Coogan, R. T.R. T.CooganSargent, M. T.M. T.SargentDaddi, E.E.DaddiValentino, F.F.ValentinoSTRAZZULLO, VERONICAVERONICASTRAZZULLOBéthermin, M.M.BétherminGobat, R.R.GobatLiu, D.D.LiuMagdis, G.G.Magdis2021-01-132021-01-1320190035-8711http://hdl.handle.net/20.500.12386/29748We study a population of significantly sub-solar enrichment galaxies at z = 1.99, to investigate how molecular gas, dust, and star formation relate in low-metallicity galaxies at the peak epoch of star formation. We target our sample with several deep Atacama Large Millimeter/submillimeter Array and Very Large Array datasets, and find no individual detections of CO[4-3], CO[1-0], or dust, in stark contrast to the >60 per cent detection rate expected for solar-enrichment galaxies with these MS H α star formation rates (SFRs). We find that both low- and high-density molecular gas (traced by CO[1-0] and CO[4-3], respectively) are affected by the low enrichment, showing sample average (stacked) luminosity deficits >0.5-0.7 dex below expectations. This is particularly pertinent for the use of high-J CO emission as a proxy of instantaneous SFR. Our individual galaxy data and stacked constraints point to a strong inverse dependence ∝ Z<SUP>γ</SUP> of gas-to-dust ratios (G/D) and CO-to-H<SUB>2</SUB> conversion factors (α<SUB>CO</SUB>) on metallicity at z ∼ 2, with γ<SUB>G/D</SUB> <-2.2 and γ _{α _CO}< -0.8, respectively. We quantify the importance of comparing G/D and α<SUB>CO</SUB> versus metallicity trends from the literature on a common, suitably normalized metallicity scale. When accounting for systematic offsets between different metallicity scales, our z ∼ 2 constraints on these scaling relations are consistent with the corresponding relations for local galaxies. However, among those local relations, we favour those with a steep/double power-law dependence of G/D on metallicity. Finally, we discuss the implications of these findings for (a) gas mass measurements for sub-M* galaxies, and (b) efforts to identify the characteristic galaxy mass scale contributing most to the comoving molecular gas density at z = 2.STAMPAenArticle10.1093/mnras/stz4092-s2.0-85067027911000474886200044https://academic.oup.com/mnras/article/485/2/2092/53157772019MNRAS.485.2092CFIS/05 - ASTRONOMIA E ASTROFISICAERC sectors::Physical Sciences and Engineering::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation::PE9_6 Stars and stellar systems