Astronomy. Astrophysics. Looking for high-mass young stellar objects: H 2 O and OH masers in ammonia cores

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1 DOI: / / c ESO 2010 Astronomy & Astrophysics Looking for high-mss young stellr objects: H 2 O nd OH msers in mmoni cores C. Codell 1, R. Cesroni 1, A. López-Sepulcre 1, M. T. Beltrán 1, R. Furuy 2, nd L. Testi 1,3 1 INAF, Osservtorio Astrofisico di Arcetri, Lrgo E. Fermi 5, Firenze, Itly e-mil: [codell;ces;sepulcre;mbeltrn;lt]@rcetri.stro.it 2 Subru Telescope, Ntionl Astronomicl Observtory of Jpn, 650 North A ohoku Plce, Hilo, HI 96720, USA e-mil: rsf@subru.noj.org 3 ESO, Krl Schwrzschild srt. 2, Grching, Germny e-mil: ltesti@eso.org Received 29 September 2009 / Accepted 5 November 2009 ABSTRACT Context. The erliest stges of high-mss str formtion hve yet to be chrcterised well, becuse high-ngulr resolution observtions re required to infer the properties of the moleculr gs hosting the newly formed strs. Aims. We serch for high-mss moleculr cores in lrge smple of 15 high-mss str-forming regions tht re observed t highngulr resolution, extending pilot survey bsed on smller number of objects. Methods. The smple ws chosen from surveys of H 2 O nd OH msers to fvour the erliest phses of high-mss str formtion. Ech source ws first observed with the 32-m single-dish Medicin ntenn in the (1, 1) nd (2, 2) inversion trnsitions t 1.3 cm of mmoni, which is n excellent trcer of dense gs. High-resolution mps in the NH 3 (2, 2) nd (3, 3) lines nd the 1.3 cm continuum were obtined successively with the VLA interferometer. Results. We detect continuum emission in lmost ll the observed str-forming regions, which corresponds to extended nd UCHii regions creted by young stellr objects with typicl luminosities of 10 4 L. However, only in three cses do we find projected overlp between Hii regions nd H 2 O nd OH mser spots. On the other hnd, the VLA imges detect eight mmoni cores closely ssocited with the mser sources. The mmoni cores hve sizes of 10 4 AU, nd high msses (up to 10 4 M ), nd re very dense (from 10 6 to few 10 9 cm 3 ). The typicl reltive NH 3 bundnce is 10 7, in greement with previous mesurements in highmss str-forming regions. Conclusions. The sttisticl nlysis of the distribution between H 2 OndOHmsers,NH 3 cores, nd Hii regions confirms tht the erliest stges of high-mss str formtion re chrcterised by high-density moleculr cores with tempertures of on verge 30 K, either without detectble ionised region or ssocited with hypercompct Hii region. Key words. strs: formtion strs: evolution ISM: clouds ISM: molecules rdio lines: ISM 1. Introduction Understnding the process of high-mss (O-B type) str formtion represents chllenge from both theoreticl nd observtionl point of view. While low-mss strs re believed to form by mens of ccretion onto protostr, more high-mss strs re expected to exert strong rdition pressure on the inflling gs, thus hlting the ccretion bove M str 8 M (Wolfire & Cssinelli 1987; Pll & Sthler 1993). To circumvent this theoreticl problem, two lterntive modes of high-mss str formtion hve been proposed (Sthler et l. 2000): (i) ccretion t high rte cross thin disk; nd (ii) colescence of dense cluster of lower mss strs (e.g., Bonnell & Bte 2005; Bonnell et l. 2007), lthough the controversy remins (e.g., Bonnell et l. 2007; Beuther et l. 2007). Discriminting between these possibilities is chllenging observtionl tsk mostly becuse high-mss strs form in rich clusters tht emit copious mounts of ionising photons tht profoundly lter the surrounding environment. This mkes it very difficult to scertin the primordil configurtion of the moleculr cloud tht represents the initil conditions of str formtion. Therefore, observtionl studies of high-mss str-forming regions (SFRs) must consider moleculr cores contining young stellr objects (YSOs) tht re still in very erly phse of their evolution so tht in their impct on the surrounding mteril should be limited. One possibility is to identify the erliest stges of high-mss SFRs by mens of mmoni (NH 3 ) emission, which trces highdensity cores tht host newly born O-B type strs. As first step, we conducted survey towrds 6 SFRs with the Very Lrge Arry (VLA), to detect emission t 1.3 cm of mmoni inversion trnsitions. The results llowed us to identify 4 sites of high-mss str formtion in phse prior to the ppernce of n ultrcompct (UC) Hii region (Codell et l. 1997, herefter Pper I). This successful survey hs led to extensive follow-up studies t cm- nd mm-wvelengths tht detected the unique cse of G A1, n object chrcterised by ll the ingredients of typicl high-mss str formtion recipe : 20 M str surrounded by hypercompct Hii region, driving SiO jet nd CO bipolr outflow, nd locted t the center of rotting toroid undergoing infll towrds the str (Furuy et l. 2002; Cesroni et l. 2003; Beltrán et l. 2004, 2005, 2006). These findings support the ccretion scenrio, but need to be consolidted on sttisticl grounds by observing more objects of this type. With this in mind, we extended the pilot VLA survey reported in Pper I to lrger smple of trgets. The finl gol Article published by EDP Sciences Pge 1 of 16

2 of the whole project is to ssess how n O-B-type str forms. The min im of the new observtions is twofold: (i) to imge nd chrcterise the ntl high-density cores tht hve not yet been destroyed by the high-mss YSOs, nd (ii) to identify the youngest nd most promising objects t which to pply the sme follow-up studies performed for G Source selection In order to obtin sttisticlly relible results, we selected 15 objects from homogeneous VLA surveys towrds wter msers in high-mss YSOs (Hofner & Churchwell 1996; Forster& Cswell 1989, 2000). Interstellr 22.2 GHz wter mser emission represents n excellent tool to serch for young protostrs, becuse it is ssocited with hot moleculr cores (HMCs) where the newly formed str is efficiently heting the surrounding medium up to tempertures of hundreds of Kelvin (Cesroni et l. 1994; Hofner & Churchwell 1996; Kurtz et l. 2000). Severl sources of the observed smple re lso ssocited with OH msers t 1.7 GHz (Forster & Cswell 1989), which re usully excited in the mteril surrounding lredy formed UC Hii regions s well s moleculr outflows (e.g., Wlsh et l. 2003). Finlly, in some sources of the present smple, Clss II 6.7 GHz methnol (CH 3 OH) msers hve lso been detected (Wlsh et l. 1998), which re nother excellent tool for the erliest phses of OB-type str formtion (e.g., Wlsh et l. 2001, 2003). The H 2 O mser positions hve n ccurcy of To bis the smple towrds the youngest sources, we selected msers tht re not ssocited with developed Hii regions. Tble 1 lists nmes, coordintes used s phse centers for the present VLA observtions, locl stndrd-of-rest (LSR) velocities, nd kinemticl distnces from the literture. We note tht for G no distnce mesurement ws found in the literture, wheres for G , G , G , G , nd G , the distnces vilble in literture were derived using Glctocentric distnce of 10 kpc. For these sources, we derived revised distnce by using the Glctic rottion curve of Brnd (1986), which ssumes the distnce of 8.5 kpc to the Glctic Centre. 3. Observtions nd dt reduction 3.1. Single-dish Medicin observtions The Medicin 32-m rdiotelescope ws used during severl runs in October 2002 nd My 2004 to observe the NH 3 (1, 1) nd (2, 2) inversion trnsitions t nd MHz, respectively. The hlf power bem width (HPBW) is The zenith system temperture rnged from 200 K to 800 K depending on wether conditions. The ntenn efficiency ws 0.38 nd the mximum gin 0.11 K Jy 1. The intensity scle of the spectr ws clibrted on the continuum source DR21, with resulting uncertinty of 20%. The spectr were corrected for telescope chnges with elevtion. The pointing ccurcy is round 20. The observtions hve been performed in position-switching mode with 5 min integrtion time on-source nd 5 min offsource. Severl scns of ech source were obtined for totl integrtion time between 30 nd 140 min. The resulting rms noise is of between 0.05 nd 0.15 K in min brightness temperture. The spectr were obtined with 1024-chnnel utocorreltor spectrometer, bndwidth of 8 MHz, nd totl velocity coverge of 130 km s 1, which produces lines brod enough Tble 1. Coordintes used s phse centers for the VLA observtions, LSR velocities of the cloud nd distnces. Source α δ V LSR d b (J2000) (J2000) (km s 1 ) (kpc) G :12: :24: c G M 18:12: :24: c G :16: :39: d G :34: :31: e G :48: :33: e G :48: :36: e G :48: :26: c G :51: :12: e G :54: :01: e G :58: :40: f G :01: :13: f G :14: :22: g G :20: :55: e G :21: :44: g G :21: :26: g Notes. () Bsed on the present single-dish survey for ll sources but G (single-dish CS survey, Plume et l. 1992), G (bsed on the H 2 O mser emission pttern, Angld et l. 1996), G (present VLA dt), nd G (single-dish CS survey, Bronfmn et l. 1996). (b) Whenever the ner-fr mbiguity is not resolved out both vlues re reported. (c) Wlsh et l. (1997). (d) Plume et l. (1992). (e) Present work. ( f ) Zhng et l. (2009). (g) Hofner & Churchwell (1996). to cover both ΔF = 0, 1 stellites. The spectrl resolution ws 0.11 km s 1, smoothed to 0.5 km s 1 when needed. The conversion fctor from min bem brightness temperture to flux density is 5.6 Jy K Interferometric VLA observtions The sources were observed with 26 ntenns of the NRAO Very Lrge Arry (VLA) to mesure the (2, 2) nd (3, 3) ( nd MHz, respectively) inversion trnsitions of mmoni nd the 1.3 cm continuum emission. The observtions were crried out in the K-bnd with the C-configurtion on 2004 Februry, 22 nd 27, nd 2004 Mrch, 13 nd 18. The HPBW of the ntenns is 2. 3, which infers the field-of-view of the imges. The lrgest structure visible in the C-configurtion is 30. The phse centers of the 15 sources re listed in Tble 1. The NH 3 (2, 2) line nd the continuum were observed simultneously by using the correltor in 2 IF mode: (i) 6.25 MHz bndwidth centered on the line frequency, with spectrl resolution of khz (2.468 km s 1 ); (ii) 25 MHz bndwidth centered on MHz to collect continuum emission. For the NH 3 (3, 3) line, only one IF ws used, centered on the line rest frequency, with 12.5 MHz bndwidth, nd spectrl resolution of khz (9.811 km s 1 ). As for the Medicin observtions, the bndwidths were chosen for both lines to be brod enough to cover ll the hyperfine components. The observtions were performed in fst-switching mode for totl integrtion time for ech source of bout 20 min. Bndpss nd phse were clibrted by observing , , nd , while the flux density scle ws derived by observing All dt editing nd clibrtion were crried out using the tsks in the NRAO AIPS pckge. When both line nd continuum were detected, following Pper I, the line cubes were obtined by subtrcting the continuum from Pge 2 of 16

3 C. Codell et l.: Looking for high-mss young stellr objects: H 2 O nd OH msers in mmoni cores Fig. 1. Contour plots of the rdio continuum emission in the sources where it hs been detected. The squres, green circles, nd mgent tringles mrk the positions of the H 2 O, CH 3 OH, nd OH mser spots, respectively (Forster & Cswell 1989; Wlsh1998). The rms 1σ of the mps is 8 mjy bem 1 (G ), 2 mjy bem 1 (G , G , G , G ), nd 10 mjy bem 1 (G ), while the first (negtive) contours nd the steps correspond to 3 ( 3; dotted contour) nd 12σ, respectively, for ll the sources prt from G nd G , where the step corresponds to 6 nd 24σ. The ellipses in the bottom-right corners show the HPBW. the line. Imges were produced using nturl weighting, nd restored with typicl clen bem of , nd finl rms noise of mjy bem 1, depending on the source. 4. Continuum emission For 12 out of the 15 sources of the entire smple, we detected continuum emission in the observed field. For two cses (G , G ) two Hii regions were observed (lbelledndbinfig.2), wheres for G , prt from compct emission, two elongted structures, probbly ssocited with rdio-jet oriented in the N-S direction nd detected in the mid- nd ner-ir (Fuller et l. 2001; De Buizer 2006) were detected (lbelled jet1 nd jet2 in Fig. 2). Detils of individul sources re reported in Sect. 5. Figures 1 nd 2 report the contour mps, s well s the positions of the H 2 O, OH (tringles), nd CH 3 OH (only for G nd G , plus G , not detected in continuum) mser spots, observed by Forster & Cswell (1989) nd Wlsh et l. (1998). The results confirm the findings of our previous survey (Pper I): the mser spots re observed in the sme region, but in most cses they do not coincide positionlly with free-free continuum source, thus trcing different str-forming site. Three exceptions re G , G B, nd G On the other hnd, the CH 3 OH mser groups in G nd G do not hve ny continuum counterprt. In Tble 2, we report the min prmeters of the continuum emission in the detected sources: the position of the pek, the flux mesured t this position (F pek ), the corresponding synthesized bem brightness temperture (T SB ), the observed ngulr dimeter t hlf power of the emitting region (Θ HP ), the bem deconvolved ngulr dimeter (Θ S ), nd the integrted flux density over the whole emitting region (S ν ). For the sources sptilly unresolved, we rbitrrily ssume bout one third of the synthesized bem s representing n upper limit to Θ S.In Tble 3, we providethe upperlimits to the non-detectedsources, corresponding to 3σ rms vlues. In Tble 4, the min physicl quntities of the relted Hii regions re given, nmely: the physicl dimension (D); the excittion prmeter (U); the electron density (n e ); the number of Lymn continuum photons emitted by the str per unit time (N Ly ), computed s in Pper I using the formule of Schrml & Metzger (1969) nd bsed on the ssumption of opticlly thin emission t 1.3 cm; the luminosity (L bol ); nd the spectrl type of the str, derived from U using the tbles of Pngi (1973). The properties of the Hii regions will be discussed in Sect. 4.2 in the context of the NH 3 observtions Continuum non-detections We used the upper limits to the continuum emission to constrin the prmeters of the (possibly) undetected Hii regions, s in Pper I. For sphericl, homogeneous, nd isotherml Hii region of given electron temperture (T e ), the pek T SB t given frequency is function of only the Strömgren rdius (R S ) nd N Ly. Thus, for given distnce nd frequency it is possible to derive the brightness temperture expected in our synthetised bem T SB (clc) s function of R S nd N Ly. Pge 3 of 16

4 Fig. 2. Contour plots of the rdio continuum emission in the sources where it hs been detected. The squres nd mgent tringles mrk the positions of the H 2 O nd OH mser spots, respectively (Forster & Cswell 1989;Wlsh1998). The rms 1σ of the mps is 2 mjy bem 1 (G ), 3 mjy bem 1 (G ), 8 mjy bem 1 (G , G ), 4 mjy bem 1 (G ), 5 mjy bem 1 (G ), while the first (negtive) contours nd the steps correspond to 3 ( 3; dotted contour) nd 12σ, respectively. Tble 2. Prmeters of the observed continuum sources shown in Figs. 1 nd 2. Nme α δ F pek T SB Θ HP Θ S S ν (J2000) (J2000) (mjy bem 1 ) (K) ( ) ( ) (mjy) Hii regions sptilly coincident with H 2 O msers G :51: :12: G B 18:54: :01: G :58: :40: Hii regions not ssocited with H 2 O msers G :12: :24: G :48: :26: G :48: :33: G :48: :36: G A 18:54: :01: G A 19:01: :13: G B 19:01: :13: G :14: :22: G :20: :55: G :21: :44: G :21: :26: Notes. () When the mmoni cores re not sptilly resolved, Θ HP is mesure of the HPBWs of the NH 3 (2, 2) nd (3, 3) mps, wheres we rbitrrily ssume bout one third of the synthesized bem s n upper limit (used to derive the prmeters listed in the tble) on Θ S (see text). Figure 3 plots curves of constnt T SB corresponding to 3σ upper limits (see Tble 3): for ech source, only points of the R S N Ly plne flling below the corresponding curve (i.e., stisfying the condition T SB (clc) T SB (mesured)) re llowed. Ech curve cn be divided into three sections: (1) t low R S,the size remins constnt nd corresponds to opticlly thick nd unresolved Hii regions; (2) the curve then shows section where N Ly is constnt, corresponding to n unresolved opticlly thin source; (3) t high R S, we hve resolved nd opticlly thin Hii region, with N Ly R S 2. Given the selection criteri, it is resonble to ssume when looking t Fig. 3 tht if ny UC Hii is ssocited with the mser spots, it my not be detected if it is either too smll (< pc) nd opticlly thick or too fint (N Ly < s 1, depending on the source) nd opticlly thin. These two possibilities cn be discriminted by estimting the luminosity of the Pge 4 of 16

5 C. Codell et l.: Looking for high-mss young stellr objects: H 2 O nd OH msers in mmoni cores Tble 3. Upper limits (3σ rms) of the 1.3 cm continuum emission t the H 2 O mser position. Nme F pek T SB (mjy bem 1 ) (K) G <2.7 <3.9 G M <1.2 <1.8 G <0.6 <0.9 G <0.3 <0.6 G <0.6 <1.2 G <2.7 <5.1 G <0.6 <0.9 G <3.0 <6.3 G <2.4 <4.5 G <0.9 <1.5 G <0.9 <1.2 G <2.4 <4.5 Fig. 3. Curves corresponding to constnt vlues of pek brightness temperture in the synthesised bem of sphericl, homogeneous, nd isotherml (T e = K) Hii region. R S nd N Ly re the Strömgren rdius nd the Lymn luminosity, respectively. On the right-hnd-side xis, the spectrl types corresponding to N Ly ccording to Pngi (1973) re indicted. The contours correspond to the 3σ upper limits in units of T SB (see Tble 3). region. This cn be chieved for subsmple of mser sources (those reported in Fig. 3), which re ssocited with IRAS point sources. In this wy, we obtin high luminosities (between nd L ) for ll the sources prt from G ( L ;spectrltype B1): the corresponding spectrl type vlues suggest the opticlly thick nd sptilly unresolved cse, supporting the ssocition of H 2 O msers with the erliest evolutionry stges of high-mss str formtion. Given the low ngulr resolution of the IRAS ctlogue, we note tht the corresponding IRAS bolometric luminosities should be considered s upper limits. As reported in Pper I, it is resonble to expect vlues lower by fctor 5. Nevertheless, lthough it is cler tht only future detections of ionised sources will prove this scenrio, this reduction is not enough to invlidte the present suggestion. 5. Ammoni emission 5.1. Line spectr We detected NH 3 (1, 1) nd (2, 2) emission in 11 sources (ll but G , G , G , nd G ) with the single-dish Medicin ntenn. The spectr re described in Figs The 3σ rms upper limits for sources undetected with Medicin re 60 mk (G , G , G ) nd 120 mk (G ). Tble 5 summrises the observed mmoni spectr prmeters: for ech line trnsition we indicte the min bem brightness temperture (T MB ), the rms noise, the LSR velocity (V LSR ), nd the FWHM linewidth (ΔV) of ech hyperfine component. Finlly, when the stellite lines re detected, we derive the totl opticl depth over ll the hyperfine components of trnsition (τ tot, see Ungerechts et l. 1986). By using the VLA, we serched for NH 3 (2, 2) nd (3, 3) emission, detecting both lines in 11 of the 15 observed objects: i.e., ll prt from G , G , G , nd G One sees tht G is detected only in the single-dish spectrum, wheres G ws detected only with the VLA. The VLA 3σ rms upper limits for the undetected sources re 0.6 nd 0.3 K for the NH 3 (2, 2) nd (3, 3) lines, respectively. Figures 3 5 show the VLA spectr, obtined by integrting over the whole re where mmoni emission is detected. We note tht the Medicin NH 3 (1, 1) spectr were smoothed to 1 km s 1 resolution, wheres the NH 3 (2, 2) spectr were smoothed to the resolution of the VLA spectr (2.5 km s 1 ) to llow direct comprison. The min line-intensity rtios of the Medicin to VLA spectr re >1 for ll the sources prt from G , where the rtio is 1. We note tht, besides G , G , nd G , the lines observed with the single-dish re more intense by t lest n order of mgnitude. This suggests tht, s found in Pper I, there is n importnt contribution from n extended emission filtered out by the VLA mesurement. In ddition, for three sources (G , G M, nd G ) the rtio of the hyperfine stellites to the min line (indicted by the verticl mrks in Figs. 3 5) is higher in the VLA spectr. This finding grees with the occurrence of compct opticlly thick core embedded inside n opticlly thinner envelope (see lso Pper I). In conclusion, including the 6 sources observed in Pper I, we hve detected NH 3 in 18 (86%) out of smple of 21 wter mser sites, confirming close ssocition of H 2 O msers with dense mmoni cores. In the next section, we investigte in more detil the distribution of the mmoni emission Ammoni cores hosting H 2 O msers Figures 7 10 show the mps of the NH 3 (2,2) nd NH 3 (3,3) emission integrted beneth the min line. Five sources (G , G , G , G , nd G ) exhibit wek nd/or extended emission nd do not hve distinctive morphology. This could be cused by more extended ( 40 ) emission tht is filtered out by the VLA interferometer. On the other hnd, 6 regions re ssocited with 1 or 2 NH 3 cores (8 in totl), defined here s bright nd roundish structures: G (A nd B), G M, G , G (A nd B), G , nd G Tble 6 summrises the mmoni prmeters (T MB, V LSR, ΔV, τ tot ) for the sources with extended emission, wheres Tble 7 reports those for the 8 NH 3 cores. The corresponding NH 3 (2, 2) nd (3, 3) bem-verged spectr re reported in Fig. 11. In Figs. 7 10, we mrk the positions of the H 2 O spots (Forster & Cswell 1989) with blck squres. The positions of the OH (tringles) nd, in three cses, CH 3 OH (G , G , nd G ; circles) spots re reported Pge 5 of 16

6 Tble 4. Derived physicl quntities of the Hii regions. Nme d D U n e N Ly L bol Spectrl (kpc) (pc) (pc cm 2 ) (cm 3 ) (10 46 s 1 ) (L ) Type Hii regions sptilly coincident with H 2 O msers G B0.5 G B B1 G B2 Hii regions not ssocited with H 2 O msers G O6.5 G O9 G B0 G B0 G A B0.5 G A O7.5/O8 G B O9.5/B0 G O9.5 G B0 G O9.5 G B0.5 Fig. 4. Comprison between the spectr observed with Medicin nd VLA. The VLA spectr were derived by verging the emission over n re covering the whole emitting regions (see text). The verticl lines mrk the positions of the hyperfine stellites. (Wlsh 1998; Forster & Cswell 1989). The mps confirm the close ssocition of both the H 2 O nd OH msers with mmoni emission. We note lso from the kinemticl point of view tht there is good greement between H 2 O, OH, nd NH 3 emission, where the velocities of the mser spots re within 20 km s 1. On the other hnd, the three CH 3 OH mser groups seem to correspond to different sources: they re observed towrds both n mmoni clump in G nd wek nd extended moleculr structure in G , wheres in G they re not ssocited with ny mmoni emission. In G nd G , there is good greement between the CH 3 OH nd NH 3 velocities (to within 10 km s 1 ). Pge 6 of 16

7 C. Codell et l.: Looking for high-mss young stellr objects: H 2 O nd OH msers in mmoni cores Fig. 5. Comprison between the spectr observed with Medicin nd VLA. The VLA spectr were derived by verging the emission over n re covering the whole emitting regions (see text). The verticl lines mrk the positions of the hyperfine stellites. By compring the mmoni nd continuum distributions (see Figs. 1 nd 2), we see tht ll 8 moleculr cores pert from G B show mser emission nd no Hii region. This result is outlined in the zoom-in of Fig. 12, where the contour plots of the NH 3 (2, 2) nd (3, 3) line stellites, which, being opticlly thinner with respect to the min line component, re expected to trce the densest prt of the mmoni cores. In prticulr, we plot the G , G M, nd G regions, i.e., those where both the NH 3 (2, 2) nd (3, 3) stellites re clerly detected. The upper pnels of Fig. 12 show superposition of the sptil distribution of the NH 3 (2, 2) stellites on tht of the 1.3 cm continuum, wheres the lower pnels compre the mps of the NH 3 (3, 3) min line with tht of the corresponding stellites. In summry, compring the 1.3 cm continuum nd NH 3 mps presented here nd in Pper I, we obtin the following results: 1. in 8 (38%) out of 21 cses, no 1.3 cm continuum emission hs been detected; 2. in only 4 (19%) cses (the three of the present pper plus G A) out of 21, the projected position of the H 2 O nd OH mser spots coincides with tht of the Hii regions. The size of these ionised regions is unresolved ( ), except in the cse of G , whose size is pc. On the other hnd, the Hii regions present in the observed SFRs but not ssocited with the mser groups re sptilly resolved in ll cses prt form G nd G A, with lrger sizes, of up to 0.43 pc, of on verge 0.1 pc; 3. in 5 cses (see the G , G , G , G , nd G mps), the mser spots re offset from the UCHii regions detected in the sme field. The offsets re in the rnge 2 16, i.e., of projected distnce between 0.06 nd 0.39 pc. In prticulr, in the 3 cses where n NH 3 core nd n UCHii region hve been observed in the sme SFR (G , G , G ), the verge distnce between the mser spots nd the ionised region is up to 10 times lrger thn tht between mser spots nd mmoni cores. In the light of these results, we cn confirm tht H 2 OndOH msers trce moleculr cores representing the erly stges of high-mss str formtion, prior to the development of detectble ionised region or ssocited with hypercompct Hii regions Prmeters of the mmoni cores Using the NH 3 (1, 1) nd (2, 2) spectr observed with Medicin nd ssuming tht the mmoni energy levels re populted ccording to LTE, we estimted the rottion temperture (T rot )nd Pge 7 of 16

8 Fig. 6. Comprison between the spectr observed with Medicin nd VLA. The VLA spectr were derived by verging the emission over n re covering the whole emitting regions (see text). The verticl lines mrk the positions of the hyperfine stellites. the totl column density (N tot ). The results re summrised in Tble 8. We confirm the findings of Pper I, i.e., tht the singledish mesurements re sensitive to reltively cold (15 30 K) mteril. The totl mmoni column densities re in the rnge cm 2. It is very likely tht this gs is distributed over more extended regions thn those observed with the VLA, s one cn rgue from the comprison of the line profiles (see Sect. 4.1). Becuse of the low spectrl resolution used for the NH 3 (3, 3) VLA observtions (see Sect. 2.2), we cnnot derive relible opticl depth estimte nd thus estimte of T rot from the comprison with the NH 3 (2,2)profiles.Thus,wehveconservtivelyssumed lower limit to the rottion temperture s the mximum brightness temperture mesured in the (2, 2) nd (3, 3) spectr. As n upper limit we rbitrrily ssumed tht 100 K is typicl vlue for HMCs. With this rnge of tempertures, we clculted the totl NH 3 column density from tht in the (2, 2) level N 22. This is given in Tble 9, where we lso list the mmoni bemverged column densities of the 8 NH 3 cores, obtined from the bem-verged spectr of Fig. 11. Where no core ws detected, we derived the vlues from the men spectr by verging the extended line emission over the 3σ contours. In Tble 10, we list the physicl prmeters for the 8 mmoni cores: the observed ngulr dimeter (Θ HP ), the bem deconvolved ngulr (Θ S ) nd liner dimeter (D), nd the mmoni mss (M NH3 ), clculted from totl column density nd size. The dimeters of the cores correspond to the full width t hlf power (FWHP) of the mps of the min mmoni line, verging the vlues derived from the NH 3 (2, 2) nd (3, 3) imges. From the liner dimeters of the cores nd their NH 3 (2, 2) linewidths, one cn derive the corresponding viril msses (McLren et l. 1998) ofm vir /M = (d/kpc) (Θ S /rcsec) (Δv/km s 1 ) 2. To derive n estimte of the hydrogen density (n H2 ) nd NH 3 bundnce (X NH3,seeTble10), we ssume s we did in Pper I, tht the mmoni cores re virilised. Only n estimte of the mss from mm-continuum emission would llow us to verify this ssumption. However, for two sources of the Pper I smple (G nd G M), we find n greement of within fctor 2 between the msses derived from the fit to the continuum spectr (Furuy et l. 2002) nd the viril msses clculted from the NH 3 mps (Codell et l. 1997). We re then confident tht the errors cused by our previous ssumption re smller thn the typicl uncertinties ffecting bundnce estimtes. When we compre the properties of the 8 mmoni cores detected in the present pper, with those of the 5 cores reported in Pper I, we detect some differences. Our cores re smller ( AU) thn those of Pper I ( AU). Since the FWHM of the NH 3 (2, 2) lines re lmost the sme ( 6 kms 1 Pge 8 of 16

9 C. Codell et l.: Looking for high-mss young stellr objects: H 2 O nd OH msers in mmoni cores Fig. 7. Contour plots of the NH 3 (2, 2) line emission integrted under the min line for the sources where it hs been detected. When lso the continuum emission hs been observed, the sme region s tht of the continuum mps (see Figs. 1 nd 2) is shown. The squres, green circles, nd mgent tringles mrk the positions of the H 2 O, CH 3 OH, nd OH mser spots, respectively (Forster & Cswell 1989; Wlsh1998). The rms 1σ of the mps is 1.3 mjy bem 1 (G ), 0.8 mjy bem 1 (G M, G ), 0.9 mjy bem 1 (G ), nd 1.5 mjy bem 1 (G , G ), while both the first (negtive) contours nd the steps correspond to 3 ( 3; dotted contour) σ. The ellipse in the bottom right corner represents the HPBW. Tble 5. Results of fits to the spectr observed t Medicin. Nme Line T MB rms V LSR ΔV τ tot (K) (mk) (km s 1 ) (km s 1 ) G (1,1) 0.52(0.07) (0.2) 4.5(0.4) 0.6 (2, 2) 0.26(0.06) (0.4) 6.7(1.6) b G M (1, 1) 0.70(0.08) (0.1) 3.1(0.4) 0.1 (2, 2) 0.36(0.08) (0.3) 2.8(0.6) b G (1, 1) 1.02(0.13) (0.2) 4.7(0.3) 4.6 (2, 2) 0.53(0.08) (0.2) 4.0(0.7) 1.2 G (1, 1) 0.29(0.03) (0.1) 4.0(0.2) 2.7 (2, 2) 0.12(0.01) (0.2) 4.6(0.7) 0.6 G (1, 1) 0.31(0.03) (0.1) 3.4(0.2) 2.2 (2, 2) 0.18(0.03) (0.2) 3.9(0.9) b G (1, 1) 0.26(0.02) (0.1) 3.2(0.3) 1.1 (2, 2) 0.15(0.02) (0.2) 2.8(0.6) b G (1, 1) 1.19(0.04) (0.1) 3.1(0.1) 2.3 (2, 2) 0.66(0.02) (0.1) 3.8(0.2) b G (1, 1) 0.44(0.03) (0.1) 2.9(0.2) 1.7 (2, 2) 0.27(0.02) (0.1) 2.9(0.3) 1.1 G (1, 1) 0.56(0.07) (0.1) 3.0(0.3) 1.7 (2, 2) 0.19(0.04) (0.4) 5.3(1.0) b G (1, 1) 0.08(0.01) (0.2) 3.7(0.5) 1.0 (2, 2) 0.03(0.01) (0.5) 3.1(1.1) b G (1, 1) 0.69(0.06) (0.1) 4.1(0.3) 0.6 (2, 2) 0.38(0.05) (0.2) 3.5(0.7) b Notes. () Given the sptil resolution of the Medicin ntenn, the spectr collect the contributions due to both A nd B cores (see Figs. 7 10). (b) Stellites not detected. here versus 5 kms 1 in Pper I), this infers smller viril msses (2 337 M versus M in Pper I). For the sme Tble 6. Extended mmoni emission: results of fits to the spectr derived from the VLA mps. Nme line T MB rms V LSR ΔV τ tot (K) (mk) (km s 1 ) (km s 1 ) G (2, 2) 9.0(0.4) (0.1) 5.0(0.4) 0.6 (3, 3) 5.3(0.1) (0.3) 10.7(0.5) 0.7 G (2, 2) 13.9(2.1) (0.3) 4.3(0.5) b (3, 3) 3.7(0.4) (2.4) 11.5(6.9) b G (2, 2) 8.9(0.4) (0.1) 3.9(0.4) 0.5 (3, 3) 4.0(0.1) (0.5) 11.1(1.1) 2.4 G (2, 2) 5.8(0.6) (0.3) 5.7(1.3) b (3, 3) 2.5(1.2) (0.8) 10.3(1.7) b G (2, 2) 6.3(0.8) (0.3) 3.9(1.0) b (3, 3) 1.0(0.1) (3.6) 9.2(5.1) b Notes. () The lrger ΔV vlues obtined from the (3, 3) spectr re due to the low spectrl resolution (9.8 km s 1 ; see Sect. 2.2). (b) Stellites not detected. reson, we lso obtin higher densities ( cm 3 versus cm 3 in Pper I). On the other hnd, the mmoni mss M NH3 is quite low in G A nd B (10 8 M ) nd G (10 7 M ) nd is in the rnge M, wheres it hs vlues of between 1 nd M in Pper I. As consequence, we infer lower NH 3 bundnces ( versus in Pper I). The verge distnces of the mmoni cores of the present smple nd of PperIresimilrt 8 kpc. In other words, with the present Pge 9 of 16

10 Fig. 8. Contour plots of the NH 3 (2, 2) line emission integrted under the min line for the sources where it hs been detected. When lso the continuum emission hs been observed, the sme region s tht of the continuum mps (see Figs. 1 nd 2) is shown. The squres nd mgent tringles mrk the positions of the H 2 O nd OH mser spots, respectively (Forster & Cswell 1989; Wlsh1998). The rms 1σ of the mps is 1.2 mjy bem 1 (G , G ), 1.0 mjy bem 1 (G , G ), nd 0.9 mjy bem 1 (G ), while both the first (negtive) contours nd the steps correspond to 3 ( 3; dotted contour) σ. Tble 7. The mmoni cores: results of fits to the spectr derived from the VLA mps. Nme Line T MB rms V LSR ΔV τ tot (K) (mk) (km s 1 ) (km s 1 ) G A (2, 2) 28.6(2.9) (0.3) 6.8(0.3) 12.6 (3, 3) 46.9(1.4) (0.4) 8.4(0.2) 14.4 G B (2, 2) 35.3(4.3) (0.3) 4.2(0.3) 9.9 (3, 3) 33.6(0.9) (0.3) 9.4(0.4) 22.2 G M (2, 2) 29.0(2.9) (0.1) 3.6(0.2) 13.1 (3, 3) 28.3(0.9) (0.2) 7.7(0.2) 15.3 G (2, 2) 24.6(2.2) (0.2) 4.1(0.3) 6.0 (3, 3) 21.8(0.7) (0.9) 6.1(1.0) 6.3 G A (2, 2) 48.7(2.9) (0.1) 2.4(0.1) 13.3 (3, 3) 17.3(1.4) (0.3) 6.3(1.0) G B (2, 2) 31.0(3.2) (0.2) 3.3(0.8) 2.1 (3, 3) 13.6(1.1) (0.7) 9.5(0.9) 8.6 G (2, 2) 6.8(1.5) (1.0) 11.6(3.8) 1.2 (3, 3) 5.8(0.3) (0.4) 9.5(0.4) 25.0 G (2, 2) 27.9(1.3) (0.1) 4.5(0.3) 2.3 (3, 3) 27.9(0.9) (0.3) 8.9(0.4) 5.6 Notes. () The lrger ΔV vlues obtined from the (3, 3) spectr re due to the low spectrl resolution (9.8 km s 1 ; see Sect. 2.2). pper we enhnce the work of Pper I by observing weker NH 3 cores. Tble 8. Ammoni column densities derived from the Medicin spectr. Nme T rot N 22 N tot (K) (10 12 cm 2 ) (10 14 cm 2 ) G b 26(6) 22.7(2.3) 1.5(0.1) G M 20(4) 13.4(4.3) 1.4(0.1) G (2) 27.5(6.0) 29.8(2.8) G (3) 7.0(1.3) 10.8(1.4) G (6) 9.0(2.7) 6.9(1.2) G (3) 5.4(1.5) 0.5(0.1) G b 21(2) 32.5(1.6) 9.2(0.6) G (2) 10.1(1.1) 0.8(0.3) G (4) 13.1(3.8) 1.1(0.1) G (4) 1.3(0.7) 0.2(0.1) G (3) 17.4(4.0) 1.8(0.1) () Notes. For ll the sources but G , G , nd G (where the opticl depths of both mmoni trnsitions hve been derived, see Tble 5), we hve ssumed opticlly thin emission for the NH 3 (2, 2) line. (b) Given the sptil resolution of the Medicin ntenn, the spectr collect the contributions due to both A nd B cores (see Figs. 7 10). In Fig. 13, we present the distributions of the size nd the NH 3 reltive bundnce of the mmoni cores (present pper: 8 cores, Pper I: 5 cores). The distributions of Fig. 13 show tht the typicl size is 10 4 AU, while the typicl NH 3 reltive bundnce is 10 7, in greement with the typicl Pge 10 of 16

11 C. Codell et l.: Looking for high-mss young stellr objects: H 2 O nd OH msers in mmoni cores Fig. 9. Contour plots of the NH 3 (3, 3) line emission integrted under the min line for the sources where it hs been detected. When the continuum nd/or NH 3 (2, 2) emission hve lso been observed, the sme region s tht of the continuum nd NH 3 (2, 2) mps (see Figs. 1 nd 2) is shown. The squres, green circles, nd mgent tringles mrk the positions of the H 2 O, CH 3 OH, nd OH mser spots, respectively (Forster & Cswell 1989; Wlsh1998). The rms 1σ of the mps is 1.2 mjy bem 1 (G ), 1.5 mjy bem 1 (G M, G ), 0.9 mjy bem 1 (G , G ), nd 1.1 mjy bem 1 (G ), while both the first (negtive) contours nd the steps correspond to 3 ( 3; dotted contour) σ. The ellipse in the bottom right corner represents the HPBW. Tble 9. Ammoni column densities derived from the VLA mps. Nme T rot N 22 N tot (K) (cm 2 ) (cm 2 ) Extended mmoni emission b G G b G b G G b Ammoni cores G A G B G M G G A G B G G () Notes. Given the low spectrl resolution (see Sect. 2.2) of the NH 3 (3, 3) spectr, we estimted lower limit for T rot s the mximum T MB vlue shown by the (2, 2) nd (3, 3) spectr. As n upper limit we rbitrrily ssumed 100 K. (b) The column densities derived for G , G , nd G re very pproximtive due to no opticl depth mesurement (see Tble 5): in this cse τ tot = hs been rbitrrily ssumed. vlues observed for Orion ( ; vn Dishoeck & Blke 1998). 6. Comments on individul sources 6.1. G Although mmoni hs lredy been observed towrds this region (Cesroni et l. 1992; Angld et l. 1996), until now no mps hve been obtined for ny NH 3 trnsition. In Fig. 12,two mmoni peks devoid of 1.3 cm continuum emission re seen, which re offset from the continuum pek. Given the proximity of the H 2 O msers to the mmoni cores, it is likely tht the three sources within the mp field (the two mmoni cores nd the UC Hii region) re ssocited with high-mss YSOs. The position nd distribution of the 1.3 cm continuum emission re consistent with those obtined t 3 cm with the Austrli Telescope Compct Arry (ATCA) by Forster & Cswell (2000), who describe it s cometry UC Hii region. The sme uthors suggest tht this source might be locted t distnce smller thn 16.1 kpc, becuse of the extent of the UC Hii region nd the H 2 O mser spots. The flux density, S ν, ws mesured towrds the UC Hii region t 9 GHz by Forster & Cswell (2000) nd t 1.4 nd 5 GHz by Becker et l. (1994): the index of the spectrl energy distribution between 23 nd 9 or 5 GHz is , indicting tht t 23 GHz the free-free emission is opticlly thin. G ws detected in different moleculr trcers tht, beside NH 3, include CS (Plume et l. 1992) ndch 3 CN (Olmi et l. 1993), thus mking it relible hot moleculr core (HMC) cndidte. It is resonble to conclude tht the CH 3 CN line emission mostly origintes in the NH 3 cores of Fig. 12. Thisregion ws lso mpped t 450 nd 850 μm by Htchell et l. (2000)nd Pge 11 of 16

12 Fig. 10. Contour plots of the NH 3 (3, 3) line emission integrted under the min line for the sources where it hs been detected. When the continuum nd/or NH 3 (2, 2) emission hve lso been observed, the sme region s tht of the continuum nd NH 3 (2, 2) mps (see Figs. 1 nd 2) is shown. The squres nd mgent tringles mrk the positions of the H 2 O nd OH mser spots, respectively (Forster & Cswell 1989;Wlsh1998). The rms 1σ of the mps is 1.3 mjy bem 1 (G ) 0.5 mjy bem 1 (G ), 2.6 mjy bem 1 (G ), 0.7 mjy bem 1 (G ), 0.9 mjy bem 1 (G ), while both the first (negtive) contours nd the steps correspond to 3 ( 3; dotted contour) σ. Tble 10. Prmeters of the mmoni cores derived from the VLA mps. Nme Θ HP Θ S D M NH3 M vir n H2 X NH3 ( ) ( ) (10 3 AU) (10 6 M ) (M ) (10 9 cm 3 ) (10 9 ) G A G B G M G G A G B G G Notes. () When the mmoni cores re not sptilly resolved, Θ HP is equl to the HPBWs of the NH 3 (2, 2) nd (3, 3) mps, wheres we rbitrrily ssume tht HPBW/3 is n upper limit (used to derive the prmeters listed in the tble) of Θ S (see text). t 350 μm by Hunter et l. (2000). In ll three cses, the emission comes from the whole re mpped in Fig. 12 nd the ngulr resolution is too low to sfely ssocite the pek of the emission with ny of the three sources resolved by our observtions G M This source ws detected nd mpped t severl submillimeter wvelengths by Htchell et l. (2000; 450 nd 850 μm) nd Hunter et l. (2000; 350 μm). Although ssocited with H 2 O nd OH msers, nd with NH 3 emission (Angld et l. 1996; see lso Fig. 12), it shows detectble continuum emission t neither 3 cm (Forster & Cswell 2000) nor 1.3 cm (this work). All of these findings suggest tht this source hosts one or more high-mss YSOs deeply embedded in dense moleculr core where no detectble Hii region hs yet been formed G Previous rdio continuum observtions crried out by Dent et l. (1984; 5 GHz) nd Gibb et l. (2003; 5 nd 8.5 GHz) with the VLA detected north-to-south rdio jet in this region, which is lso detected in the mid- nd ner-ir by De Buizer (2006) nd Fuller et l. (2001), respectively. The mps obtined by Gibb et l. (2003) show evidence tht the jet is precessing. This cn be seen from the S-shped distribution of most of the rdio sources detected by the cited uthors (denoted by circles in Fig. 14). The present 1.3 cm continuum observtions confirm the presence of rdio jet oriented long the N-S direction (Fig. 2), nd Pge 12 of 16

13 C. Codell et l.: Looking for high-mss young stellr objects: H 2 O nd OH msers in mmoni cores Fig. 11. Ammoni (2, 2) nd (3, 3) VLA bem verged spectr of the 8 NH 3 cores (see text) shown in Figs The verticl lines mrk the positions of the hyperfine stellites. Due to technicl problems, prt of the NH 3 (2, 2) spectr of G nd G is missing. the shpes nd orienttions of the southern nd northern components (lbeled jets 1 nd 2, respectively) re lso consistent with precession, in greement with the results reported by Gibb et l. (2003). A close-up view of the centrl prt of this region revels two NH 3 cores, clled A nd B in Fig. 12. Source A is clerly detected in both NH 3 (2, 2) nd (3, 3), but hs no detectble 1.3 cm continuum emission. In contrst, source B displys 1.3 cm continuum emission nd wek mmoni emission. The coordintes of source B coincide with those of the UC Hii region known s G35.20N (lso nmed Source 7 by Gibb et l. 2003). According to these uthors this source drives the precessing rdio-jet. Source A does not hve rdio continuum counterprt t either 5 or 8.5 GHz, (see Fig. 6 of Gibb et l. 2003). However, it ppers to be centered on the pek of the H 13 CN(1 0) emission presented by the sme uthors. Added to the presence of H 2 O nd OH msers, this suggests tht source A contins one or more high-mss YSOs nd is more deeply embedded nd possibly less evolved thn source B. A moleculr outflow oriented in the SW-NE direction ws observedbygibbetl.(2003) nd López-Sepulcre et l. (2009; Fig. 14) in 12 CO nd 13 CO, respectively. On the bsis of these different jet/outflow orienttions, Gibb et l. (2003) rgue tht this region contins multiple outflows, insted of the precessing flow proposed by Little et l. (1998). They lso suggest tht the CO outflow is driven by the millimeter source G35MM2 (mrked with n sterisk in Fig. 14). However, by exmining Fig. 14, it seems more plusible tht the center of the flow is either source A or B, nd thus the ide of precession should not be excluded, even if it implies precession ngle of 58. Assuming the velocity of the jet to be 100 km s 1, we derive kinemticl ge of yr, nd hence the ngulr velocity of the precession comes to 20 yr 1. This vlue is similr to tht found for IRAS ( 60 yr 1 ) by Cesroni et l. (2005), mking the interprettion of precession plusible. Higher ngulr resolution observtions in suitble moleculr outflow trcer would help us to identify the driver nd discriminte between precession nd outflow multiplicity. Finlly, C 18 O(2 1) velocity mps obtined by López- Sepulcre et l. (2009) show NW-SE velocity grdient of 1.3 km s 1 over 0.3 pc, perpendiculr to the 13 CO outflow xis. Although sources A nd B re ligned long the direction of this grdient, they both hve the sme V LSR velocities, s seen from Tble 7, i.e., for both A nd B. Therefore, the present NH 3 mps imply tht the observed velocity grdient is not cused by sources A nd B hving different systemic velocities, nd the interprettion of flttened structure rotting perpendiculrly to the outflow xis remins plusible G Towrds G evidence of compct nd hightemperture gs ( 85 K) hs been found using single-dish observtions of hot-core trcers such s CH 3 CN nd NH 3 (4, 4) Pge 13 of 16

14 Fig. 12. Upper pnels: contour plots of the NH 3 (2, 2) line intensity integrted under the stellites for G (left), G M (middle), nd G (right). The rms 1σ of the mps is 0.6 (G ), 0.5 (G M), nd 0.4 mjy bem 1 (G ). Both the first contours nd the steps correspond to 3σ. The colour scle represents the 1.3 cm continuum (see Figs. 1 nd 2). The squres, circles, nd tringles mrk the positions of the H 2 O, CH 3 OH, nd OH mser spots, respectively (Forster & Cswell 1989; Wlsh1998). Lower pnels: contour plots of the NH 3 (3, 3) intensity integrted by the stellites. The rms 1σ of the mps is 0.6 (G ), 0.5 (G M), nd 0.4 mjy bem 1 (G ). Both the first (negtive) contours nd the steps correspond to 3 ( 3; dotted contour) σ. The colour scle represents the integrted NH 3 (3, 3) min line intensity (see Figs. 9 nd 10). two different sources re seen in G : one with 1.3 cm continuum emission nd only wek mmoni emission, nd second one detected in the mmoni lines but not in the 1.3 cm continuum, locted bout 2 south of the rdio continuum source (Figs. 2, 8,nd10). Evidence of moleculr outflows hs been found in this region. Shepherd et l. (1997) crried out high-ngulr resolution 12 CO nd SiO observtions with the Berkeley-Illinois-Mrylnd Arry (BIMA), detecting totl of four outflows. On the bsis of their loction, two of these (referred to s Centrl nd Western by the sme uthors) could be ssocited with one or both sources detected in the present work, lthough the resolution of their imges is not high enough to permit cler identifiction. Further evidence of outflowing motions ws reported by López-Sepulcre et l. (2009), who imged the region in the 13 CO(2 1) line with the IRAM 30-m telescope. The resulting blue nd red lobe mps re represented s contours in Fig. 15, superimposed on the 1.3 continuum mp (upper pnel) nd NH 3 (2, 2) min lineemission mp (lower pnel). Even though the outflow lobes re not very clerly defined, the disposition of the blue-shifted emission suggests n ssocition with the rdio continuum source. However, only sufficiently high-sptil resolution imges cn confirm this, nd whether the YSOs hidden in the NH 3 core re lso powering n outflow. Fig. 13. Distributions of the size of the NH 3 cores (upper pnel) nd their reltive NH 3 bundnce with respect to H 2 (lower pnel). The vlues correspond to the 13 cores (present pper: 8, Pper I: 5). nd (5, 5) by Olmi et l. (1993). The present NH 3 mps indicte tht, s described for the three regions previously discussed, 7. Summry nd conclusions We hve investigted 15 high-mss SFRs in the NH 3 (1, 1), (2, 2), nd (3, 3) lines s well s in the 1.3 cm continuum emission with the single-dish Medicin ntenn nd the VLA interferometer. The smple hs been selected from surveys of H 2 OndOH msers, to trget erliest phses of high-mss str formtion. The Pge 14 of 16

15 C. Codell et l.: Looking for high-mss young stellr objects: H 2 O nd OH msers in mmoni cores Fig. 14. Upper pnel: contour plots of the 13 CO(2 1) blue (solid) nd red (dshed) line wing emission (from López-Sepulcre et l. 2009), superimposed on the VLA 1.3 cm continuum mp (colour scle) of G Lower pnel: contour plots of the 13 CO(2 1) blue (solid) nd red (dshed) line wing emission superimposed on the NH 3 (2, 2) emission integrted beneth the min line (colour scle). Contours strt from 5σ nd increse in steps of 5σ, with 1σ = 0.2 K for both the blue nd red lobe emission. The squres nd tringles mrk the positions of the H 2 O nd OH mser spots, respectively (Forster & Cswell 1989; Wlsh et l. 1998). The white cross nd the sterisk correspond to the rdio source G35.2N (Source B) nd the millimeter source G35MM2, respectively (coordintes tken from Gibb et l. 2003). Circles represent the rdio sources detected by Gibb et l. (2003) t 5 nd 8.5 GHz. present project completes the pilot survey strted in Pper I with the im of chrcterising the ntl high-density moleculr cores not yet destroyed by the newly formed high-mss YSOs. The min results re the following: 1. We hve detected continuum emission in lmost ll the observed str-forming regions tht trces extended nd UCHii regions creted by YSOs with typicl luminosities of 10 4 L. In only 3 cses do we observe positionl coincidence between UCHii regions nd H 2 O nd OH mser spots. The upper limits to the continuum emission towrds the rest of the mser spots cn be used to constrin the prmeters of the undetected Hii regions. We suggest tht the lck of detection is cused by opticlly thick nd sptilly unresolved sources. 2. Ammoni emission hs been detected towrds 12 SFRs with Medicin nd/or VLA. By compring between the Medicin nd VLA spectr, we identify n extended envelope resolved Fig. 15. Upper pnels: contour plots of the 13 CO(2 1) blue (solid) nd red (dshed) line wing emission (from López-Sepulcre et l. 2009), superimposed on the VLA 1.3 cm continuum mp (colour scle) of G Lower pnel: contour plots of the 13 CO(2 1) blue (solid) nd red (dshed) line wing emission superimposed on the NH 3 (2, 2) emission integrted under the min line (colour scle). Contours strt t 5σ nd increse by steps of 1σ, with 1σ = 0.4 K for the blue lobe emission nd 0.5 K for the red lobe emission. The squres nd tringles mrk the positions of the H 2 O nd OH mser spots, respectively (Forster & Cswell 1989). by the interferometer. The VLA mmoni imges detect wek extended emission without cler morphology in 5 SFRs, wheres 6 regions re clerly relted to 1 or 2 NH 3 cores (8 in totl) closely ssocited with the H 2 OndOH mser spots. 3. The sttisticl nlysis of the distribution between H 2 Ond OH msers, NH 3 cores, nd Hii regions llows us to confirm tht the moleculr cores trce the erly stges of highmss str formtion, prior to the development of detectble ionised region or, t most, ssocited with hypercompct Hii regions ( 0.01 pc). 4. The mmoni cores hve typicl size of 10 4 AU nd high msses (up to 10 4 M ), nd re very dense (up to fews 10 9 cm 3 ). The tempertures re estimted to be on verge greter thn 30 K. Most of the moleculr cores hve reltive NH 3 bundnce of 10 7, in greement with the vlues observed in the Orion region. Acknowledgements. A.L.S. knowledges support from the FP6 Mrie-Curie reserch Trining Network Constelltion: the origin of stellr msses (MRTN- CT ). R.S.F. is supported by Grnt-in-Aid from the Ministry of Eduction, Culture, Sports, Science nd Technology of Jpn (No ). Pge 15 of 16