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research in the last decade showed that to understand the assembly and formation of massive galaxies it is critical to study submillimeter galaxies ( smgs ; see * ? ? ? * for a review ) . since their first detection ten years ago @xcite , more than three hundred dust - enshrouded high - z objects ( z @xmath72 ) have been detected by scuba and by mambo in the submillimeter and millimeter regime ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) . due to the large beam size in the ( sub)mm ( scuba : 15 , mambo : 11 ) , it is impossible to do a proper identification in other wavebands ( such as the optical and near - infrared ) based on bolometer data only . thus , typically interferometric observations at radio wavelength with the vla were used to identify the location of the smgs , yielding a radio identification rate of @xmath8% ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) , depending on both the depths of the radio and the bolometer maps . the main drawback of this technique is , however , that the radio flux is redshift dependent , whereas the ( sub)mm flux density at z  @xmath9 is not ( due to the inverse k correction ; e.g. , * ? ? ? * ) : one would thus expect the highest redshift ( z  @xmath10 ) sources ( e.g. , * ? ? ? * ) to be very faint at radio wavelengths if they were to follow the radio - fir correlation ( e.g. , * ? ? ? we note that the radio - identified smg with the highest redshift lies at z  @xmath11 @xcite . based on this sample , co observations of radio identified smgs ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) lead to the main conclusion that smgs are massive galaxies in formation and @xcite argue that the contribution to the star - formation rate density ( sfrd ) from this population is missed by uv - selected surveys . if one only uses radio - identified sources ( e.g. , * ? ? * ; * ? ? ? one thus has to be aware of the fact that the radio selection introduces a bias towards the low end of the true redshift distribution . to summarize , our knowledge about the nature and properties of the smg population is mainly based on radio - identified smgs  a biased sample . one of the open questions in the investigations of smgs is if there exists a significant very high - redshift tail ( z  @xmath12 ; e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? the existence of such a tail would not be in contradiction to constraints from measurements of the cosmic infrared background @xcite . interferometric observations in the ( sub)mm hold the promise to locate the positions of bright smgs to sub - arcsec accuracy . one of the brightest scuba sources in the goods north field is goods  850 - 5 ( wang et al . 2004 ; this source is labeled gn  10 in pope et al . 2005 ) with a submm flux @xmath13  mjy @xcite  mjy ] . until very recently this bright smg did not have a known counterpart which motivated observations with the iram plateau de bure interferometer ( pdbi ; * ? ? ? * ) to obtain an accurate position for this source . in the meanwhile , @xcite reported the location of goods  850 - 5 through sma observations . based on their detection in the submm ( and subsequent identification in ir observations ) and a 2  @xmath14 detection in the radio ( @xmath15jy ) , @xcite argue that the redshift of goods  850 - 5 is z  @xmath12 and could even lie between z  @xmath16 - with a much lower probability at z@xmath17 .    here we report the results based on our pdbi observations . we adopt the cosmological parameters @xmath18 and @xmath19 @xcite . furthermore , we assume a salpeter initial mass function from 0.1 to 100  @xmath20 . we use the ab magnitude scale @xcite . the final map resulting from our observations between december 2005 and august 2006 with the plateau de bure millimeter interferometer in c and d configuration are based on 6.8  hours of on - source observing time . the phase center ( see table [ tab : position ] ) was set at the nominal scuba position published in @xcite . the source was observed in the 1  mm and 3  mm band simultaneously . the 1  mm receiver was tuned at 240.000  ghz ( corresponding to 1.25  mm ) to obtain an accurate position . the 3  mm receiver was tuned to 98.3188  ghz , i.e. , the frequency of the co(2 - 1 ) transition redshifted to z  @xmath21 . this is the redshift of the optical source goods850 - 5a @xcite which is situated close ( @xmath22 ) to the scuba bolometer position . the total bandwith of 580  mhz covers a redshift space of @xmath23 at that redshift ( i.e. within the redshift uncertainty of the source , cf : z  @xmath24 in cohen et al . 2000 and pope et al . 2006 ; z  @xmath25 in wang et al . 2004 ; z  @xmath26 in wirth et al . 2004 ) . the data were calibrated through observations of standard bandpass ( 3c273 , j0418@xmath0380 ) , phase / amplitude ( 1044@xmath0719 , 1150@xmath0497 ) and flux calibrators ( crl  618 , 3c273 , 1044@xmath0719 , 1150@xmath0497 ) and reduced with the gildas software packages clic and map . the fwhm of the beam is @xmath27 at 240  ghz and @xmath28 at 98.3  ghz . we detected the dust continuum emission of goods  850 - 5 at 5 @xmath14 significance at @xmath29  mjy . the derived position is ra(j2000)@xmath3012:36:33.45 , dec(j2000)@xmath30 62:14:08.95 ( hereafter : mm  j123633@xmath06214.1 ) with an estimated position uncertainty of @xmath310.3 . the position and flux density of mm  j123633@xmath06214.1 are derived from point source fits of the visibilities in the uv plane and are consistent with the values derived in the image plane . the difference between the scuba @xcite and our millimeter interferometric position is only 0.02   in ra and 0.48   in dec , and our position is consistent with the sma position from @xcite , see summary in table  [ tab : position ] . in the 3  mm band no line was detected down to a rms of 0.8  mjy  beam@xmath32 ( channel width : 40  mhz , 120  km  s@xmath32 ) on the position of the optical source at z  @xmath21 ( and also at the position of goods  850 - 5 ) . this corresponds to an upper limit ( 3  @xmath14 ) of the integrated flux intensity of 1.2  jy  km  s@xmath32 , adopting a typical co width for a smg of 500  km  s@xmath32 ( e.g. , * ? ? ? * ) . however , we note that a number of co detections of smgs have even lower integrated flux intensities than this 3  @xmath14 upper limit ( e.g. , * ? ? ? * ) . we have used new , deep vla radio continuum observations ( morrison et al . 2008 ) to constrain the radio flux density of goods  850 - 5 . these observations reveal a highly significant radio source ( @xmath33jy ) ; i.e. a source that is significantly brighter than the upper limit reported in @xcite . our derived flux density is however in agreement with the 3  @xmath14 detection reported in @xcite . the radio emission is unresolved with a fwhm  @xmath34 .    in our analysis , we use the exquisite multi - wavelength dataset available for the goods north field ( e.g. , alexander et al . 2003 ; giavalisco et al . 2004 ; dickinson et al . , in preparation ) and have corrected these data products for the offset of 0.38 in declination between vla and the goods imaging products ( see also * ? ? ? the pdbi / vla source is undetected in the deep acs images down to @xmath35  mag . however goods  850 - 5 is detected at low significance in spitzer irac measurements at the few @xmath4jy level @xcite as summarized in table [ tab : flux ] . the source is also detected at 24  @xmath4 m ( table  [ tab : flux ] ) but undetected both at mips 70  @xmath4 m and 160  @xmath4 m at a 3  @xmath14 level ( @xmath36  mjy and @xmath37  mjy ) . however , due to the large beam size ( 18 at 70  @xmath4 m and 40 at 160  @xmath4 m ) our source would be confused with other objects within the beam . we conclude that the irac counterpart presented in @xcite is the proper counterpart of mm  j123633@xmath06214.1 m fluxes by @xcite are consistent within 1.5  @xmath14 with the measurements reported by @xcite ] .    due to the lack of a spectroscopic identification , we apply several photometric redshift estimators focusing on different parts of the sed in order to put constraints on the possible redshift range of the source . applying the radio/(sub)millimeter index @xcite on the pdbi flux and the radio flux we estimate a redshift z@xmath38 . furthermore , we use the infrared galaxy sed templates from @xcite to fit the sed of our source ( using the mips  24  @xmath4 m , scuba , pdbi and vla flux ) and this method proposes a redshift of z  @xmath39 ,  within the errors consistent with the radio/(sub)mm spectral index estimates  and infrared luminosity @xmath40 . we obtain the same result by only using the mips  24  @xmath4 m and the vla flux . the use of the 850/1.2  mm ratio as a proper redshift indicator is very limited ( see fig .  13 in * ? ? ? * ) . however , the scuba to pdbi flux ratio of 2.6 limits the possible redshift range from z  @xmath41 ( see plot in * ? ? ? as @xcite we have also applied the widely used photometric redshift code _ hyperz _ @xcite on the optical / near - infrared data from acs and irac . our redshift estimates give a redshift z  @xmath6 , i.e. consistent with the range of values proposed by @xcite . however , we note that with this method only the stellar component of the source is fitted and the applied templates do not reflect the characteristic properties of infrared galaxies .    assuming a redshift z  @xmath5 , taking into account the optical / near - ir measurements from acs / spitzer and applying the reddening law by @xcite we estimate the extinction to be a@xmath42 . for comparison , @xcite and @xcite derived for smg samples mean reddening of a@xmath43 and 3.0 , based on optical / near - ir colors . the source is undetected both in the soft ( 0.5 - 2  kev ) and hard ( 2 - 8  kev ) bands in the 2  ms chandra observations of goods north ( e.g. , * ? ? ? however , the lack of x - ray detection can not exclude the presence of an heavily obscured agn in goods  850 - 5 . using irac , @xcite proposed a diagnostic tool in order to distinguish between agn and starburst as dominating energy source . applying this tool on mm j123633@xmath06214.1 would propose an agn at redshift z  @xmath44 . however , we note that @xcite and @xcite pointed out that starbursts at z  @xmath5 contaminate the irac selection for z  @xmath45 agns .    using either the template fitting from @xcite ( resulting in an infrared luminosity @xmath40 and taking into account the conversion between infrared luminosity @xmath46 and sfr @xcite ) , we derive a star formation rate sfr  @xmath47 . by simply using the pdbi flux of 5.0  mjy at 1.25  mm we obtain a star formation rate sfr  @xmath48 @xcite . this is consistent with the sfr derived from the radio flux for a source at z  @xmath5 of sfr  @xmath49 ( see discussion in ivison et al . 2002 ) . we conclude that the multi - wavelength data suggests that mm  j123633@xmath06314 is a starburst at z  @xmath504 .      a total of 21 smgs in goods north are securely identified @xcite . in addition to mm  j123633@xmath06214.1 there are four smgs that have even fainter vla 20  cm fluxes ( @xmath51jy ) than our source . similar to the counterpart of mm j123633@xmath06214.1 none of them has an acs counterpart and their irac fluxes are faint ( @xmath52jy ) . one of these smgs is the well - studied source hdf850.1 @xcite which is one of the excellent candidates to lie at z  @xmath5 or higher . to summarize , about 20% of securely identified smgs could lie at high redshift z  @xmath5 or higher . @xcite and @xcite also reported the discovery of reliable candidates of redshift z  @xmath5 or higher in other deep fields . we have used the iram plateau de bure interferometer to obtain an accurate position and flux at 1.3  mm wavelengths of the smg mm  j123633@xmath06214.1 alias goods 850 - 5 ( @xmath1  mjy ) . this source is coincident with a source detected in deep vla radio continuum observations at high significance ( @xmath33jy ) . the source has also been detected by recent observations obtained at the sma @xcite and by spitzer @xcite in the irac and 24  @xmath4 m bands . the photometric redshift indicators using the mir- and fir sed of mm  j123633@xmath06214.1 all point towards a redshift of z  @xmath5 . based on our millimeter and radio detection , we consider a much higher redshift ( z  @xmath6 , as proposed by wang et al . 2007 ) unlikely . however , only future facilities with wide mm - receivers planned e.g. the upgraded pdbi or the lmt will unambiguously solve the question of the true redshift of goods  850 - 5 ( alma will unfortunately not be able to reach goods north ) . in any case , goods  850 - 5 represent one of the few solid candidates of a high - z ( z  @xmath10 ) smg that contribute to the cosmic sfrd at early cosmic times .    we would like to thank the iram staff for help provided during the observations and especially arancha castro - carrizo and roberto neri for helpful support during the data reduction at iram grenoble . furthermore , we are grateful to dave frayer for 70 and 160  @xmath4 m measurements on the pdbi position and emanuele daddi for instructive conversations and help in applying the @xcite sed templates on goods  850 - 5 . finally , we appreciate the comments of the anonymous referee which clarified a number of points and improved our manuscript . acs @xmath53 , irac 8.0  @xmath4 m , mips  24  @xmath4 m and radio images of the field of mm  j123633@xmath06214.1 . pdbi contours of 1.25 continuum emission of mm  j123633@xmath06214.1 overlaid on the acs @xmath53 image and start at 3@xmath14 with steps of 1  mjy . 3.0 circles are drawn on the pdbi position in the irac 8.0  @xmath4 m , mips  24  @xmath4 m and radio images . ]
we have obtained a position ( at sub - arcsecond accuracy ) of the submillimeter bright source goods  850 - 5 ( also known as gn10 ) in the goods north field using the iram plateau de bure interferometer at 1.25  mm wavelengths ( mm  j123633@xmath06214.1 , flux density : @xmath1  mjy ) . 
 this source has no optical counterpart in deep acs imaging down to a limiting magnitude of i@xmath2  mag and its position is coincident with the position found in recent sub - millimeter mapping obtained at the sma @xcite . using deep vla imaging at 20  cm , we find a radio source ( @xmath3jy ) at the same position that is significantly brighter than reported in wang et al . 
 the source is detected by spitzer in irac as well as at 24  @xmath4 m . we apply different photometric redshift estimators using measurements of the dusty , mid / far - infrared part of the sed and derive a redshift z  @xmath5 . 
 given our detection in the millimeter and radio we consider a significantly higher redshift ( e.g. , z  @xmath6 * ? ? ? 
 * ) unlikely . 
 mm  j123633@xmath06214.1 alias goods  850 - 5 nevertheless constitutes a bright representative of the high - redshift tail of the submillimeter galaxy population that may contribute a significant fraction to the ( sub)millimeter background .