The 6-GHz multibeam maser survey - I. Techniques

Green, James; Caswell, J. L.; Fuller, G. A.; Avison, A.; Breen, S. L.; Brooks, Kate; Burton, M. G.; Chrysostomou, A.; Cox, James; Diamond, P. J.; Ellingsen, S. P.; Gray, M. D.; Hoare, M. G.; Masheder, M. R. W.; McClure-Griffiths, N. M.; Pestalozzi, M.; Phillips, Chris; Quinn, Lyshia; Thompson, M. A.; Voronkov, M. A.; Walsh, A. J.; Ward-Thompson, Derek; Wong-McSweeney, D.; Yates, J.; Cohen, R. J.

doi:10.1111/j.1365-2966.2008.14091.x

Cited by 157 publications

(167 citation statements)

References 49 publications

Supporting

Mentioning

163

Contrasting

Order By: Relevance

“…Recently a Galactic plane survey of this maser transition using a 7-beam receiver on the Parkes telescope has been completed (Green et al 2009). These maser detections were followed up at high angular-resolution with the Australian Telescope Compact Array to obtain sub-arcsecond positional accuracy.…”

Section: Methanol Masersmentioning

confidence: 99%

ATLASGAL – compact source catalogue: 330° < ℓ < 21°

Contreras

Schüller

Urquhart

et al. 2012

A&A

237

325

View full text Add to dashboard Cite

Context. The APEX Telescope Large Area Survey of the GALaxy (ATLASGAL) is the first systematic survey of the inner Galactic plane in the sub-millimetre. The observations were carried out with the Large APEX Bolometer Camera (LABOCA), an array of 295 bolometers observing at 870 μm (345 GHz). Aims. Here we present a first version of the compact source catalogue extracted from this survey. This catalogue provides an unbiased database of dusty clumps in the inner Galaxy. Methods. The construction of this catalogue was made using the source extraction routine SExtractor. We have cross-associated the obtained sources with the IRAS and MSX catalogues, in order to constrain their nature. Results. We have detected 6639 compact sources in the range from 330 ≤ ≤ 21 degrees and |b| ≤ 1.5 degrees. The catalogue has a 99% completeness for sources with a peak flux above 6σ, which corresponds to a flux density of ∼0.4 Jy beam −1 . The parameters extracted for sources with peak fluxes below the 6σ completeness threshold should be used with caution. Tests on simulated data find the uncertainty in the flux measurement to be ∼12%, however, in more complex regions the flux values can be overestimated by a factor of 2 due to the additional background emission. Using a search radius of 30 we found that 40% of ATLASGAL compact sources are associated with an IRAS or MSX point source, but, ∼50% are found to be associated with MSX 21 μm fluxes above the local background level, which is probably a lower limit to the actual number of sources associated with star formation. Conclusions. Although infrared emission is found towards the majority of the clumps detected, this catalogue is still likely to include a significant number of clumps that are devoid of star formation activity and therefore excellent candidates for objects in the coldest, earliest stages of (high-mass) star formation.

show abstract

Section: Methanol Masersmentioning

confidence: 99%

ATLASGAL – compact source catalogue: 330° < ℓ < 21°

Contreras

Schüller

Urquhart

et al. 2012

A&A

237

325

View full text Add to dashboard Cite

show abstract

“…The MMB system is detailed in Green et al (2009). Only two beams of the receiver were used, performing beam switching with a 2 min cycle time.…”

Section: Parkes Observationsmentioning

confidence: 99%

Zeeman splitting of 6.7 GHz methanol masers

Vlemmings

Torres

Dodson

2011

A&A

View full text Add to dashboard Cite

Context. To properly determine the role of magnetic fields during massive star formation, a statistically significant sample of field measurements probing different densities and regions around massive protostars needs to be established. However, relating Zeeman splitting measurements to magnetic field strengths needs a carefully determined splitting coefficient. Aims. Polarization observations of, in particular, the very abundant 6.7 GHz methanol maser, indicate that these masers appear to be good probes of the large scale magnetic field around massive protostars at number densities up to n H 2 ≈ 10 9 cm −3 . We thus investigate the Zeeman splitting of the 6.7 GHz methanol maser transition. Methods. We have observed of a sample of 46 bright northern hemisphere maser sources with the Effelsberg 100-m telescope and an additional 34 bright southern masers with the Parkes 64-m telescope in an attempt to measure their Zeeman splitting. We also revisit the previous calculation of the methanol Zeeman splitting coefficients and show that these were severely overestimated making the determination of magnetic field strengths highly uncertain. Results. In total 44 of the northern masers were detected and significant splitting between the right-and left-circular polarization spectra is determined in >75% of the sources with a flux density >20 Jy beam −1 . Assuming the splitting is due to a magnetic field according to the regular Zeeman effect, the average detected Zeeman splitting corrected for field geometry is ∼0.6 m s −1 . Using an estimate of the 6.7 GHz A-type methanol maser Zeeman splitting coefficient based on old laboratory measurements of 25 GHz E-type methanol transitions this corresponds to a magnetic field of ∼120 mG in the methanol maser region. This is significantly higher than expected using the typically assumed relation between magnetic field and density (B ∝ n 0.47 H 2 ) and potentially indicates the extrapolation of the available laboratory measurements is invalid. The stability of the right-and left-circular calibration of the Parkes observations was insufficient to determine the Zeeman splitting of the Southern sample. Spectra are presented for all sources in both samples.Conclusions. There is no strong indication that the measured splitting between right-and left-circular polarization is due to nonZeeman effects, although this cannot be ruled out until the Zeeman coefficient is properly determined. However, although the 6.7 GHz methanol masers are still excellent magnetic field morphology probes through linear polarization observations, previous derivations of magnetic fields strength turn out to be highly uncertain. A solution to this problem will require new laboratory measurements of the methanol Landé-factors.

show abstract

“…The most recent of these searches, after having covered 60% of the galactic plane, has yielded some 800 sources (see e.g. Green et al 2009). Of these, 520 objects were already reported in the literature and show a variety of characteristics (Pestalozzi et al 2005).…”

Section: Methanol Masers Discs and Outflowsmentioning

confidence: 99%

A differentially rotating disc in a high-mass protostellar system

Pestalozzi¹,

Elitzur²,

Conway³

2009

A&A

View full text Add to dashboard Cite

Context.A strong signature of a circumstellar disc around a high-mass protostar has been inferred from high resolution methanol maser observations in NGC 7538-IRS1 N. This interpretation has however been challenged, with a bipolar outflow proposed as an alternative explanation. Aims. We compare the two proposed scenarios for best consistency with the observations. Methods. Using a newly developed formalism, we model the optical depth of the maser emission at each observed point in the map and LOS velocity for the two scenarios. Results. We find that if the emission is symmetric around a central peak in both space and LOS velocity, then it has to arise from an edge-on disc with sufficiently fast differential rotation. Disc models successfully fit ∼100 independent measurement points in position-velocity space with 4 free parameters to an overall accuracy of 3−4%. Solutions for Keplerian rotation require a central mass of at least 4 M . Close to best-fitting models are obtained if Keplerian motion is assumed around a central mass equaling ∼30 M , as inferred from other observations. In contrast, we find that classical bipolar outflow models cannot fit the data, although it could be applicable in other sources. Conclusions. Our results strongly favour the differentially rotating disc hypothesis to describe the main feature of the 12.2 (and 6.7) GHz methanol maser emission in NGC 7538 IRS1 N. Furthermore, for Keplerian rotation around a ∼30 M protostar, we predict the position and velocity at which tangentially amplified masers should be detected in high dynamic range observations. Also, our model predicts the amplitude of the proper motion of some of the maser features in our data. Confirmation of a large central mass would strongly support the idea that even the highest mass stars (>20 M ) form via accretion discs, similarly to low-mass stars. Finally we note that our new formalism can readily be used to distinguish between discs and outflows for thermal emitting line sources as well as masers.

show abstract

The 6-GHz multibeam maser survey - I. Techniques

Cited by 157 publications

References 49 publications

ATLASGAL – compact source catalogue: 330° < ℓ < 21°

ATLASGAL – compact source catalogue: 330° < ℓ < 21°

Zeeman splitting of 6.7 GHz methanol masers

A differentially rotating disc in a high-mass protostellar system

Contact Info

Product

Resources

About