A Complete Survey of the Central Molecular Zone in NH$_3$

摘要

Wepresentamapofthemajorpartofthecentralmolecularzone(CMZ)ofsimultaneousobservationsintheNH$$_3(J,K)=$$(1,1)and(2,2)linesusingtheKagoshima6a€‰mtelescope.Themappedareais$$-$$1$$ lap{.}{}^{circ}$$000$$leqlleq$$1$$ lap{.}{}^{circ}$$625and$$-$$0$$ lap{.}{}^{circ}$$375$$leqbleq$$0$$ lap{.}{}^{circ}$$250.Thekinetictemperaturesderivedfromthe(2,2)to(1,1)intensityratiosare20a€“80K,orexceed80K.Thegasescorrespondingtotemperaturesof20a€“80Kand$$geq$$80Kcontain75%and25%ofthetotalNH$$_3$$flux,respectively.ThesetemperaturesindicatethatthedensemoleculargasintheCMZisdominatedbygasthatiswarmerthanthemajorityofthedustpresentthere.AcomparisonofourobservationswithaCOsurveybySawadaetal.(2001,ApJS,136,189)showsthattheNH$$_3$$emittingregionissurroundedbyahigh-pressureregiononthelongitudea€“velocity($$l-v$$)plane.AlthoughNH$$_3$$emissiontracesdensegas,itdoesnotextendoverahigh-pressureregion.Therefore,thehigh-pressureregionislessdenseandhastobehotter.Thisindicatesthatthemolecular-cloudcomplexintheGalacticcenterregionhasaa€?corea€?ofdenseandwarmcloudsthataretracedbytheNH$$_3$$emission,andana€?envelopea€?ofless-denseandhottergasclouds.Besidesheatingbyambipolardiffusion,thehotplasmagasemittingtheX-rayemissionmayheatthehota€?envelopea€?.