M. Pestalozzi

The 6-GHz methanol multibeam maser catalogue - I. Galactic Centre region, longitudes 345° to 6°

Original article can be found at: http://www3.interscience.wiley.com/journal/ Copyright Royal Astronomical Society

The 6-GHz multibeam maser survey – I. Techniques

A new 7-beam 6 7 GHz receiver has been built to survey the Galaxy and the Magellanic Clouds for newly forming high-mass stars that are pinpointed by strong methanol maser emission at 6668 MHz. The receiver was jointly constructed by Jodrell Bank Observatory (JBO) and the Australia Telescope National Facility (ATNF) and allows simultaneous coverage at 6668 and 6035 MHz. It was successfully commissioned at Parkes in January 2006 and is now being used to conduct the Parkes-Jodrell multibeam maser survey of the Milky Way. This will be the first systematic survey of the entire Galactic plane for masers of not only 6668-MHz methanol, but also 6035-MHz excited-state hydroxyl. The survey is two orders of magnitude faster than most previous systematic surveys and has an rms noise level of �0.17Jy. This paper describes the observational strategy, techniques and reduction procedures of the Galactic and Magellanic Cloud surveys, together with deeper, pointed, follow-up observations and complementary observations with other instruments. It also includes an estimate of the survey detection efficiency. The 111 days of observationswith the Parkes telescope have so far yielded >800 methanol sources, of which �350 are new discoveries. The whole project will provide the first comprehensive Galaxy-wide catalogue of 6668-MHz and 6035-MHz masers.

Star-forming Protoclusters Associated with Methanol Masers

We present a multiwavelength study of five methanol maser sites which are not directly associated with a strong (>100 mJy) radio continuum source: G 31.28+0.06, G 59.78+0.06, G 173.49+2.42 (S231, S233IR), G 188.95+0.89 (S252, AFGL5180) and G 192.60-0.05 (S255IR). These radio-quiet methanol maser sites are often interpreted as precursors of ultra- compact H uf769uf769 regions or massive protostar sites. In this work, the environment of methanol masers is probed from mid-IR to millimetre wavelengths at angular resolutions of 8 �� −34 �� . Spectral energy distribution (SED) diagrams for each site are pre- sented, together with mass and luminosity estimates. Each radio-quiet maser site is always associated with a massive (>50 M� ), deeply embedded (Av > 40 mag) and very luminous (>10 4 L� ) molecular clump, with Ltotal ∝ M 0.75 gas . These physical properties characterise massive star-forming clumps in earlier evolutionary phases than H uf769uf769 regions. In addition, colder gas clumps seen only at mm-wavelengths are also found near the methanol maser sites. These colder clumps may represent an even earlier phase of massive star formation. These results suggest an evolutionary sequence for massive star formation from a cold clump, seen only at mm wavelengths, evolving to a hot molecular core with a two-component SED with peaks at far-IR and mid-IR wave- lengths, to an (ultra-compact) H uf769uf769 region. Alternatively, the cold clumps might be clusters of low-mass YSOs, in formation near the massive star-forming clusters. Finally, the values of the dust grain emissivity index (β) range between 1.6 and 1.9.

A Circumstellar Disk in a High-Mass Star-forming Region

We present an edge-on Keplerian disk model to explain the main component of the 12.2 and 6.7 GHz methanol maser emission detected toward NGC 7538 IRS 1N. The brightness distribution and spectrum of the line of bright masers are successfully modeled with high amplification of background radio continuum emission along velocity-coherent paths through a maser disk. The bend seen in the position-velocity diagram is a characteristic signature of differentially rotating disks. For a central mass of 30 M-., suggested by other observations, our model fixes the masing disk to have inner and outer radii of similar to 350 and similar to 1000 AU.

Herschel observations of the W43 "mini-starburst"

Aims: To explore the infrared and radio properties of one of the closest Galactic starburst regions. Methods: Images obtained with the Herschel Space Observatory at wavelengths of 70, 160, 250, 350, and 500 microns using the PACS and SPIRE arrays are analyzed and compared with radio continuum VLA data and 8 micron images from the Spitzer Space Telescope. The morphology of the far-infrared emission is combined with radial velocity measurements of millimeter and centimeter wavelength transitions to identify features likely to be associated with the W43 complex. Results: The W43 star-forming complex is resolved into a dense cluster of protostars, infrared dark clouds, and ridges of warm dust heated by massive stars. The 4 brightest compact sources with L > 1.5 x 10^4 Lsun embedded within the Z-shaped ridge of bright dust emission in W43 remain single at 4 (0.1 pc) resolution. These objects, likely to be massive protostars or compact clusters in early stages of evolution are embedded in clumps with masses of 10^3 to 10^4 Msun, but contribute only 2% to the 3.6 x 10^6 Lsun far-IR luminosity of W43 measured in a 16 by 16 pc box. The total mass of gas derived from the far-IR dust emission inside this region is ~10^6 Msun. Cometary dust clouds, compact 6 cm radio sources, and warm dust mark the locations of older populations of massive stars. Energy release has created a cavity blowing-out below the Galactic plane. Compression of molecular gas in the plane by the older HII region near G30.684-0.260 and the bipolar structure of the resulting younger W43 HII region may have triggered the current mini-star burst.

Multibeam maser survey of methanol and excited OH in the Magellanic Clouds: new detections and maser abundance estimates

We present the results of the first complete survey of the Large (LMC) and Small (SMC) Magellanic Clouds for 6668-MHz methanol and 6035-MHz excited-state hydroxyl masers. In addition to the survey, higher sensitivity targeted searches towards known star formation regions were conducted. The observations yielded the discovery of a fourth 6668-MHz methanol maser in the LMC, found towards the star-forming region N160a, and a second 6035-MHz excited-state hydroxyl maser, found towards N157a. We have also re-observed the three previously known 6668-MHz methanol masers and the single 6035-MHz hydroxyl maser. We failed to detect emission from either transition in the SMC. All observations were initially made using the Methanol Multibeam (MMB) survey receiver on the 64-m Parkes telescope as part of the MMB project and accurate positions have been measured with the Australia Telescope Compact Array. We compare the maser populations in the Magellanic Clouds with those of our Galaxy and discuss their implications for the relative rates of massive star formation, heavy metal abundance and the abundance of complex molecules. The LMC maser populations are demonstrated to be smaller than their Milky Way counterparts. Methanol masers are underabundant by a factor of ∼45, whilst hydroxyl and water masers are a factor of ∼10 less abundant than our Galaxy.

A tale of two cores: Triggered massive star formation in the bright-rimmed cloud SFO 75

Context. Bright-rimmed clouds (BRCs) are isolated molecular clouds located on the edges of evolved HII regions. Star formation within the BRCs may have been triggered through the propagation of photoionisation-induced shocks driven by the expansion of the HII region. Aims. The main focus of this paper is to investigate the current level of star formation within one of these clouds and evaluate to what extent, if any, star formation may have been triggered. Methods. We present a detailed multi-wavelength study of the BRC SFO 75, including 1.3 cm and 1.2 mm continuum, and 13 CO and ammonia spectral line observations. To build up a comprehensive picture of the local environment we complement our observations with archival data from the 2MASS, GLIMPSE and IRAS surveys. Results. The 13 CO and 1.2 mm emission reveals the presence of a dense core located behind the bright rim of the cloud which is approximately coincident with that of the IRAS point source. From an analysis of the IRAS and 1.2 mm fluxes we derive a dust – –

Discovery of two new methanol masers in NGC 7538 - Locating of massive protostars

Context. NGCu20097538 is known to host a 6.7 and 12.2u2009GHz methanol maser cospatial with a Ultra Compact (UC)u2009

A general catalogue of 6.7 GHz methanol masers - II. statistical analysis

ion{H}{ii}

A differentially rotating disc in a high-mass protostellar system

region, IRSxa01. Aims. We report on the serendipitous discovery of two additional 6.7u2009GHz methanol masers in the same region, not associated with IRSxa01. Methods. Interferometry maser positions are compared with recent single-dish and interferometry continuum observations. Results. The positions of the masers agree to high accuracy with the 1.2u2009mm continuum peak emission in NGCu20097538xa0IRSxa09 and NGCu20097538xa0S. This clear association is also confirmed by the positional agreement of the masers with existing high resolution continuum observations at cm and/or mm wavelengths. Conclusions. Making use of the established strong relation between methanol masers and high-mas star formation, we claim that we have accurately positioned the high-mass protostars within the regions where they are detected. The variety of objects hosting a 6.7u2009GHz methanol maser in NGCu20097538 shows that this emission probably traces different evolutionary stages within the protostellar phase.