Molecular Gas in Luminous Infrared Galaxies
Session 39 -- Interferometry II
Oral presentation, Tuesday, 2:00-6:30, Zellerbach Playhouse Room

## [39.08] Molecular Gas in Luminous Infrared Galaxies

P.M.Bryant, N.Z.Scoville (Caltech)

\def\arcsec{$^{\prime\prime}$} \def\arcmin{$^{\prime}$} \def\sun{\ifmmode_{\mathord\odot} \else$_{\mathord\odot}$\fi}

Using the Owens Valley millimeter array, we have observed several ultraluminous infrared galaxies in CO(1--0) at resolutions as small as 3\arcsec . We have also observed and detected one galaxy, NGC 3690, in \hbox{HCN(1--0)}. The galaxies in our sample all have infrared luminosities in excess of 10$^{11.5}$~L\sun . These observations are part of an ongoing project to determine the amount and distribution of the large masses (10$^{10}$--10$^{11}$~M\sun ) of molecular gas that exist in ultraluminous galaxies.

Previous interferometric CO observations have revealed that the molecular gas of ultraluminous galaxies is largely confined to within a couple kiloparsecs or less of the nucleus, so that at a resolution of 6\arcsec , less than or equal to the resolution of almost all previous observations, the molecular gas is unresolved or poorly-resolved. The observations reported here significantly increase the sample of ultraluminous galaxies that have been observed in CO at a resolution of 3\arcsec.

Interferometric HCN observations of ultraluminous galaxies have been very rare as of this date. Our HCN detection of NGC 3690, along with a previous Owens Valley CO map from Sargent and Scoville (1991), allows a detailed comparison of the HCN and CO emission in this relatively nearby system (42 Mpc), allowing a comparison of the amount and distribution of molecular gas in dense, potential star-forming cores ($n(H_2) \approx 10^{5}$~cm$^{-3}$) versus more diffuse molecular clouds ($n(H_2) \approx 10^{2}$--10$^{3}$~cm$^{-3}$).