J/A+A/597/A45ivo://CDS.VizieR/J/A+A/597/A45doi:10.26093/cds/vizier.35970045CDSVastel C.Mookerjea B.Pety J.Gerin M.2016-12-21T08:15:05Z2016-12-21T08:57:53ZCDS support team

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

cds-question@unistra.frmolecular-cloudsspectroscopyHerschel/HIFI observations toward the compact HII region W51 has revealed the presence of a cold dense core along its line of sight in a high-velocity stream located just in front of W51. This detection has been made possible through absorption measurements of low-energy transitions of HDO, NH_3_, and C_3_ against the bright background emitted by the star-forming region. We present a follow-up study of this core using the high sensitivity and high spectral resolution provided by the IRAM 30m telescope. We report new detections of this core in absorption for DCO^+^ (2-1, 3-2), H^13^CO^+^ (1-0), DNC (3-2), HN^13^C (1-0), p-H_2_CO (2_0,2_-1_0,1_, 3_0,3_-2_0,2_), and in emission for o-NH2D. We also report interferometric observation of this last species using the IRAM/NOEMA telescope, revealing the fragmented nature of the source through the detection of two cores, separated by 0.19-0.24pc, with average sizes of less than 0.16-0.19pc. From a non-LTE analysis, we are able to estimate the density (~2.5x10^4^cm^-3^) and temperature (~10K) of this component, typical of what is found in dark clouds. This component (called W51-core) has the same DCO^+^/HCO^+^ ratio (0.02) as TMC-1 and a high DNC/HNC ratio (0.14). Detection of these deuterated species indicates that W51-core is similar to an early-phase low-mass star-forming region, formed from the interaction between the W51 giant molecular cloud and the high-velocity stream in front of it. The W51 complex being at about 5kpc, these findings lead to what is the first detection of the earliest phase of low-mass star-forming region at such a large distance.2017A&A...597A..45Vhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/597/A45CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/ApJS/191/232 : CO survey of W51 molecular cloud (Bieging+, 2010)J/MNRAS/424/1658 : Molecular clumps in W51 giant mol. cloud (Parsons+, 2012)J/A+A/582/A64 : W51/e2 and G34.3+0.2 IRAM spectra (Lykke+, 2015)J/A+A/589/A44 : W51 Main NH_3_ and CH_3_OH data cubes (Goddi+, 2016)J/A+A/595/A27 : JVLA images of W51A (Ginsburg+, 2016)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/597/A45https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/597/A45http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/597/A45https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/597/A45https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/597/A45http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/597/A45GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/597/A45/list (List of fits spectra)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/597/A45/list?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/597/A45/list?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/597/A45/list?GETtext/xml+votable180.050000true290.9329214.508470.0055555555555555566/30694https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/597/A45?format=asciiOpticaldefaultJ/A+A/597/A45/listList of fits spectrarecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRAJ2000Right Ascension of center (J2000)degpos.eq.ra;meta.mainDEJ2000Declination of center (J2000)degpos.eq.dec;meta.mainNxNumber of pixels along X-axismeta.numberintObs.DateObservation date (YYYY-MM-DDThh:mm:ss.sss)time.epoch;obscharbFreqLower value of frequency intervalGHzem.freq;stat.mindoubleBFreqUpper value of frequency intervalGHzem.freq;stat.maxfloatdFreqFrequency resolutionHzspect.resolutionfloatsizeSize of FITS fileKibytephys.size;meta.fitsintspShow the spectrummeta.ref.urlcharFileNameName of FITS file, in subdirectory fitsmeta.id;meta.fitscharTitleTitle of the FITS filemeta.title;meta.fits