Passive early-type galaxies dominate cluster cores at z ≲ 1.5. At higher redshift, cluster core galaxies are observed to have on-going star-formation, which is fueled by cold molecular gas. We measured the molecular gas reservoir of the central region around the radio-loud active galactic nucleus (AGN) in the cluster CARLA J1103 + 3449 at z = 1.44 using NOEMA. The AGN synchrotron emission dominates the continuum emission at 94.48 GHz, and we measured its flux at the AGN position and at the position of two radio jets. Combining our measurements with published results over the range 4.71–94.5 GHz, and assuming Ssynch ∝ ν−α, we obtain a flat spectral index of α = 0.14 ± 0.03 for the AGN core emission, and a steeper index of α = 1.43 ± 0.04 and α = 1.15 ± 0.04 at positions close to the western and eastern lobes, respectively. The total spectral index is α = 0.92 ± 0.02 over the range 73.8 MHz–94.5 GHz. We detect two CO(2–1) emission lines, both blueshifted with respect to the AGN. Their emission corresponds to two regions, ~17 kpc southeast and ~14 kpc southwest of the AGN, not associated with galaxies. In these two regions, we find a total massive molecular gas reservoir of Mgastot = 3.9 ± 0.4 × 1010 M⊙, which dominates (≳60%) the central total molecular gas reservoir. These results can be explained by massive cool gas flows in the center of the cluster. The AGN early-type host is not yet quenched; its star formation rate is consistent with being on the main sequence of star-forming galaxies in the field (star formation rate ~30–140 M⊙ yr−1), and the cluster core molecular gas reservoir is expected to feed the AGN and the host star formation before quiescence. The other confirmed cluster members show star formation rates at ~2σ below the field main sequence at similar redshifts and do not have molecular gas masses larger than galaxies of similar stellar mass in the field.

Recent ALMA large surveys unveiled the presence of significant dust continuum emission in star-forming galaxies at z > 4. Unfortunately, such large programs – i.e. ALPINE (z ∼ 5) and REBELS (z ∼ 7) – only provide us with a single Far-Infrared (FIR) continuum data point for their individual targets. Therefore, high-z galaxies FIR spectral energy densities (SEDs) remain mostly unconstrained, hinging on an assumption for their dust temperature (Td) in the SED fitting procedure. This introduces uncertainties in the inferred dust masses (Md), infrared luminosities (LIR), and obscured Star Formation Rate (SFR) fraction at z > 4. In this work we use a method that allows us to constrain Td with a single band measurement by combining the 158 μm continuum information with the overlying [C $\scriptstyle \rm II$] emission line. We analyse the 21 [C $\scriptstyle \rm II$] and FIR continuum detected z ∼ 5 galaxies in ALPINE, finding a range of Td = 25 − 60 K and Md = 0.6 − 25.1 × 107 M⊙. Given the measured stellar masses of ALPINE galaxies, the inferred dust yields are around Md/M⋆ = (0.2 − 8) × 10−3, consistent with theoretical dust-production constraints. We find that 8 out of 21 ALPINE galaxies have LIR ≥ 1012 L⊙, comparable to UltraLuminous IR Galaxies (ULIRGs). Relying on ultraviolet-to-optical SED fitting, the SFR was underestimated by up to 2 orders of magnitude in 4 of these 8 ULIRGs-like galaxies. We conclude that these 4 peculiar sources should be characterised by a two-phase interstellar medium structure with “spatially-segregated” FIR and ultraviolet emitting regions.

Context. A tight relation between [C ii] 158 µm line luminosity and the star formation rate (SFR) has been observed for local galaxies. At high redshift (z > 5), galaxies instead deviate downwards from the local Σ [C ii] − Σ SFR relation. This deviation might be caused by different interstellar medium (ISM) properties in galaxies at early epochs. Aims. To test this hypothesis, we combined the [C ii] and SFR data with C iii] 1909Å line observations and our physical models. We additionally investigated how ISM properties, such as burstiness, κ s , total gas density, n, and metallicity, Z, affect the deviation from the Σ [C ii] − Σ SFR relation in these sources. Methods. We present the VLT/X-SHOOTER observations targeting the C iii] λ1909 line emission in three galaxies at 5.5 < z < 7.0. We include archival X-SHOOTER data of two other sources at 5.5 < z < 7.0 and the VLT/MUSE archival data of six galaxies at z ∼ 2. We extend our sample of galaxies with eleven star-forming systems at 6 < z < 7.5, with either C iii] or [C ii] detection reported in the literature. Results. We detected C iii] λλ1907, 1909 line emission in HZ10 and we derived the intrinsic, integrated flux of the C iii] λ1909 line. We constrained the ISM properties for our sample of galaxies, κ s , n, and Z, by applying our physically motivated model based on the MCMC algorithm. For the most part, high-z star-forming galaxies show subsolar metallicities. The majority of the sources have log (κ s ) 1, that is, they overshoot the Kennicutt-Schmidt (KS) relation by about one order of magnitude. Conclusions. Our findings suggest that the whole KS relation might be shifted upwards at early times. Furthermore, all the high-z galaxies of our sample lie below the Σ [C ii] − Σ SFR local relation. The total gas density, n, shows the strongest correlation with the deviation from the local Σ [C ii] − Σ SFR relation, namely, low-density high-z systems have lower [C ii] surface brightness, in agreement with theoretical models.