Search

Using the Mopra telescope, we have targeted 61 regions in the Carina Nebula, covering an area of 1.5 deg2, of bright and compact 870 |$\mu$| m dust continuum emission for molecular line emission from a host of 16 spectral lines at 3 mm, including several dense gas tracers. We found that the clumps detected in Carina in general have in average higher temperatures (27 K compared to 21 K), and lower masses (214 M⊙ compared to 508 M⊙) than clumps located at a similar distance to us in the Galactic plane. We compare the properties of the molecular line emission of these clumps with the MALT90 survey, finding that the detection rates of the molecular lines are similar to MALT90 clumps that are classified as photodissociation regions. However, most of the clumps located within 10 arcmin of η Carina have little molecular line emission detected in our observations. Given the lack of maser detection in the Carina region, we also compared the properties of the clumps in Carina to those of Galactic clumps associated with 6.7-GHz methanol masers. We found that the clumps in Carina are warmer, less massive, and show less emission from the four most commonly detected molecules, HCO+, N2H+, HCN, and HNC, compared to clumps associated with masers in the Galactic Plane. Overall our results are consistent with the scenario in which the high radiation field of η Carina is dramatically affecting its local environment, and therefore the chemical composition of the dense clumps. [ABSTRACT FROM AUTHOR]

The Galactic supernova remnant $$\rm{HESS\,J1534}-{\rm 571}$$ (also known as G323.7 − 1.0) has a shell-like morphology in TeV gamma-ray emission and is a key object in the study of cosmic ray origin. Little is known about its distance and local environment. We examine Mopra 12CO/13CO(1–0) data, Australian Telescope Compact Array $$\rm{H\,{\small I}}$$, and Parkes $$\rm{H\,{\small I}}$$ data towards $$\rm{HESS\,J1534}-{\rm 571}$$. We trace molecular clouds in at least five velocity ranges, including clumpy interstellar medium structures near a dip in $$\rm{H\,{\small I}}$$ emission at a kinematic velocity consistent with the Scutum–Crux arm at ∼3.5 kpc. This feature may be a cavity blown-out by the progenitor star, a scenario that suggests $$\rm{HESS\,J1534}-{\rm 571}$$ resulted from a core-collapse event. By employing parametrizations fitted to a sample of supernova remnants of known distance, we find that the radio continuum brightness of $$\rm{HESS\,J1534}-{\rm 571}$$ is consistent with the ∼3.5 kpc kinematic distance of the Scutum–Crux arm $$\rm{H\,{\small I}}$$ dip. Modelling of the supernova evolution suggests a ∼8–24 kyr age for $$\rm{HESS\,J1534}-{\rm 571}$$ at this distance. [ABSTRACT FROM AUTHOR]

We present a study of the three-dimensional structure of the molecular clouds in the Galactic Centre (GC) using CO emission and OH absorption lines. Two CO isotopologue lines, 12CO(J = 1 → 0) and 13CO(J = 1 → 0), and four OH ground-state transitions, surveyed by the Southern Parkes Large-Area Survey in Hydroxyl, contribute to this study. We develop a novel method to calculate the OH column density, excitation temperature and optical depth precisely using all four OH lines, and we employ it to derive a three-dimensional model for the distribution of molecular clouds in the GC for six slices in Galactic latitude. The angular resolution of the data is 15.5 arcmin, which at the distance of the GC (8.34 kpc) is equivalent to 38 pc. We find that the total mass of OH in the GC is in the range of 2400–5100 M⊚. The face-on view at a Galactic latitude of b = 0° displays a bar-like structure with an inclination angle of 67.5±2.1° with respect to the line of sight. No ring-like structure in the GC is evident in our data, likely due to the low-spatial resolution of the CO and OH maps. [ABSTRACT FROM AUTHOR]

Three bright molecular line sources in G333 have recently been shown to exhibit signatures of infall. We describe a molecular line radiative transfer (RT) modelling process which is required to extract the infall signature from Mopra and Nanten2 data. The observed line profiles differ greatly between individual sources but are reproduced well by variations upon a common unified model where the outflow viewing angle is the most significant difference between the sources. The models and data together suggest that the observed properties of the high-mass star-forming regions such as infall, turbulence and mass are consistent with scaled-up versions of the low-mass case with turbulent velocities that are supersonic and an order of magnitude larger than those found in low-mass star-forming regions. Using detailed RT modelling, we show that the G333 cores are essentially undergoing a scaled-up version of low-mass star formation. This is an extension of earlier work in that the degree of infall and the chemical abundances are constrained by the RT modelling in a way that is not practical with a standard analysis of observational data. We also find high velocity infall and high infall mass rates, possibly suggesting accelerated collapse due to external pressure. Molecular depletion due to freeze-out on to dust grains in central regions of the cores is suggested by low molecular abundances of several species. Strong evidence for a local enhancement of 13C-bearing species towards the outflow cloud cores is discussed, consistent with the presence of shocks caused by the supersonic motions within them. [ABSTRACT FROM AUTHOR]

We present new detections of cyanodiacetylene (HC5N) towards hot molecular cores, observed with the Tidbinbilla 34 m radio telescope (DSS–34). In a sample of 79 hot molecular cores, HC5N was detected towards 35. These results are counter to the expectation that long chain cyanopolyynes, such as HC5N, are not typically found in hot molecular cores, unlike their shorter chain counterpart HC3N. However, it is consistent with recent models which suggest HC5N may exist for a limited period during the evolution of hot molecular cores. [ABSTRACT FROM PUBLISHER]

We have conducted a Galactic plane survey of methanol masers at 6668 MHz using a seven-beam receiver on the Parkes telescope. Here we present results from the first part, which provides sensitive unbiased coverage of a large region around the Galactic Centre. Details are given for 183 methanol maser sites in the longitude range 345° through the Galactic Centre to 6°. Within 6° of the Galactic Centre, we found 88 maser sites, of which more than half (48) are new discoveries. The masers are confined to a narrow Galactic latitude range, indicative of many sources at the Galactic Centre distance and beyond, and confined to a thin disc population; there is no high-latitude population that might be ascribed to the Galactic bulge. Within 2° of the Galactic Centre the maser velocities all lie between −60 and , a range much smaller than the range observed in CO. Elsewhere, the maser with highest positive velocity occurs, surprisingly, near longitude 355° and is probably attributable to the Galactic bar. The maser with the most negative velocity is near longitude 346°, within the longitude–velocity locus of the near side of the ‘3-kpc arm’. It has the most extreme velocity of a clear population of masers associated with the near and far sides of the 3-kpc arm. Closer to the Galactic Centre the maser space density is generally low, except within 0.25 kpc of the Galactic Centre itself, the ‘Galactic Centre zone’, where it is 50 times higher, which is hinted at by the longitude distribution, and confirmed by the unusual velocities. [ABSTRACT FROM AUTHOR]

We have undertaken a Parkes ammonia spectral line study, in the lowest two inversion transitions, of southern massive star formation regions, including young massive candidate protostars, with the aim of characterizing the earliest stages of massive star formation. 138 sources from the submillimetre continuum emission studies of Hill et al. were found to have robust (1,1) detections, including two sources with two velocity components, and 102 in the (2,2) transition. We determine the ammonia line properties of the sources: linewidth, flux density, kinetic temperature, NH3 column density and opacity, and revisit our spectral energy distribution modelling procedure to derive the mass for 52 of the sources. By combining the continuum emission information with ammonia observations we substantially constrain the physical properties of the high-mass clumps. There is clear complementarity between ammonia and continuum observations for derivations of physical parameters. The MM-only class, identified in the continuum studies of Hill et al., displays smaller sizes, mass and velocity dispersion and/or turbulence than star-forming clumps, suggesting a quiescent prestellar stage and/or the formation of less massive stars. [ABSTRACT FROM AUTHOR]

We present multimolecular line maps obtained with the Mopra telescope towards the southern giant molecular cloud (GMC) complex G333, associated with the H ii region RCW 106. We have characterized the GMC by decomposing the 3D data cubes withgaussclumps, and investigated spatial correlations among different molecules with principal component analysis (PCA). We find no correlation between clump size and linewidth, but a strong correlation between emission luminosity and linewidth. PCA classifies molecules into high- and low-density tracers, and reveals that HCO+ and N2H+ are anticorrelated. [ABSTRACT FROM AUTHOR]

We present the results of a targeted 3-mm spectral line survey towards the eighty-three 6.67 GHz methanol maser selected star-forming clumps observed by Purcell. In addition to the previously reported measurements of HCO+ (1–0), H13CO+ (1–0) and CH3CN (5–4) and (6–5), we used the Mopra antenna to detect emission lines of N2H+ (1–0), HCN (1–0) and HNC (1–0) towards 82/83 clumps (99 per cent), and CH3OH (2–1) towards 78/83 clumps (94 per cent). The molecular line data have been used to derive virial and local thermodynamic equilibrium masses, rotational temperatures and chemical abundances in the clumps, and these properties have been compared between subsamples associated with different indicators of evolution. The greatest differences are found between clumps associated with 8.6 GHz radio emission, indicating the presence of an Ultra-Compact H ii (UCH ii) region, and ‘isolated’ masers (without associated radio emission), and between clumps exhibiting CH3CN emission and those without. In particular, thermal CH3OH is found to be brighter and more abundant in UCH ii regions and in sources with detected CH3CN, and may constitute a crude molecular clock in single dish observations. Clumps associated with 8.6 GHz radio emission tend to be more massive and more luminous than clumps without radio emission. This is likely because the most massive clumps evolve so rapidly that a Hyper-Compact H ii or UCH ii region is the first visible tracer of star formation. The gas mass to submm/infrared luminosity relation for the combined sample was found to be , considerably shallower than expected for massive main-sequence stars. This implies that the mass of the clumps is comparable to, or greater than, the mass of the stellar content. We also find that the mass of the hot core is correlated with the mass of the clump in which it is embedded. [ABSTRACT FROM AUTHOR]

We present results from a time-dependent gas-phase chemical model of a hot core based on the physical conditions of G305.2+0.2. While the cyanopolyyne HC3N has been observed in hot cores, the longer chained species, HC5N, HC7N and HC9N, have not been considered as the typical hot-core species. We present results which show that these species can be formed under hot core conditions. We discuss the important chemical reactions in this process and, in particular, show that their abundances are linked to the parent species acetylene which is evaporated from icy grain mantles. The cyanopolyynes show promise as ‘chemical clocks’ which may aid future observations in determining the age of hot core sources. The abundance of the larger cyanopolyynes increases and decreases over relatively short time-scales, . We present results from a non-local thermodynamic equilibrium statistical equilibrium excitation model as a series of density, temperature and column density dependent contour plots which show both the line intensities and several line ratios. These aid in the interpretation of spectral-line data, even when there is limited line information available. In particular, non-detections of HC5N and HC7N in Walsh et al. are analysed and discussed. [ABSTRACT FROM AUTHOR]

We present a fully sampled C18O (1–0) map towards the southern giant molecular cloud (GMC) associated with the H ii region RCW 106, and use it in combination with previous 13CO (1–0) mapping to estimate the gas column density as a function of position and velocity. We find localized regions of significant 13CO optical depth in the northern part of the cloud, with several of the high-opacity clouds in this region likely associated with a limb-brightened shell around the H ii region G333.6−0.2. Optical depth corrections broaden the distribution of column densities in the cloud, yielding a lognormal distribution as predicted by simulations of turbulence. Decomposing the 13CO and C18O data cubes into clumps, we find relatively weak correlations between size and linewidth, and a more sensitive dependence of luminosity on size than would be predicted by a constant average column density. The clump mass spectrum has a slope near −1.7, consistent with previous studies. The most massive clumps appear to have gravitational binding energies well in excess of virial equilibrium; we discuss possible explanations, which include magnetic support and neglect of time-varying surface terms in the virial theorem. Unlike molecular clouds as a whole, the clumps within the RCW 106 GMC, while elongated, appear to show random orientations with respect to the Galactic plane. [ABSTRACT FROM AUTHOR]

Using the Mopra telescope, we have undertaken a 3-mm spectral-line imaging survey of a 5 × 5 arcmin2 area around Sgr B2. We covered almost the complete spectral range from 81.7 to 113.5 GHz, with 2.2 MHz wide spectral channels or and have observed 24 lines, with 0.033 MHz wide, or channels. We discuss the distribution of around 50 lines, and present velocity-integrated emission images for 38 of the lines. In addition, we have detected around 120 more lines, mostly concentrated at the particularly spectral-line-rich Sgr B2(N) source. There are significant differences in molecular emission, pointing to both abundance and excitation differences throughout the region. Seven distinct spatial locations are identified for the emitting species, including peaks near the prominent star-forming cores of Sgr B2(N), (M) and (S) that are seen in infrared (IR)-to-radio continuum images. The other features are a ‘north ridge’ and a ‘north cloud’ to the north of the Sgr B2 N-M-S cores, a ‘south-east peak’ and a ‘west ridge’. The column density, as evident through C18O, peaks at the Sgr B2(N) and (M) cores, where strong absorption is also evident in otherwise generally bright lines such as HCO+, HCN and HNC. Most molecules trace a ridge line to the west of the Sgr B2 N-M-S cores, wrapping around the cores and extending north-east to the north cloud. This is most clearly evident in the species HC3N, CH3CN, CH3OH and OCS. They are found to be closer in distribution to the cooler dust traced by the submillimetre continuum than either the warmer dust seen in the mid-IR or to the radio continuum. The molecule CN, in contrast, is reasonably uniform over the entire region mapped, aside from strong absorption at the positions of the Sgr B2(N) and (M) cores. [ABSTRACT FROM AUTHOR]

We present observations of the (1,1), (2,2), (4,4) and (5,5) inversion transitions of para-ammonia (NH3) and 24-GHz continuum, taken with the Australia Telescope Compact Array towards 21 southern Galactic hot molecular cores traced by 6.7-GHz methanol maser emission. We detect NH3(1,1) emission towards all 21 regions and 24-GHz continuum emission towards 12 of the regions, including six with no reported 8-GHz continuum counterparts. In total, we find the 21 regions contain 41 NH3(1,1) cores but around half of the regions only contain a single core. We extract characteristic spectra for every core at each of the NH3 transitions and present both integrated intensity maps and channel maps for each region. NH3(2,2) emission was detected towards all NH3(1,1) cores. NH3(4,4) emission was detected in 13 of the NH3(1,1) cores with NH3(5,5) emission coincident with 11 of these. The NH3(4,4) and (5,5) emission is always unresolved and found at the methanol maser position. An analysis of the NH3(1,1) and (2,2) line ratios suggests that the cores with NH3(4,4) and (5,5) emission are warmer than the remaining cores rather than simply containing more ammonia. The coincidence of the maser emission with the higher spatial resolution NH3(4,4) and (5,5) emission indicates that the methanol masers are found at the warmest part of the core. In all cores detected at NH3(4,4) (with the exception of core 4), the measured linewidth increases with transition energy. The NH3(1,1) spectra of several cores show an emission and absorption component slightly offset in velocity but it is unclear whether or not this is due to systematic motion of the gas. We observe large asymmetries in the NH3(1,1) hyperfine line profiles and conclude that this is due to non-local thermodynamic equilibrium conditions arising from a number of dense, small clumps within the beam, rather than systematic motions of gas in the cores. Assuming that the 24-GHz continuum emission is optically-thin bremsstrahlung, we derive properties of the ionized gas. The rate of Lyman continuum photons required to ionize the gas of 1045–1048 s−1 suggests that the continuum emission is powered by stars of mass . We investigate the nature of the 24-GHz continuum sources which were not detected at 8 GHz and find that these are always coincident with both ammonia and methanol maser emission. This is in contrast to those detected at both 8 and 24 GHz which are generally offset from the methanol maser emission. We investigate the possibility that these may be hypercompact H ii regions. Finally, we separate the cores into five groups, based on their association with , methanol maser and continuum emission. From the different physical properties of the cores in the groups, we discuss the possibility that these groups may represent cores at different evolutionary stages of the massive star formation process. [ABSTRACT FROM AUTHOR]

We report the results of a blind search for 22-GHz water masers in two regions, covering approximately half a square degree, within the giant molecular cloud associated with RCW 106. The complete search of the two regions was carried out with the 26-m Mount Pleasant radio telescope and resulted in the detection of nine water masers, five of which are new detections. Australia Telescope Compact Array (ATCA) observations of these detections have allowed us to obtain positions with arcsecond accuracy, allowing meaningful comparison with infrared and molecular data for the region. We find that for the regions surveyed there are more water masers than either 6.7-GHz methanol, or main-line OH masers. The water masers are concentrated towards the central axis of the star formation region, in contrast to the 6.7-GHz methanol masers which tend to be located near the periphery. The colours of the GLIMPSE point sources associated with the water masers are similar to those of 6.7-GHz methanol masers, but slightly less red. We have made a statistical investigation of the properties of the 13CO and 1.2-mm dust clumps with and without associated water masers. We find that the water masers are associated with the more massive, denser and brighter 13CO and 1.2-mm dust clumps. We present statistical models that are able to predict those 13CO and 1.2-mm dust clumps that are likely to have associated water masers, with a low misclassification rate. [ABSTRACT FROM AUTHOR]

We have used the Mopra Telescope to search for glycine and the simple chiral molecule propylene oxide in the Sgr B2 (LMH) and Orion KL, in the 3-mm band. We have not detected either species, but have been able to put sensitive upper limits on the abundances of both molecules. The 3σ upper limits derived for glycine conformer I are in both Orion-KL and Sgr B2 (LMH), comparable to the reported detections of conformer I by Kuan et al. However, as our values are 3σ upper limits rather than detections we conclude that this weighs against confirming the detection of Kuan et al. We find upper limits for the glycine II column density of in both Orion-KL and Sgr B2 (LMH), in agreement with the results of Combes et al. The results presented here show that glycine conformer II is not present in the extended gas at the levels detected by Kuan et al. for conformer I. Our ATCA results have ruled out the detection of glycine (both conformers I and II) in the compact hot core of the LMH at the levels reported, so we conclude that it is unlikely that Kuan et al. have detected glycine in either Sgr B2 or Orion-KL. We find upper limits for propylene oxide abundance of in Orion-KL and in Sgr B2 (LMH). We have detected fourteen features in Sgr B2 and four features in Orion-KL which have not previously been reported in the interstellar medium, but have not been able to plausibly assign these transitions to any carrier. [ABSTRACT FROM AUTHOR]

Methanol maser emission has proven to be an excellent signpost of regions undergoing massive star formation (MSF). To investigate their role as an evolutionary tracer, we have recently completed a large observing program with the ATCA to derive the dynamical and physical properties of molecular/ionised gas towards a sample of MSF regions traced by 6.7GHz methanol maser emission. We find that the molecular gas in many of these regions breaks up into multiple sub-clumps which we separate into groups based on their association with/without methanol maser and cm continuum emission. The temperature and dynamic state of the molecular gas is markedly different between the groups. Based on these differences, we attempt to assess the evolutionary state of the cores in the groups and thus investigate the role of class II methanol masers as a tracer of MSF. [ABSTRACT FROM PUBLISHER]

We present the initial results of a 3-mm spectral-line survey towards 83 methanol maser-selected massive star-forming regions. Here, we report observations of the J = 5–4 and 6–5 rotational transitions of methyl cyanide (CH3CN) and the J = 1–0 transition of HCO+ and H13CO+. CH3CN emission is detected in 58 sources (70 per cent of our sample). We estimate the temperature and column density for 37 of these using the rotational diagram (RD) method. The temperatures we derive range from 28–166 K, and are lower than previously reported temperatures, derived from higher J transitions. We find that CH3CN is brighter and more commonly detected towards ultracompact H ii (UCH ii) regions than towards isolated maser sources. Detection of CH3CN towards isolated maser sources strongly suggests that these objects are internally heated and that CH3CN is excited prior to the UCH ii phase of massive star formation. HCO+ is detected towards 82 sources (99 per cent of our sample), many of which exhibit asymmetric line profiles compared to H13CO+. Skewed profiles are indicative of inward or outward motions, however, we find approximately equal numbers of red- and blue-skewed profiles among all classes. Column densities are derived from an analysis of the HCO+ and H13CO+ line profiles. 80 sources have mid-infrared (mid-IR) counterparts: 68 seen in emission and 12 seen in absorption as ‘dark clouds’. Seven of the 12 dark clouds exhibit asymmetric HCO+ profiles, six of which are skewed to the blue, indicating infalling motions. CH3CN is also common in dark clouds, where it has a 90 per cent detection rate. [ABSTRACT FROM AUTHOR]

We have successfully used a new on-the-fly mapping technique with the Mopra radio telescope to image G305.2+0.2 in transitions of 13CO, HCO+, N2H+, CH3CN and CH3OH. All these species appear to be concentrated towards the infrared-quiet methanol maser site G305A (G305.21+0.21). We suggest that this region contains an extremely deeply embedded site of massive star formation, with comparable qualities to the low-mass Class 0 stage. The infrared-bright methanol maser site G305B (G305.21+0.20) also exhibits emission in all the mapped transitions, but always at a lower level. We suggest this is because it harbours a site of massive star formation older and more developed than G305.21+0.21. All transitions appear to be extended beyond the size of the Mopra beam (30 arcsec). 13CO and HCO+ line wings are suggestive of an outflow in the region, but the spatial resolution of these data is insufficient to identify the powering source. A narrow-lined (1.6 km s−1 compared to a typical line FWHM of 6.4 km s−1) N2H+ source (G305SW) is found 90 arcsec to the south-west of the main star-forming centres, which does not correspond to any CH3CN or CH3OH source, nor does it correspond well to 13CO or HCO+ emission in the vicinity. We suggest this may be a massive, cold, quiescent and possibly pre-stellar core. [ABSTRACT FROM AUTHOR]

We present a model for empirically reproducing line profiles of molecular hydrogen emission in bow shocks. The model takes into account bow velocity, dissociation limit, a cooling function, viewing angle, bow shape and a limited form of extinction. Our results show that both geometrical factors and shock physics can significantly affect the profile morphology. In a companion paper we will apply this model to Fabry–Perot observations of bow shocks in the Orion BN–KL outflow. [ABSTRACT FROM AUTHOR]

We have imaged the emission from the near-infrared v=1–0 S(1), 1–0 S(7), 2–1 S(1) and 6–4 O(3) lines of molecular hydrogen in the Northern and South Western Bars of M17, together with the hydrogen Brγ and Br10 lines. This includes the first emission-line image ever to be obtained of a line from the highly excited v=6 level of molecular hydrogen. In both Bars, the H[sub 2] emission is generally distributed in clumps along filamentary features. The 1–0 S(1) and 2–1 S(1) images have similar morphologies. Together with their relative line ratios, this supports a fluorescent origin for their emission, within a photodissociation region. The SW-Bar contains a clumpy medium, but in the N-Bar the density is roughly constant. The 1–0 S(7) line image is also similar to the 1–0 S(1) image, but the 6–4 O(3) image is significantly different from it. Since the emission wavelengths of these two lines are similar (1.748 to 1.733 μm), this cannot be due to differential extinction between the v=6 and the v=1 lines. We attribute the difference to the pumping of newly formed H[sub 2] into the v=6 , or to a nearby, level. However, this also requires a time-dependent photodissociation region (where molecule formation does not balance dissociation), rather than it to be in steady state, and/or for the formation spectrum to vary with position in the source. If this interpretation of formation pumping of molecular hydrogen is correct, it is the first clear signature from this process to be seen. [ABSTRACT FROM AUTHOR]

We have obtained wide-field thermal infrared (IR) images of the Carina nebula, using the SPIREX/Abu telescope at the South Pole. Emission from polycyclic aromatic hydrocarbons (PAHs) at 3.29 μm, a tracer of photodissociation regions (PDRs), reveals many interesting well-defined clumps and diffuse regions throughout the complex. Near-IR images (1–2 μm) , along with images from the Midcourse Space Experiment (MSX) satellite (8–21 μm) have been incorporated to study the interactions between the young stars and the surrounding molecular cloud in more detail. Two new PAH emission clumps have been identified in the Keyhole nebula, and have been mapped in [sup 12]CO(2–1) and (1–0) using the Swedish–ESO Submillimetre Telescope (SEST). Analysis of their physical properties reveals that they are dense molecular clumps, externally heated with PDRs on their surfaces and supported by external pressure in a similar manner to the other clumps in the region. A previously identified externally heated globule containing IRAS 10430-5931 in the southern molecular cloud shows strong 3.29-, 8- and 21-μm emission, the spectral energy distribution (SED) revealing the location of an ultracompact (UC) H iiregion. The northern part of the nebula is complicated, with PAH emission intermixed with mid-IR dust continuum emission. Several point sources are located here, and through a two-component blackbody fit to their SEDs we have identified three possible UC H iiregions as well as a young star surrounded by a circumstellar disc. This implies that star formation in this region is ongoing and not halted by the intense radiation from the surrounding young massive stars. [ABSTRACT FROM AUTHOR]

ABSTRACT We used the University of New South Wales Infrared Fabry-Perot (UNSWIRF) to investigate the photodissociation region (PDR) associated with the `elephant trunk' features in the M16 H ii region (the Eagle nebula). Images were made in the H2 1--0 S(1) and 2--1 S(1) lines at 2.122 and 2.248 μ m, respectively, and in the H i Br γ line at 2.166 μ m. The trunk-like features have an average H2 number density of ∼ 104 cm-3 and are irradiated by a far-UV field &sim 104 × the ambient interstellar value. The H2 intensity profile across the trunks is consistent with a simple model in which cylindrical columns of gas are illuminated externally, primarily by a direct component (the stars of NGC 6611), with an additional contribution from an isotropic component (scattered light). We find that most of the H2 emission from the source is consistent with purely fluorescent excitation, however a significant fraction of the H2 emission (∼ 25 per cent) from the northernmost column shows evidence for `collisional fluorescence', i.e. redistribution of H2 level populations through collisions. This emission is confined to clumps up to ∼ 0.01 pc in diameter, with densities ≥ 105 cm-3, and perhaps > 106 cm-3, filling at most a few per cent of the volume of the trunks. The line intensities and ratios are consistent with steady-state and not time-dependent PDR models. [ABSTRACT FROM AUTHOR]

We report the results of a blind search for 22 GHz water masers in two regions, covering approximately half a square degree, within the G 333.2–0.6 giant molecular cloud. The complete search of the two regions was carried out with the 26 m Mount Pleasant radio telescope and resulted in the detection of nine water masers, five of which are new detections. Australia Telescope Compact Array (ATCA) observations of these detections have allowed us to obtain positions with arcsecond accuracy, allowing meaningful comparison with infrared and molecular data for the region. We find that for the regions surveyed there are more water masers than either 6.7 GHz methanol, or main-line OH masers. The water masers are concentrated towards the central axis of the star formation region, in contrast to the 6.7 GHz methanol masers which tend to be located near the periphery. The colours of the GLIMPSE point sources associated with the water masers are slightly less red than those associated with methanol masers. Statistical investigation of the properties of the 13CO and 1.2 mm dust clumps with and without associated water masers shows that the water masers are associated with the more massive, denser and brighter 13CO and 1.2 mm dust clumps. We present statistical models that can predict those 13CO and 1.2 mm dust clumps likely to have associated water masers. [ABSTRACT FROM PUBLISHER]

We report the detection of the SiO transition from the massive cold dense core G333.125−0.562. The core remains undetected at wavelengths shorter than 70 μm and has compact 1.2-mm dust continuum. The SiO emission is localized to the core. The observations are part of a continuing multi-molecular line survey of the giant molecular cloud G333. Other detected molecules in the core include 13CO, C18O, CS, , HCN, HNC, CH3OH, , SO, HC3N, NH3, and some of their isotopes. In addition, from NH3 (1,1) and (2,2) inversion lines, we obtain a temperature of 13 K. From fitting to the spectral energy distribution we obtain a colour temperature of 18 K and a gas mass of . We have also detected a 22-GHz water maser in the core, together with methanol maser emission, suggesting that the core will host massive star formation. We hypothesize that the SiO emission arises from shocks associated with an outflow in the cold core. [ABSTRACT FROM AUTHOR]

We are studying the molecular clouds in the region around G333.6-0.2 in a number of 3-mm transitions from different molecular species, to probe, among other things, the turbulent properties. The observations are being made by on-the-fly mapping with the 22-m diameter single-dish Mopra radio telescope. See Bains et al. (2006) and Cunningham et al. (2006 in these proceedings) for more details. During 2004 and 2005 we obtained 13 CO (1 – 0), C18O, CS (2 – 1) and C34S data. Using the different molecular tracers gives complementary information about the gas density structure, due to the different critical densities, and different isotopomers allows correction for optical depth effects. [ABSTRACT FROM PUBLISHER]

Any successful model of star formation must be able to explain the low star forming efficiency of molecular clouds in our Galaxy. If the collapse of gas is regulated only by gravity, then the star formation rate should be orders of magnitude larger than the 1 M per year within our galaxy. The standard model invokes magnetic fields to slow down the rate of collapse, but does not explain star formation in cluster mode, or the lack of observed variations in the chemistry of molecular clouds if they are long-lived entities. [ABSTRACT FROM PUBLISHER]

A new 7-beam methanol multibeam receiver was successfully commissioned at Parkes Observatory in January 2006, and has begun surveying the Milky Way for newly forming massive stars, that are pinpointed by strong methanol maser emission at 6.7 GHz. The receiver was jointly constructed by Jodrell Bank Observatory and the Australia Telescope National Facility for use on the Parkes and Lovell Telescopes. The whole galactic plane is being surveyed within latitudes ±2°, with a velocity resolution of 0.1 km s−1 and a 5-σ sensitivity of ~0.7 Jy. Altogether 200 days of observing will be required. [ABSTRACT FROM PUBLISHER]