Characterising the relationship between dense gas and star formation is critical for understanding the assembly of galaxies throughout cosmic history. However, due to the faintness of standard dense-gas tracers-HCN, HCO⁺, and HNC-dense gas in high-redshift galaxies remains largely unexplored. We present ALMA and NOEMA observations targeting HCN/HCO⁺/HNC (3–2) and (4–3) emission lines in 11 (mostly) gravitationally lensed dusty star-forming galaxies (DSFGs) at redshift z = 1.6 − 3.2. We detect at least one line in 10 out of 11 galaxies. Altogether, we detect 34 dense-gas transitions, more than quadrupling the number of extant high-redshift detections. Additionally, in two targets, we detect lower-abundance CO isotopologues ¹³CO and C¹⁸O, as well as CN emission. We derive excitation coefficients for HCN, HCO⁺, and HNC in DSFGs, finding them to be systematically higher than those in nearby luminous infrared galaxies. Assuming the canonical dense-mass conversion factor (α _HCN = 10), we find that DSFGs have shorter dense-gas depletion times (median 23 Myr) than nearby galaxies (≈60 Myr), with a star-forming efficiency per free-fall time of 1−2%, a factor of a few higher than in local galaxies. We find a wide range of dense-gas fractions, with HCN/CO ratios ranging between 0.01 and 0.15. Finally, we put the first constraints on the redshift evolution of the cosmic dense-gas density, which increases by a factor of 7 ± 4 between z = 0 and z = 2.5, consistent with the evolution of the cosmic molecular-gas density.

We present JWST NIRCam imaging targeting 13 z ~ 3 infrared-luminous (L_IR ∼ 5 × 10¹²L_⊙) galaxies from the ALESS survey with uniquely deep, high-resolution (0 . ″ 08-0 . ″ 16) Atacama Large Millimeter/submillimeter Array 870 μm imaging. The 2.0-4.4 μm (observed frame) NIRCam imaging reveals the rest-frame near-infrared stellar emission in these submillimeter-selected galaxies at the same (sub)kiloparsec resolution as the 870 μm dust continuum. The newly revealed stellar morphologies show striking similarities with the dust continuum morphologies at 870 μm, with the centers and position angles agreeing for most sources, clearly illustrating that the spatial offsets reported previously between the 870 μm and Hubble Space Telescope morphologies were due to strong differential dust obscuration. The F444W sizes are 78% ± 21% larger than those measured at 870 μm, in contrast to recent results from hydrodynamical simulations that predict larger 870 μm sizes. We report evidence for significant dust obscuration in F444W for the highest-redshift sources, emphasizing the importance of longer-wavelength MIRI imaging. The majority of the sources show evidence that they are undergoing mergers/interactions, including tidal tails/plumes—some of which are also detected at 870 μm. We find a clear correlation between NIRCam colors and 870 μm surface brightness on ∼1 kpc scales, indicating that the galaxies are primarily red due to dust—not stellar age—and we show that the dust structure on ∼kpc scales is broadly similar to that in nearby galaxies. Finally, we find no strong stellar bars in the rest-frame near-infrared, suggesting the extended bar-like features seen at 870 μm are highly obscured and/or gas-dominated structures that are likely early precursors to significant bulge growth.

Dusty star-forming galaxies (DSFGs) at redshift z ≥ 1 are among the most vigorously star-forming galaxies in the Universe. However, their dense (≥10 ⁵cm ^-3) gas phase - typically traced by HCN(1-0) - remains almost entirely unexplored: only two DSFGs have been detected in HCN(1-0) to date. We present the results of a Karl G. Jansky Very Large Array survey of the J = 1-0 transition of HCN, HCO+, and HNC(1-0) in six strongly lensed DSFGs at z = 2:5-3:3, effectively doubling the number of DSFGs with deep observations of these lines. We detect HCN(1-0) emission in one source (J1202+5354, 4.6 σ), with a tentative HCO+(1-0) detection in another (J1609+6045, 3.3). Spectral stacking yields strict upper limits on the HCN/FIR (≤3:6 × 10 ^-4) and HCN/CO(1-0) ratios (≤0.045). The inferred HCN/FIR ratios (a proxy for the star-formation efficiency) are consistent with those in z ∼ 0 far-infrared-luminous starbursts. However, the HCN/CO ratios - a proxy for the dense-gas fraction - are a factor of a few lower than suggested by the two previous DSFG detections. Our results imply that most DSFGs have low dense-gas fractions. A comparison with theoretical models of star-forming galaxies indicates that the bulk of gas in DSFGs is at lower densities (≈10 ²cm ^-3), similar to normal star-forming galaxies, rather than ultraluminous starbursts.

Recent uneven land use dynamics in urban areas resulting from demographic change, economic pressure and the cities' mutual competition in a globalising world challenge both scientists and practitioners, among them social scientists, modellers and spatial planners. Processes of growth and decline specifically affect the urban environment, the requirements of the residents on social and natural resources. Social and environmental research is interested in a better understanding and ways of explaining the interactions between society and landscape in urban areas. And it is also needed for making life in cities attractive, secure and affordable within or despite of uneven dynamics. The position paper upon "Actors and factors - bridging social science findings and urban land use change modeling" presents approaches and ideas on how social science findings on the interaction of the social system (actors) and the land use (factors) are taken up and formalised using modelling and gaming techniques. It should be understood as a first sketch compiling major challenges and proposing exemplary solutions in the field of interest.