Molecular Gas in Nearby Dwarf Galaxies: Single Dish and Interferometric Results

Abstract

During the past two years we have undertaken a systematic millimeter-wave survey of molecular gas in a sample of 150 nearby, northern dwarf galaxies with IRAS emission. We have called this survey MIDGET (Millimeter Interferometry of Dwarf Galaxies). MIDGET has two parts: a single-dish search for CO done at the UASO Kitt Peak 12m telescope (Leroy et al., in preparation), and an interferometric follow-up of the galaxies with strong CO emission carried out at the Berkeley-Illinois-Maryland Array (BIMA). The single-dish survey targeted the centers of northern galaxies that are nearby (VLSR ≤ 1000 km s^-1), of small mass (HI linewidths W20 ≤ 200 km s¹), compact in size, and detected by IRAS. The single-dish observations were very successful, finding 41 new CO emitters and more than doubling the number of previously known CO sources within the defined sample. The typical 1 σ sensitivity attained was ∼ 0.2 K km s^_1. Carbon monoxide emission was detected in galaxies with 12 + log([O/H]) ∼ 7.9-8.5, a metallicity regime similar to that of the Magellanic Clouds. We are using these data to address several questions related to molecular cloud and star formation in these objects. This paper concentrates on the issue of how CO traces molecular gas as a function of heavy element abundance Z.

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