The Discovery of a New Massive Molecular Gas Component Associated with the Submillimeter Galaxy SMM J02399-0136

Abstract

We present CO(1-0), CO(3-2), and CO(7-6) observations using the Green Bank Telescope (GBT) and the Atacama Large Millimeter Array (ALMA) of the z = 2.8 submillimeter galaxy SMM J02399-0136. This was the first submillimeter-selected galaxy discovered and remains an archetype of the class, comprising a merger of several massive and active components, including a quasar-luminosity AGN and a highly obscured, gas-rich starburst spread over a ∼25 kpc extent. The GBT CO(1-0) line profile is comprised of two distinct velocity components separated by about 600 km s^-1 and suggests the presence of a new component of molecular gas that had not been previously identified. The CO(3-2) observations with ALMA show that this new component, designated W1, is associated with a large extended structure stretching 13 kpc westward from the AGN. W1 is not detected in the ALMA CO(7-6) data, implying that this gas has much lower CO excitation than the central starburst regions, which are bright in CO(7-6). The molecular gas mass of W1 is about 30% of the total molecular gas mass in the system, depending on the CO-to-H₂ conversion factor. W1 is arguably a merger remnant; alternatively, it could be a massive molecular outflow associated with the AGN, or perhaps inflowing metal-enriched molecular gas fueling the ongoing activity.