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Register a new userHigh resolution imaging of NGC 2346 with GSAOI/GeMS: disentangling the planetary nebula molecular structure to understand its origin and evolution
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We present high spatial resolution ($approx$ 60--90 milliarcseconds) images of the molecular hydrogen emission in the Planetary Nebula (PN) NGC 2346. The data were acquired during the System Verification of the Gemini Multi-Conjugate Adaptive Optics System + Gemini South Adaptive Optics Imager. At the distance of NGC 2346, 700 pc, the physical resolution corresponds to $approx$ 56 AU, which is slightly higher than that an [N II] image of NGC 2346 obtained with HST/WFPC2. With this unprecedented resolution we were able to study in detail the structure of the H$_2$ gas within the nebula for the first time. We found it to be composed of knots and filaments, which at lower resolution had appeared to be a uniform torus of material. We explain how the formation of the clumps and filaments in this PN is consistent with a mechanism in which a central hot bubble of nebular gas surrounding the central star has been depressurized, and the thermal pressure of the photoionized region drives the fragmentation of the swept-up shell.
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This paper presents new near-infrared observations of the planetary nebula NGC 2346. The data include a broad K-band image, an image in the H2 vibrationally excited 1-0S(1) line and K band slit spectra at three positions in the nebula. In the H2 1-0S(1) line, the nebula is characterized by a central, bright torus, surrounded by weaker emission with a typical butterfly shape, as seen in Halpha and CO lines. The K band spectra show 11 H2 lines with excitation energies from 6150 to 12552 K. The H2 data have been compared to the predictions of models which follow the evolution with time of the H2 emission in PNe of different core mass and shell properties (Natta & Hollenbach 1998). These models compute the emission originating in the photodissociation region (PDR) created at the inner edge of the neutral shell by the UV radiation of the central core, as well as the emission in the shock associated to the expansion of the shell inside the precursor red-giant wind. In NGC 2346, a PDR origin of the H2 emission in a low-density molecular shell (n<~10^4 cm^-3) is indicated. At these low densities, time-dependent H2 chemistry and X-ray heating of the neutral gas enhance the predicted PDR H2 line intensity by large factors.
We present the first direct image of the high-metallicity gas component in a planetary nebula (NGC 6778), taken with the OSIRIS Blue Tunable Filter centered on the O II 4649+50 angstroms optical recombination lines (ORLs) at the 10.4m Gran Telescopio Canarias. We show that the emission of these faint O II ORLs is concentrated in the central parts of the planetary nebula and is not spatially coincident either with emission coming from the bright [O III] 5007 angstroms collisionally excited line (CEL) or the bright H alpha recombination line. From monochromatic emission line maps taken with VIMOS at the 8.2m Very Large Telescope, we find that the spatial distribution of the emission from the auroral [O III] 4363 line resembles that of the O II ORLs but differs from nebular [O III] 5007 CEL distribution, implying a temperature gradient inside the planetary nebula. The centrally peaked distribution of the O II emission and the differences with the [O III] and H I emission profiles are consistent with the presence of an H-poor gas whose origin may be linked to the binarity of the central star. However, determination of the spatial distribution of the ORLs and CELs in other PNe, and a comparison of their dynamics is needed to further constrain the geometry and ejection mechanism of the metal-rich (H-poor) component and hence, understand the origin of the abundance discrepancy problem in PNe.
We present high resolution images of the 12CO(2-1) emission in the central 1 (1 kpc) of NGC 5128 (Centaurus A), observed using the SMA. We elucidate for the first time the distribution and kinematics of the molecular gas in this region with a resolution of 6.0 x 2.4 (100 pc x 40 pc). We spatially resolve the circumnuclear molecular gas in the inner 24 x 12 (400 pc x 200 pc), which is elongated along a position angle P.A. = 155 deg and perpendicular to the radio/X-ray jet. The SE and NW components of the circumnuclear gas are connected to molecular gas found at larger radii. This gas appears as two parallel filaments at P.A. = 120 deg, which are coextensive with the long sides of the 3 kiloparsec parallelogram shape of the previously observed dust continuum, as well as ionized and pure rotational H2 lines. Spatial and kinematical asymmetries are apparent in both the circumnuclear and outer gas, suggesting non-coplanar and/or non-circular motions. We extend to inner radii (r < 200 pc) previously studied warped disk models built to reproduce the central parallelogram-shaped structure. Adopting the warped disk model we would confirm a gap in emission between the radii r = 200 - 800 pc (12 - 50), as has been suggested previously. Although this model explains this prominent feature, however, our 12CO(2-1) observations show relevant deviations from this model. Namely, the physical connection between the circumnuclear gas and that at larger radii, brighter SE and NW sides on the parallelogram-shaped feature, and an outer curvature of its long sides. Overall it resembles more closely an S-shaped morphology, a trend that is also found in other molecular species. Hence, we explore qualitatively the possible contribution of a weak bi-symmetric potential which would naturally explain these peculiarities.
The spatial structure of the emission lines and continuum over the 50 arcsecond extent of the nearby, O-rich, planetary nebula NGC 7009 (Saturn Nebula) have been observed with the MUSE integral field spectrograph on the ESO Very Large Telescope. Science Verification data, in <0.6 arcsecond seeing, have been reduced and analysed as images over the wavelength range 4750-9350A. Emission line maps over the bright shells are presented, from neutral to the highest ionization available (He II and [Mn V]). For collisionally excited lines (CELs), maps of electron temperature (T_e from [N II] and [S III]) and electron density (N_e from [S II] and [Cl III]) are available and for optical recombination lines (ORLs) temperature (from the Paschen jump and ratio of He I lines) and density (from high Paschen lines). These estimates are compared: for the first time, maps of the differences in CEL and ORL T_es have been derived, and correspondingly a map of t^2 between a CEL and ORL temperature, showing considerable detail. Total abundances of He and O were formed, the latter using three ionization correction factors. However the map of He/H is not flat, departing by ~2% from a constant value, with remnants corresponding to ionization structures. Ionization correction factor methods are compared for O abundance, but none delivers a flat map. An integrated spectrum over an area of 2340 square arcseconds was also formed and compared to 1D photoionization models. The spatial variation of a range of nebular parameters illustrates the complexity of the ionized media in NGC 7009. These MUSE data are very rich with detections of many lines over areas of hundreds of square arcseconds and follow-on studies are indicated. (Abridged)
The large field and wavelength range of MUSE is well suited to mapping Galactic planetary nebulae (PN). The bright PN NGC 7009 was observed with MUSE on the VLT during the Science Verification of the instrument in seeing of 0.6. Emission line maps in hydrogen Balmer and Paschen lines were formed from analysis of the MUSE cubes. The measured electron temperature and density from the MUSE cube were employed to predict the theoretical hydrogen line ratios and map the extinction distribution across the nebula. After correction for the interstellar extinction to NGC 7009, the internal dust-to-gas ratio (A_V/N_H) has been mapped for the first time in a PN. The extinction map of NGC 7009 has considerable structure, broadly corresponding to the morphological features of the nebula. A large-scale feature in the extinction map, consisting of a crest and trough, occurs at the rim of the inner shell. The nature of this feature was investigated and instrumental and physical causes considered; no convincing mechanisms were identified to produce this feature, other than mass loss variations in the earlier asymptotic giant branch phase. The dust-to-gas ratio A_V/N_H increases from 0.7 times the interstellar value to >5 times from the centre towards the periphery of the ionized nebula. The integrated A_V/N_H is about 2 times the mean ISM value. It is demonstrated that extinction mapping with MUSE provides a powerful tool for studying the distribution of PN internal dust and the dust-to-gas ratio. (Abridged.)
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