Abstract
We present observations of CO(3−2) in 13 main-sequence z = 2.0-2.5 star-forming galaxies at log ( M * / M ⊙ ) = 10.2 - 10.6 that span a wide range in metallicity (O/H) based on rest-optical spectroscopy. We find that L CO ( 3 − 2 ) ′ /SFR decreases with decreasing metallicity, implying that the CO luminosity per unit gas mass is lower in low-metallicity galaxies at z ∼ 2. We constrain the CO-to-H2 conversion factor (α CO) and find that α CO inversely correlates with metallicity at z ∼ 2. We derive molecular gas masses (M mol) and characterize the relations among M *, SFR, M mol, and metallicity. At z ∼ 2, M mol increases and the molecular gas fraction (M mol/M *) decreases with increasing M *, with a significant secondary dependence on SFR. Galaxies at z ∼ 2 lie on a near-linear molecular KS law that is well-described by a constant depletion time of 700 Myr. We find that the scatter about the mean SFR−M *, O/H−M *, and M mol−M * relations is correlated such that, at fixed M *, z ∼ 2 galaxies with larger M mol have higher SFR and lower O/H. We thus confirm the existence of a fundamental metallicity relation at z ∼ 2, where O/H is inversely correlated with both SFR and M mol at fixed M *. These results suggest that the scatter of the z ∼ 2 star-forming main sequence, mass-metallicity relation, and M mol-M * relation are primarily driven by stochastic variations in gas inflow rates. We place constraints on the mass loading of galactic outflows and perform a metal budget analysis, finding that massive z ∼ 2 star-forming galaxies retain only 30% of metals produced, implying that a large mass of metals resides in the circumgalactic medium.
Document Type
Article
Publication Date
2023
Digital Object Identifier (DOI)
https://doi.org/10.3847/1538-4357/aca46f
Funding Information
This paper makes use of the following ALMA data: ADS/JAO.ALMA#2018.1.01128.S. ALMA is a partnership of ESO (representing its member states), NSF (USA), and NINS (Japan), together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. Support for this work was provided by NASA through the NASA Hubble Fellowship grant #HST-HF2-51469.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. We acknowledge support from NSF AAG grants AST-1312780, 1312547, 1312764, and 1313171, archival grant AR-13907 provided by NASA through the Space Telescope Science Institute, and grant NNX16AF54G from the NASA ADAP program. We also acknowledge a NASA contract supporting the \u201CWFIRST Extragalactic Potential Observations (EXPO) Science Investigation Team\u201D (15-WFIRST15-0004), administered by GSFC. We additionally acknowledge the 3D-HST collaboration for providing spectroscopic and photometric catalogs used in the MOSDEF survey. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.
Repository Citation
Sanders, Ryan L.; Shapley, Alice E.; Jones, Tucker; Shivaei, Irene; Popping, Gergö; Reddy, Naveen; Davé, Romeel; Price, Sedona H.; Mobasher, Bahram; Kriek, Mariska; Coil, Alison L.; and Siana, Brian, "CO Emission, Molecular Gas, and Metallicity in Main-sequence Star-forming Galaxies at z ∼ 2.3" (2023). Physics and Astronomy Faculty Publications. 694.
https://uknowledge.uky.edu/physastron_facpub/694
Notes/Citation Information
© 2023. The Author(s). Published by the American Astronomical Society.
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