J/AJ/170/74ivo://CDS.VizieR/J/AJ/170/74CDSChen J.L.Zhang J.S.Ge J.X.Wang Y.X.Yu H.Z.Zou Y.P.Yan Y.T.,Wang X.Y.Wei D.Y.2026-05-22T11:39:10Z2026-05-22T12:20:59ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frh-ii-regionschemical-abundancesmolecular-physicsradio-astronomystar-forming-regionsUsing the Institut de Radioastronomie Millmetrique 30m telescope, we presented observations of N_2_H^+^J=1-0, CCS J_N_=8_7_-7_6_ and 7_7_-6_6_ lines toward a large sample of ultracompact H II regions (UC H IIs). Among our 88 UC H IIs, 87 and 33 sources were detected in the N_2_H^+^J=1-0 and CCS J_N_=8_7_-7_6_ lines, respectively. For the CCS 7_7_-6_6_ transition, we detected emission in 10 out of 82 targeted sources, all of which also exhibited emission in the CCS J_N_=8_7_-7_6_ line. Physical parameters are derived for our detections, including the optical depth and excitation temperature of N_2_H^+^, the rotational temperature of CCS and the column density. Combining our results and previous observation results in different stages of high-mass star-forming regions (HMSFRs), we found that the column density ratio N(N_2_H^+^)/N(CCS) increases from high-mass starless cores through high-mass protostellar cores to UC H IIs. This implies that N(N_2_H^+^)/N(CCS) can trace the evolution process of HMSFRs. It was supported by our gas-grain chemical model, which shows that N(N_2_H^+^)/N(CCS) increases with the evolution age of HMSFRs. The temperature, density and chemical age were also constrained from our best-fit model at each stage. Thus, we propose N(N_2_H^+^)/N(CCS) as a reliable chemical clock of HMSFRs.2025AJ....170...74Chttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/AJ/170/74CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/A+AS/133/29 : Molecular line survey towards UC HII (Hatchell+ 1998)J/ApJ/566/945 : Massive star forming regions at 1.2mm (Beuther+, 2002)J/A+A/417/615 : Maser and outflows in UC HII region (Codella+, 2004)J/AJ/129/348 : Radio compact HII regions in the Milky Way (Giveon+, 2005)J/AJ/130/156 : Galactic radio compact HII regions at 1.4GHz (Giveon+, 2005)J/ApJ/641/389 : Millimetric observations of IRDC cores (Rathborne+, 2006)J/A+A/453/1003 : SCUBA ultracompact HII regions (Thompson+, 2006)J/A+A/461/11 : Radio observations of MYSO candidates (Urquhart+, 2007)J/A+A/498/147 : High mass protostellar objects physical param. (Grave+, 2009)J/A+A/501/539 : RMS survey. 6cm observations of YSOs (Urquhart+, 2009)J/ApJ/741/110 : The BGPS. VII. Massive star-forming regions (Dunham+, 2011)J/MNRAS/418/1689 : Red MSX water maser and ammonia emissions (Urquhart+, 2011)J/A+A/527/A88 : Chemistry in infrared dark clouds (Vasyunina+, 2011)J/ApJ/756/60 : A 3mm line survey in 37 IR dark clouds (Sanhueza+, 2012)J/ApJ/777/157 : 90GHz obs. of high-mass star-forming regions (Hoq+, 2013)J/ApJS/205/1 : CORNISH project. II. Source catalog (Purcell+, 2013)J/MNRAS/435/400 : ATLASGAL. Properties of compact HII regions (Urquhart+, 2013)J/A+A/565/A75 : ATLASGAL: dust condensations in Gal. plane (Csengeri+, 2014)J/A+A/567/L5 : W3(OH) high angular resolution 7mm images (Dzib+, 2014)J/A+A/563/A97 : IRAM 30m reduced spectra of 59 sources (Gerner+, 2014)J/ApJ/783/130 : Parallaxes of high mass star forming regions (Reid+, 2014)J/A+A/579/A71 : Infrared emission of young HII regions (Cesaroni+, 2015)J/A+A/579/A80 : Star-forming regions deuteration (Gerner+, 2015)J/ApJS/219/28 : C^18^O/C^17^O ratios in the Galactic center (Zhang+, 2015)J/ApJ/833/18 : Ultra-compact HII regions & methanol masers. I. (Hu+, 2016)J/ApJ/822/59 : BGPS. XIV. Molecular cloud clumps GBT obs. (Svoboda+, 2016)J/ApJS/231/11 : High-mass starless clump candidates from ATLASGAL (Yuan+, 2017)J/A+A/615/A103 : CORNISH project. III. UCHII region catalogue (Kalcheva+, 2018)J/A+A/611/A6 : ATLASGAL massive clumps H_2_CO data (Tang+, 2018)J/MNRAS/487/1057 : Massive SFR beyond the solar circle (Djordjevic+, 2019)J/ApJS/244/35 : VLA observations of the Central Molecular Zone (Lu+, 2019)J/ApJ/885/131 : ~200 high-mass SFR plx & proper motion with VLBI (Reid+, 2019)J/ApJ/877/154 : H_2_CO TMRT obs. of Galactic molecular clouds (Yan+, 2019)J/ApJ/899/145 : Sulfur isotopes in SFR with 12m ARO and 30m IRAM (Yu+, 2020)J/ApJS/249/6 : Galactic interstellar ratio ^18^O/^17^O. I. (Zhang+, 2020)J/ApJS/257/39 : NH3 isotope ratios of Galactic disk sources (Chen+, 2021)J/ApJS/258/19 : 12.2GHz methanol maser surv. toward 6.7GHz masers (Song+, 2022)J/MNRAS/510/3389 : High-mass star formation evol. trends (Urquhart+, 2022)J/MNRAS/520/1073 : CORNISH-South Survey and Catalogue (Irabor+, 2023)J/ApJS/264/48 : HC3N & N2H+ obs. toward 61 ultracomp. HII reg. (Wang+, 2023)J/ApJS/266/29 : IRAM 3mm, 2mm & 1.3mm obs. of star-forming reg. (Zhao+, 2023)J/ApJS/268/56 : Obs. of Gal. interstellar ratio ^18^O/^17^O. II. (Zou+, 2023)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/AJ/170/74https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/AJ/170/74http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/AJ/170/74https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/AJ/170/74https://vizier.iucaa.in/viz-bin/votable?-source=J/AJ/170/74http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/AJ/170/74GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/AJ/170/74/table1 (Detailed information of our Ultracompact (UC) HII sample)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/AJ/170/74/table1?https://vizier.iucaa.in/viz-bin/conesearch/J/AJ/170/74/table1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/AJ/170/74/table1?GETtext/xml+votable180.050000true36.767416761.87372220.005555555555555556Cone search capability for table J/AJ/170/74/table9 (Basic information of High-Mass Starless Cores (HMSC) and High-Mass Protostellar Cores (HMPO) from Chen+2025 (in preparation))https://vizier.cds.unistra.fr/viz-bin/conesearch/J/AJ/170/74/table9?https://vizier.iucaa.in/viz-bin/conesearch/J/AJ/170/74/table9?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/AJ/170/74/table9?GETtext/xml+votable180.050000true275.322917-14.4952780.0055555555555555566/3649 14314 14353-14356 14604 14626 15390 15473 15671 15681 28825 28827 28830-28831 28875 28913 28918-28919 29091 29096-29097 29101 29114 29118 29154 29160 29461 29504-29505 29509-29511 29513 29529 29532-29534 30218 30245 30256 30258 30262-30263 30268-30269 30312-30313 30315 30317-30319 30330 30405 30416 30420 30425 30595 30600 30604 30616-30617 30622 30644 30691-30692 30694https://cdsarc.cds.unistra.fr/viz-bin/moc/J/AJ/170/74?format=asciiRadiodefaultJ/AJ/170/74/table1Detailed information of our Ultracompact (UC) HII samplerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintNameUC HII object namemeta.id;meta.maincharprimaryRAJ2000Hour of Right Ascension (J2000)pos.eq.ra;meta.mainDEJ2000Degree of Declination (J2000)pos.eq.dec;meta.mainDist[0.7/20.41] Heliocentric Distancekpcpos.distancefloate_Dist[0.04/10.29] Uncertainty in Distkpcstat.error;pos.distancefloatr_Dist[1/9] References (1)meta.ref;pos.distanceintJ/AJ/170/74/table3Our UC HII observational parameters of N2H+(J=1-0) and CCS obtained from Gaussian fitsNameUC HII object namemeta.id;meta.maincharprimaryrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintTransMolecule and transition lines (1)phys.atmol.transitioncharExpTime[3.8/119.8]? Total integration timemintime.duration;obs.exposurefloatnullableRMS[6e-3/0.12]? RMS NoiseKinstr.det.noisefloatnullableTmbdv[0.07/81.14]? Integrated line intensity for Trans (1)K.km/sspect.line.intensityfloatnullablee_Tmbdv[0.01/1.64]? Uncertainty TmbdvK.km/sstat.error;spect.line.intensityfloatnullableVLSR[-80.0/126.13]? Radial velocity relative to local standard of rest (1)km/sspect.dopplerVeloc;pos.lsrfloatnullablee_VLSR[0.01/0.63]? Uncertainty in VLSRkm/sstat.error;phys.veloc;pos.lsrfloatnullableDV[0.63/7.84]? Line width, {Delta} V (1)km/sspect.line.widthfloatnullablee_DV[0.01/1.44]? Uncertainty in DVkm/sstat.error;spect.line.widthfloatnullableTmb[0.04/12.35]? Main beam brightness temperature (1)Kphys.temperature;meta.mainfloatnullableJ/AJ/170/74/table4Derived parameters of CCS and N2H+ in our UC HII sampleNameUC HII object namemeta.id;meta.maincharprimaryrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordinttau-N2H+[0.03/5.24]? Optical depth, {tau}, N2H+phys.absorption.opticalDepthfloatnullablee_tau-N2H+[0.04/0.41]? Uncertainty in tau-N2H+stat.error;phys.absorption.opticalDepthfloatnullableTex-N2H+[2.99/19.02]? Excitation temperature, N2H+Kphys.atmol.excitationfloatnullablee_Tex-N2H+[0.07/7.53]? Uncertainty in Tex-N2HKstat.errorfloatnullableN-N2H+[0.2/24.08]? Column density, N2H+1e+13cm**-2phys.columnDensityfloatnullablee_N-N2H+[0.1/2.84]? Uncertainty in N-N2H+1e+13cm**-2stat.error;phys.columnDensityfloatnullableTrot-CCS[4.88/24.65]? Rotational temperature, CCSKphys.temperature;phys.mol.rotationfloatnullablee_Trot-CCS[0.59/17.7]? Uncertainty in Trot-CCSKstat.error;phys.temperature;phys.mol.rotationfloatnullablef_Trot-CCSFlag on Trot-CCS (1)meta.code;phys.temperature;phys.mol.rotationcharN-CCS[0.85/16.6]? Column density, CCS1e+11cm**-2phys.columnDensityfloatnullablee_N-CCS[0.21/2.41]? Uncertainty in N-CCS1e+11cm**-2stat.error;phys.columnDensityfloatnullablef_N-CCSFlag on N-CCS (1)meta.code;phys.columnDensitycharNRatio[13.39/375.03]? Column density Ratio, N(N2H+)/N(CCS)phys.density;arith.ratiofloatnullablee_NRatio[2.78/97.66]? Uncertainty in NRatiostat.error;phys.density;arith.ratiofloatnullableJ/AJ/170/74/table5Derived Parameters of CCS and N2H+ in HMSCs and HMPOse_tau-N2H+[0.01/2.0]? Uncertainty in tau-N2H+stat.error;phys.absorption.opticalDepthfloatnullableTex-N2H+[3.0/44.1]? Excitation temperature, N2H+Kphys.atmol.excitationfloatnullablee_Tex-N2H+[0.05/4.0]? Uncertainty in Tex-N2HKstat.errorfloatnullableN-N2H+[0.24/3.61]? Column density, N2H+1e+13cm**-2phys.columnDensityfloatnullablee_N-N2H+[0.05/2.27]? Uncertainty in N-N2H+1e+13cm**-2stat.error;phys.columnDensityfloatnullablerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintStageEvolutionary State (1)phys.atmol.ionStagecharNameObject namemeta.id;meta.mainchartau-N2H+[0.1/5.0]? Optical depth, {tau}, N2H+phys.absorption.opticalDepthfloatnullableN-CCS[0.51/18.83]? Column density, CCS1e+11cm**-2phys.columnDensityfloatnullablee_N-CCS[0.25/4.96]? Uncertainty in N-CCS1e+11cm**-2stat.error;phys.columnDensityfloatnullableNRatio[3.35/242.98]? Column density Ratio, N(N2H+)/N(CCS)phys.density;arith.ratiofloatnullablee_NRatio[1.41/161.78]? Uncertainty in NRatiostat.error;phys.density;arith.ratiofloatnullableRefReferences for measurementsmeta.refcharJ/AJ/170/74/table9Basic information of High-Mass Starless Cores (HMSC) and High-Mass Protostellar Cores (HMPO) from Chen+2025 (in preparation)NameHMSC and HMPO Sample namemeta.id;meta.maincharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRAJ2000Hour of Right Ascension (J2000)pos.eq.ra;meta.mainDEJ2000Degree of Declination (J2000)pos.eq.dec;meta.mainDist[3.04/10.8] Heliocentric Distancekpcpos.distancefloate_Dist[0.46/1.61] Uncertainty in Distkpcstat.error;pos.distancefloatStageEvolutionary State (1)phys.atmol.ionStagecharRef[1/2] References (2)meta.refint