Kiloparsec-scale Imaging of the CO(1-0)-traced Cold Molecular Gas Reservoir in a z 3.4 Submillimeter Galaxy
Abstract
We present a high-resolution study of the cold molecular gas as traced by CO(1-0) in the unlensed z ~ 3.4 submillimeter galaxy SMM J13120+4242, using multiconfiguration observations with the Karl G. Jansky Very Large Array (JVLA). The gas reservoir, imaged on 0.″39 (~3 kpc) scales, is resolved into two components separated by ~11 kpc with a total extent of 16 ± 3 kpc. Despite the large spatial extent of the reservoir, the observations show a CO(1-0) FWHM linewidth of only 267 ± 64 km s-1. We derive a revised line luminosity of ${L}_{\mathrm{CO}(1-0)}^{{\prime} }$ = (10 ± 3) × 1010 K km s-1 pc2 and a molecular gas mass of M gas = (13 ± 3)× 1010 (α CO/1) M ⊙. Despite the presence of a velocity gradient (consistent with previous resolved CO(6-5) imaging), the CO(1-0) imaging shows evidence for significant turbulent motions that are preventing the gas from fully settling into a disk. The system likely represents a merger in an advanced stage. Although the dynamical mass is highly uncertain, we use it to place an upper limit on the CO-to-H2 mass conversion factor α CO of 1.4. We revisit the SED fitting, finding that this galaxy lies on the very massive end of the main sequence at z = 3.4. Based on the low gas fraction, short gas depletion time, and evidence for a central AGN, we propose that SMM J13120 is in a rapid transitional phase between a merger-driven starburst and an unobscured quasar. The case of SMM J13120 highlights how mergers may drive important physical changes in galaxies without pushing them off the main sequence.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- May 2022
- DOI:
- 10.3847/1538-4357/ac6105
- arXiv:
- arXiv:2203.15811
- Bibcode:
- 2022ApJ...930...35F
- Keywords:
-
- Galaxy evolution;
- High-redshift galaxies;
- Starburst galaxies;
- Interstellar medium;
- 594;
- 734;
- 1570;
- 847;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 19 pages, 12 figures, accepted for publication in ApJ