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Spectroscopy at 8-13 microns with T-ReCS on Gemini-S is presented for 3 galaxies with substantial silicate absorption features, NGC 3094, NGC 7172 and NGC 5506. In the galaxies with the deepest absorption bands, the silicate profile towards the nuclei is well represented by the emissivity function derived from the circumstellar emission from the red supergiant, mu Cephei which is also representative of the mid-infrared absorption in the diffuse interstellar medium in the Galaxy. There is spectral structure near 11.2 microns in NGC 3094 which may be due to a component of crystalline silicates. In NGC 5506, the depth of the silicate absorption increases from north to south across the nucleus, suggestive of a dusty structure on scales of 10s of parsecs. We discuss the profile of the silicate absorption band towards galaxy nuclei and the relationship between the 9.7 micron silicate and 3.4 micron hydrocarbon absorption bands., Comment: 7 pages, accepted for publication in MNRAS

High spatial resolution spectroscopy at 8-13microns with T-ReCS on Gemini-S has revealed striking variations in the mid-infrared emission and absorption in the nucleus of the Circinus galaxy on sub-arcsecond scales. The core of Circinus is compact and obscured by a substantial column of cool silicate dust. Weak extended emission to the east and west coincides with the coronal line region and arises from featureless dust grains which are probably heated by line emission in the coronal emission zone. The extended emission on the east side of the nucleus displays a much deeper silicate absorption than that on the west, indicating significant columns of cool material along the line of sight and corresponding to an additional extinction of A(V) 25 mag. Emission bands from aromatic hydrocarbons are not subject to this additional extinction, are relatively weak in the core and in the coronal line region, and are much more spatially extended than the continuum dust emission; they presumably arise in the circumnuclear star-forming regions. These data are interpreted in terms of an inclined disk-like structure around the nucleus extending over tens of parsecs and possibly related to the inner disk found from observations of water masers by Greenhill et al (2003)., Comment: MNRAS in press, 11 pages

The 3.1 micron absorption feature of water-ice has been observed spectroscopically in many molecular clouds and, when it has been observed spectropolarimetrically, usually a corre- sponding polarization feature is seen. Typically on these occasions, and particularly for the BN object, a distinct position angle shift between the feature and continuum is seen, which indicates both a fractionation of the icy material and a changing alignment direction along the line of sight. Here the dependence of circular polarimetry on fractionation along the line of sight is investigated and it is shown that the form of its spectrum, together with the sign of the position angle shift, indicates where along the line of sight the icy material lies. More specifically a coincidence between the sign of the position angle displacement in the ice feature, measured north through east, and that of the circular polarization ice feature means that the icy grains are overlaid by bare grains. Some preliminary circular polarimetry of BN has this characteristic and a similar situation is found in the only two other cases for which relevant observations so far exist., Comment: 9 pages, 4 figures, accepted for MNRAS

We present 850micron imaging polarimetry of two high-mass star forming regions - W48 and S152. Within these regions we have identified two candidate high-mass protostellar objects - W48W and S152SE. The submillimetre continuum emission from the candidate HMPOs is bright in comparison to the nearby HII regions. W48W is a cold dense source, with no radio or mid-infrared emission. S152SE has an IRAS source IRAS 22566+5828 in the Southwestern part of the region, which appears in the mid-infrared 8.28micron emission, but there is no radio emission. The 850micron data shows another core within the region, in the Northeast. The polarimetry is ordered and the degree of polarisation is high over the candidate HMPOs - ~6% for W48W and ~8% for S152SE. Polarimetry results of this nature indicate a strong, ordered magnetic field threading the candidate HMPOs. The magnetic field direction in both S152SE and W48W is perpendicular to the direction of elongation of the cloud which would imply collapse along the field lines. Estimates of the magnetic field strength are derived using the Chandrasekhar & Fermi method. We calculate plane of the sky field strengths of ~0.7 mG for W48W and ~0.2 mG for S152SE. We discuss the drawbacks of using the Chandrasekhar & Fermi method with a large beam size. Mass-to-flux ratios have been calculated and both clouds are found to be roughly critical., Comment: 9 pages, 4 figures, accepted Astronomy & Astrophysics

We present 850 micron imaging polarimetry of the W51A massive star forming region performed with SCUBA on the JCMT. From the polarimetry we infer the column-averaged magnetic field direction, projected onto the plane of the sky. We find that the magnetic field geometry in the region is complicated. We compare the field geometry with 6 cm and CS J=7-6 emission and determine that the magnetic field must be relatively weak and plays a passive role, allowing itself to be shaped by pressure forces and dynamics in the ionised and neutral gases. Comparisons are drawn between our data and 1.3 mm BIMA interferometric polarimetry data, from which we conclude that the magnetic field must increase in importance as we move to smaller scales and closer to sites of active star formation., Comment: Accepted for publication in A&A (3 figures)

A sample of 25 IR-bright planetary nebulae (PNe) towards the Galactic bulge is analysed through 8-13um spectroscopy. The classification of the warm-dust emission features provides a measure of the C/O chemical balance, and represents the first C/O estimates for bulge PNe. Out of 13 PNe with identified dust types, 4 PNe have emission features associated with C-based grains, while the remaining 9 have O-rich dust signatures. The low fraction of C-rich PNe, <30%, contrasts with that for local PNe, around 80%, although it follows the trend for a decreasing frequency of C-rich PNe with galactocentric radius (paper~I). We investigate whether the PNe discussed here are linked to the bulge stellar population (similar to type~IV, or halo, PNe) or the inner Galactic disk (a young and super-metal-rich population). Although 60% of the PNe with warm dust are convincing bulge members, none of the C-rich PNe satisfy our criteria, and they are probably linked to the inner Galactic disk. In the framework of single star evolution, the available information on bulge PNe points towards a progenitor population similar in age to that of local PNe (type I PNe are found in similar proportions), but super-metal-rich (to account for the scarcity of C-rich objects). Yet the metallicities of bulge PNe, as inferred from [O/H], fail to reach the required values - except for the C-rich objects. It is likely that the sample discussed here is derived from a mixed disk/bulge progenitor population and dominated by type IV PNe, as suggested by Peimbert (1992). The much higher fraction of O-rich PNe in this sample than in the solar neighbourhood should result in a proportionally greater injection of silicate grains into the inner Galactic medium., Comment: accepted by MNRAS

We investigate the galactic disk distribution of a sample of planetary nebulae characterised in terms of their mid-infrared spectral features. The total number of galactic disk PNe with 8-13mum spectra is brought up to 74 with the inclusion of 24 new objects, whose spectra we present for the first time. 54 PNe have clearly identified warm dust emission features, and form a sample which we use to construct the distribution of the C/O chemical balance in galactic disk PNe. The dust emission features complement the information on the progenitor masses brought by the gas-phase N/O ratios: PNe with unidentified infrared emission bands have the highest N/O ratios, while PNe with the silicate signature have either very high N enrichment or close to none, and SiC emission features coincide with a range of moderate N-enrichments. We find a trend for a decreasing proportion of O-rich PNe towards the third and fourth galactic quadrants. Two independent distance scales confirmed that the proportion of O-rich PNe decreases from 30+-9% inside the solar circle, to 14+-7% outside. PNe with warm dust are also the youngest. PNe with no warm dust are uniformly distributed in C/O and N/O ratios, and do not appear to be confined to C/O~1. They also have higher 6cm fluxes, as expected from more evolved PNe. We show that the IRAS fluxes are a good representation of the bolometric flux for warm-dust PNe. The requirement F(12um)>0.5Jy should probe a good portion of the galactic disk, and the dominant selection effects are rooted in the PN catalogues., Comment: accepted by MNRAS

We report the detection of linear polarization from SgrA* at 750, 850, 1350 and 2000 microns which confirms the contribution of synchrotron radiation. From the lack of polarization at longer wavelengths it appears to arise in the millimetre/sub-millimetre excess. There are large position angle changes between the millimetre and sub-millimetre results and these are discussed in terms of a polarized dust contribution in the sub-millimetre and various synchrotron models. In the model which best explains the data the synchrotron radiation from the excess is self-absorbed in the millimetre region and becomes optically thin in the sub-millimetre. This implies that the excess arises in an extremely compact source to the order of 2 Schwarzschild radii., Comment: (12 pages, 1 figure, accepted by ApJ Letters)

We present ISOPHOT_S, ISOSWS and 8 to 13 micron ground based observations of Centaurus A that show prominent PAH and silicate features. These and other data are used to construct a model for the infrared continuum. We find that in a nuclear sized aperture (~4 arcsec, ~60 pc) the SED is characteristic of emission from a starburst and AGN torus; in larger apertures an additional component of cirrus emission is required. Based on our model, the torus diameter is estimated to be 3.6 pc and the best fitting inclination angle of the torus is 45 degrees. This result has implications for the detectability of tori in low power AGN and in particular for the use of the IRAS 60/25 micron flux ratio as an indicator of the torus inclination., Comment: 4 pages, 5 figures, published in the proceedings of ESA conference 'The Universe as seen by ISO', eds. P. Cox & M. F. Kessler. (ESA Special Publications series SP-427). Latex style files included with submission