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We present the full data release for the Southern Parkes Large-Area Survey in Hydroxyl (SPLASH), a sensitive, unbiased single-dish survey of the Southern Galactic Plane in all four ground-state transitions of the OH radical at 1612, 1665, 1667, and 1720 MHz. The survey covers the inner Galactic Plane, Central Molecular Zone, and Galactic Centre over the range | b | < 2°, 332 |$^{\circ }\, \lt l \lt $| 10°, with a small extension between 2 |$^{\circ }\, \lt b \lt $| 6°, 358 |$^{\circ }\, \lt l \lt $| 4°. SPLASH is the most sensitive large-scale survey of OH to-date, reaching a characteristic root-mean-square sensitivity of ∼15 mK for an effective velocity resolution of ∼0.9 km s−1. The spectral line datacubes are optimized for the analysis of extended, quasi-thermal OH, but also contain numerous maser sources, which have been confirmed interferometrically and published elsewhere. We also present radio continuum images at 1612, 1666, and 1720 MHz. Based on initial comparisons with 12CO(J  = 1–0), we find that OH rarely extends outside CO cloud boundaries in our data, but suggest that large variations in CO-to-OH brightness temperature ratios may reflect differences in the total gas column density traced by each. Column density estimation in the complex, continuum-bright Inner Galaxy is a challenge, and we demonstrate how failure to appropriately model sub-beam structure and the line-of-sight source distribution can lead to order-of-magnitude errors. Anomalous excitation of the 1612 and 1720 MHz satellite lines is ubiquitous in the inner Galaxy, but is disabled by line overlap in and around the Central Molecular Zone. [ABSTRACT FROM AUTHOR]

The afterglow of a gamma-ray burst (GRB) can give us valuable insight into the properties of its host galaxy. To correctly interpret the spectra of the afterglow we need to have a good understanding of the foreground interstellar medium (ISM) in our own Galaxy. The common practice to correct for the foreground is to use neutral hydrogen (H  i) data from the Leiden/Argentina/Bonn (LAB) survey. However, the poor spatial resolution of the single dish data may have a significant effect on the derived column densities. To investigate this, we present new high-resolution H  i observations with the Australia Telescope Compact Array (ATCA) towards four GRBs. We combine the interferometric ATCA data with single dish data from the Galactic All Sky Survey (GASS) and derive new Galactic H  i column densities towards the GRBs. We use these new foreground column densities to fit the Swift XRT X-ray spectra and calculate new intrinsic hydrogen column density values for the GRB host galaxies. We find that the new ATCA data show higher Galactic H  i column densities compared to the previous single dish data, which results in lower intrinsic column densities for the hosts. We investigate the line-of-sight optical depth near the GRBs and find that it may not be negligible towards one of the GRBs, which indicates that the intrinsic hydrogen column density of its host galaxy may be even lower. In addition, we compare our results to column densities derived from far-infrared data and find a reasonable agreement with the H  i data. [ABSTRACT FROM AUTHOR]

We present water maser and ammonia (1, 1) and (2, 2) observations, towards six regions in the Carina Nebula, conducted with the Australia Telescope Compact Array. In total five water masers were detected within two of the target fields, and we provide their accurate positions and characteristics. These five water masers constitute all of the known masers detected towards star formation regions in the Carina Nebula and we argue, that given the evidence for active star formation, and the presence of many high-mass stars, the Carina Nebula is uncharacteristically devoid of masers. Our results are consistent with the Carina Nebula having a lack of young high-mass stars, despite the presence of older high-mass stars. Ammonia (1, 1) and (2, 2) emission was detected towards all but one of the target fields and we find that their linewidths and derived temperatures are consistent with the presence of young star formation regions. [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 results from a study of the dense circumnuclear molecular gas of starburst galaxies. The study aims to investigate the interplay between starbursts, active galactic nuclei and molecular gas. We characterize the dense gas traced by HCN, HCO+ and HNC and examine its kinematics in the circumnuclear regions of nine starburst galaxies observed with the Australia Telescope Compact Array. We detect HCN (1-0) and HCO+ (1-0) in seven of the nine galaxies and HNC (1-0) in four. Approximately 7 arcsec resolution maps of the circumnuclear molecular gas are presented. The velocity-integrated intensity ratios, HCO+ (1-0)/HCN (1-0) and HNC (1-0)/HCN (1-0), are calculated. Using these integrated intensity ratios and spatial intensity ratio maps, we identify photon-dominated regions (PDRs) in NGC 1097, NGC 1365 and NGC 1808. We find no galaxy which shows the PDR signature in only one part of the observed nuclear region. We also observe unusually strong HNC emission in NGC 5236, but it is not strong enough to be consistent with X-ray-dominated region chemistry. Rotation curves are derived for five of the galaxies and dynamical mass estimates of the inner regions of three of the galaxies are made. [ABSTRACT FROM AUTHOR]

Using spectral line observations of HNCO, N2H+, and HNC, we investigate the kinematics of dense gas in the central ~250 pc of the Galaxy. We present SCOUSE (Semi-automated multi-COmponent Universal Spectral-line fitting Engine), a line-fitting algorithm designed to analyse large volumes of spectral line data efficiently and systematically. Unlike techniques which do not account for complex line profiles, SCOUSE accurately describes the {l, b, υLSR} distribution of Central Molecular Zone (CMZ) gas, which is asymmetric about Sgr A* in both position and velocity. Velocity dispersions range from 2.6 km s-1 < σ < 53.1 km s-1. A median dispersion of 9.8 km s-1, translates to a Mach number, M3D ⩾ 28. The gas is distributed throughout several 'streams', with projected lengths ~100-250 pc. We link the streams to individual clouds and sub-regions, including Sgr C, the 20 and 50 km s-1 clouds, the dust ridge, and Sgr B2. Shell-like emission features can be explained by the projection of independent molecular clouds in Sgr C and the newly identified conical profile of Sgr B2 in {l, b, υLSR} space. These features have previously invoked supernova-driven shells and cloud-cloud collisions as explanations. We instead caution against structure identification in velocity-integrated emission maps. Three geometries describing the 3D structure of the CMZ are investigated: (i) two spiral arms; (ii) a closed elliptical orbit; (iii) an open stream. While two spiral arms and an open stream qualitatively reproduce the gas distribution, the most recent parametrization of the closed elliptical orbit does not. Finally, we discuss how proper motion measurements of masers can distinguish between these geometries, and suggest that this effort should be focused on the 20 km s-1 and 50 km s-1 clouds and Sgr C. [ABSTRACT FROM AUTHOR]

We present molecular line imaging observations of three massive molecular outflow sources, G333.6-0.2, G333.1-0.4, and G332.8-0.5, all of which also show evidence for infall, within the G333 giant molecular cloud (GMC). All three are within a beam size (36 arcsec) of IRAS sources, 1.2-mm dust clumps, various masing species, and radio continuum-detected H II regions and hence are associated with high-mass star formation. We present the molecular line data and derive the physical properties of the outflows including the mass, kinematics, and energetics and discuss the inferred characteristics of their driving sources. Outflow masses are of 10-40 M in each lobe, with core masses of the order of 103 M. Outflow size scales are a few tenth of a parsec, time-scales are of several ×104 years, mass-loss rates a few ×10-4 M yr-1. We also find the cores are turbulent and highly supersonic. [ABSTRACT FROM AUTHOR]

ABSTRACT The H2O Southern Galactic Plane Survey (HOPS) has mapped a 100° strip of the Galactic plane (−70° > l > 30°, | b| < 0°.5) using the 22 m Mopra antenna at 12 mm wavelengths. Observations were conducted in on-the-fly mode using the Mopra spectrometer (MOPS), targeting water masers, thermal molecular emission and radio-recombination lines. Foremost among the thermal lines are the 23 GHz transitions of NH3 J,K = (1,1) and (2,2), which trace the densest parts of molecular clouds ( n > 104 cm−3). In this paper, we present the NH3 (1,1) and (2,2) data, which have a resolution of 2 arcmin and cover a velocity range of ±200 km s−1. The median sensitivity of the NH3 data cubes is [ABSTRACT FROM AUTHOR]

ABSTRACT HCN is becoming a popular choice of molecule for studying star formation in both low- and high-mass regions and for other astrophysical sources from comets to high-redshift galaxies. However, a major and often overlooked difficulty with HCN is that it can exhibit dramatic non-local thermodynamic equilibrium (non-LTE) behaviour in its hyperfine line structure. Individual hyperfine lines can be strongly boosted or suppressed. In low-mass star-forming cloud observations, this could possibly lead to large errors in the calculation of opacity and excitation temperature, while in massive star-forming clouds, where the hyperfine lines are partially blended due to turbulent broadening, errors will arise in infall measurements that are based on the separation of the peaks in a self-absorbed profile. This is because the underlying line shape cannot be known for certain if hyperfine anomalies are present. We present a first observational investigation of these anomalies across a wide range of conditions and transitions by carrying out a survey of low-mass starless cores (in Taurus and Ophiuchus) and high-mass protostellar objects (in the G333 giant molecular cloud) using hydrogen cyanide (HCN) and emission lines. We quantify the degree of anomaly in these two rotational levels by considering ratios of individual hyperfine lines compared to LTE values. We find that all the cores observed demonstrate some degree of anomaly while many of the lines are severely anomalous. We conclude that HCN hyperfine anomalies are common in both lines in both low-mass and high-mass protostellar objects, and we discuss the differing hypotheses for the generation of the anomalies. In light of the results, we favour a line overlap effect for the origins of the anomalies. We discuss the implications for the use of HCN as a dynamical tracer and suggest in particular that the hyperfine line should be avoided in quantitative calculations. [ABSTRACT FROM AUTHOR]

ABSTRACT We have mapped 20 spectral lines in the Central Molecular Zone (CMZ) around the Galactic Centre, emitting from 85.3 to 93.3 GHz. This work used the 22-m Mopra radio telescope in Australia, equipped with the 8-GHz bandwidth University of New South Wales-Mopra Spectrometer (UNSW-MOPS) digital filter bank, obtaining ∼2 km s−1 spectral and ∼40 arcsec spatial resolution. The lines measured include emission from the c-C3H2, CH3CCH, HOCO+, SO, H13CN, H13CO+, SO, H13NC, C2H, HNCO, HCN, HCO+, HNC, HC3N, 13CS and N2H+ molecules. The area covered is Galactic longitude −07 to 18 and latitude −03 to 02, including the bright dust cores around Sgr A, Sgr B2, Sgr C and G1.6−0.025. We present images from this study and conduct a principal component analysis on the integrated emission from the brightest eight lines. This is dominated by the first component, showing that the large-scale distribution of all molecules is very similar. We examine the line ratios and optical depths in selected apertures around the bright dust cores, as well as for the complete mapped region of the CMZ. We highlight the behaviour of the bright HCN, HNC and HCO+ line emission, together with that from the 13C isotopologues of these species, and compare the behaviour with that found in extragalactic sources where the emission is unresolved spatially. We also find that the isotopologue line ratios (e.g. HCO+/H13CO+) rise significantly with increasing redshifted velocity in some locations. Line luminosities are also calculated and compared to that of CO, as well as to line luminosities determined for external galaxies. [ABSTRACT FROM AUTHOR]

ABSTRACT We present first results of the H2O Southern Galactic Plane Survey (HOPS), using the Mopra Radio Telescope with a broad-band backend and a beam size of about 2 arcmin. We have observed 100 deg2 of the southern Galactic plane at 12 mm (19.5-27.5 GHz), including spectral line emission from H2O masers, multiple metastable transitions of ammonia, cyanoacetylene, methanol and radio recombination lines. In this paper, we report on the characteristics of the survey and H2O maser emission. We find 540 H2O masers, of which 334 are new detections. The strongest maser is 3933 Jy and the weakest is 0.7 Jy, with 62 masers over 100 Jy. In 14 maser sites, the spread in the velocity of the H2O maser emission exceeds 100 km s−1. In one region, the H2O maser velocities are separated by 351.3 km s−1. The rms noise levels are typically between 1 and 2 Jy, with 95 per cent of the survey under 2 Jy. We estimate completeness limits of 98 per cent at around 8.4 Jy and 50 per cent at around 5.5 Jy. We estimate that there are between 800 and 1500 H2O masers in the Galaxy that are detectable in a survey with similar completeness limits to HOPS. We report possible masers in NH3 (11,9) and (8,6) emission towards G19.61−0.23 and in the NH3 (3,3) line towards G23.33−0.30. [ABSTRACT FROM AUTHOR]

BSTRACT [ABSTRACT FROM AUTHOR]

We have undertaken a spectral-line imaging survey of a arcmin area around Sagittarius (Sgr) B2 near the centre of the Galaxy, in the range from 30 to 50 GHz, using the Mopra telescope. The spatial resolution varies from 1.0 to 1.4 arcmin and the spectral resolution varies from 1.6 to 2.7 km s over the frequency range. We present velocity-integrated emission images for 47 lines: 38 molecular lines and nine radio recombination lines. There are significant differences between the distributions of different molecules, in part due to spatial differences in chemical abundance across the complex. For example, HNCO and HOCO are found preferentially in the north cloud, and CHNH near Sgr B2 (N). Some of the differences between lines are due to excitation differences, as shown by the 36.17- and 44.07-GHz lines of CHOH, which have maser emission, compared to the 48.37-GHz line of CHOH. Other major differences in integrated molecular line distribution are due to absorption of the 7-mm free-free continuum emission (spatially traced by the radio recombination line emission) by cool intervening molecular material, causing a central dip in the molecular line distributions. These line distribution similarities and differences have been statistically described by Principal Component Analysis and interpreted in terms of simple Sgr B2 physical components of the cooler, lower density envelope, and dense, hot cores Sgr B2 (N), (M) and (S). [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]

An example of a cold massive core, JCMT 18354−0649S which is a possible high-mass analogue to a low-mass star-forming core, is studied. Line and continuum observations from James Clerk Maxwell Telescope, Mopra Telescope and Spitzer are presented and modelled in detail using a 3D molecular line radiative transfer code. In almost every way, JCMT 18354−0649S is a scaled-up version of a typical low-mass core with similar temperatures, chemical abundances and densities. The difference is that both the infall velocity and the turbulent width of the line profiles are an order of magnitude larger. While the higher infall velocity is expected due to the large mass of JCMT 18354−0649S, we suggest that the dissipation of this highly supersonic turbulence may lead to the creation of dense clumps of gas that surround the high-mass core. [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]

Concatenating data from the millimetre regime to the infrared, we have performed spectral energy distribution (SED) modelling for 227 of the 405 millimetre continuum sources of Hill et al. which are thought to contain young massive stars in the earliest stages of their formation. Three main parameters are extracted from the fits: temperature, mass and luminosity. The method employed was the Bayesian inference, which allows a statistically probable range of suitable values for each parameter to be drawn for each individual protostellar candidate. This is the first application of this method to massive star formation. The cumulative distribution plots of the SED modelled parameters in this work indicate that collectively, the sources without methanol maser and/or radio continuum associations (MM-only cores) display similar characteristics to those of high-mass star formation regions. Attributing significance to the marginal distinctions between the MM-only cores and the high-mass star formation sample, we draw hypotheses regarding the nature of the MM-only cores, including the possibility that the population itself comprises different types of source, and discuss their role in the formation scenarios of massive star formation. In addition, we discuss the usefulness and limitations of SED modelling and its application to the field. From this work, it is clear that within the valid parameter ranges, SEDs utilising current far-infrared data cannot be used to determine the evolution of massive protostars or massive young stellar objects. [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 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]

We have used the Australia Telescope Compact Array (ATCA) to conduct a search for the simplest amino acid, glycine (conformers I and II), and the simple chiral molecule propylene oxide at 3 mm in the Sgr B2 LMH. We searched 15 portions of spectrum between 85 and 91 GHz, each of 64 MHz bandwidth, and detected 58 emission features and 21 absorption features, giving a line density of 75 emission lines and 25 absorption lines per GHz stronger than the 5σ level of 110 mJy. Of these, 19 are transitions previously detected in the interstellar medium (ISM), and we have made tentative assignments of a further 23 features to molecular transitions. However, as many of these involve molecules not previously detected in the ISM, these assignments cannot be regarded with confidence. Given the median line width of 6.5 km s−1 in Sgr B2 LMH, we find that the spectra have reached a level where there is line confusion, with about 1/5 of the band being covered with lines. Although we did not confidently detect either glycine or propylene oxide, we can set 3σ upper limits for most transitions searched. We also show that if glycine is present in the Sgr B2 LMH at the level of found by Kuan et al. in their reported detection of glycine, it should have been easily detected with the ATCA synthesized beam size of 17.0 × 3.4 arcsec2, if it were confined to the scale of the LMH continuum source (<5 arcsec). This thus puts a strong upper limit on any small-scale glycine emission in Sgr B2, for both of conformers I and II. [ABSTRACT FROM AUTHOR]

We report the results of a submillimetre continuum emission survey targeted towards 78 star formation regions, 72 of which are devoid of methanol maser and UC H ii regions, identified in the Swedish ESO Submillimetre Telescope (SEST)/SEST IMaging Bolometer Array (SIMBA) millimetre continuum survey of Hill et al. At least 45 per cent of the latter sources, dubbed ‘mm-only’, detected in this survey are also devoid of the mid-infrared MSX emission. The 450- and 850-μm continuum emission was mapped using the Submillimetre Common User Bolometer Array (SCUBA) instrument on the James Clerk Maxwell Telescope (JCMT). Emission is detected towards 97 per cent of the 78 sources targeted as well as towards 28 other SIMBA sources lying in the SCUBA fields. In total, we have identified 212 cores in this submillimetre survey, including 106 previously known from the SIMBA survey. Of the remaining 106 sources, 53 result from resolving a SIMBA source into multiple submillimetre components, whilst the other 53 sources are submillimetre cores, not seen in the SIMBA. Additionally, we have identified two further mm-only sources in the SIMBA images. Of the total 405 sources identified in the SIMBA survey, 255 are only seen at millimetre wavelengths. We concatenate the results from four (sub)millimetre continuum surveys of massive star formation, together with the Galactic plane map of Pierce-Price et al. in order to determine the dust grain emissivity index β for each of the sources in the SIMBA source list. We examine the value of β with respect to temperature, as well as for the source classes identified in the SIMBA survey, for variation of this index. Our results indicate that β is typically 2, which is consistent with previous determinations in the literature, but for a considerably larger sample than previous work. [ABSTRACT FROM AUTHOR]

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]

The 3-mm transitions of HCN, HCO+ and HNC in the dense molecular clouds near the nucleus of the southern starburst galaxy NGC 4945 have been observed with three antennas of the Australia Telescope Compact Array (ATCA). Molecular-line emission was detected within the velocity range (300–800 km s−1) seen in single-dish spectra, although emission with extent greater than about 15 arcsec would not have been detected because of the lack of sufficiently small Compact Array (CA) baselines. Imaging the results at velocity intervals of 22.5 km s−1 and with a restoring beam of dimension yielded images of typical deconvolved dimensions for an assumed galaxy distance of 4 Mpc). The positions of the images vary systematically with velocity, consistent with the result expected for a rotating molecular cloud ensemble viewed edge-on and inclined at a position angle (PA) of 45°. Although the brightest images occurred at velocities of the two major features (∼430 and ∼710 km s−1) in Swedish-ESO Submillimetre Telescope (SEST) spectra, the images at intervening velocities were unexpectedly faint or even in absorption. The results have been interpreted in terms of an extended cloud component not detected by the CA in conjunction with absorption against the nuclear continuum emission. Some of the HCO+ images are dominated by absorption and the overall results do not truly represent the cloud structure. The HNC results appear to contain little absorption, and the emission integrated over velocity yielded an elliptical image centred on an H2O ‘megamaser’ located at the galaxy's nucleus. The HNC position–velocity distribution along the major axis is consistent with an edge-on circumnuclear molecular ring with a rotational velocity of 135 km s−1. However, the ring radius of ∼60 km s−1 is significantly less than previously derived from carbon monoxide (CO) observations. It can be reconciled with the CO results if the HNC ring traces high-density gas concentrated around the inside of the molecular ring, whereas the CO traces low-density gas that extends to higher radii. The HNC feature appears to be associated with features revealed in published infrared (IR) studies of the distribution of dust and star formation regions in the nuclear region of NGC 4945. Limited results on the variation of HNC/HCN abundance ratios within the nuclear molecular clouds support previous conclusions that the clouds are at an advanced evolutionary stage within a starburst period. [ABSTRACT FROM AUTHOR]