ALMA observations of the dense and shocked gas in the nuclear region of NGCa€‰4038 (Antennae galaxies)

摘要

Wepresent1a€3(100a€‰pc)resolutionmapsofmillimeteremissionfromfivemoleculesa€”CN,HCN,HCO+,CH3OH,andHNCOa€”obtainedtowardsNGCa€‰4038,whichisthenortherngalaxyofthemid-stagemerger,Antennaegalaxies,withtheAtacamaLargeMillimeter/submillimeterArray.Threemolecules(CN,CH3OH,andHNCO)weredetectedforthefirsttimeinthenuclearregionofNGCa€‰4038.High-resolutionmappingrevealsasystematicdifferenceindistributionsofdifferentmolecularspeciesandcontinuumemission.Activestar-formingregionsidentifiedbythe3a€‰mmand850a€‰??mcontinuumemissionareoffsetfromthegas-richregionassociatedwiththeHCN(1a€“0)andCO(3a€“2)peaks.TheCN(1a€“0)/HCN(1a€“0)lineratiosareenhanced(CN/HCNa‰?0.8a€“1.2)inthestar-formingregions,suggestingthattheregionsarephotondominated.Thelargemoleculargasmass(108a€‰Ma??)withina0$${^{primeprime}_{.}}$$6(a??60a€‰pc)radiusoftheCO(3a€“2)peakandahighdensegasfraction(20%)suggestedbytheHCN(1a€“0)/CO(3a€“2)lineratiomaysignifyafutureburstofintensestarformationthere.TheshockedgastracedintheCH3OHandHNCOemissionindicatessub-kpc-scalemolecularshocks.Wesuggestthatthemolecularshocksmaybedrivenbycollisionsbetweeninflowinggasandthecentralmassivemolecularcomplex.