CO (3-2) observations of early-type galaxies with the Heinrich Hertz Telescope

We present Heinrich Hertz Telescope CO (3 - 2) observations of a sample of 10 early-type galaxies detected both in far-infrared (IRAS) and in CO (1 - 0). Six of the objects (i.e., 60% of the sample) were detected in the CO (3 - 2) transition. Comparison of the beam-matched CO (3 - 2)/ CO (1 - 0) and CO (2 - 1)/ CO (1 - 0) intensity ratios with simple large velocity gradient and photodissociation region models reveals that early-type objects can be broadly classified into two categories. The majority of objects have a molecular interstellar medium of moderate density (n(H2) less than or equal to 1000 cm(-3)) and temperature (T less than or equal to 30 K). Two objects, NGC 3593 and NGC 4691, show indications of quite denser and warmer environments, as well as gradients in their physical properties, compatible with their classification as starbursts. The heating source of the molecular gas and dust in all the objects in our sample appears to be ongoing star formation.