Boogaard, Leindert A.Leindert A.BoogaardBouwens, Rychard J.Rychard J.BouwensRiechers, DominikDominikRiechersVan Der Werf, PaulPaulVan Der WerfBacon, RolandRolandBaconMatthee, JorrytJorrytMattheeStefanon, MauroMauroStefanonFELTRE, ANNAANNAFELTREMaseda, MichaelMichaelMasedaInami, HanaeHanaeInamiAravena, ManuelManuelAravenaBrinchmann, JarleJarleBrinchmannCarilli, ChrisChrisCarilliContini, ThierryThierryContiniDECARLI, ROBERTOROBERTODECARLIGonzález-López, JorgeJorgeGonzález-LópezNanayakkara, ThemiyaThemiyaNanayakkaraWalter, FabianFabianWalter2022-05-272022-05-2720210004-637Xhttp://hdl.handle.net/20.500.12386/32100We study the molecular gas content of 24 star-forming galaxies at z = 3-4, with a median stellar mass of 109.1 M o˙, from the MUSE Hubble Ultra Deep Field (HUDF) Survey. Selected by their Lyα λ1216 emission and H F160W-band magnitude, the galaxies show an average Å, below the typical selection threshold for Lyα emitters (Å), and a rest-frame UV spectrum similar to Lyman-break galaxies. We use rest-frame optical spectroscopy from KMOS and MOSFIRE, and the UV features observed with MUSE, to determine the systemic redshifts, which are offset from Lyα by Δv(Lyα) = 346 km s-1, with a 100 to 600 km s-1 range. Stacking 12CO J = 4 → 3 and [C i]3P1 → 3P0 (and higher-J CO lines) from the ALMA Spectroscopic Survey of the HUDF, we determine 3σ upper limits on the line luminosities of 4.0 108 K km s-1pc2 and 5.6 108 K km s-1pc2, respectively (for a 300 km s-1 line width). Stacking the 1.2 mm and 3 mm dust-continuum flux densities, we find a 3σ upper limits of 9 μJy and 1.2 μJy, respectively. The inferred gas fractions, under the assumption of a "Galactic"CO-to-H2 conversion factor and gas-to-dust ratio, are in tension with previously determined scaling relations. This implies a substantially higher α CO ≥ 10 and δ GDR ≥ 1200, consistent with the subsolar metallicity estimated for these galaxies (). The low metallicity of z ≥ 3 star-forming galaxies may thus make it very challenging to unveil their cold gas through CO or dust emission, warranting further exploration of alternative tracers, such as [C ii].STAMPAenArticle10.3847/1538-4357/ac01d72-s2.0-85112596395https://api.elsevier.com/content/abstract/scopus_id/85112596395https://iopscience.iop.org/article/10.3847/1538-4357/ac01d72021ApJ...916...12BFIS/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