We report molecular gas observations of IRAS 20100−4156 and IRAS 03158+4227, two local ultraluminous infrared galaxies (ULIRGs) hosting some of the fastest and most massive molecular outflows known. Using ALMA and PdBI observations, we spatially resolve the CO(1 − 0) emission from the outflowing molecular gas in both and find maximum outflow velocities of v max ∼ 1600 and ∼ 1700 km s −1 for IRAS 20100−4156 and IRAS 03158+4227, respectively. We find total gas mass outflow rates ofṀ OF ∼ 670 and ∼ 350 M yr −1 , respectively, corresponding to molecular gas depletion timescales τ dep OF ∼ 11 and ∼ 16 Myr. This is nearly 3 times shorter than the depletion timescales implied by star formation, τ dep SFR ∼ 33 and ∼ 46 Myr, respectively. To determine the outflow driving mechanism, we compare the starburst (L * ) and AGN (L AGN ) luminosities to the outflowing energy and momentum fluxes, using mid-infrared spectral decomposition to discern L AGN . Comparison to other molecular outflows in ULIRGs reveals that outflow properties correlate similarly with L * and L IR as with L AGN , indicating that AGN luminosity alone may not be a good tracer of feedback strength and that a combination of AGN and starburst activity may be driving the most powerful molecular outflows. We also detect the OH 1.667 GHz maser line from both sources and demonstrate its utility in detecting molecular outflows.

We report NOrthern Extended Millimetre Array (NOEMA) observations of warm molecular gas traced by CO(5 − 4) in a z ∼ 3.2 gas-rich main-sequence galaxy (MS), initially serendipitously detected in CO(3 − 2) emission in 'blind' deep NOEMA observations. Our target shows a gas excitation consistent with that seen in z ∼ 1.5 MS galaxies (L CO(5−4) /L CO(3−2) = 0.41 ± 0.14), albeit toward the low end, as well as a similar star formation efficiency based on the CO(3 − 2) line luminosity and the L IR . However, it shows a high molecular gas fraction (f gas = 0.9 ± 0.2) as compared to z ∼ 1.5 MS galaxies (f gas ∼ 0.42), consistent with a cosmologically increasing gas fraction beyond z 3 and our current understanding of scaling relations between z, f gas , the stellar mass M * , and the specific star formation rate sSFR. Our results are consistent with recent findings by the COLDz and ASPECS molecular line scan surveys and suggest that deep searches for CO emission are a powerful means to identify gas-rich, star-forming galaxies at high redshift.

We report observations of dense molecular gas in the star-forming galaxy EGS 13004291 (z = 1.197) using the Plateau de Bure Interferometer. We tentatively detect HCN and HNC J = 2 → 1 emission when stacked together at 4σ significance, yielding line luminosities of L HCN(J=2→1) = (9 ± 3) × 10 9 K km s −1 pc 2 and L HNC(J=2→1) = (5 ± 2) × 10 9 K km s −1 pc 2 respectively. We also set 3σ upper limits of < 7-8 × 10 9 K km s −1 pc 2 on the HCO + (J = 2 → 1), H 2 O(3 13 → 2 20 ) and HC 3 N(J = 20 → 19) line luminosities. We serendipitously detect CO emission from two sources at z ∼ 1.8 and z ∼ 3.2 in the same field of view. We also detect CO(J = 2 → 1) emission in EGS 13004291, showing that the excitation in the previously detected CO(J = 3 → 2) line is subthermal (r 32 = 0.65 ± 0.15). We find a line luminosity ratio of L HCN /L CO = 0.17 ± 0.07, as an indicator of the dense gas fraction. This is consistent with the median ratio observed in z > 1 galaxies (L HCN /L CO = 0.16 ± 0.07) and nearby ULIRGs (L HCN /L CO = 0.13 ± 0.03), but higher than in local spirals (L HCN /L CO = 0.04 ± 0.02). Although EGS 13004291 lies significantly above the galaxy main sequence at z ∼ 1, we do not find an elevated star formation efficiency (traced by L FIR /L CO ) as in local starbursts, but a value consistent with main-sequence galaxies. The enhanced dense gas fraction, the subthermal gas excitation, and the lower than expected star formation efficiency of the dense molecular gas in EGS 13004291 suggest that different star formation properties may prevail in high-z starbursts. Thus, using L FIR /L CO as a simple recipe to measure the star formation efficiency may be insufficient to describe the underlying mechanisms in dense star-forming environments inside the large gas reservoirs.