Maria Cunningham

Spectral imaging of the Central Molecular Zone in multiple 3-mm molecular lines

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 −0bsl000647 to 1bsl000648 and latitude −0bsl000643 to 0bsl000642, 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.

Triggered star formation on the borders of the Galactic Hii region RCW 82

Context. To investigate the process of star formation triggered by th e expansion of an H region, we present a multi-wavelength analysis of the Galactic H region RCW 120 and its surroundings. The collect and collaps e model predicts that the layer of gas and dust accumulated between the ionization and shock fronts during the expansio n of the H region collapses and forms dense fragments, giving rise to p otential sites of massive-star formation. Aims. The aim of our study is to look for such massive fragments and m assive young stars on the borders of RCW 120. Methods. We mapped the RCW 120 region in the cold dust continuum emissi on at 1.2 mm to search for these fragments. We supplemented this study with the available near(2MASS) and mid-IR (GLIM PSE) data to locate the IR sources observed towards this regi on and to analyse their properties. We then compared the observational resul ts with the predictions of Hosokawa & Inutsuka’s model (2005 , 2006). Results. At 1.2 mm we detected eight fragments towards this region, fiv e located on its borders. The largest fragment has a mass of ab out 370 M⊙. Class I and Class II young stellar objects are detected all o ver the region, with some observed far from the ionization fr ont. This result emphasises the possible importance of distant interactions between the radiation, escaping from the ioni zed region, and the surrounding

The Millimeter Astronomy Legacy Team 90 GHz (MALT90) pilot survey

We describe a pilot survey conducted with the Mopra 22 m radio telescope in preparation for the Millimeter Astronomy Legacy Team Survey at 90 GHz (MALT90). We identified 182 candidate dense molecular clumps using six different selection criteria and mapped each source simultaneously in 16 different lines near 90 GHz. We present a summary of the data and describe how the results of the pilot survey shaped the design of the larger MALT90 survey. We motivate our selection of target sources for the main survey based on the pilot detection rates and demonstrate the value of mapping in multiple lines simultaneously at high spectral resolution.

The H2O Southern Galactic Plane Survey: NH3 (1,1) and (2,2) catalogues

The H₂O Southern Galactic Plane Survey (HOPS) has mapped a 100 degrees strip of the Galactic plane (-70° > l > 30°, |b| 10⁴cm⁻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 σT(mb) =0.20 ± 0.06 K. For the (1,1) transition, this sensitivity equates to a 3.2 kpc distance limit for detecting a 20 K, 400 M⊙ cloud at the 5σ level. Similar clouds of mass 5000 M⊙ would be detected as far as the Galactic Centre, while 30000 M⊙ clouds would be seen across the Galaxy. We have developed an automatic emission finding procedure based on the Australian Telescope National Facility (ATNF) duchamp software and have used it to create a new catalogue of 669 dense molecular clouds. The catalogue is 100 per cent complete at the 5s detection limit (T(mb) = 1.0 K). A preliminary analysis of the ensemble cloud properties suggests that the near-kinematic distances are favoured. The cloud positions are consistent with current models of the Galaxy containing a long bar. Combined with other Galactic plane surveys this new molecular-line data set constitutes a key tool for examining Galactic structure and evolution. Data cubes, spectra and catalogues are available to the community via the HOPS website.

Molecular line mapping of the giant molecular cloud associated with RCW 106 - II. Column density and dynamical state of the clumps

We present a fully sampled C 18 O (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 1 3 CO (1-0) mapping to estimate the gas column density as a function of position and velocity. We find localized regions of significant 13 CO 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 HII 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 13 CO and C 18 O 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.

Molecular line mapping of the giant molecular cloud associated with RCW 106 – III. Multimolecular line mapping

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 with gaussclumps, 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.

A search for propylene oxide and glycine in Sagittarius B2 (LMH) and Orion

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 3 sigma upper limits derived for glycine conformer I are 3.7 x 10(14) cm(-2) 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 3s 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 7.7 x 10(12) cm(-2) 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 3.0 x 10(14) cm(-2) in Orion-KL and 6.7 x 10(14) cm(-2) 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.

A Search for biomolecules in Sagittarius B2 (LMH) with the Australia Telescope Compact Array

We have used the Australia Telescope Compact Array 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, 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 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 N = 4×10 cm found by Kuan et al. (2003) in their reported detection of glycine, it should have been easily detected with the ATCA synthesized beam size of 17.0 x 3.4 arcsec, 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.

ABUNDANCES AND ISOTOPE RATIOS IN THE MAGELLANIC CLOUDS: THE STAR-FORMING ENVIRONMENT OF N 113*

With the goal of deriving the physical and chemical conditions of star-forming regions in the Large Magellanic Cloud (LMC), a spectral line survey of the prominent star-forming region N 113 is presented. The observations cover parts of the frequency range from 85 GHz to 357 GHz and include 63 molecular transitions from a total of 16 species, among them are the spectra of rare isotopologues. Maps of selected molecular lines as well as the 1.2 mm continuum distribution are also presented. Molecular abundances in the core of the complex are consistent with a photon-dominated region in a nitrogen deficient environment. While carbon monoxide (CO) shows optical depths of the order of τ ~ 10, 13CO is optically thin. The most prominent lines of carbon monosulfide (CS), HCN, and HCO+show signs of weak saturation (τ ~ 0.5). Densities range from 5 × 103 cm–3 for CO to almost 106 for CS, HCN, and a few other species, indicating that only the densest regions provide sufficient shielding, even for some of the most common species. An ortho- to para-formaldehyde (H2CO) ratio of ~ 3 hints at H2CO formation in a warm ( 40 K) environment. Isotope ratios are 12C/13C ~ 49 ± 5, 16O/18O ~2000 ± 250, 18O/17O ~ 1.7 ± 0.2, and 32S/34S ~ 15. Agreement with data from other star-forming clouds shows that the gas is well mixed in the LMC. The isotope ratios not only differ from those seen in the Galaxy, they also do not form a continuation of the trends observed with decreasing metallicity from the inner to the outer Galaxy. This implies that the outer Galaxy, even though showing an intermediate metallicity, is not providing a transition zone between the inner Galaxy and the metal-poor environment of the Magellanic Clouds. A part of this discrepancy is likely caused by differences in the age of the stellar populations in the outer Galaxy and the LMC. While, however, this scenario readily explains measured carbon and oxygen isotope ratios, nitrogen and sulfur still lack a self-consistent interpretation.

Millimetre continuum observations of southern massive star formation regions – II. SCUBA observations of cold cores and the dust grain emissivity index (β)

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 HII 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 ‘mmonly’, 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 mmonly 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.