doing and what gas/disk it took along with it in the time it was traveling through the low-density region between NGC 7023 and its current home is an open one. Recent numerical simulations have suggested that condensed objects should be ejected at high velocity before they have finished forming in a cluster. Prior to this work, a handful of pre-main-sequence stars have been shown to be moving at speeds greater than 10 km s-1. To the best of our knowledge, though, the analysis of PV Cep and NGC 7023 described here is the first observational work associating a speeding young star with a distant ancestral cluster. These high-speed ejections from clusters will create a class of rapidly moving young stars in molecular clouds. If these ejections are at all common, their existence confounds both calculations of clouds' star-forming efficiency and theories of star formation that do not allow for stars to move rapidly through a reservoir of star-forming material while they form.

Physical conditions in the planetary nebula NGC 6543

We present analysis of spectra and Hubble Space Telescope (HST) images of NGC 6543, the Cat's Eye Nebula. Using HST WFPC2 images taken in narrow-band filters isolating Halpha and Hbeta, we have produced an extinction map towards the nebula, and find that c(Hbeta)is low, at similar to0.1, and exhibits only very small spatial variations across the surface of the nebula. Using filters isolating [O III] emission lines, we have produced a temperature map of NGC 6543, accounting carefully for contamination due to continuum emission and other lines within the filter bandpasses. We find that the temperature over most of the nebula is between 7000 and 9000 K, with higher values seen towards the edge of the bright core. The value of t(A)(2), the temperature fluctuation parameter, is low at around 0.005 in the central regions. We have obtained long-slit scanning spectra of NGC 6453, which, when combined with the total Hbeta flux, give integrated fluxes for all the lines in our spectra. We determine ionic and total abundances within the nebula from both recombination lines and forbidden lines, and we find that recombination lines yield a higher abundance by a factor of approximately three. A temperature fluctuation parameter of 0.053 would resolve the discrepancy, but several factors argue against temperature fluctuations as the main cause: the value of t(2) required is inconsistent with the results derived from the temperature map; the agreement of the temperatures derived from the hydrogen Balmer jump and [O III] line diagnostics also implies a low value of t(2); and the agreement of abundances derived from temperature-insensitive infrared fine-structure lines and temperature-sensitive optical forbidden lines is inconsistent with the temperature fluctuation scenario.We argue that a more likely explanation for the observed temperature and abundance discrepancies is the presence within the nebula of some hydrogen-deficient material at low temperatures. Weakly temperature-dependent line ratios of He I and O II imply lower temperatures than those found from forbidden-line temperature diagnostics and the hydrogen Balmer jump, as is expected in the presence of cold hydrogen-deficient material.

The Irradiated Herbig‐Haro Jets Near σ Orionis

We present high-resolution echelle spectra of the irradiated Herbig-Haro jets HH 444, 445, 446, and 447 from the Keck I telescope. The structural, kinematic, and physical properties of the jets near their sources are analyzed in detail. In particular, spatio-kinematic electron density variations and evidence for excited, low-velocity entrained material are found. Despite their proximity to the massive stars in the σ Orionis system, the inner portions of these jets generally exhibit low-excitation conditions, consistent with shadowing from circumstellar material. The outflow sources show Hα and forbidden line emission on top of late-type photospheric spectra and strong lithium absorption, indicative of typical classical T Tauri stars. These spectroscopic data are discussed in the context of theoretical models that attempt to account for the generation of outflows. In addition, narrowband Hubble Space Telescope (HST) WFPC2 images of HH 444 and 445 are presented and compared with the spectroscopic data. In addition to the jets, the images of both sources reveal extended emission structures that point directly away from σ Ori and are therefore interpreted as photoevaporating proplyds.

Fragmentation of Globules in HiiRegions:Hubble Space TelescopeImages of Thackeray's Globules

We present Hubble Space Telescope WFPC2 images through an Hα filter of Thackeray's globules in the southern H II region IC 2944. The images document the state of the globule complex during its current highly dynamical phase of breakup. A population of very small and short-lived splinters suggests that continuous fragmentation must play an important role in increasing the surface-to-mass ratio of the neutral gas, thus accelerating the processes of photoevaporation and photoablation. We are not able to single out which of various theoretical mechanisms for breakup is operating in the globule complex.

Hubble Space Telescope imaging and ground-based spectroscopy of old nova shells - II. The bipolar shell of the slow nova HR Del

We present Hubble Space Telescope (HST) WFPC2 imaging of HR Del in filters centred on the lines of Hα, [N ii] and [O iii], with corresponding William Herschel Telescope (WHT) ISIS slit spectroscopy for the lines of Hα, Hβ, [N ii] and [O iii]. The data show that the ejected shell of HR Del is composed of many small bright knots. These are distributed in a bipolar structure with an equatorial ring, and polar rings or caps. The [O iii] emission is significantly more bipolar than that seen in Hα/[N ii]. Diffuse material which extends radially outward from these knots may be further evidence for a fast wind from the central binary system. There are also [N ii] and [O iii] knots at both higher and lower velocity than that of the main shell which follow the general bipolar symmetry and may be associated with secondary mass ejections at outburst or interactions with the fast wind. Three-dimensional models of the shell that reproduce the observed emission-line images and longslit spectra in both the [O iii] and Hα morphologies are presented. We use these models to estimate an inclination for the shell of 35°± 3°, a polar expansion velocity of 560 ± 50 km s−1, an axial ratio of 1.75 ± 0.15 and a distance of 970 ± 70 pc. We discuss how these parameters can be used to improve the shell shape and maximum magnitude versus rate of decline (SSRD and MMRD, respectively) relationships for novae.

A triple nucleus in the brightest cluster galaxy in Abell 193

We present a ground-based, near-infrared, K-band image and a Hubble Space Telescope (HST) WFPC2 image of the brightest cluster galaxy in Abell 193 (IC 1695). This object was selected as the central cluster galaxy using X-ray information. Both images reveal a triple nucleus structure. Previously, this galaxy was thought to have only two nuclei. We present colours and magnitudes and a colour plot of the three nuclei. The nuclear structure and colours of the nuclei in this galaxy suggest that a merger may have taken place in its recent history.

Hubble Space TelescopeWFPC2 Imaging of the Disk and Jet of HV Tauri C

We have obtained Hubble Space Telescope (HST) WFPC2 images of the HV Tauri young triple system. The tertiary star appears as a compact bipolar nebula at visual wavelengths as already known in the near-infrared. New, deeper adaptive optics observations made at the Canada-France-Hawaii Telescope show no point source in the nebula to a limiting magnitude of K > 15. The results therefore confirm that HV Tau C is an optically thick circumstellar disk seen close to edge-on. Clear evidence for small, chromatic dust particles in the outer disk is provided by the color structure of the nebula: the thickness of the central dust lane shrinks by 30% between 0.55 and 2.2 μm. Bipolar jets extending 03-07 perpendicular to the dust lane are seen in HST narrowband [S II] and [O I] images. The continuum images are compared to multiple scattering models, with optimal density model parameters derived through χ2 minimization. A disk density distribution provides a reasonable fit to the K-band image but is unable to reproduce the vertical extent of the nebula at I band without resorting to an unreasonably large scale height. Adding an envelope structure around the disk results in a much better fit to the HST image, and with a physically reasonable disk scale height. Our preferred model has a disk outer radius of 50 AU, inclination of 6°, and scale height of 6.5 AU at r = 50 AU. The thickness of the dark lane establishes a disk mass near 2 × 10-3 M☉ (~2MJup) of dust and gas, if the dust grains have interstellar properties and remain fully mixed vertically. The envelope, with a much smaller mass ~4 × 10-5 M☉, would be very short-lived unless replenished by new material from the star or surrounding medium.

HALO EMISSION OF THE CAT’S EYE NEBULA, NGC 6543: SHOCK EXCITATION BY FAST STELLAR WINDS

Images taken with the Chandra X-ray telescope have for the the first time revealed the central, wind-driven, hot bubble (Chu et al. 2001), while Hubble Space Telescope (HST) WFPC2 images of the Cat`s Eye nebula, NGC 6543, show that the temperature of the halo region of angular radius ~ 20, is much higher than that of the inner bright H II region. With the coupling of a photoionization calculation to a hydrodynamic simulation, we predict the observed 〔O III〕 line intensities of the halo region with the same O abundance as in the core H II region: oxygen abundance gradient does not appear to exist in the NGC 6543 inner halo. An interaction between a (leaky) fast stellar wind and halo gas may cause the higher excitation temperatures in the halo region and the inner hot bubble region observed with the Chandra X-ray telescope.

INTEGRAL Field Spectroscopy of IRAS 15206+3342: Gas Inflows and Starbursts in an Advanced Merger

Integral field optical spectroscopy using the INTEGRAL system (complemented with Hubble Space Telescope WFPC2 imaging) is used to characterize the kinematic and ionization properties of the warm ionized gas in the ultraluminous infrared galaxy IRAS 15206+3342. These data present kinematic and morphological evidence for a tidal tail connecting the nuclear star-forming regions with a remnant stellar system located at a projected distance of 20 kpc away from the nucleus. The velocity field and the velocity dispersion map indicate the presence of gas flowing inward along the tidal tail, feeding the nuclear regions where the previously detected arc-shaped chain of young stellar clusters is forming stars at a rate of about 150 M☉ yr-1. According to theoretical models by Mihos & Hernquist, these characteristics (e.g., large gas inflows and massive starbursts) are expected during the final coalescence phase of two disk galaxies with bulges. No kinematic evidence for a second nucleus, nor for the presence of young star-forming regions located along the external parts of the tidal tail, is found, further supporting the conclusion that this system is an advanced merger of two galaxies. Furthermore, photometric and geometrical arguments indicate that the progenitors of this ultraluminous infrared system were two low-luminosity (<L*) spirals that could have suffered a retrograde encounter.

HSTlarge-field weak lensing analysis of MS 2053−04: study of the mass distribution and mass-to-light ratio of X-ray luminous clusters at 0.22&lt;z&lt;0.83

We have detected the weak lensing signal induced by the cluster of galaxies MS 2053-04 (z =0.58) from a two-colour mosaic of six Hubble Space Telescope (HST ) WFPC2 images. The best-fitting singular isothermal sphere model to the observed tangential distortion yields an Einstein radius r (E) =6.2+/-1.8 arcsec, which corresponds to a velocity dispersion of (Omega (m) =0.3, Omega(Lambda) =0.0). This result is in good agreement with the observed velocity dispersion of 817+/-80 km s(-1) from cluster members. The observed average rest-frame mass-to-light ratio within a radius aperture is 184+/-56 h (50) M-./L (B.). After correction for luminosity evolution to z =0, this value changes to 291+/-89+/-19 h (50) M-. /L (B .) (where the first error indicates the statistical uncertainty in the measurement of the mass-to-light ratio, and the second error is due to the uncertainty in luminosity evolution). MS 2053 is the third cluster we have studied using mosaics of deep WFPC2 images. For all three clusters we find good agreement between dynamical and weak lensing velocity dispersions, in contrast to weak lensing studies based on single WFPC2 pointings on cluster cores. This result demonstrates the importance of wide-field data. We have compared the ensemble-averaged cluster profile of the clusters in our sample with the predicted Navarro, Frenk & White (NFW) profile, and find that an NFW profile can fit the observed lensing signal well. The best-fitting concentration parameter is found to be (68 per cent confidence) times the predicted value from an open cold dark matter (CDM) model. The observed mass-to-light ratios of the clusters in our sample evolve with redshift, and are inconsistent with a constant, non-evolving, mass-to-light ratio at the 99 per cent confidence level. The evolution is consistent with the results derived from the evolution of the fundamental plane of early-type galaxies. The resulting average mass-to-light ratio for massive clusters at z =0 is found to be 239+/-18+/-9 h (50) M-. /L (B .).

ITAL]Hubble Space Telescope[/ITAL] Expansion Parallaxes of the Planetary Nebulae NGC 6578, NGC 6884, NGC 6891, and IC 2448

We have combined two epochs of Hubble Space Telescope WFPC2 imaging data with ground-based expansion velocities to determine distances to three planetary nebulae (NGC 6578, NGC 6884, and IC 2448). We used two variants of the expansion parallax technique—a gradient method and a magnification method—to determine the distances. The results from the two methods agree to within the errors. A fourth nebula was included in the study (NGC 6891), but the expansion was too small to determine the distance, and only a lower limit was obtained. This is the second paper in a series that will examine at least 24 nebulae in total.

NGC 4314. IV. Photometry of Star Clusters with the [ITAL]Hubble Space Telescope:[/ITAL] History of Star Formation in the Vicinity of a Nuclear Ring

Using Hubble Space Telescope (HST) WFPC2 images, we have obtained U, B, V, I, and Hα photometry for 76 star clusters in the nuclear star-forming ring of the barred spiral galaxy NGC 4314. These clusters are likely associated with an inner inner Lindblad resonance (IILR). The blue colors and Hα emission for most of these clusters imply very young ages of 1–15 Myr. Age estimates based on several reddening-free parameters indicate that the present epoch of star formation has lasted at least 30 Myr. By estimating the masses of stars in the clusters and comparing with the Hα luminosity, we conclude that a significant fraction of ongoing star formation in the nuclear ring of NGC 4314 occurs in clusters. The cluster masses identify these as young open clusters, not young globular clusters. Farther out in the galaxy, just exterior to the ring of young stars, previous ground-based observations revealed two symmetric stellar spiral arms that may be associated with an outer inner Lindblad resonance (OILR). With our HST data, we have revealed part of this structure and its colors in more detail. The spiral arm colors are consistent with stellar ages between 40 and 200 Myr. The age difference between the inner ring of young stars (IILR) and the larger oval-like feature containing the blue arms (OILR) supports an interpretation of the morphology of the nuclear region of NGC 4314 that requires a reservoir of gas that becomes more compact over time. We speculate that as the gas distribution becomes more centrally concentrated, it interacts with these two resonances. Each resonance triggers star formation, resulting in two distinct epochs of star formation.

Kinematics of Star Clusters in M33: Distinct Populations

We present velocity measurements for 107 star clusters in the nearby, low-luminosity spiral galaxy M33, from a homogeneous data set taken with the WIYN HYDRA spectrograph. The target clusters were chosen primarily from our previous catalogs based on multiband Hubble Space Telescope WFPC2 imaging and therefore have previous age estimates based on integrated colors. Our sample includes objects spanning the entire range of cluster ages found in M33, allowing us to study cluster kinematics as a function of age. We find that the cluster velocity dispersion with respect to the local disk motion increases dramatically with age. The young clusters have a maximum circular velocity of 87 ± 11 km s-1, similar to the previous rotation solution for H II regions in M33. When clusters are divided into age groups, the old clusters clearly have very different kinematics from the young population and from the gas disk. Monte Carlo simulations comparing synthetic disk plus halo systems with the observed velocity distribution for our old M33 clusters suggest that old clusters are likely to be composed of two distinct subpopulations, an 85% ± 5% halo component plus a 15% ± 5% disk component. This is the first evidence for distinct kinematic subpopulations among the old M33 clusters, and this galaxy appears to have a higher halo/bulge fraction of old stellar objects than found in the Galaxy. To further study the properties of halo clusters in M33, we use spectroscopic line index measurements for 17 clusters with the largest departure from disk motion, and thus the most pristine halo objects in our sample, to determine ages and approximate metal abundances. When compared with the Worthey models and with similar measurements for 12 Galactic globulars, our clusters have an age spread of ~5-7 Gyr, ~2 times as large as the spread among the Galactic sample. This small halo sample shows little evidence for a progression in metal abundance with age. There is also some support for different size (core radius) distributions when comparing "young" and "old" halo M33 clusters. We discuss these findings in the context of different galaxy formation models.

The star cluster system of the 3-Gyr-old merger remnant NGC 1316: clues from optical and near-infrared photometry

The giant merger remnant galaxy NGC 1316 (Fornax A) is an ideal probe for studying the long-term effects of a past major merger on star cluster systems, given its spectroscopically derived merger age of � 3 Gyr which we reported in a recent paper (Goudfrooij et al. 2001). Here we present new ground-based, large-area optical and near-IR imaging of star clusters in NGC 1316. The ground-based photometry is complemented with deep Hubble Space Telescope WFPC2 imaging, constituting an excellent combination for studying globular cluster systems. We find that the optical-near-IR colours and lumino sities of the brightest � 10 clusters in NGC 1316 are consistent with those of intermediate-age (2 ‐ 3 Gyr) populations. In particular, the near-IR data preclude ages 4 Gyr for those clusters. Unlike ‘normal’ giant ellipticals, the B I colour distribution of clusters in NGC 1316 is not clearly bimodal. However, the luminosity functions (LFs) of the blue and red parts of the cluster colour distribution are different: The red cluster LF is well represented by a power law, �(L)dL / L 1.2±0.3 dL, extending to about 1.5 mag brighter (in B) than those of typical giant ellipticals. In contrast, the shape of the blue cluster LF is consistent with that of ‘normal’ spiral and elliptical galaxies. We conclude that t he star cluster system of NGC 1316 is a combination of a population of age � 3 Gyr having roughly solar metallicity and a population of old, metal-poor clusters which probably belonged to the pre-merger galaxies. After the 3 Gyr old, metal-rich clusters fade to an age of 10 Gyr, they will form a red ‘peak’ in a bimodal cluster colour distribution. This ‘red peak’ will have a colour consistent with that found in ‘normal, old’ giant ellipticals of the same galaxy l uminosity (taking age dimming into account). The surface density profile of clusters in the innermost regions is lower than that of the integrated light of the galaxy, presumably due to the collective effect of extended star formation in the inner regions of NGC 1316 and tidal shocking of the inner clusters. Outside the core, the surface density profile of clusters is cons istent with that of the underlying starlight, suggesting that the cluster system originally e xperienced the same violent relaxation as did the main body of the merger remnant. The specific cluste r frequency is presently SN = 1.7 ± 0.4 down to the 50 per cent completeness limit of the WFPC2 photometry, and will increase to SN > 2.0 as the merger-induced stellar (and star cluster) popula tion fades to an age of � 10 Gyr (barring further merger events), consistent with specific frequencies of typical giant ellipticals in the field and in poor groups. These f eatures of the star cluster system of NGC 1316 are fully consistent with scenarios for forming ‘normal’ giant elliptical galaxies through gas-rich mergers at look-back times > 10 Gyr.

New Proplyds, Outflows, Shocks, and a Reflection Nebula in M43 and the Outer Parts of the Orion Nebula

Hubble Space Telescope WFPC2 images made as planned parallel observations have produced emission-line images of fields in the outer portions of the Orion Nebula and near the center of the companion H II region, M43. Examination of these images have uncovered three new bright proplyds and one silhouette proplyd. Two of the bright proplyds lie within M43 and are photoionized by its central star, NU Ori. The new bright proplyd in the Orion Nebula shows a monopolar microjet, and analysis of its size and surface brightness indicates that it lies well in the foreground. Symmetric shocks indicate bipolar flow around the K8e star V1348 Ori (304-539) near θ2 Ori C. Evidence for multiple outflows from a source southeast of 036-927, well south of the bright bar feature of the nebula, is indicated. A bright reflection nebula was found around the B1.5 Vp star LP Ori (098-753). The form of this object indicates that this star is moving within the veil of neutral material that lies in front of M42.

Scattered Light Models of Protostellar Envelopes: Multiple Outflow Cavities and Misaligned Circumstellar Disks

Ground-based imaging, imaging polarimetry, and recent Hubble Space Telescope WFPC2 and NICMOS images of protostars have revealed very complex scattered light patterns that cannot be entirely explained by two-dimensional radiation transfer models. We present here for the first time radiation transfer models of T Tau and IRAS 04016+2610 that are fully three-dimensional, with the aim of investigating the effects on image morphology of multiple illuminating sources and infalling envelopes that have been shaped by multiple outflows. For T Tau we have constructed scattered light models where the illumination of the surrounding envelope is by a binary, with each source surrounded by its own small circumstellar disk or envelope. We find that the asymmetries in the WFPC2 image of T Tau can be reproduced if the disks in the binary system are misaligned, consistent with a recently discovered bipolar outflow believed to originate from the secondary. For IRAS 04016+2610 we find that the observed scattered light pattern can be reproduced by scattering in an envelope with cavities carved by two sets of bipolar outflows, suggestive of an embedded binary system.

Interstellar Bubbles in Two Young H [CSC]ii[/CSC] Regions

Massive stars are expected to produce wind-blown bubbles in the interstellar medium; however, ring nebulae, suggesting the existence of bubbles, are rarely seen around main-sequence O stars. To search for wind-blown bubbles around main-sequence O stars, we have obtained high-resolution Hubble Space Telescope WFPC2 images and high-dispersion echelle spectra of two pristine H II regions, N11B and N180B, in the Large Magellanic Cloud. These H II regions are ionized by OB associations that still contain O3 stars, suggesting that the H II regions are young and have not hosted any supernova explosions. Our observations show that wind-blown bubbles in these H II regions can be detected kinematically, but not morphologically, because their expansion velocities are comparable to or only slightly higher than the isothermal sound velocity in the H II regions. Bubbles are detected around concentrations of massive stars, individual O stars, and even an evolved red supergiant (a fossil bubble). Comparisons between the observed bubble dynamics and model predictions show a large discrepancy (1–2 orders of magnitude) between the stellar wind luminosity derived from bubble observations and models and that derived from observations of stellar winds. The number and distribution of bubbles in N11B differ from those in N180B, which can be explained by the difference in the richness of stellar content between these two H II regions. Most of the bubbles observed in N11B and N180B show a blister structure, indicating that the stars were formed on the surfaces of dense clouds. Numerous small dust clouds, similar to Bok globules or elephant trunks, are detected in these H II regions, and at least one of them hosts on-going star formation.

An HST Study of Jovian Chromophores

A principal components analysis was performed on Hubble Space Telescope WFPC2 images of Jupiter from October 1995 and October 1996. Global maps in the F410M, F555W, F673N, and F953N filters were analyzed. These are continuum wavelengths in Jupiter's spectrum, sensitive to reflection from the visible cloud deck. The primary principal components correspond approximately to gray spectral brightness variations, accounting for ∼91% of the variance in the images, and a component with a red spectral slope, which accounts for ∼8% of the variance. This color component probably corresponds to a constituent in the ammonia cloud deck. Another color component, which is blue/green, may correspond to upper tropospheric clouds or haze and accounts for ∼1% of the image variance. Although small, this component may explain differences seen in the color of the Great Red Spot and other features.

Jet‐ and Wind‐driven Ionized Outflows in the Superbubble and Star‐forming Disk of NGC 3079

Hubble Space Telescope WFPC2 images are presented that span the inner ~19 kpc diameter of the edge-on galaxy NGC 3079; they are combined with optical, emission-line imaging spectrophotometry and VLA images of radio polarization vectors and rotation measures. Ionized gas filaments within 9 kpc diameter project up to 3 kpc above the disk, with the brightest forming the ≈1 kpc diameter superbubble. They are often resolved into strands ≈03 (25 pc) wide, which emerge from the nuclear CO ring as five distinct streams with large velocities and velocity dispersions (FWHM ≈ 450 km s-1). The brightest stream emits ≈10% of the superbubble Hα flux and extends for 250 pc along the axis of the VLBI radio jet to one corner of the base of the superbubble. The other four streams are not connected to the jet, instead curving up to the vertical ≈0.6 kpc above the galaxy disk, then dispersing as a spray of droplets each with ≈103 M☉ of ionized gas (the volume filling factor f > 3 × 10-3). Shredded clumps of disk gas form a similar structure in hydrodynamical models of a galaxy-scale wind. The pattern of magnetic fields and the gaseous kinematics also suggest that a wind of mechanical luminosity Lw ≈ 1043 ergs s-1 has stagnated in the galaxy disk at a radius of ~800 pc, has flared to larger radii with increasing height as the balancing interstellar medium pressure reduces above the disk, and has entrained dense clouds into a mushroom vortex above the disk. Hα emissivity of the filaments limits densities to ne > 4.3f-1/2 cm-3, hence kinetic energy and momentum to (0.4-5) × 1055 ergs and (1.6-6) × 1047 dyne s, respectively; the ranges result from uncertain space velocities. A prominent star-forming complex elsewhere in the galaxy shows a striking spray of linear filaments that extend for hundreds of parsecs to end in unresolved bullets.