CO Emission, Molecular Gas, and Metallicity in Main-Sequence Star-Forming Galaxies at $z\sim2.3$

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-H 2 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 molecular gas fraction (M mol /M * ) decrease 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.

MusE GAs FLOw and Wind (MEGAFLOW) IX. The impact of gas flows on the relations between the mass, star formation rate and metallicity of galaxies

“…This scenario is supported by observations and simulations that have shown that several major galaxy properties correlate, forming so-called scaling relations. Amongst the most notable correlations, those of interest for this work are: (i) the correlation between 𝑀 ★ and SFR, dubbed the "main sequence" (MS; Noeske et al 2007, Elbaz et al 2011, Speagle et al 2014, Whitaker et al 2014, Renzini & Peng 2015, Boogaard et al 2018 the correlation between 𝑀 ★ and gas metallicity, referred to as the "mass-metallicity relation" (MZR; Tremonti et al 2004, Maiolino et al 2008, Erb et al 2006, Zahid et al 2011, Sanders et al 2022. The MS shows that 𝑀 ★ and SFR are positively correlated, meaning that an increasing stellar mass is directly linked to an increasing SFR, over 10 7 M ≤ 𝑀 ★ ≤ 10 11.5 M .…”

A super-linear ‘radio-AGN main sequence’ links mean radio-AGN power and galaxy stellar mass since z ∼ 3

“…While the scenario of 'expulsive' AGN feedback is not fully backed up by observations (e.g. Sanders et al 2022), alternative manifestations of AGN feedback have recently been gaining consensus. For instance, compact (<1 kpc), low-power radio jets have been widely observed in local ('radio-quiet') Seyferts (e.g.…”