arXiv:astro-ph/9909422v1 24 Sep 1999 eyhg aisaenvrosre vni togstarburst strong high in extremely even between observed link never physical are ratios high very nsm efr aaisw n xrml high extremely find we galaxies Seyfert some In on,K ta.19c nTePyisadCeityo Inters of Chemistry and Physics The 1011 in 23, 1999c, Res. al. Space et K. Adv. 15 1999b, Kohno, 511, al. ApJ, et 1999a, K. Vila-Vilar´o, B. Kohno, & R., Kawabe, K., Kohno, on,K ta.19,i h eta ein fGlx n Gal and Galaxy of ApJ, Regions Central 1996, The K. in S. 1998, Okumura, al. & et K. T., Kohno, Tosaki, R., Kawabe, K., Kohno, References from cl.Tefato of i efficiency, fraction star-formation The of indicator scale. an is which ratios, nteps-trus uli ept h togC concent CO dec t strong quickly of the and decrease despite remarkable regions, nuclei, a R starburst find post-starburst the we the in contrast, in 0.2 In to regions. 0.1 these as high as r eylw .2t .4 og orlto between correlation rough A 0.04. to 0.02 low, very are 99;Siask ta.19) iue1sospeiiayi preliminary shows 1 Figure 1998 1999). HCO 1996, al. al. et et Shibatsuka (Kohno 1999c; (NMA) Array Millimeter Nobeyama the Oitgae neste ntebihns eprtr sc temperature r brightness The the on regions. star-forming intensities and integrated gas CO molecular dense between nodrt td h itiuino es oeua a and gas have we HCN(1 molecular galaxies, of dense in survey AGN) of and distribution (starburst activities the central study to Galaxies order in In Gas Molecular Dense 1. HCN + R / CO Abstract. 384-1305 Nagano, Minamisaku, Matsushita Observatory, S. Radio and Nobeyama Shibatsuka, T. Kawabe, R. Kohno, K. Array Millimeter in Nobeyama Gas the Molecular with Dense Galaxies of Nearby Images Synthesis Aperture in rmnab aaismd ihteNAaepresented. are NMA the with made galaxies nearby from sions npes(astro-ph/9902251) press in lwr odeh,239 Dordrecht, Kluwer: nglxe.I trus aais efidteei odspat good is there find we galaxies, starburst In galaxies. in HCN ausi h eta e 0 crgoso hs uecn g quiescent these of regions pc 100 few a central the in values / CO a ea motn aaee htcnrl trformation star controls that parameter important an be may , − )adHCO and 0) ihrslto mgso HCN(1 of images resolution High dense oeua a nthe in gas molecular + (1 − )eisosfo erysia aaiswith galaxies spiral nearby from emissions 0) R 1 HCN / CO n efr activity. Seyfert and R total HCN − / )adHCO and 0) oeua a,measured gas, molecular CO on tafw10pc 100 few a at found s R odce nimaging an conducted xedn ..These 0.3. exceeding HCN ae fHNand HCN of mages ein,ipyn a implying regions, ain hr.The there. rations ale, t eaint the to relation its eHNemission HCN he / 7 to fHNto HCN of atios CO es usd of outside rease xe,Y Sofue, Y. axies, elrMedium, tellar 99,1999b, 1999a, , a coincidence ial R + HCN n H and 6,L29 461, (1 Japan , − / )emis- 0) CO alaxies α are , /CO . 28d 14 40 47d -30d N1097 N3504 HCN 27 45 N5194 HCN 28 50









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Figure 1. High resolution HCN and HCO+ images of nearby spiral galaxies. HCO+ images were obtained simultaneously with the Ultra Wide-Band Correlator of the NMA (1024 MHz band-width). The thick horizontal line in each image corresponds to 500 pc. The cross marks the position of a 6 cm radio continuum peak. The contour interval is 2 σ for NGC 3079, NGC 3504, NGC 6764, and NGC 6946, and 1.5 σ for NGC 1097, NGC 4527, NGC 5194, and NGC 6951. Contour levels are -3, -1.5, 1.5, and 3 σ for NGC 4736. Noise levels are 1.7, 1.5, 0.46, 0.71, 0.91, 0.44, 0.36, 0.83, and 0.58 Jy beam−1 km s−1 for NGC 1097, NGC 3079, NGC 3504, NGC 4527, NGC 4736, NGC 5194, NGC 6764, NGC 6946, and NGC 6951, respectively. A nuclear starburst is hosted by NGC 3079, NGC 3504, NGC 4527, NGC 6764, and NGC 6946, whereas a circumnuclear star-forming ring is observed in NGC 6951. Good spatial coincidence between HCN and Hα (and radio continuum) emission can be seen in these star-forming galaxies (Kohno et al. 1999a). Note that there is a remarkable decrease of dense gas in the post-starburst galaxy NGC 4736; the current massive star formation is suppressed in the central r ∼ 10′′ region, even though there R is a CO peak. The resultant HCN/CO is very small, less than 0.044 (2 σ upper limit). The sample contains one type-1 Seyfert (NGC 1097) and three type-2 Seyferts (NGC 3079, NGC 5194, and NGC 6951). A cohabitation of AGN and starburst has been reported to have taken place in NGC 1097, NGC 3079, and NGC 6951. 2 Shibatsuka, T. et al. 1999, in Proceedings of Star Formation 1999, in press (astro-ph/9909313)

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