J/ApJ/853/171ivo://CDS.VizieR/J/ApJ/853/171doi:10.26093/cds/vizier.18530171CDSGinsburg A.Bally J.Barnes A.Bastian N.Battersby C.Beuther H.,Brogan C.Contreras Y.Corby J.Darling J.De Pree C.Galvan-Madrid R.,Garay G.Henshaw J.Hunter T.Kruijssen J.M.D.Longmore S.Lu X.,Meng F.Mills E.A.C.Ott J.Pineda J.E.Sanchez-Monge A.Schilke P.,Schmiedeke A.Walker D.Wilner D.2018-12-11T13:39:58Z2018-12-10T15:46:27ZCDS support team

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

cds-question@unistra.frmolecular-cloudsh-ii-regionsyoung-stellar-objectsmillimeter-astronomysubmillimeter-astronomyWe report ALMA observations with resolution ~0.5" at 3mm of the extended Sgr B2 cloud in the Central Molecular Zone (CMZ). We detect 271 compact sources, most of which are smaller than 5000au. By ruling out alternative possibilities, we conclude that these sources consist of a mix of hypercompact HII regions and young stellar objects (YSOs). Most of the newly detected sources are YSOs with gas envelopes that, based on their luminosities, must contain objects with stellar masses M*>~8M_{sun}_. Their spatial distribution spread over a ~12x3pc region demonstrates that Sgr B2 is experiencing an extended star formation event, not just an isolated "starburst" within the protocluster regions. Using this new sample, we examine star formation thresholds and surface density relations in Sgr B2. While all of the YSOs reside in regions of high column density (N(H_2_)>~2x10^23^cm^-2^), not all regions of high column density contain YSOs. The observed column density threshold for star formation is substantially higher than that in solar vicinity clouds, implying either that high-mass star formation requires a higher column density or that any star formation threshold in the CMZ must be higher than in nearby clouds. The relation between the surface density of gas and stars is incompatible with extrapolations from local clouds, and instead stellar densities in Sgr B2 follow a linear {Sigma}_*_-{Sigma}_gas_ relation, shallower than that observed in local clouds. Together, these points suggest that a higher volume density threshold is required to explain star formation in CMZ clouds.2018ApJ...853..171Ghttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/853/171CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toVIII/96 : 6-GHz methanol multibeam maser catalogue (Caswell+, 2010-12)J/A+A/291/943 : Protostellar cores (Ossenkopf+, 1994)J/ApJS/155/577 : H2O masers in W49 North and Sagittarius B2 (McGrath+, 2004)J/ApJS/155/421 : Survey of Galactic Center region at 20cm (Yusef-Zadeh+, 2004)J/ApJS/175/277 : Submillimeter-Continuum SCUBA detections (Di Francesco+, 2008)J/A+A/487/993 : MAMBO Mapping of c2d Clouds and Cores (Kauffmann+, 2008)J/ApJS/181/321 : Properties of Spitzer c2d dark clouds (Evans+, 2009)J/ApJS/184/18 : Spitzer survey of young stellar clusters (Gutermuth+, 2009)J/ApJS/181/110 : Galactic center X-ray sources (Muno+, 2009)J/ApJ/702/178 : YSOs in the central 400pc of the Galaxy (Yusef-Zadeh+, 2009)J/ApJ/721/137 : The Bolocam Galactic Plane Survey (BGPS) (Bally+, 2010)J/ApJ/723/1019 : Galactic SFR and gas surface densities (Heiderman+, 2010)J/ApJS/208/9 : Intrinsic colors and temperatures of PMS stars (Pecaut+, 2013)J/A+A/568/A56 : mm continuum and line images of G0.253+0.016 (Johnston+, 2014)J/A+A/566/A45 : Orion optical-depth and column-density maps (Lombardi+, 2014)J/ApJ/783/130 : Parallaxes of high mass star forming regions (Reid+, 2014)J/ApJS/213/1 : The MSFRs Omnibus X-ray Catalog (MOXC) (Townsley+, 2014)J/ApJ/830/17 : GC secondary IR astrometric standards (Boehle+, 2016)J/ApJS/224/5 : Herschel Orion Protostar Survey (HOPS) SEDs (Furlan+, 2016)J/A+A/586/A50 : Central Molecular Zone H2CO temperature maps (Ginsburg+, 2016)J/A+A/595/A94 : Temp. structures in Galactic center clouds (Immer+, 2016)J/A+A/591/A149 : Hi-GAL. inner Milky Way: +68>=l>=70 (Molinari+, 2016)J/A+A/588/A30 : Properties of cores in OMC 2/3 (Sadavoy+, 2016)J/A+A/606/A100 : YSOs in California Molecular Cloud (Lada+, 2017)J/A+A/604/A6 : SgrB2 ALMA continuum and spectral index (Sanchez-Monge+, 2017)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/853/171https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/853/171http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/853/171https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/853/171https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/853/171http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/853/171GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/ApJ/853/171/table3 (Continuum source identifiers and photometry)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/853/171/table3?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/853/171/table3?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/853/171/table3?GETtext/xml+votable180.050000true266.833775-28.38436916670.0055555555555555566/28830https://cdsarc.cds.unistra.fr/viz-bin/moc/J/ApJ/853/171?format=asciiMillimeterdefaultJ/ApJ/853/171/table3Continuum source identifiers and photometryrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintIDIdentifier (1)meta.id;meta.maincharOIDOther identifiermeta.idcharRAJ2000[266.78/266.88] Right Ascension (J2000)degpos.eq.ra;meta.mainDEJ2000[-28.5/-28.3] Declination (J2000)degpos.eq.dec;meta.mainClustCluster code (2)meta.id.parentcharn_IDS=strong source; W=weak or low-confidence sourcemeta.notecharM09X=match with Muno+ 2009, J/ApJS/181/110 Chandra X-ray source catalog ("_"=no match)meta.codecharC10M=match with Caswell+ 2010, VIII/96 Methanol Multibeam Survey CH_3_OH maser cat.meta.codecharM04W=match with McGrath+ 2004, J/ApJS/155/577 water maser survey ("_"=no match)meta.codecharClassSimbad object typesrc.classcharSmax[0/1640] Peak flux densitymJy/beamphot.flux.density;stat.max;em.mm.50-100GHzdoubleTBmax[0/861] Brightness temperatureKphys.temperaturefloatStot[0.01/2390]? Integrated flux density; within a 0.5" radius beammJyphot.flux.density;stat.max;em.mm.50-100GHzdoublenullablesigmabg[0/49] Background RMS flux levelmJy/beaminstr.backgroundfloatalpha[-7/11] Spectral indexspect.indexdoublee_alpha[0/12.6] Error in alphastat.error;pos.eq.radoubleM40K[0/1160]? Mass (3)solMassphys.massfloatnullableNH2[0/3.6e+26]? H_2_ column density (3)cm**-2phys.columnDensitydoublenullable