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

TL;DR

This study uncovers a previously unidentified massive molecular gas component in the archetypal submillimeter galaxy SMM J02399-0136, revealing complex gas dynamics and structures associated with galaxy mergers, outflows, or inflows at high redshift.

Contribution

It reports the discovery of a new extended molecular gas component W1 in SMM J02399-0136, characterized by lower excitation and significant mass, using combined GBT and ALMA observations.

Findings

Identification of a new molecular gas component W1

W1 accounts for about 30% of total molecular gas

W1 shows lower CO excitation than central regions

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 sub-millimeter 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 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--H_2 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.