BIMA CO (1­0) Observations of the Dwarf Elliptical NGC 404 Christopher L. Taylor California State University Sacramento Glen R. Petitpas Harvard­Smithsonian Center for Astrophysics Soledad del Rio Instituto Nacional de Astrofisica, Optica Y Electronica

Abstract We present high resolution observations of the CO emission in NGC 404, a nearby dwarf elliptical (dE) galaxy (D = 3.3 Mpc). NGC 404 is only the third dwarf elliptical to have its CO emission mapped by interferometric observations, and is the first outside the . Our observations show a very concentrated, marginally resolved structure about 9 x 9 arcseconds in diameter. This corresponds to a very small cloud at the center of a much larger distribution of . NGC 404 is surrounded by a doughnut shaped distribution of HI gas centered on the stellar component. The CO and HI appear to be kinematically distinct components, suggesting that the HI may be part of the galaxy's original gas distribution, while the CO may be recycled from the products of stellar evolution. Introduction Conventional wisdom has long held that among dwarf , dwarf irregulars (dIs) and Blue Compact Dwarfs (BCDs) are gas rich , while dwarf ellipticals (dEs) are gas poor. This dichotomy in the properties of the ISM is directly analogous to that between spiral galaxies and ellipticals. Even as it has been revealed that the giant galaxies do not always follow this simple picture, dwarf galaxies too have proven more complex than originally thought. In particular, the old picture of dEs as simply low mass stellar systems which have exhausted their initial allotment of gas through billions of years of formation has been challenged by the increasing awareness that at least a few dEs have an observable ISM; e.g. NGC 205 (Unwin 1980, Sage & Wrobel 1989) and NGC 185 (Johnson 1980,Wiklind & Rydbeck 1986).

To this list of dEs with detected interstellar gas must now be added NGC 404. This galaxy has been a known source of CO emission since 1989 (Wiklind & Henkel 1989), but only recently has its distance been accurately determined. Previous estimates were as high as 10 Mpc, but observations of the TRG with Hubble put the distance at ~3 Mpc (Karachentsev et al. 2002), making NGC 404 a dwarf , one of only three with detected CO emission. Figure 2: (Left) Integrated intensity of HI emission. The dark circle shows the Observations size of the synthesized beam. (Right) HI emission within the green box on the left, with the CO contours from Figure 1 superposed. The stellar component of We mapped CO (1­0) emission in NGC 404 using the 10 element BIMA millimeter NGC 404 is roughly the size of the hole in the center of the HI. interferometer. The observations were taken in the B, C and D configurations. The data were calibrated and reduced using the MIRIAD package. The resolution of our synthesized beam is 7'.0 x 6'.7 and the velocity resolution of the final data cube is 10 km/s. The map of integrated CO intensity is shown below in Figure 1.

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Figure 3: (Left) HI velocity field superposed on integrated intensity map. (Right) CO velocity field superposed on integrated intensity map. Note the difference in the angle of the kinematic major axis. Preliminary Results

* The CO emission forms a small, marginally resolved structure at the center of the Figure 1: Integrated intensity of CO emission. The contours represent 20, 40, and stellar and HI components of NGC 404. 80% of the peak emission of 29.7 Jy/beam km/s. The dark circle shows the size of the synthesized beam. * The molecular gas in NGC 404 is kinematically distinct from the extremely large References HI ring that surrounds the optical galaxy.

Johnson, D.W. 1980, Ph.D. thesis, University of Florida. * It is possible the HI component is a remnant from the primordial gas from which Karachentsev, I.D. et al. 2002, A&A, 380, 812. NGC 404 formed, while the small molecular component could originate from Sage, L.J. & Wrobel, J. 1989, ApJ, 344, 204. recycled stellar material. If so, then the CO should share the kinematics of the Unwin, S.C. 1980, MNRAS, 190, 551. stars in NGC 404. Wiklind, T. & Henkel, C. 1989, A&A, 225, 1. Wiklind, T. & Rydbeck, G. 1986, A&A, 164, L22. Acknowledgements C.L.T. has been supported by CSU Sacramento via a Research and Creative Activity Award. G.R.P. has been supported by the Laboratory for Millimeter­Wave Astronomy through NSF grant AST 99­81289