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the methanol multibeam ( mmb ) survey was conceived ( by r. j. cohen and j. l. caswell together with m. sinclair , see the proceeding by j. l. caswell for further details on the historical aspect of the project ) as the first unbiased , systematic galactic plane survey for 6.7-ghz methanol masers .
6.7-ghz methanol masers are exclusively associated with high - mass star formation ( minier et al .
2003 , xu et al .
2008 ) and so are constrained to spiral arms and prominent features of galactic structure .
we expect high densities of high - mass star formation at the origins of the spiral arms and the ends of the bar and the central velocity of 6.7-ghz methanol maser emission is typically within 3 km / s of the systemic velocity ( szymczak et al .
, 2007 , pandian et al . 2009 ) .
these factors combine to make these masers ideal tracers of the structure and dynamics of the milky way , in addition to their benefits to understanding the processes of high - mass star formation .
the observations involved the initial blind survey with the parkes radio telescope using the purpose - built 7-beam receiver shown in figure 1 and covering a latitude range of @xmath02@xmath1 .
these were followed by high - resolution observations with the australia telescope compact array in order to position ( to within 0.4 arcsec ) any new sources or sources without previous high - resolution positions . finally , all detections were re - observed with the parkes telescope again , at the precise positions , to obtain high signal  to  noise spectra ( termed ` mx ' observations ) .
the main survey observations were made between 2006 january and 2007 december , whilst the mx observations were made between 2007 january and 2009 april .
the techniques of the mmb survey are detailed in full by green et al .
( 2009a ) .
the completion of the survey resulted in the detection of @xmath21000 galactic 6.7-ghz methanol masers and thus established an important legacy resource .
the survey catalogue is being released sequentially , with the first region covering galactic longitudes 345@xmath1 to 6@xmath1(caswell et al .
2010 ) , the second galactic longitudes 6@xmath1 to 20@xmath1 ( green et al .
2010 ) , the third galactic longitudes 330@xmath1 to 345@xmath1 ( caswell et al .
2011 ) , and the fourth concludes the southern hemisphere portion of the catalogue , presenting detections within galactic longitudes 186@xmath1 and 330@xmath1 ( green et al .
the last , more northerly region , galactic longitudes 20@xmath1 and 60@xmath1 , is currently in preparation .
an online database has been set up at www.astromasers.org .
follow - up observations of the 12.2-ghz methanol maser transition have been made and galactic longitudes 330@xmath1 to 10@xmath1 are presented in breen et al .
( 2012 ) and 186@xmath1 to 330@xmath1 in breen et al .
( in prep . ) .
one of the first scientific results of the survey was from the completion of a blind survey of the small and large magellanic clouds ( observed during the non - galactic hours between the main survey observations ) . a new methanol and excited - state hydroxyl maser were discovered ( bringing the respective totals to four and two ) .
comparison of the abundances of masers within the large magellanic cloud and the milky way shows maser populations are a factor of 10 - 50 times smaller in the large magellanic cloud . in more detail ,
the hydroxyl and water maser populations are about 10 times smaller than our galaxy and thus accounted for by the smaller star formation rate in the large magellanic cloud . in contrast methanol is underabundant by a factor of 50 , with the additional factor attributed to the lower metallicity of the magellanic clouds ( green et al .
2008 ) .
the second result was a simple study of the 3-kpc arms , an inner structure of the galaxy , located between the galactic bars and the spiral arms .
the near arm has long been known ( van woerden et al . 1957 ) but
the far - side counterpart was only recently discovered ( dame & thaddeus 2008 ) .
there has been a continuing question over the existence of star formation within these structures , although some evidence ( e.g. caswell and haynes , 1987 ) existed .
however , both arms were shown by 6.7-ghz methanol maser detections to clearly exhibit high - mass star formation ( green et al .
2009b ) .
following on from the previous result , 6.7-ghz methanol masers were shown to highlight regions of enhanced star formation indicating the starting points of the spiral arms and the interaction of the ( long , thin ) galactic bar ( green et al .
furthermore masers also provide many candidates for tracing the full 3-kpc arm structure ( a continuous ellipse rather than separate near and far components ) .
additionally , the 12.2-ghz methanol companions detected in the follow - up observations were found to have smaller velocity ranges and lower flux densities than their 6.7-ghz methanol counterparts ( breen et al .
there was an 80% coincidence in velocity of the strongest maser features of the 6.7-ghz and 12.2-ghz transitions .
the 12.2-ghz are associated with a later evolutionary stage and an increase in velocity range and luminosity with age was found for both transitions .
a comparison of the sites of 6.7-ghz methanol maser emission with infrared emission as detected by the glimpse survey has been made , and found @xmath380% of the maser sites had associated infrared emission ( gallaway et al . in prep . ) .
the bright and compact nature of the maser sources makes them ideal for astrometry with very long baseline interferometry ( vlbi ) .
such measurements provide accurate distances ( @xmath010 micro arcsec parallaxes ) and full three - dimensional motion ( @xmath01 km / s ) .
maser astrometry can provide valuable data for both the structure of our galaxy and its velocity field .
the nrao very long baseline array , european vlbi network and japanese vlbi network are currently being used , with @xmath230 parallaxes now published , and southern hemisphere observations are underway with the long baseline array .    another area
that this project has provided the foundation for is in the study of magnetic fields .
although the 6.7-ghz methanol maser itself can not easily be used for measuring in situ magnetic fields , due to the molecule being non - paramagnetic , the often associated hydroxyl maser can be .
as such all the detections of the mmb have been observed with the australia telescope compact array for the ground - state transitions of hydoxyl ( as part of the ` magmo ' project ) and measurements of the zeeman splitting of components will provide estimates of the in situ magnetic field strength and line - of - sight orientation .
finally it is the hope of the collaboration to follow up the survey with a northern hemisphere counterpart .
+ the mmb project is dedicated to jim cohen who sadly passed away in 2006 .
+ we are grateful to all the staff and engineers at both the parkes radio telescope and the australia telescope compact array .
a purpose built 7-beam methanol receiver , installed on the parkes radio telescope , was used to survey the galactic plane for newly forming high mass stars , pinpointed by strong methanol maser emission at 6.7 ghz . 
 the methanol multibeam ( mmb ) survey observed over 60% of the galactic plane , detecting close to 1000 sources . 
 the mmb survey provides a huge resource for studies of high - mass star formation , an important stage in the evolution of the interstellar medium . 
 the mmb survey is also a valuable resource for investigations into the structure and dynamics of our galaxy : with narrow velocity ranges of emission ( typically only a few km / s ) and velocities closely correlated with the systemic velocity of their surrounding molecular clouds , 6.7-ghz methanol masers provide estimates of the spiral arm velocities and their structure . 
 i will discuss the techniques and properties of the mmb survey , before outlining recent results , which include the identification of regions of enhanced star formation believed to be indicative of the origins of the spiral arms and the interaction of the galactic bar with the 3-kpc arms . 
 i will also discuss the various follow - up programmes including a study of magnetic fields through associated hydroxyl masers .