ALMA Observations of the Molecular Gas in the Elliptical Galaxies NGC 2865 and NGC 4697

We present the results of our Atacama Large Millimeter/submillimeter Array (ALMA) 2.6 mm observations of the bona fide elliptical galaxies NGC 2865 and NGC 4697. Both targets were detected in 2.6 mm continuum and in CO(1–0) emission. The continuum is unresolved in both sources at scales of ∼ 0 . ″ 8. The detected molecular gas masses are (1.5 ± 0.5) × 10 7 M ⊙ (NGC 2865) and (1.2 ± 0.1) × 10 7 M ⊙ (NGC 4697). The extent of the molecular gas is similar (i.e., within 300 pc of the center) for both targets, but the distributions are quite different, with NGC 2865 showing a centrally peaked distribution with an extension westwards of the nucleus, while NGC 4697 has a highly inclined, slightly warped molecular disk (8° variation in the inclination as a function of radial distance) with offset symmetric peaks. The kinematics of the molecular gas for NGC 2865 could not be studied in detail, but NGC 4697 shows a clear rotation pattern. On average, the excitation of the molecular interstellar medium in these objects is subthermal, with CO(2–1)/CO(1–0) ∼ 0.5. At least for NGC 4697, this seems to be due to a higher fraction of low-excitation gas when compared with spiral galaxies. The molecular disk in NGC 4697 appears stable against gravitational collapse, which seems to justify the very low star formation rates reported in the literature.