ASTE CO (3–2) Observations of the Barred Spiral Galaxy M 83: I. Correlation between CO (3–2)/CO (1–0) Ratios and Star Formation Efficiencies

[摘要] WepresentCO($$J=3$$–2)emissionobservationswiththeASTEtowardthe$$5'imes5'$$(or6.6kpc$$imes$$6.6kpcatthedistance$$D$$=4.5Mpc)regionofthenearbybarredspiralgalaxyM83.Wesuccessfullyresolvedthemajorstructures,i.e.,thenuclearstarburstregion,bar,andinnerspiralarmsataresolutionof$$22''$$(480pc),showingagoodspatialcoincidencebetweenCOand6cmcontinuumemissions.Wefoundagloballuminosity,$$L'_{mCO(3-2)}$$,of$$5.1imes10^8$$Kkms$$^{-1}$$pc$$^2$$withintheobservedregion.Wealsofound$$L'_{mCO(3-2)}$$inadiskregion($$0.5lt;rlt;3.5$$kpc)of$$4.2imes10^8$$Kkms$$^{-1}$$pc$$^2$$,indicatingthat($$J=3$$–2)emissioninthediskregionsignificantlycontributestotheglobal$$L'_{mCO(3-2)}$$.FromacomparisonofCO($$J=3$$–2)datawithCO($$J=1$$–0)intensitiesmeasuredwiththeNobeyama45-mtelescope,wefoundthattheradialprofileoftheCO($$J=3$$–2)$$/$$CO($$J=1$$–0)integratedintensityratio,$$R_{3-2/1-0}$$,isalmostunityinthecentralregion($$rlt;0.25$$kpc),whereasitdropstoaconstantvalue,0.6–0.7,inthediskregion.Theradialprofileofstarformationefficiencies(SFEs),determinedfrom6cmradiocontinuumandCO($$J=1$$–0)emission,showsthesametrendasthatof$$R_{3-2/1-0}$$.Atthebar-end($$rsim2.4$$kpc),theamountsofmoleculargasandthemassivestarsareenhancedwhencomparedwithotherdiskregions,whereasthereisnoexcessof$$R_{3-2/1-0}$$andSFEinthatregion.Thismeansthatasimplesummationofthestar-formingregionsatthebar-endandthediskcannotreproducethenuclearstarburstofM83,implyingthatthespatialvariationofthedensegasfractiontracedby$$R_{3-2/1-0}$$governsthespatialvariationofSFEinM83.

[学科分类] 天文学(综合)

[关键词] "galaxies: individual (M 83 = NGC 5236)";"galaxies: ISM";"galaxies: starburst"